A TLR robot has a rotational joint (R) whose output link is connected to the wri

Question

A TLR robot has a rotational joint (R) whose output link is connected to the wrist assembly. Considering the design of this joint only, the output link is 600 mm long, and the total range of rotation of the joint is 40 degrees. The spatial resolution of this joint is expressed as a linear measure at the wrist and is specified to be 1.0 mm. It is known that the mechanical inaccuracies in the joint have a normal distribution with a standard deviation of 0.006 degrees of rotation. It is assumed that the output link is perfectly rigid so as to cause no additional errors due to deflection. a. Determine the minimum number of bits required in the robot's control memory in order to obtain the spatial resolution specified. b. Determine the linear repeatability of this axis.

Explanation / Answer

a) Spatial resolution to an angular measure

Spatial resolution = (1 * 360)/( 2 * pi * 600) = 0.095492966 degree

Spatial resolution = Control Resolution + 6* Standard Deviation

Control resolution = Spatial resolution - 6* standard deviation = 0.0595 degree

Joint range L = 40 degree, Control resolution = 40 degree/( 2n -1 )= 0.00595

n=9.395

Therefore 10 bits required in robot control memory.

b) Linear repeatability of the axis = +/- 0.5 mm

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