Breakpoints with Analog FeedbackHardware: Motion Control>>Controllers>>PCI-7350, Motion Control>>Controllers>>PCI-7352, Motion Control>>Controllers>>PCI-7354, Motion Control>>Controllers>>PCI-7356, Motion Control>>Controllers>>PCI-7358
Problem: I have a PCI-735x motion control board and I would like to be able to generate a breakpoint output signal corresponding to my analog feedback. Do NI motion controllers support breakpoints with analog feedback? If they are not supported, what are some other options? Solution: Currently, breakpoints with analog feedback are not supported on National Instruments motion controllers. In the NI-Motion User Manual† it states the following about breakpoints (in chapter 12, on page 12-2): "The current position is continuously compared against the specified breakpoint position by the encoder circuitry to produce a latency of less than 100 ns." This means that the FPGA circuitry on the motion controller actually uses encoder inputs to determine the breakpoint outputs. Because this is done on the FPGA, it allows the 735x to have the high speed buffered breakpoint functionality. The reason that breakpoints with analog feedback are not supported is that the FPGAs are not configured to do so. Also, if analog feedback was to be programmed on the FPGA to work with breakpoints, it would be difficult to determine when an actual breakpoint would be triggered, as there are no rising or falling edges with the analog feedback, just a specific voltage level. One workaround would be to perform some calculations in software to programmatically trigger the breakpoints. The program would constantly poll the ADC voltage and then compare it with a desired voltage level. When the desired voltage is reached, a digital output would be sent out on a trigger line. This method it will most likely not be fast enough for high speed motion and synchronization. Another option that you can consider is to find an analog-to-encoder converter. With the converter, you will be able to generate an encoder signal that you can use to give you a position feedback similar to normal encoders, thus allowing you to use the breakpoint functionality. † In versions of NI-Motion later than version 7.5, the NI-Motion User Manual has been replaced by NI-Motion Help which installs with NI-Motion an can be found at Programs»National Instruments»NI-Motion»Documentation»NI-Motion Help. Related Links: Product Manuals: NI-Motion User Manual Developer Zone Tutorial: 10 Essential Technologies for High-Performance Motion Control Developer Zone Example: Motion Breakpoints used as Triggers for Finite Retriggerable Analog DAQ Acquisition Attachments:
Report Date: 05/10/2006 Last Updated: 02/11/2009 Document ID: 3X9LH6HB |
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