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SINUMERIK 840D sl. Service - Functions. Manual (2018-2020) - page 35

K3: Compensations

5.5 Interpolatory compensation

The compensation values and additional table parameters are entered in the compensation

tables using special system variables. Data can be loaded in two different ways:

● By starting an NC program with the parameter values.

● By transferring the compensation tables from an external computer to the control.

Note

The respective compensation tables can only be loaded if the corresponding compensation

function is not active for all axes:

● MD32700 $MA_ENC_COMP_ENABLE[<axis>] == 0

● MD32710 $MA_CEC_ENABLE[<axis>] == 0

As the compensation data is also retained when the controls are switched off.

Note

When changing machine data:

● MD18342 $MN_MM_CEC_MAX_POINTS

● MD38000 $MA_MM_ENC_COMP_MAX_POINTS

is formatted during the next system run-up of the static user memory (see Section "S7: Memory

configuration (Page 827)").

Interim value calculation

The traversing distance defined via the start and end position within which compensation is to

apply, is divided into several sub-paths of equal size. The number of sub-paths is defined

depending on the error curve and the desired precision. The positions that limit these sub-

paths are referred to as interpolation points below. An interpolation and a compensation value

must be assigned to each interpolation point. Between two interpolation points, the effective

compensation value is determined by linear interpolation.

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② Position of basic axis

Figure 5-12

Intermediate value calculation by linear interpolation

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

●

$AA_ENC_COMP[<e>,<N>,<AXi>] (correction value for interpolation point N of the

compensation table)

<N> = interpolation point (axis position)

For every individual interpolation point the compensation value must be entered in the table.

<N> is limited by the maximum number of interpolation points of the particular compensation

table (MD38000 $MA_MM_ENC_COMP_MAX_POINTS):

0 ≤ N ≤ MD38000 -1

The size of the compensation value is not limited.

Note

The first and last compensation values remain active over the entire traversing range;

i.e. these values should be set to "0" if the compensation table does not cover the entire

traversing range.

●

$AA_ENC_COMP_IS_MODULO[<e>,<AXi>] (compensation with modulo function)

System variable to activate/deactivate the compensation with modulo function:

- $AA_ENC_COMP_IS_MODULO[<e>,<AXi>] = 0: Compensation without modulo

function

- $AA_ENC_COMP_IS_MODULO[<e>,<AXi>] = 1: Compensation with modulo function

When compensation with modulo function is activated, the compensation table is repeated

cyclically, i.e. the compensation value at position $AA_ENC_COMP_MAX (≙ interpolation

point $AA_ENC_COMP[<e>,<k>,<AXi>]) is immediately followed by the compensation

value at position $AA_ENC_COMP_MIN (≙ interpolation point

$AA_ENC_COMP[<e>,<0>,<AXi>]).

For rotary axes with modulo 360° degrees it is therefore suitable to program 0°

($AA_ENC_COMP_MIN) as the initial position and 360° ($AA_ENC_COMP_MAX) as the

end position.

The compensation values entered for these two positions should be the same as otherwise

the compensation value jumps from MAX to MIN at the transition point and vice versa.

CAUTION

Wrong correction values

When writing the correction values for a correction table, it must be ensured that all

interpolation points within the parameterized range are assigned a value. Correction

values which are not described otherwise contain random values.

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Note

Table parameters containing position information are automatically converted when the

system of units is changed (change from MD10240

$MN_SCALING_SYSTEM_IS_METRIC).

The position information is always interpreted in the current measuring system. Conversion

must be implemented externally.

Automatic conversion of the position data can be configured as follows:

MD10260 $MN_CONVERT_SCALING_SYSTEM = 1

External conversion is no longer necessary.

References:

Function Manual Basic Functions; Velocities, Setpoint/Actual Value Systems, Closed-Loop

Control (G2)

5.5.2.3

Example

Sample parameterization of a compensation table:

● Machine axis: X1

● Measuring system: 1

● Starting position: -200 mm

● End position: 600 mm

● Distance between interpolation points: 1 mm

● Number of interpolation points: MD38000 $MA_MM_ENC_COMP_MAX_POINTS = ((600

- -200) / 1) + 1 = 801

The memory requirement in the static user memory is: 801 * 8 Byte = 6408 Byte

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K3: Compensations

5.5 Interpolatory compensation

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① Position error in Z1 as a function of the position of Y1

Figure 5-13

Example: Sag errors

Error compensation

For error compensation, at various interpolation points (setpoint positions) of the basic axis

(Y1), the particular position error should be determined and entered into the compensation

table. When the basic axis (Y1) traverses, in the interpolation clock cycle, the control system

calculates the actual compensation value for the compensation axis (Z1) by linearly

interpolating between the points. The compensation value is added to the setpoint of the

compensation axis (Z1). A positive compensation value causes the compensation axis (Z1) to

traverse in the negative direction.

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Figure 5-14

Compensation table

Summed compensation value

Compensation values from several compensation tables can be applied to a compensation

axis. The resulting summed compensation value is the sum of all of the individual

compensation values.

Parameterization options

● Anaxis can be defined as a basic axis for severalcompensation tables.

● Severalcompensation tables can act on onecompensation axis. The total (summed)

compensation value is derived from the sum of the compensation values of the individual

compensation tables.

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

● An axis can be both a base axis and a compensation axis at any one time. The programmed

position setpoint is used to calculate the compensation values.

● The scope of action of the compensation (starting and end position of the base axis) and

the distance between the interpolation points can be defined for every compensation table.

● The compensation can act as a function of the direction.

● Every compensation table has a modulo function for cyclic evaluation.

● A weighting factor can be taken into account for each compensation table, with which the

value in the table is multiplied.

● Using table multiplication, the actual compensation value K_A of compensation table A can

be multiplied with the actual compensation value K_x of any arbitrary compensation table X,

i.e. also with itself. The result of the table multiplication is added to the actual compensation

value K_A of compensation table A, and this is then the sum compensation value SK_A, which

is then effective in the compensation axis.

SK_A = K_A + K_A * K_x

● Axes-specific activation for all compensation relationships of the axis via the machine data:

MD32710 $MA_CEC_ENABLE[<axis>]

● Table-specificactivation via the setting data:

SD41300 $SN_CEC_TABLE_ENABLE[<table>]

Application example: Processing-dependent change to the compensation ratio by switching

the active compensation table via part program/synchronous actions or PLC user program.

Application examples

Compensation of repetitive errors with short wavelength

To compensate for repetitive errors with short wavelength in an axis, a compensation table

with modulo function for the repetitive error components (short wavelength) together with a

second compensation table without modulo function for the aperiodic error component are

parameterized for the same axis.

User-specific leadscrew error compensation

For user-specific leadscrew error compensation, a compensation table with the same axis is

parameterized as basic and compensation axis.

However, in this case there is a disadvantage in so much that contrary to the standard function

a measuring system switchover cannot be automatically taken into consideration.

5.5.3.2

Commissioning: Machine data

Number

Identifier

Meaning

NC-specific machine data

MD10240

$MN_SCALING_SYS-

Metric basic system

TEM_IS_METRIC.

MD10260

$MN_CONVERT_SCAL-

Basic system switchover active

ING_SYSTEM

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K3: Compensations

5.5 Interpolatory compensation

Number

Identifier

Meaning

MD18342

$MN_MM_CEC_MAX_POINTS

Number of interpolation points per compensation ta-

ble

Axis-specific machine data

MD32710

$MA_CEC_ENABLE

Enabling sag compensation

MD32711

$MA_CEC_SCALING_SYS-

System of units for sag compensation

TEM_METRIC

MD32720

$MA_CEC_MAX_SUM

Maximum compensation value for sag compensation

MD32730

$MA_CEC_MAX_VELO

Maximum velocity change for CEC

System of units (MD10240, MD10260, MD32711)

The system of units effective in the control system (metric or inch) is defined using:

MD10240 $MN_SCALING_SYSTEM_IS_METRIC = <system of units>

System of units switchover without automatic conversion

Table parameters with position data are automatically converted if the system of units changes.

