Why Use Robots?
Yasuo Yamauchi  gives four major reasons why Nissan use automation and in particular industrial robots.
- Quality improvement.
- Improvement of working environment.
- Better cost effectiveness.
- Flexibility to change.
They currently employ around 2200 robots and are actively developing their own robots for specific applications. It is interesting to note that most of the companies that use robots well within their manufacturing areas also develop and build their own robots. This is probably due to them having personnel available with a deep understanding of how these complex machines operate as well as having a vested interest in the technology being successful. Many failures of this technology in the UK have been caused by the operators not buying into the project or not being sufficiently well trained to be capable of running the equipment.
For certain tasks robots can be superior to humans in terms of the quality of the work that is produced. This has been found to be the case where one or more of the following are required :-
- High positioning precision.
- High repeatability.
- No deviation due to fatigue.
- Highly accurate inspection and measurement using sensors.
These process improvements not only improve the visual appearance of the product and hence the perceived quality of the product but in terms of the spot welding give better welds due to the tighter control of the gun angle and higher strength joints due to the guaranteed spacing and number of the welds. For seam sealing the better accuracy in terms of positioning and the tighter control of the bead diameter allow less sealant to be applied while still assuring that the joint is sealed. This improves the appearance of the joint considerably and gives a major saving in material use and therefore cost. Similar improvements can be achieved for paint spraying, arc welding, assembly and many other operations.
An example of how robots can be linked with sensors to perform inspections is the Nissan painted surface inspection system. This uses laser lighting to detect any dust or dirt causing imperfections in the finished paint work of the car. This system was introduced in 1984 and increased the fault detection rate from 60% to 100%. In areas where high levels of concentration are required over long periods fatigue in humans can be a problem. The correct use of robots can eliminate this.
Improvement of the Working Environment
In order to get the best long term performance from the work force it is important to make the
working environment as conducive as possible to high quality, high output work. The human
body if used incorrectly is susceptible to short term fatigue or long term injury or disability.
Where possible automation should be used to reduce fatigue and to minimise the risk of injury. With the current trend of increased health and safety legislation it is predicted that companies that do not see the sense in introducing automation in these areas voluntarily will in the long term be forced to by legislation. The four areas where automation should be considered are as follows:-
- Heavy lifting.
- Repetitive work.
- Contaminated environments.(solvents, noise, heat, dust)
- Jobs requiring continuously high levels of concentration.
Guide lines quoted by Yamauchi show that where the total weight lifted per shift exceeds 20 tons or the number of repetitions of a single action per shift exceed 4000 then Nissan would consider that those tasks should be automated. An example of where this has been applied is in mounting wheels onto car bodies where wheels weighing 20-30Kg are handled 1000 times per shift. A robot has been developed using both vision and tactile sensors to pick up the wheels and mount them correctly onto the hub. Examples of repetitive tasks are palletising of pressed or injection moulded parts.
Many jobs within the manufacturing industry take place in an environment that is hostile to
the human body. Many organic solvents from paint spraying are known to be carcinogenic,
press shops are noisy and can cause hearing damage and foundries and welding shops are
generally hot and dusty with danger of injury from sparks and hot components. Robots can
easily handle these environments with no danger to themselves in fact one of the largest
research areas in robotics at this moment in time is for decommissioning nuclear power
stations and performing repairs within existing reactors. Obviously the environment here
precludes the use of humans and much of the work requires very intelligent robots with a
large range of sensors. As well as physical work being tiring jobs requiring high levels of concentration can also lead to mental fatigue and stress. The surface inspection task described earlier is a prime example of this.
Cost effectiveness of robots is not always an easy calculation to perform. Most of the cost is
up front in terms of the robot and tooling costs. Often due to the lack of intelligence in robots
the tooling costs are the most significant. In comparison to this performing the operations
using humans the largest cost is in wages and for hazardous environments such as a paint
shop, environmental control (i.e. providing a clean air source for the operator to breathe) can
also be expensive. Where possible robots should be installed such that they can operate
continuously for 24 hours per day in order to get the best productivity from them. This is
however not possible where they are operating on lines utilising humans who require breaks. Often it is the humans in the process who limit the output of robot cells.
Flexibility to Change
In the correct circumstances robots can not only be more flexible to change than fixed automation but can also be faster than what is often regarded as the most flexible solution humans. With the globalisation of markets the life time of a product on the market is steadily decreasing. This requires that new products can be brought to market quicker and also that production lines are flexible and can handle more than one product. The solution to this is to use re-programmable automation and wherever possible to remove hard tooling. Rolls-Royce have succeeded in eliminating hard tooling and reducing lead time by some 75% because of this in their chemical machining cell. The old process involved coating the components in maskant and then manually scribing the maskant using a scalpel and a template before peeling off the relevant areas of maskant and etching way the correct amount of metal. The scribing process is now performed using a robot programmed off-line using CAD data. This eliminates the need for the templates to be made. A number of other benefits have been gained by the use of a robot for this application the main one being that the quality of the resulting components has increased.
Nissan are looking to take the concept of flexible manufacturing to the limit. They are currently working on an Intelligent Body Assembly System + which is effectively a fully programmable car body framing line. The aim of it is to be able to produce any one of their car models on the same assembly line. The way that they are planning to achieve this is by using simple robots to replace fixturing. In order to produce such a complex robotic cell they are using computer based simulation techniques and off-line programming.