High-Speed Capture

Description

High-speed capture inputs are an enhancement to the encoder FPGA and are available when the encoders are operating as axis feedback or as independent encoder resources. The Enable High-Speed Position Capture function/VI enables high-speed capture inputs to capture instantaneous encoder position when an input becomes active. The position capture is implemented in the encoder FPGA to reduce capture latency to the sub-100 nanosecond range.

High-speed capture functionality is performed by the encoder resources themselves. When this function/VI is sent to axes, it is actually being sent to the mapped encoder resources. High-speed inputs are only available on the FPGA encoder resources (0x21 through 0x24).

The high-speed inputs have programmable polarity. You can set the active state of the input as active-low (inverting) or active-high (noninverting) with the Set High-Speed Capture Polarity function/VI. You can determine the results of the high-speed capture from the Read High-Speed Capture Status and Read Captured Position functions/VIs.

High-speed capture is useful in registration and synchronization applications. You can calculate subsequent moves relative to the captured position. Refer to the Set Operation Mode function/VI for information on relative-to-capture mode.

High-speed capture functionality is available on servo and closed-loop stepper axes FlexMotion controllers.

The high-speed capture inputs can also function as latching general-purpose inputs. Configure them as you would for high-speed capture operation, but ignore the captured position. You can then read the state of the latched inputs.

Using the Making a Move Relative to a High-Speed Capture Input example, you can perform a move of a specified length relative to the position at which a trigger input is received. You can think of this conceptually as a conveyor belt application running at a constant velocity. Each time a manufactured item moves down the conveyor belt and breaks a light beam across the belt, a stamp is placed on the item a set distance from the point where the beam is broken. This allows all items to be stamped in the same relative position without necessarily being equally spaced along the conveyor belt.

Common Applications

Motion/Vision applications

Related Links:
Making a Move Relative to a High-Speed Capture Input
High-Speed Input Capture Example.vi

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