Some tips for those considering the purchase of robots
Thinking of using robots in your factory? Here are a few tips you would do well to consider – many a manufacturer has learnt these simple guidelines the hard way!
A robot is a very flexible tool. The object of using a robot is to exploit this flexibility. This means both hardware and software flexibility. There are a number of reasons for using robots, here are a few of them:
1. The process you hope to use is new and you are not sure how it will run
at the end of the development stage - here a robot can help you develop the
process through a series of experiments thus helping you to determine the exact
requirements which may be met by hard automation (or by robot) at a later stage.
2. Your products are manufactured in small batches (tens, hundreds or even
thousands) and their design is subject to change - in such cases hard automation
is unlikely to be economically viable. Provided they satisfy the necessary economic
criteria the flexibility of robots can be very helpfull.
3. Your batch sizes are big, not subject to change and each task is different - robots may be helpful here if the same type of robot can accomplish each (or many) of the tasks. You will then have a general purpose machine for all (or most) of your manufacturing. Only one type of spares and only one area of programming expertise is needed.
A robot will rarely be able to run as fast as a piece of dedicated hard automation designed specifically for the task in hand. Consequently, for products whose design is not going to change and whose batch numbers are in the region of many millions per year then robots may not be helpful unless you can employ a large number of them (see note 3 above).
The degree of mechanical flexibility depends heavily on the robot configuration (Cartesian, Cylindrical or Spherical) and the number of joints the robot possesses. The task to be performed should be analysed in collaboration with an independent automation expert to ascertain which type of robot is most suitable (don’t just talk to the robot vendor!).
The gripper is the working tool used by the robot and its importance should not be underestimated. Again, talk to an expert first. Removing and replacing 4 nuts and bolts every time to change a gripper can be time consuming. Tool changers can serve to enhance the degree of mechanical flexibility considerably. They can be simple manual devices or more sophisticated automatic systems.
Software flexibility can be extremely important. If you wish to exploit this to the full then your robots should be controlled from an interpreter, NOT a compiler! Editing, compiling and linking for every small program change makes program development extremely clumsy. Furthermore, there is nothing to be gained from faster running compiled programs – modern computers run much faster than the robots mechanical joints anyway.
Do NOT buy robots which rely on control from a PC with dongled software. You lose the dongle and your in real trouble. The use of general PCs for robot control should be avoided where possible. People have a habit of installing all sorts of irrelevant software on PCs. You turn on one day and the robot won’t run anymore – someone has installed a utility which has overwritten all the device drivers! Furthermore, a virus in your CAD programming is annoying. A virus in your robot control program can be disastrous!
Some robots are controlled via PLC systems. These are great for those already trained and experienced in PLC programming, but tend to be a little clumsy for those with structured programming backgrounds. Get the staff who will be expected to use the robot involved at the initial stages – do NOT simply buy a system and expect them to cope with it if you cannot program it yourself!
When planning the task to be performed, first draw a flowgraph (or flowchart). Each line (or block) of this plan should result in a single subroutine of program code. It may seem excessive to write a subroutine for one or two lines of executable code but when the program grows (which it will) debugging will be much easier. Fully document all programs and don’t forget to update the flowgraph (or flowchart) as and when the program is changed.
For full flexibility a robot control system should have some form of parallel input/output interface to enable it to communicate with sensors, actuators etc. These I/O ports should by opto-isolated to prevent what can turn out to be very expensive damage through glitches, accidental short circuits etc. Do NOT buy robots whose IO lines are connected directly to a PIO chip! Though not always essential for smaller systems, serial field bus interfaces can be very useful where large automation systems are concerned.
Do NOT buy products which are not supported in your country - the cost of even minor repairs can be very high when the serviceman must come from abroad!
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