The speed capabilities of current industrial robots range up to a maximum of about 500 degrees per second for certain joints. Current day industrial robots can have cycle times as low as 0.8 sec (e.g., Adept Viper). The highest end effector speeds can be obtained by large robots with the arm extended to its maximum distance from the vertical axis of the robot. As mentioned previously, hydraulic robots tend to be faster than electric drive robots.
The speed, of course, determines how quickly the robot can accomplish a given work cycle. It is generally desirable in production to minimize the cycle time of a given task. Nearly all robots have some means by which adjustments in the speed can be made.
Determination of the most desirable speed, in addition to merely attempting to minimize the production cycle time, would also depend on other factors, such as
- The accuracy with which the wrist (end effector) must be positioned
- The weight of the object being manipulated
- The distances to be moved
There is generally an inverse relationship between the accuracy and the speed of robot motions. As the required accuracy is increased, the robot needs more time to reduce the location errors in its various joints to achieve the desired final position.
The weight of the object moved also influences the operational speed. Heavier objects mean greater inertia and momentum, and the robot must be operated more slowly to safely deal with these factors.
The influence of the distance to be moved by the robot manipulator is illustrated in fig. Because of acceleration and deceleration problems, a robot is capable of traveling long distances in less time than a sequence of short distances whose sum is equal to the long distance. The short distances may not permit the robot to ever reach the programmed operating speed.
Load Carrying Capacity
The size, configuration, construction, and drive system determine the load-carrying capacity of the robot. This load capacity should be specified under the condition that the robot’s arm is in its weakest position.
In the case of a polar, cylindrical, or jointedarm configuration, this would mean that the robot arm is at maximum extension. Just as in the case of a human, it is more difficult to lift a heavy load with arms fully extended than when the arms are held in close to the body.
The rated weight-carrying capacities of industrial robots ranges from less than a kilogram for some of the small robots up to several hundred kilograms for very large robots which has a rated load capacity of 2000 1b.
An example is the Adept viper that can carry 20kg. The small assembly robots, such as the MAKER 110, have weight-carrying capabilities of approximately a few kilograms. The manufacturer’s specification of this feature is the gross weight capacity.
To use this specification, the user must consider the weight of the end effector.
For example, if the rated load capacity of a given robot were 5 kg, and the end effector weighed 2 kg, then the net weight-carrying capacity of the robot would be only 3kg.
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