The position data is always interpreted in the actual system of units. Conversion must be

implemented externally.

System of units switchover with automatic conversion

The automatic conversion of position data is activated using:

MD10260 $MN_CONVERT_SCALING_SYSTEM = TRUE

As a consequence, the system of units set in the following machine data is effective for all

compensation tables of the axis:

MD32711 $MA_CEC_SCALING_SYSTEM_METRIC = <system of units>

As a consequence, all position data is interpreted together with the summed compensation

value in the configured system of units. External conversion of position data is no longer

necessary when the system of units changes.

Axes-specific activation (MD32710)

Axis-specific activation for all compensation relationships of the axis is realized using:

MD32710 $MA_CEC_ENABLE[<axis>] = TRUE

Number of interpolation points per compensation table (MD18342)

The number of interpolation points per compensation table is parameterized using:

MD18342 $MN_MM_CEC_MAX_POINTS[<table index>] = <number of interpolation points>

The number of interpolation points required in a compensation table is calculated from the

maximum, minimum and step width (increment) set in System variables (Page 290) of table:

<Number of interpolation points> = ($AN_CEC_MAX - $AN_CEC_MIN) / $AN_CEC_STEP +

1

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Monitoring (MD32720, MD32730)

Absolute limiting

To avoid inadmissibly high compensation motion of the compensation axis, the summed

compensation value is monitored against the maximum value specified in the machine data:

MD32720 $MA_CEC_MAX_SUM[<compensation axis>] = <maximum value>

When the value is exceeded, the summed compensation value is limited to the maximum value

and alarm 20124 "Summed compensation value too high" is displayed.

Limiting the change

To avoid inadmissibly high dynamic loads on the compensation axis, the summed

compensation value change is monitored against the maximum value specified in machine

data:

MD32730 $MA_CEC_MAX_VELO[<compensation axis>] = <percentage of the maximum axis

velocity (MD32000 $MA_MAX_AX_VELO)>

When exceeded, the summed compensation value change is limited to the maximum value

and alarm 20125 "Compensation value change too fast" is displayed.

The reduced traversing distance as result of the limiting is output as soon as the compensation

value is no longer being limited.

5.5.3.3

Commissioning: Setting data

Number

Identifier

Meaning

SD41300

$SN_CEC_TABLE_ENABLE

Compensation table enable

SD41310

$SN_CEC_TABLE_WEIGHT

Weighting factor

Compensation table enable (SD41300)

The evaluation of the compensation table is enabled using the setting data:

SD41300 $SN_CEC_TABLE_ENABLE[<table index>] = TRUE

The compensation value determined using the compensation table is only added to the

summed compensation value of the compensation axis when the evaluation is enabled.

Weighting factor (SD41310)

The weighting factor should be entered in the setting data, with which the compensation value

determined from the compensation table is multiplied:

SD41310 $SN_CEC_TABLE_WEIGHT[<table index>] = <weighting factor>

As standard, the weighting factor has a value of 1.0. The compensation table becomes inactive

with a weighting factor of 0.0.

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

5.5.3.4

Commissioning: System variable

Identifier

Meaning

NC-specific system variables

$AN_CEC

Compensation values

$AN_CEC_DIRECTION

Direction dependency

$AN_CEC_INPUT_AXIS

Basic axis

$AN_CEC_INPUT_NCU

Basic axis on the NCU:

$AN_CEC_IS_MODULO

Modulo function

$AN_CEC_MAX

End position

$AN_CEC_MIN

Starting position

$AN_CEC_MULT_BY_TABLE

Multiplication

$AN_CEC_OUTPUT_AXIS

Compensation axis

$AN_CEC_OUTPUT_NCU

Compensation axis on the NCU

$AN_CEC_STEP

Distance between interpolation points

$AN_CEC_TYPE

Table type

Axis-specific system variables

$VA_CEC_COMP_VAL

Actual compensation value

Compensation values ($AN_CEC)

The compensation values of the compensation table should be entered into system variable:

$AN_CEC[<table index>, <interpolation point index>] = <compensation value>

<Interpolation point index> = 0 ≤ x ≤ (value of MD18342[<table index>]) - 1

Note

Before writing to system variable $AN_CEC, all of the compensation functions for all of the

axes must be deactivated:

● MD32700 $MA_ENC_COMP_ENABLE[<axis>] = 0

● MD32710 $MA_CEC_ENABLE[<axis>] = 0

Basic axis ($AN_CEC_INPUT_AXIS)

The basic axis should be entered into the system variable, i.e. the name of the axis whose

position setpoint is to be used as the input for the compensation table.

$AN_CEC_INPUT_AXIS[<table index>] = "<channel axis name>" or "<machine axis name>"

Compensation axis ($AN_CEC_OUTPUT_AXIS)

The compensation axis should be entered in the system variable, i.e. the name of the axis to

whose setpoint the compensation value is added.

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

$AN_CEC_OUTPUT_AXIS[<table index>] = "<channel axis name>" or "<machine axis

name>"

Note

If the names of channel and machine axes are the same in multi-channel systems, the standard

axis names AX1, AX2, etc. must be used.

Distance between interpolation points ($AN_CEC_STEP)

The distance between two interpolation points should be entered into the system variable

(position values of the basic axis) of the compensation table.

$AN_CEC_STEP[<table index>] = <distance between interpolation points>

Within a compensation table, the distance between interpolation points remains constant.

Starting position ($AN_CEC_MIN)

The setpoint position of the basic axis for the first interpolation point or the start of the

compensation table should be entered in the system variable.

$AN_CEC_MIN[<table index>] = <starting position>

Note

Setpoint position less than the starting position

The compensation value of the first interpolation point is used for all setpoint positions less

than the starting position.

Exception: Compensation tables with modulo function

End position ($AN_CEC_MAX)

The setpoint position of the basic axis for the last interpolation point or the end of the

compensation table should be entered in the system variable.

$AN_CEC_MAX[<table index>] = <end position>

Note

Setpoint position greater than the end position

The compensation value of the last interpolation point is used for all setpoint positions higher

than the starting position.

Exception: Compensation tables with modulo function

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

5.5.3.6

Commissioning: Overview diagram

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Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

5.5.3.8

Example 2: Compensation with table multiplication

Compensation of sag of the foundation of a drilling machine with table multiplication.

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Sag of the foundation

On large machines, sagging of the foundation can cause inclination of the whole machine.

The compensation in axis X1 depends on:

● The position of axis X1 because it determines the angle of inclination β

● The position of axis Z1, in which the drill is located.

The summed compensation value ΔX1_total is calculated from the compensation values ΔX1

and ΔZ1:

ΔX1_total = ΔZ1 * ΔX1 = ΔZ1 * sinβ(X1) ≈ ΔZ1 * β(X1)

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Table multiplication

Compensation table 1 (table index: 0)

● Basic axis: X1

● Compensation axis: X1

● Compensation values: Sine of the position-dependent tilt angle β, with β = f(position of X1)

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Compensation table 2 (table index: 1)

● Basic axis: Z1

● Compensation axis: X1

● Compensation values: Reaction of the position of axis Z1 on the measured position of axis

X1

Table multiplication

For compensation relationship 1 (table index: 0) the table multiplication should be set with the

compensation relationship 2:

$AN_CEC_MULT_BY_TABLE[ 0 ] = 2

5.5.3.9

Example 3: 2-dimensional array of compensation values

For flat-bed machines, the use case often arises in practice in which the sag compensation

values of the Z-axis depend on the axis positions of the X axis and Y axis. This is why it makes

sense to organize compensation values in a 2-dimensional array.

