Optimizing the Velocity Controller
Optimizing complex mechanical control systems require hands-on experience with controller tuning. This includes the ability to calculate control loop parameters and to apply identification procedures.
Less complex mechanical systems can often be optimized by means of experimental adjustment using the aperiodic limit method. The following parameters are used for this:
|
Parameter name HMI menu HMI name |
Description |
Unit Minimum value Factory setting Maximum value |
Data type R/W Persistent Expert |
Parameter address via fieldbus |
|---|---|---|---|---|
|
(ConF) → (drC-) ( Pn1) |
Velocity controller P gain. The default value is calculated on the basis of the motor parameters.
In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.0001 A/RPM. Modified settings become effective immediately. |
A/RPM 0.0001 - 2.5400 |
UINT16 R/W per. - |
Modbus 4610 IDN P-0-3018.0.1 |
|
(ConF) → (drC-) ( Pn2) |
Velocity controller P gain. The default value is calculated on the basis of the motor parameters.
In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.0001 A/RPM. Modified settings become effective immediately. |
A/RPM 0.0001 - 2.5400 |
UINT16 R/W per. - |
Modbus 4866 IDN P-0-3019.0.1 |
|
(ConF) → (drC-) (tin1) |
Velocity controller integral action time. The default value is calculated.
In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.01 ms. Modified settings become effective immediately. |
ms 0.00 - 327.67 |
UINT16 R/W per. - |
Modbus 4612 IDN P-0-3018.0.2 |
|
(ConF) → (drC-) (tin2) |
Velocity controller integral action time. The default value is calculated.
In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.01 ms. Modified settings become effective immediately. |
ms 0.00 - 327.67 |
UINT16 R/W per. - |
Modbus 4868 IDN P-0-3019.0.2 |
Verify and optimize the calculated values in a second step, see chapter Verifying and Optimizing the P Gain.
Reference Value Filter of the Velocity Controller
The reference value filter of the velocity controller allows you to improve the transient response at optimized velocity control. The reference value filter must be deactivated for the first setup of the velocity controller.
oDeactivate the reference value filter of the velocity controller. Set the parameter CTRL1_TAUnref (CTRL2_TAUnref) to the lower limit value "0".
|
Parameter name HMI menu HMI name |
Description |
Unit Minimum value Factory setting Maximum value |
Data type R/W Persistent Expert |
Parameter address via fieldbus |
|---|---|---|---|---|
|
(ConF) → (drC-) (tAu1) |
Filter time constant of the reference velocity value filter. In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.01 ms. Modified settings become effective immediately. |
ms 0.00 9.00 327.67 |
UINT16 R/W per. - |
Modbus 4616 IDN P-0-3018.0.4 |
|
(ConF) → (drC-) (tAu2) |
Filter time constant of the reference velocity value filter. In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.01 ms. Modified settings become effective immediately. |
ms 0.00 9.00 327.67 |
UINT16 R/W per. - |
Modbus 4872 IDN P-0-3019.0.4 |
Determining the Type of Mechanical System
To assess and optimize the transient response behavior of your system, group its mechanical system into one of the following two categories.
oSystem with rigid mechanical system
oSystem with a less rigid mechanical system
Rigid and less rigid mechanical systems
Determining Values for Rigid Mechanical Systems
In the case of a rigid mechanical system, adjusting the control performance on the basis of the table is possible if:
othe moment of inertia of the load and of the motor are known and
othe moment of inertia of the load and of the motor are constant
The P gain CTRL_KPn and the integral action time CTRL_TNn depend on:
oJL: Moment of inertia of the load
oJM: Moment of inertia of the motor
oDetermine the values on the basis of the following table:
|
|
JL= JM |
JL= 5 * JM |
JL= 10 * JM |
|||
|---|---|---|---|---|---|---|
|
JL |
KPn |
TNn |
KPn |
TNn |
KPn |
TNn |
|
1 kgcm2 |
0.0125 |
8 |
0.008 |
12 |
0.007 |
16 |
|
2 kgcm2 |
0.0250 |
8 |
0.015 |
12 |
0.014 |
16 |
|
5 kgcm2 |
0.0625 |
8 |
0.038 |
12 |
0.034 |
16 |
|
10 kgcm2 |
0.125 |
8 |
0.075 |
12 |
0.069 |
16 |
|
20 kgcm2 |
0.250 |
8 |
0.150 |
12 |
0.138 |
16 |
Determining Values for Less Rigid Mechanical Systems
For optimization purposes, determine the P gain of the velocity controller at which the controller adjusts velocity _v_act as quickly as possible without overshooting.
oSet the integral action time CTRL1_TNn (CTRL2_TNn) to infinite (= 327.67 ms).
If a load torque acts on the motor when the motor is at a standstill, the integral action time must not exceed a value that causes unwanted changes of the motor position.
If the motor is subject to loads when it is at a standstill, setting the integral action time to "infinite" may cause position deviations (for example, in the case of vertical axes). Reduce the integral action time if the position deviation is unacceptable in your application. However, reducing the integral action time can adversely affect optimization results.
|
|
|
UNINTENDED MOVEMENT |
|
oOnly start the system if there are no persons or obstructions in the zone of operation. oVerify that the values for the velocity and the time do not exceed the available movement range. oVerify that a functioning emergency stop push-button is within reach of all persons involved in the operation. |
|
Failure to follow these instructions can result in death, serious injury, or equipment damage. |
oTrigger a step function.
oAfter the first test, verify the maximum amplitude for the reference value for the current _Iq_ref.
Set the amplitude of the reference value just high enough so the reference value for the current _Iq_ref remains below the maximum value CTRL_I_max. On the other hand, the value selected should not be too low, otherwise friction effects of the mechanical system will determine the performance of the control loop.
oTrigger another step function if you had to modify _v_ref and verify the amplitude of _Iq_ref.
oIncrease or decrease the P gain in small increments until _v_act is obtained as fast as possible. The following diagram shows the required transient response on the left. Overshooting - as shown on the right - is reduced by reducing CTRL1_KPn (CTRL2_KPn).
Differences between _v_ref and _v_act result from setting CTRL1_TNn (CTRL2_TNn) to "Infinite".
Determining "TNn" for the aperiodic limit
In the case of drive systems in which oscillations occur before the aperiodic limit is reached, the P gain "KPn" must be reduced until oscillations can no longer be detected. This occurs frequently in the case of linear axes with a toothed belt drive.
Graphic Determination of the 63% Value
Graphically determine the point at which the actual velocity _v_act reaches 63% of the final value. The integral action time CTRL1_TNn (CTRL2_TNn) then results as a value on the time axis. The commissioning software supports you with the evaluation:
|
Parameter name HMI menu HMI name |
Description |
Unit Minimum value Factory setting Maximum value |
Data type R/W Persistent Expert |
Parameter address via fieldbus |
|---|---|---|---|---|
|
(ConF) → (drC-) (tin1) |
Velocity controller integral action time. The default value is calculated.
In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.01 ms. Modified settings become effective immediately. |
ms 0.00 - 327.67 |
UINT16 R/W per. - |
Modbus 4612 IDN P-0-3018.0.2 |
|
(ConF) → (drC-) (tin2) |
Velocity controller integral action time. The default value is calculated.
In the case of switching between the two control loop parameter sets, the values are changed linearly over the time defined in the parameter CTRL_ParChgTime. Type: Unsigned decimal - 2 bytes Write access via Sercos: CP2, CP3, CP4 In increments of 0.01 ms. Modified settings become effective immediately. |
ms 0.00 - 327.67 |
UINT16 R/W per. - |
Modbus 4868 IDN P-0-3019.0.2 |
