Delta Tau PMAC2 PCI User Manual download pdf (Page 71)

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PMAC2 User Manual

Setting Up PMAC2 for Pulse-and-Direction Control 63

Integration mode Ix34 is irrelevant if Ix33 is set to zero. If Ix33 is used, setting Ix34 to 1 turns on the

integral gain only when the commanded velocity is zero; setting Ix34 to 0 turns it on all of the time.

Acceleration Feedforward Gain: Ix35

Typically, the acceleration feedforward gain term Ix35 is set to zero, because the electronic loop has no

inertia to overcome. However, some will want to use Ix35 to compensate for the small time delays

created by the addition process in pulse generation that will cause small following errors when the

velocity is changing. For a given servo update time, an optimum Ix35 value can be found that virtually

eliminates errors at all accelerations.

Notch Filter Parameters: Ix36 - Ix39

Notch filter parameters Ix36 to Ix39 are set to zero in the open-loop case, because the electronic loop

itself has no resonance, even if the mechanical system does.

Testing the Setup

Preparing for the Test

With an open-loop system, you can test much of the initial operation of the setup without attaching

anything to the PMAC2, because the loop operates entirely within PMAC2. To do this, disable the

position limits with Ix25. For example, the default value of I125 is $C000, which dictates the use of the

first set of flags. Changing I125 to $2C000 disables the limit flag inputs, permitting an unconnected

PMAC to command moves.

The initial test should be simple monitoring of motor position and velocity as commands are given to the

motor. The position reporting window in the PMAC Executive program provides a very convenient way

to monitor this. Select the window option that displays position, velocity, and following error for the

motor you are testing. In the 3.0 Executive and newer, you can specify the units of the reported position

and velocity (counts per second for velocity equals Hertz).

Executing the Open-Loop Test

First, use the O (open-loop output) command to verify the operation of the frequency generator. This

command simply places a value proportional to the magnitude of the command into the output register.

This should generate a constant frequency output from the pulse generator that shows up as a constantly

changing position and a steady non-zero (for non-zero commands) velocity in the reporting window. Do

not worry about exact values now; just see if a change can be created. An O10 command should create a

positive velocity and a position counting in the positive direction; an O-10 command should create a

negative velocity and a position counting in the negative direction.

Troubleshooting the Open-Loop Test

If this result is not received, check the following:

1. Use the Why Am I Not Moving? screen in the Executive program to see if there is some reason

PMAC2 firmware is not permitting the command. For instance, the overtravel limit inputs may need

to be held low or the limit function disabled with Ix25.

2. If there is an oscilloscope or frequency counter, see if a pulse train is received on the output pin. This

will help isolate the problem. If the pulse train is not received with a non-zero O command and no

pulse train with an O0 command, pulses are being genereated but not being feed back properly. If

there is no pulse train, pulses are not generating properly.

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