In this example, a possible way of implementing sag compensation using a grid, having a size

of 4 x 5 (rows x columns), is explained in more detail. The size of the complete measuring

range is 2000 x 900 mm². The compensation values are each determined in increments of

500 mm along the X axis and 300 mm increments along the Y axis. The interpolation points

with the relevant compensation values are positioned at the intersections of the grid (X-Y

plane). Compensation values between these interpolation points are linearly interpolated.

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Figure 5-17

Compensation values of the Z axis

Note

SINUMERIK Operate user interface

The currently effective compensation value of the Z axis as a result of sag compensation is

displayed on the SINUMERIK Operate user interface under:

Operating area: "Diagnostics" > "Axis diagnostics" > "Service axis" > Signal: "Compensation,

sag + temperature"

Implementation

For each line of the four-line the grid, a compensation table is set up with five interpolation

points. In the first compensation table, starting at interpolation point 1, in ascending sequence,

the compensation values 0.1 to 0.5 are entered in the first line. Using the same procedure, in

the first compensation table, compensation values 0.6 to 1.0 are entered in the second line,

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

etc. These compensation tables, relevant for the position of the X axis, are now designated

with f tablesand the table values as f_i(x), with i: Table number.

Additional compensation tables are required to take into account the position of the Y axis.

These compensation tables are now designated as g tables and the table values as g_i(y).

The number of f tables and g tables is equal. In the example, four:

In the g tables, one compensation value is set to 1 - and all the others to 0. The position of

compensation value 1 within the table is determined by the table number. In the first g table,

compensation value 1 is positioned at the first interpolation point and, in the second g table,

at the second interpolation point, etc. By multiplying g tables by f tables, the correct

compensation value in each f table is selected by multiplying it by 1. All irrelevant compensation

values are concealed through multiplication by 0.

The summed compensation value D_z at position (x/y) is calculated according to the following

equation:

D_z(x/y) = f_1(x) * g_1(y) + f_2(x) * g_2(y) + f_3(x) * g_3(y) + f_4(x) * g_4(y) = k_1 + k_2 + k_3

+ k_4

At location D_z(750/450), the summed compensation value of the Z axis is calculated to be:

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f_3(750) * g_3(450) + f_4(750) * g_4(450)

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Parameterization

Parameterization of machine data using the NC program

Program code

Comment

; Number of interpolation points for the compensation tables

$MN_MM_CEC_MAX_POINTS[0]=5

; Compensation table 1

$MN_MM_CEC_MAX_POINTS[1]=5

; Compensation table 2

$MN_MM_CEC_MAX_POINTS[2]=5

; Compensation table 3

$MN_MM_CEC_MAX_POINTS[3]=5

; Compensation table 4

$MN_MM_CEC_MAX_POINTS[4]=4

; Compensation table 5

$MN_MM_CEC_MAX_POINTS[5]=4

; Compensation table 6

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Program code

Comment

$MN_MM_CEC_MAX_POINTS[6]=4

; Compensation table 7

$MN_MM_CEC_MAX_POINTS[7]=4

; Compensation table 8

; Monitoring functions for axis Z1 corresponding to the 3rd machine axis

$MA_CEC_MAX_SUM[AX3]=10.0

; Max. summed compensation value

$MA_CEC_MAX_VELO[AX3]=100.0

; Max. change

Setting the table parameters (system variables) using the NC program

Program code

Comment

; To write to the compensation tables, the

; compensation for axis Z1 (compensation axis)

; must first be deactivated.

$MA_CEC_ENABLE[Z1] = FALSE

NEWCONF

; Activate $MA_CEC_ENABLE

; Define values f_i(x) in the f tables:

; Function values f_1(x) for table with index [0]

$AN_CEC[0,0]=0.1

$AN_CEC[0,1]=0.2

$AN_CEC[0,2]=0.3

$AN_CEC[0,3]=0.4

$AN_CEC[0,4]=0.5

; Function values f_2(x) for table with index [1]

$AN_CEC[1,0]=0.6

$AN_CEC[1,1]=0.7

$AN_CEC[1,2]=0.8

$AN_CEC[1,3]=0.9

$AN_CEC[1,4]=1.0

; Function values f_3(x) for table with index [2]

$AN_CEC[2,0]=1.1

$AN_CEC[2,1]=1.2

$AN_CEC[2,2]=1.3

$AN_CEC[2,3]=1.4

$AN_CEC[2,4]=1.5

; Function values f_4(x) for table with index [3]

$AN_CEC[3,0]=1.6

$AN_CEC[3,1]=1.7

$AN_CEC[3,2]=1.8

$AN_CEC[3,3]=1.9

$AN_CEC[3,4]=2.0

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Requirement

The axis container has to be located in the start position ($AN_AXCTAS == 0) when the sag

compensation is activated.

NOTICE

Changing the machine axes

After a axis container rotation, the same channel axes remain coupled. The coupled machine

axes can change.

5.5.4.5

Configuration example 1: NCU link with rigid coupling

In configuration example 1, the two channels of NCU 1 - and the channel axis names defined

using machine data MD20080 $MC_AXCONF_CHANAX_NAME_TAB - are shown. The

configuration of NCU 2 is not shown.

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① Assignment of channel axes to machine axes:

MD20070 $MC_AXCONF_MACHAX_USED[0 ... 2]

② Assignment of logical to real machine axes:

MD10002 $MN_AXCONF_LOGIC_MACHAX_TAB

③ Machine axis names:

MD10000 $MN_AXCONF_MACHAX_NAME_TAB

Figure 5-18

Configuration 1: NCU link with rigid coupling

Channel axis ZZ (NCU1, channel 2) is connected to machine axis AX2 of NCU 2. This means

that in order that machine axis AX2 of NCU 2 traverses, in the 2nd channel of NCU 1, axis ZZ

is traversed. For example, using the following commands in an NC program:

POS[ZZ]=10 FA[ZZ]=1000

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

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③ MD10000 $MN_AXCONF_MACHAX_NAME_TAB

Axis constellation after one axis container step

After the axis container rotates through one step (increment), channel axis YR is connected

to NC2_AX2, and channel axis YY is connected to NC1_AX5.

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

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① MD20070 $MC_AXCONF_MACHAX_USED.

