How Can I Specify Acceleration, Velocity, and Deceleration for a Contoured Move? Primary Software: Driver Software>>NI-Motion/FlexMotionPrimary Software Version: 4.5 Primary Software Fixed Version: N/A Secondary Software: N/A Hardware: Motion Control>>Controllers>>PCI-7344
Problem: How can I specify acceleration, velocity, and deceleration profiles for a contoured move when the trajectory generator on the motion controller is not used during a contoured move? Solution: With a contoured move, the acceleration, deceleration, and velocity are inherent in the contour data. You are responsible for providing the points in a way that results in the appropriate acceleration, velocity and deceleration. Points at the beginning and end of your contouring data should be closer together to achieve the desired acceleration and deceleration. The NI-Motion controller processes the contouring data by splining between successive points given the Requested Interval parameter, which indicates the requested time between points (in milliseconds). Your 734x or 735x controller sends a series of step inputs to the motor at the loop update rate of the PID controller built into the motion control card. The inertia of the motor smooths out the discrete position change updates and results in the actual acceleration, velocity, and deceleration profiles observed. A cubic spline algorithm is used to determine the position points between user-specified contour points. With each loop iteration of the PID controller, the motion controller passes the next cubic-spline-generated position point to the motor. Given each new instantaneous step input, the motor then tries to attain this new position given the limitations of its own inertia and the power available from the amplifier/drive. You cannot directly specify the maximum acceleration, velocity, and deceleration values because the cubic spline algorithm is not something that you can control. The algorithm maps a smooth curve between the contour points that you specify and then places intermediary position values along that curve. In order to change your motor's trajectory profile, you need to adjust the spacing of the position points in your contour buffer and/or adjust the Requested Interval parameter. Moving points closer together reduces the acceleration/deceleration values in the trajectory, as does increasing the Requested Interval value. Please keep in mind that the Requested Interval value you specify is used as the requested time interval between all successive points in your contour buffer. For more information on contoured moves, please refer to Chapter 7 of the NI-Motion User Manual, accessible from the Motion Control Technical Library. Related Links: Developer Zone Tutorial: Motion Control Technical Library Attachments:
Report Date: 10/15/2007 Last Updated: 11/13/2007 Document ID: 4EEJKGQ7 |
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