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13.2.2 Computer Control of Robot Paths (Incremental Interpolation)

•Path Planning is a simple process where the path planning methods described before (such as straight line motion) are used before the movement begins, and then a simple real-time lookup table is used.

•The path planner puts all of the values in a trajectory table.

•The on-line path controller will look up values from the trajectory table at predetermined time, and use these as setpoints for the controller.

•The effect of the two tier structure is that the robot is always shooting for the next closest ‘knot-point’ along the path.

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• The above scheme leads to errors between the planned, and actual path, and lurches occur

when the new setpoints are updated for each servo motor.

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position

required

actual

time

•The quantization of the desired position requires a decision of what value to use, and this value is fixed for a finite time.

•The result is that the path will tend to look somewhat bumpy,