② MD10002 $MN_AXCONF_LOGIC_MACHAX_TAB

③ MD10000 $MN_AXCONF_MACHAX_NAME_TAB

NC program NC_P1: Parameterization of the machine data for NCU 1

Program code

; ########## NCU1 ##########

; NC-specific machine data

$MN_NCU_LINKNO = 1

$MN_MM_NCU_LINK_MASK = 1

$MN_MM_LINK_NUM_OF_MODULES= 2

$MN_MM_SERVO_FIFO_SIZE = 3

$MN_ASSIGN_CHAN_TO_MODE_GROUP[1]=1

$MN_AXCONF_LOGIC_MACHAX_TAB[0] = "NC1_AX1"

$MN_AXCONF_LOGIC_MACHAX_TAB[1] = "NC1_AX3"

$MN_AXCONF_LOGIC_MACHAX_TAB[2] = "NC2_AX2"

$MN_AXCONF_LOGIC_MACHAX_TAB[3] = "NC1_AX4"

$MN_AXCONF_LOGIC_MACHAX_TAB[4] = "CT1_SL3"

$MN_AXCONF_LOGIC_MACHAX_TAB[5] = "CT1_SL4"

$MN_AXCT_AXCONF_ASSIGN_TAB1[0] = "NC1_AX5"

$MN_AXCT_AXCONF_ASSIGN_TAB1[1] = "NC1_AX6"

$MN_AXCT_AXCONF_ASSIGN_TAB1[2] = "NC2_AX1"

$MN_AXCT_AXCONF_ASSIGN_TAB1[3] = "NC2_AX2"

$SN_AXCT_SWWIDTH[0] = 1

; Channel-specific machine data: Channel 1

CHANDATA(1)

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Note

Sequence for SINUMERIK 828D

For SINUMERIK 828D, steps 2 and 3 are eliminated. This is because when the "sag

compensation, multi-dimensional" option is enabled, 12 tables each with 200 interpolation

points per table for the compensation immediately become available. This cannot be extended!

NC_CEC.INI

The "NC_CEC.INI" file copied via "Commissioning" > "System data" (from the folder "NC active

data" > "sag angularity comp") includes all negotiated sag/angularity and direction-dependent

LEC tables.

Backlash

The backlash should be set to 0:

● MD32450 $MA_BACKLASH [ <measuring system> ] = 0

Compensation parameters

The compensation parameters are set via the following system variables:

● $AN_CEC[ <table>,<interpolation point> ] (compensation value)

● $AN_CEC_INPUT_AXIS[ <table> ] (basic axis)

● $AN_CEC_OUTPUT_AXIS[ <table> ] (compensation axis)

Note

For the "directional LEC," the basis and compensation axes are alwaysidentical.

● $AN_CEC_STEP[ <table> ] (distance between interpolation points)

● $AN_CEC_MIN[ <table> ] (starting position)

● $AN_CEC_MAX[ <table> ] (end position)

● $AN_CEC_DIRECTION[ <table> ] (direction)

Note

The setting $AN_CEC_DIRECTION[<t>] = 0 (table is effective for both traversing directions

of the basic axis) is not relevant for the "direction-dependent LEC".

● $AN_CEC_IS_MODULO[ <table> ] (compensation with modulo function)

Note

For a description of these system variables, see Section "Compensation of sag and angularity

error: commissioning (Page 293)".

Extended Functions

Function Manual, 12/2018, A5E40874029B AB

315

K3: Compensations

5.5 Interpolatory compensation

System of units

See Section "Compensation for droop and angularity error: Commissioning (Page 293)".

Monitoring

See Section "Compensation for droop and angularity error: Commissioning (Page 293)".

5.5.5.3

Example

The following examples shows parameterization of the directional compensation tables for an

axis (machine axis AX1). All parameter values of the compensation tables are written by means

of a program.

Compensation parameters

● Basic axis = compensation axis = machine axis AX1

● Distance between interpolation points: 58.0 mm

● Starting position: -585.0 mm

● End position: -5.0 mm

Table definition

The 1st and 2nd compensation table are defined with 11 compensation interpolation points

each for machine axis AX1 as directional compensation tables:

● MD18342 $MN_MM_CEC_MAX_POINTS[ 0 ] = 11 (table 1: positive traversing direction)

● MD18342 $MN_MM_CEC_MAX_POINTS[ 1 ] = 11 (table 2: negative traverse direction)

Note

It is not necessary to define the number of interpolation points for SINUMERIK 828D, because

when enabling the "sag compensation, multi-dimensional" option, immediately 12 tables each

with 200 interpolation points per table for the compensation are available. This cannot be

extended!

Interpolation points and correction values

Interpolation points

Deviations or correction values

Deviation with compensation

Index

Position

pos. Traversing di-

neg. Traversing di-

pos. Traversing di-

neg. Traversing di-

[mm]

rection

rection

rection

rection

[mm]

[mm]

[mm]

[mm]

0

-585 ¹⁾

0.0000

0.0020

0.0000

-0.0008

1

-527

0.0010

0.0017

-0.0005

-0.0001

2

-469

0.0040

0.0053

-0.0001

-0.0009

3

-411

0.0034

0.0061

0.0001

-0.0009

4

-353

0.0013

0.0030

-0.0005

-0.0006

Extended Functions

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K3: Compensations

5.5 Interpolatory compensation

Interpolation points

Deviations or correction values

Deviation with compensation

Index

Position

pos. Traversing di-

neg. Traversing di-

pos. Traversing di-

neg. Traversing di-

[mm]

rection

rection

rection

rection

[mm]

[mm]

[mm]

[mm]

5

-295

0.0004

0.0016

-0.0002

-0.0003

6

-237

0.0016

0.0027

-0.0004

-0.0007

7

-179

0.0026

0.0043

-0.0004

-0.0004

8

-121

-0.0010

0.0026

0.0000

-0.0011

9

-63

-0.0023

0.0000

-0.0011

-0.0003

10

-5 ²⁾

-0.0031

-0.0012

-0.0001

-0.0012

1) Starting position: $AC_CEC_MIN[ <Table> ]

2) End position: $AC_CEC_MAX[ <Table> ]

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Programming

The following actions are performed by program "BI_SSFK_TAB_AX1_X.MPF":

● Deactivation of the compensation

● Deactivation of the compensation tables to be written (active tables cannot be written).

● Writing the compensation values into the compensation tables for the positive and negative

traversing direction of the X axis

● Writing the compensation parameters

; directional LEC

; 1st axis AX1

; table 1 - positive traversing direction

Extended Functions

Function Manual, 12/2018, A5E40874029B AB

317

K3: Compensations

5.5 Interpolatory compensation

$AN_CEC_OUTPUT_AXIS[1]=(AX1)

; compensation axis

$AN_CEC_STEP[1]=58.0

; distance between interpolation points

$AN_CEC_MIN[1]=-585.0

; starting position

$AN_CEC_MAX[1]=-5.0

; end position

$AN_CEC_DIRECTION[1]=-1

; table applies to negative traversing directions

$AN_CEC_MULT_BY_TABLE[1]=0

; no multiplication (not relevant here)

$AN_CEC_IS_MODULO[1]=0

; compensation without modulo function (for rotary

axes only)

;--- Aktivierung der Kompensation und der Tabellen

$MA_CEC_ENABLE[AX1]=1

; compensation ON

$SN_CEC_TABLE_ENABLE[0]=1

; enable table 1

$SN_CEC_TABLE_ENABLE[1]=1

; enable table 2

NEWCONF

M17

; end of program

5.5.6

Cylinder error compensation

5.5.6.1

Options

The following option is required to use the "Cylindrical error compensation" function:

● SINUMERIK Grinding Advanced (6FC5800-0AS35-0YB0)

5.5.6.2

Function

The cylinder error compensation is used to compensate for clamping errors for cylindrical

grinding. In this case, a shift and/or rotation of the workpiece in the machining plane is

compensated.

Contrary to Sag and angularity error compensation (Page 285), which is used as basis for

cylinder error compensation, only two interpolation points are used to define the compensation

function (straight line).

