Overview

This block computes a servo algorithm with Proportional, Integral, and Derivative (PID) filter transformation and Feed Forwards. The integration sum is limited (MovingImax and RestImax) and the derivative may be filtered (Ksm). The block supports up to five different values for each parameter. The parameter values are loaded as text-based parameter files. At run-time, the block parameters can be simultaneously changed at any time by updating the Gain Index input to the PID_GT block.

Example

The following example demonstrates the PID with Gain Table block usage in a simple model. The application can write into the Memory User Buffer location to change the Gain Index.

PID

The coefficients for this block are as follows:

AxisNumber	Specifies the Axis object for Position, Velocity, and Acceleration information.
Kp	Proportional gain. Kp output = input * Kp
Ki	Integral gain. Ki output = Σ(input) * Ki, not to exceed MovingIMax or RestIMax.
Kd	Derivative gain. Kd output = (position error (current) - position error (previous)) * Kd
Kpff	Position feed forward — NOT USED
Kvff	Velocity feed forward. Kvff output = Cmd Velocity(axisNumber) * Kvff
Kaff	Acceleration feed forward. Kaff output = Cmd Accel(axisNumber) * Kaff
Kiff	Friction feed forward. Kfff output = (IF Cmd Velocity <> 0) * Kfff *sign(Cmd Velocity)
MovingImax	Limit value for the integration sum when Command Velocity <> 0.
RestImax	Limit value for the integration sum when Command Velocity = 0.
Ksm	Smoothing parameter. 0 = no smoothing 1 = infinite smoothing
OutputLimit	Command signal Output Limit.
OutputLimitH	Command signal High Output Limit.
OutputLimitL	Command signal Low Output Limit.
Ts	Sample period of the PID algorithm. This is the cycle time of the PID algorithm in Simulink simulation. This value has no effect on the PID execution on the controller.
Subsample Code	A code which determines the schedule for updating this block (every sample, even samples only, etc.). See Subsampling.

Matlab/Simulink

Simulink Interface

PID_Simulink

The Position Error input should connect to a position error block or equivalent (for example the output of a sum block). The Output is the torque command ready to connect to a motor output or equivalent. The Gain Index input determines which of the five gain tables are used by the servo algorithm. Valid values are 0 through 4.

IMPORTANT! The new Servo Gains are applied immediately when the Gain Index value is changed. The Position Integrator Reset input controls the resetting of the Integrator sum internal to the block. When a non-zero value is detected at the Reset input the integrator sum will be set to zero.

The block has two user data fields (User Data 0, User Data 1) to store application-specific data for convenient storage and retrieval. See User Data Storage for details.

The block's update schedule is determined by the Subsample Code (See Subsampling). The following Parameter Dialog Box is opened by double-clicking on the block in a Simulink Model

PID_GT_Blk

C++ API

PID_GTBlock

Declaration

Public Method

PID_GTBlock&   PID_GT();

Required Header: mechaware.h

Description

This block represents the standard PID algorithm as used on the ZMP-SynqNet controller including the Gain Tables and Feed Forward parameters. The only exception is the addition of Ksm value for smoothing.

Each Parameter must have corresponding .txt file containing structure with five (5) Coefficient values. Individual parameters can be modified using the API functions below.

int32_t	PID_GT().AxisNumber	Axis number
double	PID_GT().ErrorSum	Summation of position integral error.
double	PID_GT().ErrorDelta	Derivative error.
double	PID_GT().Kp[index]	Set derivative gain value at index (0 - 4). Kd output = (position error (current) - position error (previous) * Kd smoothed (See Ksm below).
double	PID_GT().Ki[index]	Set integral gain value at index (0 - 4). Ki output = Σ(input) * Ki, not to exceed IMax.
double	PID_GT().Kd[index]	Set derivative gain value at index (0 - 4). Kd output = (position error (current) - position error (previous) * Kd smoothed (See Ksm below).
double	PID_GT().Kpff[index]	Not used.
double	PID_GT().Kvff[index]	Set velocity feed forward gain at index (0 - 4).
double	PID_GT().Kaff[index]	Set friction feed forward gain at index (0 - 4).
double	PID_GT().Kfff[index]	Set friction feed forward gain at index (0 - 4).
double	PID_GT().MovingIMax	Limit for the maximum value of the integration sum when Command Velocity <> 0.
double	PID_GT().RestIMax	Limit for the maximum value of the integration sum when Velocity = 0.
double	PID_GT().Ksm[index]	Smoothing parameter. 0 = no smoothing 1 = infinite smoothing
double	PID_GT().OutputLimit[index]	Control loop output limit. The absolute value of the control output will never exceed this value. (DAC counts)
double	PID_GT().OutputLimitHigh[index]	Control loop output positive limit The control output will never exceed this value in the positive sense. The smaller (more negative) value contained between Output Limit and Output Limit High will take precedence. (DAC counts)
double	PID_GT().OutputLimitLow[index]	Control loop output negative limit. The control output will never exceed this value in the positive sense. The smaller (more negative) value contained between Output Limit and Output Limit High will take precedence. (DAC counts)
double	PID_GT().OutputOffset[index]	Control loop offset. Creates an offset to the control output. The Output Offset is not removed from the DAC in an abort condition. (DAC counts)

Methods

Block Methods

Remarks

The PID with Reset block is an alternate PID block without gain tables or feed forward terms.