The key to performing the more complex tasks with a robot is linking it intelligently to other machines for sequence control and sensors so that it can react sensibly to variations in either the components or the environment. In order to achieve this robot controllers have a range of different communication ports which are either provided as standard or are options. In designing a robot cell the types and number of communication channels required to perform the sequence control and ensure that parts, materials etc. are available will need to be calculated. The number required for even a simple task can quickly rise above the number of channels provided as standard with most controllers. Some system builders prefer to use a PLC to handle the communications and limit the number of channels used by the robot to a minimum this also reduces the complexity of the robot program but obviously adds cost to the system and requires a program for the PLC. All types of communication ports are available for robot controllers and are used for varying applications.
These are simple on/off signals represented by two different voltage levels. They can be used as inputs for simple micro switches to indicate that a component is loaded correctly or as outputs to fire relays to switch ancillary equipment on and off. They can also be used in a group to pass numbers in binary format between machines.
For applications such as temperature measurement using a thermocouple or distance measurement using a proximity sensor where a variable voltage is provided by the sensor an analogue input is required. The robot controller can then convert the voltage which must lie within an allowable range into a number which can be used to modify the robots actions. Analogue outputs are also available and convert a number within the robot controller into a voltage within a specified range. This voltage can then be fed to an amplifier or used directly to drive electric motors, arc welding power supplies etc.
Serial or Parallel Interfaces
Just as personal computers can link to peripheral equipment such as disk drives, printers etc. using standard parallel or serial ports so too can robots. These are used for program development and storage mainly but can also be used from within a robot program for producing reports on the work performed or interfacing to complex sensors such as vision systems for pattern recognition.
Networks are becoming more popular for linking together computer systems and these are available for robots. One of the first networks available for robots was MAP but apart from within a few companies, this has not been widely used due to its cost. Some robots are now also available with ethernet connections and although not widely used at the moment for robots this is used very widely throughout industry for CAD etc.
Applications such as arc welding require a large number of analogue and digital signals in order 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.