;

=

① Set position of the cylinder

② Actual position of the cylinder

Figure 5-19

Cylinder error due to incorrect clamping

Extended Functions

Function Manual, 12/2018, A5E40874029B AB

319

K3: Compensations

5.5 Interpolatory compensation

5.5.6.3

Commissioning

Number

Identifier

Meaning

SD41300

$SN_CEC_TABLE_ENABLE

Compensation table enable

SD41310

$SN_CEC_TABLE_WEIGHT

Weighting factor

SD41320

$SN_CEC_0

Compensation value at the starting position

SD41321

$SN_CEC_1

Compensation value at the end position

SD41330

$SN_CEC_BAS_0

Measuring point P1: Basic value

SD41331

$SN_CEC_BAS_1

Measuring point P2: Basic value

SD41335

$SN_CEC_BAS_STORE_0

Bit memories for measuring point P1: Basic value

SD41336

$SN_CEC_BAS_STORE_1

Bit memories for measuring point P2: Basic value

SD41340

$SN_CEC_COMP_0

Measuring point P1: Cylinder error

SD41341

$SN_CEC_COMP_1

Measuring point P2: Cylinder error

SD41350

$SN_CEC_COMP_STORE_

Bit memories for measuring point P1: Cylinder er-

0

ror

SD41351

$SN_CEC_COMP_STORE_

Bit memories for measuring point P2: Cylinder er-

1

ror

SD41355

$SN_CEC_CALC

Start of calculation by 0/1 edge

SD41356

$SN_CEC_CALC_ADD

Absolute or additive compensation values

Note

Table index

All of the subsequently described machine data, setting data and system variables with the

same index <t> belong to the same compensation table.

Compensation function

The compensation function of the cylinder error compensation is a straight line with the form:

ΔX = m*Z + b

ΔX:

Compensation value for the set position of the compensation axis

m:

Gradient of the compensation straight lines

Z:

Set position of the basic axis

b: Offset of the compensation straight lines

Measuring points

To enable the control to calculate the compensation function, the error in the compensation

axis must be measured at two points on the clamped cylindrical workpiece. In the following

figure, in accordance with the machining plane G18 (Z/X) that is usual in grinding, the basic

axis is designated Z and the compensation axis, X.

Extended Functions

320

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K3: Compensations

5.5 Interpolatory compensation

61B&(&B&203B > W!@

61B&(&B&203B > W!@

;

=

61B&(&B%$6B > W!@

61B&(&B%$6B > W!@

① Measuring point P1

② Measuring point P2

---

$SN_CEC_BAS_0/_1 : Positions of the measuring points in the basic axis (Z)

---

$SN_CEC_COMP_0/_1: Cylinder error at the measuring points in the compensation axis (X)

---

∅ D₁ == ∅ D₂

Figure 5-20

Measuring points of the cylinder error compensation

The measuring points must meet the following condition:

Z_P1 < Z_P2 ⇒ $SN_CEC_BAS_0 < $SN_CEC_BAS_1

Basic commissioning

Cylinder error compensation is based on sag compensation (CEC) (Page 285). As a

consequence, before commissioning the cylinder error compensation, the following

compensation parameters must first be set in the system variables of the sag compensation.

To this end, the required values are written to the system variables in an NC program.

Program code

Comment

$AN_CEC_INPUT_AXIS[<t>] = "<basic axis>"

; name of the basic axis

$AN_CEC_OUTPUT_AXIS[<t>] = "<compensa-

; name of the compensation axis

tion axis>"

$AN_CEC_MIN[<t>] = <starting position>

; starting position of the traversing

range in which the compensation should be

effective

$AN_CEC_MAX[<t>] = <end position>

; end position of the traversing range in

which the compensation should be effective

$AN_CEC_STEP[<t>] = <distance between in-

; distance between interpolation point =

terpolation points>

end position - starting position

$AN_CEC_DIRECTION[<t>] = 0

; no dependency on the direction

$AN_CEC_IS_MODULO[<t>] = FALSE

; no modulo functionality

Extended Functions

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321

K3: Compensations

5.5 Interpolatory compensation

Program code

Comment

$AN_CEC_MULT_BY_TABLE[<t>] = 0

; no multiplication with another table

$AN_CEC_TYPE = 1

; compensation type = cylinder error com-

pensation

Distance between interpolation points ($AN_CEC_STEP[t])

Because the compensation function is a straight line, only two interpolation points are required

for the cylinder error compensation. The distance between the interpolation points is therefore

the difference between the end and the starting position:

$AN_CEC_STEP[<t>] = $AN_CEC_MAX[<t>] - $AN_CEC_MIN[<t>]

Setting the cylinder error compensation

The following shows the principle approach when setting cylinder compensation.

1. Definition of whether the actual compensation values take effect absolutely or relatively:

Setting data

Meaning

SD41356

$SN_CEC_CALC_ADD[<t>]

Absolute or additive compensation values (0: ab-

solute, 1: relative)

2. Definition of the weighting factor to which the compensation values are added:

Setting data

Meaning

SD41310

$SN_CEC_TABLE_WEIGHT[<t>]

Weighting factor

The characteristic curve can be moved vertically via the weighting factor.

3. Determining the error in the direction of the compensation axis (X) at two measuring points.

4. Transfer the measuring points (basic value and error or compensation value) to the

compensation data:

Basic value (Z)

Compensation value (X)

Measuring point

SD41330 $SN_CEC_BAS_0[<t>]

SD41340 $SN_CEC_COMP_0[<t>]

P1

Measuring point

SD41331 $SN_CEC_BAS_1[<t>]

SD41341 $SN_CEC_COMP_1[<t>]

P2

5. Triggering a positive edge change (0→1) at the start of calculation of the compensation

function:

Setting data

Meaning

SD41355

$SN_CEC_CALC[<t>]

Start of calculation by 0→1 edge

Extended Functions

322

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K3: Compensations

5.5 Interpolatory compensation

6.

The control calculates the compensation values for the starting and end points of the

compensation straight lines, absolute or relative, depending on setting data SD41356

$SN_CEC_CALC_ADD[<t>]:

Absolute:

- SD41320 $SN_CEC_0[<t>] = <calculated compensation value at the starting position>

- SD41321 $SN_CEC_1[<t>] = <calculated compensation value at the end position>

Relative:

- SD41320 $SN_CEC_0[<t>] = SD41320 $SN_CEC_0[<t>] + <calculated compensation

value at the starting position>

- SD41321 $SN_CEC_1[<t>] = SD41321 $SN_CEC_1[<t>] + <calculated compensation

value at the end position>

Setting data

Meaning

SD41320

$SN_CEC_0[<t>]

Compensation value at the starting position

SD41321

$SN_CEC_1[<t>]

Compensation value at the end position

The measured values are written into bit memories after the calculation and then deleted:

- Bit memory = measured value

- Measured value = 0.0

Setting data

Meaning

Bit memory

SD41335

$SN_CEC_BAS_STORE_0[<t>]

Bit memories for measuring point P1: Base value

SD41350

$SN_CEC_COMP_STORE_0[<t>]

Bit memories for measuring point P1: Cylinder

error

SD41336

$SN_CEC_COMP_STORE_0[<t>]

Bit memories for measuring point P2: Base value

SD41351

$SN_CEC_COMP_STORE_1[<t>]

Bit memories for measuring point P2: Cylinder

error

Deleted measured values

SD41330

$SN_CEC_BAS_0[<t>]

Measuring point P1: Base value

SD41340

$SN_CEC_COMP_0[<t>]

Measuring point P1: Cylinder error

SD41331

$SN_CEC_BAS_1[<t>]

Measuring point P2: Base value

SD41341

$SN_CEC_COMP_1[<t>]

Measuring point P2: Cylinder error

7.

Set enable for use of the compensation table:

Setting data

Meaning

SD41300

$SN_CEC_TABLE_ENABLE[<t>]

Compensation table enable

Note

SINUMERIK Toolbox

File CNC_TAB_CONF.MPF is also provided in the SINUMERIK Toolbox. It includes an

example how cylinder error compensation can be parameterized within an NC program.

