Galil DMC-1700 a. Connect Standard Servo Motors, Check the Polarity of the Feedback Loop

Step 8a. Connect Standard Servo Motors

The following discussion applies to connecting the DMC-1700/1800 controller to standard servo motor amplifiers:

The motor and the amplifier may be configured in the torque or the velocity mode. In the torque mode, the amplifier gain should be such that a 10 Volt signal generates the maximum required current. In the velocity mode, a command signal of 10 Volts should run the motor at the maximum required speed.

Step by step directions on servo system setup are also included on the WSDK (Windows Servo Design Kit) software offered by Galil. See section on WSDK for more details.

Check the Polarity of the Feedback Loop

It is assumed that the motor and amplifier are connected together and that the encoder is operating correctly (Step B). Before connecting the motor amplifiers to the controller, read the following discussion on setting Error Limits and Torque Limits. Note that this discussion only uses the X axis as an example.

Step A. Set the Error Limit as a Safety Precaution

Usually, there is uncertainty about the correct polarity of the feedback. The wrong polarity causes the motor to run away from the starting position. Using a terminal program, such as DMCTERM, the following parameters can be given to avoid system damage:

Input the commands:

ER 2000 <CR>Sets error limit on the X axis to be 2000 encoder counts OE 1 <CR> Disables X axis amplifier when excess position error exists

If the motor runs away and creates a position error of 2000 counts, the motor amplifier will be disabled. Note: This function requires the AEN signal to be connected from the controller to the amplifier.

Step B. Set Torque Limit as a Safety Precaution

To limit the maximum voltage signal to your amplifier, the DMC-1700/1800 controller has a torque limit command, TL. This command sets the maximum voltage output of the controller and can be used to avoid excessive torque or speed when initially setting up a servo system.

When operating an amplifier in torque mode, the v

voltage output of the controller will be directly related to the torque output of the motor. The user is responsible for determining this relationship using the documentation of the motor and amplifier. The torque limit can be set to a value that will limit the motors output torque.

When operating an amplifier in velocity or voltage mode, the voltage output of the controller will be directly related to the velocity of the motor. The user is responsible for determining this relationship using the documentation of the motor and amplifier. The torque limit can be set to a value that will limit the speed of the motor.

For example, the following command will limit the output of the controller to 1 volt on the X axis:

TL 1 <CR>

Note: Once the correct polarity of the feedback loop has been determined, the torque limit should, in general, be increased to the default value of 9.99. The servo will not operate properly if the torque limit is below the normal operating range. See description of TL in the command reference.

Step C. Enable Off-On-Error as a safety precaution. To limit the maximum distance the motor will move from the commanded position, enable the Off-On-Error function using

DMC-1700/1800 Chapter 2 Getting Started • 27