Industrial Robots

Precise Speed Measurement with the LMSMA2x/3x

As if by Magic

No human can do it as quickly and as precisely. Modern robots can move workpieces around at a speed that you could once only dream of. Precise measuring instruments are needed to avoid mistakes occurring due to the incredibly quick cycle times required in modern production. For this, the manufacturer Omron Adept Technologies GmbH of Dortmund relies on systems made by Wachendorff Automation.

Small, mobile robots speed around almost without a sound – nothing more than snatches of the English language over a conference table. If it were not for the coffee machine in the black and yellow of Borussia Dortmund, you could be forgiven for thinking you’d ended up somewhere in Silicon Valley. Instead, we’re in the middle of Dortmund – in the application laboratory of Omron Adept Technologies, one of the world’s leading producers of industrial robots – with a HQ which is actually in California.

The European HQ for sales, service and training has been based here since 1986. In the local laboratory, most of the company's products – with names of the tenor of Cobra or Hornet – can be found in operation. “What we do here more than anything else is conduct feasibility studies,” explains head trainer Günter Graß. "If a customer is looking for an automation solution, then she or he can come here to perform tests, such as those to ascertain whether our robots provide the required cycle times," he explains.

Automation tasks have become much more complex in recent years and the desired cycle times have become much shorter – these days, customers demand highly efficient solutions. Within a fraction of a second, these solutions have to recognise, pick and place correctly. There are many ways of doing this. Small parts are often handled using compressed air. Others have to be grasped carefully. For yet others, it’s important that they are placed in a specific position.

Often, it’s not done with pure conveyor and feeder technology. Packaging systems for magazines, for instance, ensure automatically that a give-away is attached to each copy and that the entire package is wrapped in clear plastic. Omron Adept Technologies is a successful system provider fur just these kinds of complex applications, delivering complete software and image processing systems alongside the robots.

In order to precisely coordinate the detection range of the camera and the movement of the gripper, it is important to measure the belt speed accurately. Only when this is known can the control system calculate when the work pieces reach the gripper and thus when they can be received.

Although there are systems that decrease the belt speed directly at the motor – external influences such as band slippage are not taken into account with these. In addition to shorter cycle times, maximum precision is also key. This can only be reached if speed is decreased directly on the belt – as close as possible to the workpiece.

So as to have a secure and easy-to-integrate solution, Omron Adept Technologies decided in favour of Wachendorff Automation’s new LMSMA length measuring system. The Rheingau-based producer demonstrated the new product at the SPS/IPC/Drives fair in Nuremberg, where it won the attention of Günter Graß and his colleagues.

“We were looking for a solution that’s universally deployable, because our products find a use in many different sectors, right up to the food industry,” explained the applications engineer. In addition, they should have the longest service life possible and a high-quality look and feel, matching the robust and durable products made by Omron Adept.

The new length measuring systems – comprising a patented spring arm, rotary encoder measuring wheel and mounting bracket – were ordered straight away. The high expectations for this order were totally fulfilled. “It’s especially practical that the contact pressure can be adjusted via the resolution on the base plate,” says Graß, explaining why the system is so precise and why slippages can be avoided. A special spring ensures that the contact pressure remains constant in the long run. In the new systems, the preload of the spring is adjustable in steps of 5 N up to a maximum 30 N preload.

The measurement system is mounted using a base plate and screws. The clearance for these is adjusted to the standard mounting profiles. The measurement system can be connected quickly and easily to the base plate with a captive central screw.
If there are no direct installation options on the plant, various installation positions can be achieved using the highly-adjustable angle bracket.

The measuring wheels are available with different surfaces, making them ideally adaptable to belt or material properties (cardboard, wood, soft plastics, textiles, leather, paper, wire, steel profiles, web, cable, greased metals, painted surfaces, carpet...). They are also available in circumferences of 200 mm or 500 mm.

Especially practical is the ability to move (or even fix) the spring arm into the resting position. "When it comes to maintenance or cleaning work, it would otherwise have been necessary to always remove the whole system and adjust it again afterwards. This way, we can use a hand grip to lift the arm from the band, hold it up and simply lower it again later. The system continues to work precisely, with the original contact pressure,” says Graß on the benefits of the handling function in LMSMA Wachendorff’s length measuring system.

With the LMSMA, an incremental rotary encoder is responsible for the actual speed measurement. It is also extremely robust and can withstand high bearing loads. With resolutions of between 1.0 mm/pulse and 0.008 mm/pulse, it can easily keep pace with the high speeds of Omron Adept robot systems.

Author:

Dieter Schömel
Product Manager for Rotary Encoders
Wachendorff Automation GmbH & Co. KG

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