For robots to become a valuable asset in an automated manufacturing environment, they need to be able to communicate; either to other robots which may be part of the same system; other automation technologies; or production planning and scheduling systems to receive or transmit data.
The level and method of communication between the robot and the different parts of the surrounding manufacturing environment will depend upon the complexity of the task, and the way in which the automated cell has been configured. Traditionally, the most common methods include:
These are effectively simple on / off signals and generally used as inputs or outputs to either confirm that a part is present, or to switch on or off ancillary equipment. These signals can also be sent in a group – as a binary coded decimal – to pass numbers in a binary format between different machines.
Analogue inputs and outputs are used by robots to either receive a value, in the form of a voltage which can then be converted to a number, or alternatively send a voltage which is converted and used by an ancillary piece of equipment to set or change one or more parameters. A common use of analogue signals can be found in the communications between a robot controller and an arc-welding power source, where these signals are used to adjust and set the operating voltage and current to suit the weld being produced at the time. There are many other uses of analogue signals, where there is a requirement for the robot to react to or to influence: for example, the operating parameters or speed of ancillary items.
Serial or Parallel Interfaces
Just as personal computers (PCs) can link to peripheral equipment such as disk drives and printers, using standard parallel or serial ports so too can robots. These are often used for program development and storage, but can also be used from within a robot program for producing reports on tasks completed or interfacing to other technologies such as machine vision systems to transmit positional and orientation information on a part to be picked by the robot.
As automation started to become more sophisticated, and a greater number of different systems and devices became available, MAP (Manufacturing Automation Protocol) – developed in the 1980s - was at the time seen as a solution to enable communications between what were otherwise incompatible communications standards. For a variety of reasons, including complexity and cost, this is no longer used and Ethernet connectivity, now standard on robots, is a widely used method for communications. In addition, other commonly used methods of communication, especially on larger industrial automation systems include Fieldbus and Profibus. These provide the ability to connect and control, in real-time, a network of field devices – sensors, actuators, motors, switches and drives – to name a few, within a manufacturing plant.
Applications, such as arc welding, require several analogue and digital signals to control the welding power supply and filler wire feed drives. These are often available as standard sets from the robot vendors with specialist instructions within the robot programming language to control them in an application specific manner.