Main Criteria To Specify The Best Robot Arm For Factories

By Roger Harris, Regional Sales Manager at FANUC UK

Phil Black - PII Editor 22/09/2016

382 4 minutes read

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What determines the choice of palletising robot to handle product X at point Y on the line? With a choice of 20+ FANUC robots arms all capable of performing palletising tasks, Roger Harris Regional Sales Manager at FANUC UK picks out some of the main criteria that factories should consider in order to specify the best robot arm for the job.

What determines the choice of pick and place robot to handle product X at point Y on the line? With a market leading choice of over 300 variants of robots, FANUC are ideally placed to provide UK manufacturers with a pick and place solution for their challenges. Roger Harris, regional sales manager at FANUC UK picks out some of the main criteria that factories should consider in order to specify in order to determine the best robot arm for the job.

To the untrained eye, one robot may look very similar to another. In reality, there are a host of variables, not just in the overall type of robot, but in the precise specification which can be tailored to the particular needs of a given application.

A robot may last 20 years in a single installation. If you look after the robot, it will look after you. And ‘looking after’ the robot starts with ensuring that you have the correct specification to begin with.

Any reputable automation specialist will talk potential customers through their detailed needs and how they can best be met. But many of those with robot-shaped gaps in their production lines could benefit from a brief overview of the main considerations:

a.) Cycle time versus speed

Most manufacturers know that, in relation to any type of equipment, ‘speed’ is often less useful as a concept than it might appear. This is as true of robots as it is of other machines.

Most robots can be programmed to move extremely quickly – up to around 2,500mm a second, but they will need to ramp up to this top speed, and then slow down from it. When the distance of travel is short, the arm will never reach maximum speed. Sometimes, we slow the arm down in order to reduce the cycle time.

By focusing on cycle time rather than speed, the programmer will also reduce overheating and wear-and-tear on the axes.

The job of the robot integrator is to work out if a customer’s target cycle time is achievable over a given distance with the use of the correct pick and place end effector.

b.) Payload

A key element in productivity calculations will be the payload of the chosen robot arm, and how closely the integrator feels it is wise to approach the rated weight. For example, in a pick-and-place application, a magnetic end effector may be able to lift, say, 20 cans at a time. But choosing a smaller number may make more sense.

This will avoid excessive stress on the bearings and joints, and so prolong the life of the robot.

But remember to take into account the weight of the end effector. That is part of the payload, too.

In fact, it can form a substantial proportion of that payload.

In selecting a payload range, the customer will also be estimating future needs and how much of a margin to leave in order to accommodate any likely change in the robot’s role.

c.) Cost and return-on investment

Where an individual product or format (especially in food and drink) may only survive for two or three years, this ability to plan beyond one application is especially important when calculating return-on-investment (ROI).

In fact, when a robot supplier or integrator visits a prospective customer, the first task is to determine whether the proposed process is viable at all. Will the customer actually see a return on its investment?

Once that basic viability is established, the precise mechanics, detailed specification, layout, installation cost and ROI can be determined.

It is because the working life of the robot is at the core of any ROI calculation that decisions about cycle time, payload and overall usage are of such importance. In Germany, for example, it is quite common to buy an additional robot cell rather than running a single system into the ground.

d.) Reach and number of axes

If you are fortunate enough to be designing a new packaging line from scratch, then there should be few challenges in maximising efficiency and performance in the pick and place robot. But if the line already exists, you are going to have to conform to it. You may have to perform some ‘surgery’ on the line, but you would normally try to minimise this. It is not only cost which is typically kept to a minimum, but also disruption to the line and production.

One important element in the calculations around a given pick and place installation will be the reach of the robot. Making changes to the line to require less stretch in the robot may improve productivity and therefore make sense in terms of total cost. It may also mean that a lower-specification robot is needed.

There is a general assumption that the bigger the robot, the longer the reach will be, and the heavier the payload. This ‘rule’ normally holds, even though there are exceptions.

It is not only the required reach of the robot which may be influenced by the layout of the infeed and outfeed conveyors and of the robot cell as a whole. A 6-axis robot may be needed in applications which would otherwise suit four axes of movement because of unavoidable obstacles in the factory which the arm has to clear or negotiate.

e.) Hygiene rating

While end-of-line robot applications will not demand any special hygiene ratings, manufacturers will have to pay special attention to requirements at the production stage, particularly if robots are pick and placing pharmaceuticals or ‘naked’ food products.

Not every model is available in all hygiene grades. Some 6-axis robots may offer specifications to the splash-proof IP67 grade but not to the full-washdown IP69K rating. On the other hand, pick-and-place delta robots are more likely to have a full-washdown rating as an option.

Clean-room applications in the pharmaceutical industry will require hygiene ratings equivalent to IP69K. In FANUC’s experience, the pharmaceutical industry is not only much stricter about hygiene requirements for equipment, but also uses a far more differentiated grading system for machinery.

Finally, customers should push their robot suppliers to ensure that what is on offer is the best solution for that particular application. In this situation, even if you do not know all the answers, knowing which questions to ask your supplier can be very helpful.