General Considerations in Robot Material Handling

In planning an application in which the robot will be used to transfer parts, load a machine, or other similar operation, there are several considerations that must be reviewed.

Most of these considerations have been discussed in previous chapters of the book, and we itemize them below as a reference checklist.

Part positioning and orientation

In most parts-handling applications the parts must be presented to the robot in a known position and orientation.

Robots used in these applications do not generally possess highly sophisticated sensors (e.g., machine vision) that would enable them to seek out a part and identify its orientation before picking it up.

Gripper design

Special end effectors must be designed for the robot to grasp and hold the workpart during the handling operation.

Minimum distances moved

The material-handling application should be planned so as to minimize the distances that the parts must be moved.

This can be accomplished by proper design of the workcell layout (e.g., keeping the equipment in the cell close together), by proper gripper design (e.g., using a double gripper in a machine loading/unloading operation), and by careful study of the robot motion cycle.

Robot work volume

The cell layout must be designed with proper consideration given to the robot’s capability to reach the required extreme locations in the cell and still allow room to maneuver the gripper.

Robot weight capacity

There is an obvious limitation on the material handling operation that the load capacity of the robot must not be exceeded.

A robot with sufficient weight-carrying capacity must be specified for the application.

Accuracy and repeatability

Some applications require the materials to be handled with very high precision. Other applications are less demanding in this respect. The robot must be specified accordingly.

Robot configuration, degrees of freedom, and control

Many parts transfer operations are simple enough that they can be accomplished by a robot with two to four joints of motion.

Machine-loading applications often require more degrees of freedom. Robot control requirements are unsophisticated for most material-handling operations.

Palletizing operations, and picking parts from a moving conveyor are examples where the control requirements are more demanding.

Machine utilization problems

It is important for the application to effectively utilize all pieces of equipment in the cell.

In a machine loading/unloading operation, it is common for the robot to be idle while the machine is working, and the machine to be idle while the robot is working.

In cases where a long machine cycle is involved, the robot is idle a high proportion of the time. To increase the utilization of the robot, consideration should be given to the possibility for the robot to service more than a single machine.

One of the problems arising in the multi machine cell is machine interference.

We now proceed to deal with the specific cases of material transfer and machine loading/unloading applications in the following two sections.

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Santhakumar Raja

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