A Computer as the Workcell Controller

Some robot applications have requirements for which a digital computer is the most appropriate method of workcell controller.

The reference of the use of a stand-alone computer is used here (generally a minicomputer or microcomputer) rather than the computer which is used as the robot control unit.

In cases where a computer is the workcell controller, it would be used either in series with a programmable controller or as a substitute for the PC.

The computer might perform other functions in the plant. and so it would be implemented to control the robot cell in a time-sharing mode of operation.

Also, the computer would probably form a component in a hierarchical computer network in the factory.

connected down to the programmable controller(s) and/or robot controller(s) in the cell, and connected up to the next hierarchical level in the plant.

Programmable controllers are specialized devices that are designed to be interfaced with industrial processes.

They are provided with input/output ports that can be directly wired to the plant equipment.

This is an advantage over the digital computer, and special arrangements must be made to interface the computer to the industrial equipment in the cell.

However, the PC has certain limitations in data processing and programming languages which gives the computer an advantage in applications requiring these capabilities.

Some examples of the kinds of robot application features that might tend to favor the use of computers for workcell control would include the following:

  1. Cases in which there are several cells whose operations must be coordinated, and significant amounts of data must be communicated between the cells.
  2. Cells in which the error detection and recovery problem constitutes a significant portion of the coding that must be programmed into the workcell operation.
  3. Where several different products are made on the same robot-automated production line, the operations at the different stations have to be coordinated and sequenced properly. Computers would be well suited to the data processing chores required in this type of application. In cases where the production lines are used for assembly operations, the various sizes and styles of the component parts must be sorted and matched to the particular model being assembled at each respective workstation along the line.

Situations in which a high level of production scheduling and inventory control are required in the operation of the cell.

Again, this type of data processing function might require the use of a computer in addition to or as a substitute for a programmable controller.

The differences between digital computers and programmable controllers are principally differences in applications rather than differences in basic technology.

The PC can in fact, be considered to be a specialized form of digital computer with dedicated features for input/output control of industrial equipment. The technologies of the two types of control devices are quite similar.

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Santhakumar Raja

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