precision of movement

P.VETRIVEL

EST-IND

Precision of the robot’s movement is another measure of performance.

1. Spatial resolution

2. Accuracy

3. Repeatability

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Smallest increment of movement into which the robot can divide its work volume.

Spatial resolution depends on two factors

1. Control resolution

2. Mechanical inaccuracies

Number of Increments=2n

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1. Control resolution

Total motion range divided by the number of increments.

To obtain the Control resolution of entire robot, component resolutions for each joint would have to be summed vectorically.

The total control resolution would depend on the wrist motions as well as the arm and body moitons.

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2. Mechanical inaccuracies

Mechanical inaccuracies in the robot’s links and joint components and its feedback measurement system constitute the other factor that contributes to spatial resolution.

1. Elastic deflection in structural members

2. Gear backlash

3. Stretching of pulley cords

4. Leakage of hydraulic fluids

5. Load handled

6. Speed of arm movement

7. Maintenance

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Robot’s ability to position its wrist end at a desired target point within the work volume.

Robot’s accuracy to be one-half of its spatial resolution

Accuracy varies with work volume, worse when target in outer range of its work volume and better when closer to the base.

Accuracy is improved if the motion cycle is restricted to a limited work range

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Robot’s ability to position its wrist or an end effector attached to its wrist at a point in space that had previously been taught to the robot.

Repeatability refers to the robot’s ability to return to the programmed point when commanded to do so.

In three dimensional space, Repeatability of manipulator is the radius of the idealized sphere.

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