Extended Functions

Function Manual, 12/2018, A5E40874029B AB

323

K3: Compensations

5.5 Interpolatory compensation

5.5.6.4

Examples

In the following examples, for the cylinder error compensation, the first compensation table

(index 0) is used.

Example 1: Cylinder error compensation with absolute compensation values

Overview of the compensation parameters determining the characteristic

For the example, the compensation parameters shown in the following figure are used.

61B&(&B&203B > @

61B&(&B&203B > @

;

=

61B&(&B%$6B > @

61B&(&B%$6B > @

$1B&(&B0,1> @

$1B&(&B0$;> @

$1B&(&B67(3> @

General compensation data

Setting data $SN_...

Value

Meaning

SD41300

CEC_TABLE_ENABLE[0]

FALSE

Enable

SD41310

CEC_TABLE_WEIGHT[0]

1

Weighting factor

SD41356

CEC_CALC_ADD[0]

FALSE

Absolute compensation values ¹⁾

1) The compensation values calculated below are written into the setting data SD41320 $SN_CEC_0[0]

and SD41321 $SN_CEC_1[0], i.e. they are applied absolutely. In case of TRUE, they would be added

to the existing compensation values.

Axes, compensation range, and table properties

System variable $AN_...

Value

Meaning

CEC_INPUT_AXIS[0]

(Z)

Basic axis

CEC_OUTPUT_AXIS[0]

(X)

Compensation axis

CEC_MIN[0]

-400,000

Starting position

mm

CEC_MAX[0]

400,000

End position

mm

Extended Functions

324

Function Manual, 12/2018, A5E40874029B AB

K3: Compensations

5.5 Interpolatory compensation

System variable $AN_...

Value

Meaning

CEC_STEP[0]

800,000

Distance between interpolation points

mm

CEC_DIRECTION[0]

0

The compensation table applies to both travers-

ing directions of the basic axis.

CEC_IS_MODULO[0]

FALSE

No modulo function is active

CEC_MULT_BY_TABLE[0]

0

No table multiplication is active

Measuring points

Setting data $SN_...

Value

Meaning

SD41330

CEC_BAS_0[0]

110.0 mm

Measuring point P1: Base value

SD41331

CEC_BAS_1[0]

210.0 mm

Measuring point P2: Base value

SD41340

CEC_COMP_0[0]

0.001 mm

Measuring point P1: Cylinder error

SD41341

CEC_COMP_1[0]

0.002 mm

Measuring point P2: Cylinder error

Calculation of the compensation values

Calculation of the compensation values is performed by the control based on a rising edge

(0→1) in setting data SD41355 $SN_CEC_CALC[0]. The calculations shown below are

therefore only for illustration.

● Compensation function ΔX = f(Z):

;₃

;₃

˂; P

= E

= E

=₃

=₃

● Calculation of the gradient m:

6'

61B&(&B&203B > @

6'

61B&(&B&203B > @

P

6'

61B&(&B%$6B > @

6'

61B&(&B%$6B > @

● Calculating the offset b → measuring point P1(110.0, 0.001) and (2) used in (1):

0.001 = 1*10-5 * 110.0 + b

b = -1*10-4

(3)

● Resulting compensation function → (3) and (2) used in (1):

ΔX = 1*10^-5 * Z - 1*10^-4

● Calculating the compensation values → starting or end position used in (4):

SD41320 $SN_CEC_0[0] = ΔX_{COMP_0} = 1*10^-5 * -400000 - 1*10^-4 = -4.0001

SD41321 $SN_CEC_1[0] = ΔX_{COMP_1} = 1*10^-5 * 400000 - 1*10^-4 = 3.9999

Setting data $SN_...

Value

Meaning

SD41320

CEC_0[0]

-4.0001

Compensation value at the starting position

mm

SD41321

CEC_1[0]

3.9999

Compensation value at the end position

mm

SD41330

CEC_BAS_0[0]

0.0 mm

Measuring point P1: Base value (deleted)

SD41331

CEC_BAS_1[0]

0.0 mm

Measuring point P2: Base value (deleted)

Extended Functions

Function Manual, 12/2018, A5E40874029B AB

325

K3: Compensations

5.5 Interpolatory compensation

Setting data $SN_...

Value

Meaning

SD41335

CEC_BAS_STORE_0[0]

110.0 mm

Bit memories for measuring point P1: Base value

SD41336

CEC_BAS_STORE_1[0]

210.0 mm

Bit memories for measuring point P2: Base value

SD41340

CEC_COMP_0[0]

0.0 mm

Measuring point P1: Cylinder error (deleted)

SD41341

CEC_COMP_1[0]

0.0 mm

Measuring point P2: Cylinder error (deleted)

SD41350

CEC_COMP_STORE_0[0]

0.001 mm

Bit memories for measuring point P1: Cylinder

error

SD41351

CEC_COMP_STORE_1[0]

0.002 mm

Bit memories for measuring point P2: Cylinder

error

Example 2: Cylinder error compensation with relative compensation values

Example 2 based on the compensation data of example 1. The cylinder error compensation

is also realized using the first compensation table (index 0).

In example 2, the cylinder error is determined only at two measuring points, unlike example 1.

The compensation values are to apply relatively, i.e. they are added to the existing

compensation values from example 1.

General compensation data

Setting data $SN_...

Value

Meaning

SD41356

CEC_CALC_ADD[0]

TRUE

Relative compensation values ¹⁾

1) The compensation values calculated below are added to the setting data SD41320 $SN_CEC_0[0]

and SD41321 $SN_CEC_1[0].

Measuring points

Setting data $SN_...

Value

Meaning

SD41330

CEC_BAS_0[0]

10.0 mm

Measuring point P1: Base value

SD41331

CEC_BAS_1[0]

410.0 mm

Measuring point P2: Base value

SD41340

CEC_COMP_0[0]

0.0 mm

Measuring point P1: Cylinder error

SD41341

CEC_COMP_1[0]

-0.003

Measuring point P2: Cylinder error

mm

Extended Functions

326

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K3: Compensations

5.5 Interpolatory compensation

Calculation of the compensation values

Calculation of the compensation values is performed by the control based on a rising edge

(0→1) in setting data SD41355 $SN_CEC_CALC[0]:

● Compensation function: ΔX = m * Z + b = -7.5*10^-6 * Z + 7.5*10^-5

● Calculated compensation values:

- ΔX_{COMP_0} = 3.000075 mm

- ΔX_{COMP_1} = -2.999925 mm

● Adding the calculated compensation values to the actual compensation values:

- SD41320 $SN_CEC_CEC_0[0] = SD41320 $SN_CEC_CEC_0[0] + ΔX_{COMP_0} = -4.0001

mm + 3.000075 = -1.000025 mm

- SD41321 $SN_CEC_CEC_1[0] = SD41321 $SN_CEC_CEC_1[0] + ΔX_{COMP_1} = 3.9999

mm - 2.999925 mm = 0.999975

Setting data $SN_CEC_...

