Finding an Encoder's Index Value with a Linear Actuator Primary Software: Driver Software>>NI-Motion/FlexMotionPrimary Software Version: 6.1 Primary Software Fixed Version: 6.0 Secondary Software: Motion Assistant Hardware: Motion Control>>Controllers>>PCI-7344
Problem: I am using a National Instruments motion controller. I have an encoder attached to the actuator and have wired the Index output of my encoder to my motion control setup. In general, the encoder seems to work just fine; however, when I try to perform a Find Index move, my actuator only moves a very short distance. It then stops without ever finding the index of the encoder. Why is this happening, and what can I do to correct it? Solution: In general, motion controllers are designed to work primarily with rotary motors. When working with a rotary motor and rotary encoder, you would set the Encoder Counts per Revolution setting in Measurement & Automation Explorer (MAX). When working with a linear actuator, this setting is not relevant, as the actuator and encoder move only in a straight line. When you choose to Find Index with a rotary encoder the motion controller rotates the motor one time, assuming that it will receive the index pulse at some point during this one revolution. If it does not find this index pulse, it simply stops, and assumes that there is no index pulse to be found. This same logic still applies for linear actuators. The software does not realize that your encoder is a linear encoder, and still assumes it will find the index during a single "rotation." To avoid this, set your Encoder Counts per Revolution value to the full length of travel of your linear actuator. For example, if your actuator can move two inches, and your encoder outputs 10,000 counts per inch, then you would want to set your Encoder Counts per Revolution to 20,000 (2 x 10,000) counts. By doing this, your actuator will be sure to move the full length of travel while looking for the index pulse. Related Links: Recommended Suppliers for Linear Actuators (Stages) National Instruments Motion Control Support Homepage Attachments:
Report Date: 05/12/2004 Last Updated: 07/13/2004 Document ID: 39BJBEQX |
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