The 1940s witnessed the dawning of a modern day industrial revolution with the introduction of process automation. More recently, it could be argued that another new industrial revolution has begun of even greater significance — the widespread use of industrial robots in the world of manufacturing is now upon us.
Stephen Carradice has been a design engineer at Optima Control Solutions Ltd since 2006 and has been involved in numerous projects with values in excess of £300,000. He recently engineered a project in conjunction with KUKA Robots. The project involved installing and integrating a KUKA robot, specified by them, at a large UK-based company. Here, Steve talks in more detail about the process of integrating the robot’s control system with the rest of the production line’s controls and discusses some practical considerations involved in the application of these powerful robots. He also explores how the robot controls are integrated with the control system of a host production plant and what the technical challenges are in doing so.
NBR: Steve, tell me more about the project and why you got involved
SC: In this project, the specification was to integrate a robot at the end of the whole production line to put labels on paper rolls that have been processed upstream. We needed to integrate the robot with the existing control system to define the position and movement needed for executing the labelling task. We engineered the system so that the robot received data programmed from the existing PLC, defining the size of the batch coming down the line. The robot would then use this data to co-ordinate and adjust its position accordingly.
Generally, when a company purchases a robot like this, it buys a contained unit that has been pretested and is ready to operate … but has no application-specific functionality. The engineering challenge is to integrate the robot within a functioning production line and interface it with various parts of this line. This can be a difficult task that must be done with skill and care; control systems integrators have a critical role to play here. Obviously, there are simpler, standalone area cases in which integration is not necessary and the robot is programmed in isolation. However, often in established production plants, it is more likely that integration will be required. On this project, my main responsibility was ensuring that the robot responded correctly to varying production demands.
NBR: How did you achieve this integration and what was the biggest challenge?
SC: The biggest challenge was making sure that the robot interfaced well with other existing systems such as PLCs. Because the robot operates on a PC platform and PLCs have their own, different programming language, making them communicate with each other is difficult. I selected a ProfiBus communication system to integrate the main control system with the robot controls.
NBR: Tell me more about the programming and installation of industrial robots.
SC: Robots are usually programmed by application engineers using brand-specific tools that have been developed and supplied by the robot manufacturer. These software tools run on laptops or desktop PCs. They often have two types of programming modes, online (or a teaching mode) and offline. Once the robot program is successfully written and operational, the programming computer can be disconnected and the robot runs independently. It is an option to either retain permanent connectivity or to reconnect for diagnostic or supervisory use. Sensor-controlled robots are widely used because of their capacity to integrate with external equipment such as sensors and cameras to respond to changes in the production environment.
Online programming offers better commissioning flexibility and accommodates varying application criteria
The online programming mode for a robot means, in effect, ‘teaching’ it to execute tasks on the actual application (using manual controls to position the robot in the desired location, for example) then selecting a “teach” function to programme the controller with that target location. Programmers often use a pendant control station so that they can get close to the robot head. This method records movement and required inputs and saves them in the robot’s control system memory. Once operational, movement to preset positions is automatically performed when the robot is instructed to by the system. The technique of offline programming does not require the engineer to be physically present, as when ‘teaching’ the robot. This type of programming more resembles high-level programming and uses similar languages and is often prewritten. An alternative offline programming method is CAD programming; this is an intelligent programming function that uses interpretation of CAD drawing statistics and simulation techniques.
There are pros and cons with all methods but, in brief, offline programming is plainly more challenging to develop and commission initially because it is remote programming. However, once successfully completed, the robot programs can be easily reissued for subsequent identical systems (OEM type applications). Online programming offers better commissioning flexibility and accommodates varying application criteria, such as mechanical dimension repeatability.
NBR: How was the robot programmed in the project for KUKA?
SC: We used an online, point-to-point teaching technique, KUKA provided a teach pendant that we used to programme the robot. In effect, we showed the robot how to execute a task and it ‘remembered’ how to do it next time. The first step in the engineering exercise is to create a program file. Then, secondly, to begin teaching the robot the various positions needed to execute its task. As I mentioned earlier, the programmer works the robot through its task manually then, using the teach command, it ‘remembers’ the inputs, statuses and how to act on these inputs once automated.
NBR: What is the connection between industrial robots and servo control?
SC: Articulated robots need servo control systems to provide what are, in effect, the robot's muscles! So, what is servo control? If you excite a DC motor, or connect it to a battery, it will spin. If you connect two batteries (to excite it with a higher voltage), it will spin faster. Now, imagine that you tell the motor to turn precisely 180 degrees (1/2 revolution) and hold that position no matter how many batteries there are, then that point-to-point movement is typical of a servo control application. Central to the task of servo control is the concept of closed loop feedback. A closed loop control system relies on a feedback signal for the controlling element to regulate the system. Consider what happens when you are driving your car.
For highly repetitive tasks, robots never get ‘tired’ or ‘bored.’ How could they?
As you accelerate towards a certain speed, say 30 mph, as the driver (or the intelligent controller of the vehicle), you read the speedometer and regulate the engine power (using the accelerator pedal) to achieve and then maintain the desired 30 mph speed. Without the speedometer feedback medium, the controller would not be able to accurately control the vehicle. Position feedback in a servo control system works in a similar fashion. The servo controller having a desired position to which the motor must move to, and using a corresponding position feedback sensor that tells the motor what its actual position is. In a well tuned control system, the motor will get to exactly the right position and then will turn no more until it is commanded to a new desired position.
NBR: Finally, what do you think are the main benefits of employing industrial robots and are there any disadvantages?
SC: Robots can flawlessly execute hard tasks such as laser cutting and thermal adhesion. Owing to their high speeds, companies achieve better production rates. Improved safety is another advantage; fewer workers get hurt in the manufacturing process. For highly repetitive tasks, robots never get ‘tired’ or ‘bored.’ How could they? One major drawback, however, is that more people are made redundant. The demand for human labour is significantly decreased but that is the only socially negative impact of employing industrial robots.