Robot Assembly (1/4)

I originally presented this article, "Design for Robot Assembly", as a guest speaker at the UK's 2nd National Conference on Production Research ...

SUMMARY

The design of products and systems for robot assembly requires a new approach to that used for manual and automatic assembly.  Robot assembly is only effective if the robot’s flexibility is used to best advantage.  Additionally, peripheral devices supporting the robot must also be adaptable to handle a wide variety of products and product parts.  This is achieved by using equipment that is not designed specifically to handle a particular type of part with minor modifications to tooling, or the use of a different software application, the robot assembly system can be quickly adapted to assemble a different product or product style.  By this method, robot assembly can be economically justifiable in many situations where it would otherwise have been precluded.

This article discusses the development of robot assembly systems and describes how product design plays an important role in the design of the equipment.

INTRODUCTION

There are three categories of system used in product assembly.  These are manual assembly, automatic assembly and robot assembly.  Whilst assembly can be classified in this manner, it is not uncommon to find an assembly system consisting of two or all of these groups to form a hybrid system.  Manual assembly systems account for the majority of applications.  Automatic systems are used in situations where the demand is high and there is no, or limited, change in the product styles being assembled.  Robots have yet to make a significant impact in the field of assembly.  It’s difficult to technically justify the use of assembly robots as the operation time of programmable devices is longer than that of dedicated automatic equipment.  The economic justification of assembly by robots is equally difficult due to the characteristically small batch sizes for which these systems are appropriate.  This has the effect of increasing the handling and insertion costs of the product being assembled.

Manual assembly is still used for more than ninety per cent of all assembly tasks.  This is because many products are required in low volumes and with a high degree of variety.  Robot assembly could account for more than fifty per cent of all assembly tasks if it could be made to be economic for much smaller annual production volumes. This could be achieved by assembling more than one family of products on one system.  For this approach to be effective, two major conditions must be met.  The proportion of re-usable, or general-purpose, equipment must be high and the time taken to re-configure the system for the assembly of the next product must be low.

Using existing technology, the industrial applications where robots can readily be used have been filled.  These applications include paint spraying, spot welding and materials handling.  Only a very small proportion of existing robots are used for assembly.

Robot assembly system equipment is either general-purpose or special-purpose.  A robot assembly system should have a high proportion of general-purpose equipment and a low proportion of special-purpose equipment. The cost of a system, with a high proportion of general-purpose equipment, can be amortised by all the products that are being assembled by the robot.  This is important when trying to economically justify the use of robot assembly for products required in low volumes.  Under these conditions, many products or product styles, each with a low annual volume, can be grouped together and assembled on a single robot assembly station to obtain a high system utilisation.