Computer- integrated manufacturing: Computer-aided manufacture

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Computer-aided manufacture

Computer-aided manufacture (CAM) refers to the use of computers to control the manufacturing process, primarily by controlling the settings of tools and the way they are used in computer-numerically-controlled (CNC) machines and other automatic devices, and by controlling the deployment of industrial robots. The CAM system uses the production plans produced by the DP system, and the product designs produced by the CAD system, to work out what should be made at what times and on which machines.

To understand what's involved, you should know that factory production typically involves two major processes:

• The machining of p? ..t"

• The handling of parts and their assembly.

Today, CNC machines can carry out the first process very efficiently, even for small runs. Operating automatically under software instructions, they can apply various drilling, turning, and cutting devices to the raw material to manufac­ture an accurately-made part.

Robots can carry out the second of these processes, for they can handle materials and feed them to the CNC machines. They can also remove the finished parts and, if necessary, assemble them to make the finished products. Like CNC machines, they can be used economically for small runs. An industrial robot typically consists of a robot arm with a clasping device or other tools attached.

Early generations of CNC machines and robots lacked 'intelligence', meaning that they did not have sensory devices enabling them to respond to changes in their environment. In the case of robots, this meant that they would perform the sequence of operations dictated by the controlling software, blindly picking up and manipulating whatever object happened to be placed in the operating position, or, if nothing was there, picking up and manipulat­ing empty space.

Modern generations of CNC machines and robots are equipped with sensors enabling them to identify and locate objects, and so make adjustments to the programmed sequence of operations that they have to perform. In essence, a machine of this type consists of three systems:

• A mechanical system to operate tools or to pick up and manipulate objects. This system may include rotating shafts, drills, and other tools, as well as clasping and other handling devices.

• A sensory system to detect what the mechanical system is doing and, in the case of robots, to identify and locate objects. A variety of sensing devices are used, including, for robots, video 'eyes'.

• A control system which interprets the information received by the sensory system and uses it to control the mechanical system. This system is normally based on microchips.

In simple terms, the sequence of operations that takes place when one of these machines performs a task is as follows:

• The sensory system converts the position of a part into data in the form of an electrical signal.

• The control system compares this with an ideal computed position based on data from the controlling program.

• The difference between the two is the 'error', and is represented by tiny digital pulses of electricity.

• These pulses are fed to the mechanical system, where they are converted to analogue form, and amplified to the level needed to adjust the positions of the arms and tools.

In a CAM system, a production line consists of CNC machines, robot arms, and materials transfer systems, all under the control of a central computer.

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