Finding a Linear Encoder's Index Value with a Linear ActuatorPrimary 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 have an encoder attached to an actuator. I have wired the index output of my encoder to my motion control system. The encoder appears to work fine except when I try to perform a Find Index move. My actuator moves a short distance and stops without ever finding the index position 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 MAX (Measurement & Automation Explorer) to reflect how many encoder counts occur in one revolution of the system. When working with a linear actuator this setting is not relevant because the actuator and encoder move only in a straight line. When you perform a Find Index move 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 (2in x 10,000cpi) counts. By doing this, your actuator will be sure to move the full length of travel while looking for the index pulse. Related Links: Advisors for Motion KnowledgeBase 1KQF9LC4: Recommended Suppliers for Linear Actuators (Stages) Attachments:
Report Date: 05/12/2004 Last Updated: 06/09/2009 Document ID: 39BJBEQX |
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