Value

Meaning

SD41320

CEC_0[0]

-1.000025

Compensation value at the starting position

mm

SD41321

CEC_1[0]

0.999975

Compensation value at the end position

mm

SD41330

CEC_BAS_0[0]

0.0 mm

Measuring point P1: Base value (deleted)

SD41331

CEC_BAS_1[0]

0.0 mm

Measuring point P2: Base value (deleted)

SD41335

CEC_BAS_STORE_0[0]

10.0 mm

Bit memories for measuring point P1: Base value

SD41336

CEC_BAS_STORE_1[0]

410.0 mm

Bit memories for measuring point P2: Base value

SD41340

CEC_COMP_0[0]

0.0 mm

Measuring point P1: Cylinder error (deleted)

SD41341

CEC_COMP_1[0]

0.0 mm

Measuring point P2: Cylinder error (deleted)

SD41350

CEC_COMP_STORE_0[0]

0.0 mm

Bit memories for measuring point P1: Cylinder

error

SD41351

CEC_COMP_STORE_1[0]

-0.003

Bit memories for measuring point P2: Cylinder

mm

error

5.5.7

Supplementary conditions

Compensated actual position

The following functions are based on the compensated actual position:

● Measurement

● Teach In

● Software limit switch

Extended Functions

Function Manual, 12/2018, A5E40874029B AB

327

K3: Compensations

5.6 Dynamic feedforward control (following error compensation)

5.6

Dynamic feedforward control (following error compensation)

5.6.1

General properties

Axial following error

The remaining system deviation of the position controller when traversing a machining axis is

known as axial following error. Expressed in another way, the axial following error is the

difference between the setpoint position and the actual position of the machine axis.

Effects

Particularly during acceleration in contour curvatures, e.g. circles and corners, this following

error leads to undesirable, velocity-dependent contour violations.

Compensation

The axial following error can be reduced almost to zero with the help of the "dynamic

feedforward control". The function is therefore also called "following error compensation".

Methods

There are two "dynamic feedforward control" methods:

● Speed feedforward control (velocity-dependent)

● Torque feedforward control (acceleration-dependent)

Activation

The feedforward control method is selected and activated using the machine data:

MD32620 $MA_FFW_MODE (feedforward control mode)

Value

Meaning

0

No feedforward control

1

Speed feedforward control with PT1 balancing

2

Torque feedforward control with PT1 balancing

3

Speed feedforward control with Tt balancing

4

Torque feedforward control with Tt balancing

Activation/deactivation in part program

The following axis-specific machine data can be used to define that the feedforward control

for the respective axis/spindle can be activated and deactivated by the part program:

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K3: Compensations

5.6 Dynamic feedforward control (following error compensation)

MD32630 $MA_FFW_ACTIVATION_MODE (activate feedforward control from program)

Value

Meaning

0

The feedforward control cannot be activated and deactivated from the part program. This

means that the state specified using MD32620 $MA_FFW_MODE is always effective for the

axis/spindle.

1

The feedforward control can be activated and deactivated from the part program. The operation

becomes active immediately.

2

The feedforward control can be activated and deactivated from the part program. The operation

only becomes active the next time that the axis comes to a standstill.

The feedforward control is activated/deactivated from the part program using the operations:

FFWON: Feedforward control ON

FFWOF: Feedforward control OFF

The default setting (i.e. M30 even after reset) is entered using the channel-specific machine

data:

MD20150 $MC_GCODE_RESET_VALUES (initial setting of the G groups)

FFWON/FFWOF is active for all axes/spindles in the axis mode, where:

MD32630 $MA_FFW_ACTIVATION_MODE = 1 (or 2)

and

MD32620 $MA_FFW_MODE = 1, 2, 3 or 4

The identical MD32630 setting should be used for axes that interpolate with each other.

The feedforward control should only be activated or deactivated while the axis/spindle is

stationary in the axis mode, in order to prevent jerky motion. Hence the switchover is delayed

automatically up to the next standstill through block search stop.

Note

A preprocessing stop has no effect for command or PLC axes traversing asynchronously to

the part program processing. To ensure that FFWON/FFWOF only has an effect on the axis/

spindle when it is next stationary in the axis mode, you must explicitly set MD32630 = 2 for

each axis/spindle in the axis mode (see also "Forward feed control for command- and PLC

axes (Page 335)").

5.6.2

Speed feedforward control

Function

In the case of speed feedforward control, a velocity setpoint is also applied directly to the input

of the speed controller. With this value the following error can be reduced to nearly zero (i.e.

system deviation is 0) when the velocity is constant.

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K3: Compensations

5.6 Dynamic feedforward control (following error compensation)

Commissioning

The following axis-specific parameters must be defined for the speed feedforward control

during commissioning:

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Equivalent time constant of the speed control loop (MD32810)

The equivalent time constant of the speed control loop must be determined accurately (e.g.

graphically from a speed setpoint step response) and entered into the following machine data

to correctly set the speed feedforward control:

MD32810 $MA_EQUIV_SPEEDCTRL_TIME (equivalent time constant speed control loop for

feedforward control)

Feedforward control factor for speed feedforward control (MD32610)

The additional velocity setpoint can be weighted using a factor:

MD32610 $MA_VELO_FFW_WEIGHT

Range of values: 0 ... 1

"0" means: no feedforward control. As standard, the factor has a value of 1 (≙ 100%).

The factor should remain set at 100%, as this value is the optimum setting for an optimally set

control loop for the axis/spindle as well as a precisely determined equivalent time constant of

the speed control loop.

Fine adjustment

The speed feedforward control for the particular axis/spindle can be optimized by making slight

changes (fine tuning) to the equivalent time constants of the speed control loop (MD32810).

To make this check, the axis/spindle should be traversed at a constant velocity and in the

service display "Axis/spindle", the "System deviation" should be checked.

A small acceleration and a high feedrate should be chosen so that the values can be easily

read on the service display. This produces very long acceleration phases from which it is easy

to read off the control deviation.

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5.6 Dynamic feedforward control (following error compensation)

Commissioning

The following axis-specific parameters must be defined during commissioning for torque

feedforward control:

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Equivalent time constant of the current control loop (MD32800)

The equivalent time constant of the current control loop must be determined accurately (e.g.

graphically from the step response of the current control loop) and entered in the following

machine data in order to correctly set the torque feedforward control:

MD32800 $MA_EQUIV_CURRCTRL_TIME (equivalent time constant current control loop for

feedforward control)

Total moment of inertia of axis (MD32650)

The total moment of inertia (moment of inertia of drive plus load referred to the motor shaft) of

the axis must be determined and entered in the following machine data:

MD32650 $MA_AX_INERTIA (inertia for torque feedforward control)

Fine adjustment

The torque feedforward control for the particular axis/spindle can be optimized by making slight

changes (fine tuning) to the values in MD32800 and MD32650.

To make a check, the following error should be recorded via the trace functionality. In addition

to traversing at a constant velocity, the following error should be monitored especially when

the axis/spindle accelerates.

Note

As a result of the extremely fast sequences when accelerating, when commissioning the torque

feedforward control, the service display cannot be used to check the fine adjustment.

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K3: Compensations

5.8 Friction compensation with a constant compensation value

˂Q

˂Q_RSW

D

Δn_opt

Amplitude of the velocity setpoint pulse

a

Acceleration at the quadrant transition

5.8.2

Commissioning

To determine the axis-specific compensation value Δn_opt, the Circularity test (Page 340) must

be used to determine the optimum amplitude of the velocity setpoint pulse Δn_{opt_a} for each of

a number of acceleration values. The different acceleration values should cover the entire

dynamic range.

Calculation of the acceleration at the quadrant transition

On a circular path, the acceleration a of a machine axis on direction reversal at the quadrant

transition is calculated from the radius r of the circle and the path velocity v: a = v² / r

Note

The path velocity and therefore the axis-specific acceleration a can be varied simply via the

feedrate override.

