Why Do I Need Limit Switches to Find the Home Position? Primary Software: Driver Software>>NI-Motion/FlexMotionPrimary Software Version: 7.2 Primary Software Fixed Version: 7.2 Secondary Software: N/A Hardware: Motion Control>>Controllers
Problem: My motion setup provides a signal for the home switch, but no limit switches. Can I use the Find Reference functions in this setup? Solution: Some motion stages use a voltage-level reference switch in which the line voltage is changed on different sides of the Home switch. The voltage level can then be used to determine whether the motor is behind or in front of the Home position. This ensures that a homing routine searches in the proper direction. Figure 1 illustrates this setup.
NI 73xx series motion controllers are designed to work with momentary reference switches. This type of switch changes the circuit voltage only while closed (when the motor is at that position). Because the voltage level is the same on either side of the Home switch, the controller has no idea where the motor is currently located. When a Find Reference move is commanded, the motor moves in the Initial Search Direction (which is set on the Find Reference Settings page in MAX). If the motor begins searching in the wrong direction, it must hit a Limit switch to turn around and search in the other direction. If no Limit switch is present, the motor will continue to search indefinitely. Figure 2 illustrates this setup.
Related Links: Developer Zone: Find Reference Settings for Motion Controllers KnowledgeBase 25TFOAQ1: Must Enable Limits During Home Routine Attachments:  
Report Date: 02/21/2006 Last Updated: 07/21/2007 Document ID: 3UKJBHD3 |
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