Evaluation of the value pairs determined (a, Δn_{opt_a})

To determine the compensation value Δn_opt, we recommend graphically applying the value

pairs determined in the circularity test comprising the acceleration a and the associated

optimum amplitude of the velocity setpoint pulse Δn_{opt_a}: Δn_{opt_a} = f(a)

˂Q

˂Q_RSW

*

D

Figure 5-21

Axis-specific characteristic determination

The optimum amplitude of the velocity setpoint pulse Δn_opt is obtained by drawing in the straight

line G1.

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K3: Compensations

5.8 Friction compensation with a constant compensation value

5. The optimized parameter values are applied graphically, e.g. amplitude = f(a

n

)

6. Setting of the next acceleration a_n and continuation with point 2.

Performing the circularity test without friction compensation

A circularity test without friction compensation should be performed to determine the initial

quality of the circular contour at the quadrant transitions. To do this, switch off the friction

compensation temporarily:

MD32500 FRICT_COMP_ENABLE[ <axis> ] = 0

The following figure shows a typical example of quadrant transitions without friction

compensation:

$[LV

,,

,

$[LV

,,,

,9

Figure 5-22

Quadrant transitions without friction compensation

The friction compensation must then be activated again:

MD32500 FRICT_COMP_ENABLE[ <axis> ] = 1

Performing circularity test with friction compensation

It is recommended that a small amplitude value and a decay time of just a few position control

cycles be set as initial values for the velocity setpoint pulse, e.g.:

● MD32520 $MA_FRICT_COMP_CONST_MAX[ <axis> ] = 10 [mm/min]

● MD32540 $FRICT_COMP_TIME[ <axis> ] = 0.008 [s]

The circularity test performed with these values provides an initial assessment of the friction

compensation.

Amplitude too small

Too small an amplitude value (MD32520) is revealed in the circularity test by insufficient

compensation of the contour deviations at the quadrant transitions.

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K3: Compensations

5.8 Friction compensation with a constant compensation value

$[LV

,,

,

$[LV

,,,

,9

Figure 5-23

Amplitude too small

Amplitude too large

Too large an amplitude value (MD32520) is revealed in the circularity test by overcompensation

of the contour deviations at the quadrant transitions.

$[LV

,,

,

$[LV

,,,

,9

Figure 5-24

Amplitude too large

Decay time too short

Too short a decay time (MD32540) is revealed in the circularity test when the contour deviations

at the quadrant transitions are compensated for for a short time but immediately increase again

thereafter.

$[LV

,,

,

$[LV

,,,

,9

Figure 5-25

Decay time too short

Decay time too long

Too long a decay time (MD32540) is revealed in the circularity test when the contour deviation

at the quadrant transitions is compensated for at first. This assumes that the optimum

Extended Functions

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K3: Compensations

5.8 Friction compensation with a constant compensation value

amplitude values has already been set. If the decay time is too long, however, the

compensation applies for too long and results in overcompensation at the next circular contour.

$[LV

,,

,

$[LV

,,,

,9

Figure 5-26

Decay time too long

Good friction compensation setting

With a good friction compensation setting, "no" contour violations can be detected at the

quadrant transitions.

$[LV

,,

,

$[LV

,,,

,9

Figure 5-27

Good friction compensation setting

See also

Friction compensation with adaptive characteristic (Page 344)

5.8.3

Supplementary conditions

Reaction of setpoint-related compensation functions

The following setpoint-related compensation functions affect the position setpoint and must

therefore be deactivated for the axes that perform a circularity test:

● Sag and angularity compensation (CEC)

MD32710 $MA_CEC_ENABLE[ <axis> ] = 0

● Directional leadscrew error compensation (LEC):

MD32710 $MA_CEC_ENABLE[ <axis> ] = 0

● Temperature compensation:

MD32750 $MA_TEMP_COMP_TYPE[ <axis> ] = 0

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5.9 Friction compensation with adaptive characteristic

5.9

Friction compensation with adaptive characteristic

5.9.1

Description of functions

The friction compensation with adaptive characteristic is intended for applications with the

following requirements:

● The velocity setpoint pulse required for friction compensation depends on the acceleration.

● It is enough if the characteristic is modeled by three different acceleration interpolation

points and a minimum and maximum amplitude of the velocity setpoint pulse.

● An acceleration-dependent amplitude and an acceleration-independent decay time are

sufficient to model the velocity setpoint pulse.

● For friction compensation at the positive and negative reversal point, the same velocity

setpoint pulse is sufficient.

● For greater acceleration, a smaller compensation value is required than for smaller

acceleration.

● The requirement for contour accuracy at the reversal points is high.

The following figure shows an example characteristic that can be set with this function:

˂Q

˂Q_PD[

˂Q_PLQ

D

D

D

D

%

%

%

%

Δn_max

Maximum amplitude of the velocity setpoint pulse

Δn_min

Minimum amplitude of the velocity setpoint pulse

a₁, a_2,

Acceleration interpolation points 1, 2, and 3

a₃

B1 ... Acceleration range 1 ... 4

B4

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5.9 Friction compensation with adaptive characteristic

The amplitude of the velocity setpoint pulse Δn is calculated in the relevant acceleration range

B1 to B4 to form:

Range

Acceleration a

Amplitude of the velocity setpoint pulse Δn

B1

a < a₁

Δn = Δn_max * a / a₁

B2

a₁ ≤ a ≤ a₂

Δn = Δn_max

B3

a₂ < a < a₃

Δn = Δn_max + [(Δn_min - Δn_max) / (a₃ - a₂)] * (a - a₂)

B4

a ≥ a₃

Δn = Δn_min

5.9.2

commissioning

To determine the axis-specific characteristic parameters, the Circularity test (Page 340) must

be used to determine the optimum amplitude of the velocity setpoint pulse Δn_{opt_a} each for each

of a number of acceleration values. The different acceleration values should cover the entire

dynamic range. In particular, a sufficient number of measurements must be ensured for low

acceleration values and large circle radii.

Calculation of the acceleration at the quadrant transition

On a circular path, the acceleration a of a machine axis on direction reversal at the quadrant

transition is calculated from the radius r of the circle and the path velocity v: a = v² / r

Note

The path velocity and therefore the axis-specific acceleration a can be varied simply via the

feedrate override.

Evaluation of the value pairs determined (a, Δn_{opt_a})

To determine the acceleration interpolation points a₁, a₂, and a₃ and the minimum and

maximum amplitude of the velocity setpoint pulse Δn_min and Δn_max, we recommend graphically

applying the value pairs determined in the circularity test comprising the acceleration a and

the associated optimum amplitude of the velocity setpoint pulse Δn_{opt_a}: Δn_{opt_a} = f(a)

˂Q

*

*

˂Q_PD[

*

˂Q_PLQ

*

D

D

D

D

%

%

%

%

Figure 5-28

Axis-specific characteristic determination

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5.10 Friction compensation with adaptive characteristics

● Settable parameters for the torque setpoint pulse:

- Amplitude ¹⁾

- Delay time

- Rise time

● A temperature, leadscrew error, and/or sag compensation that is active in parallel has no

effect on the friction compensation.

1): Parameters that can be adapted depending on the acceleration

Note

In most applications, compensation by means of velocity setpoint pulse and compensation

characteristics for amplitude and decay time are sufficient. Only if no satisfactory results have

been achieved should further options be used.

Examples of adapted characteristics

Y LQ PP PLQ

W LQ PV

D LQ P V

D LQ P V

W LQ PV

0 LQ 1P

D LQ P V

D LQ P V

①②③

Velocity setpoint pulse:

● Red: Lower reversal point

● Blue: Upper reversal point

④

Torque setpoint pulse

Compensation values for acceleration between the parameterized interpolation points are

interpolated linearly.

Extended Functions

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