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Wireless clutch sensor avoids need for external limit switches

24 June, 2010

The German clutch specialist Mayr has developed a safety clutch with a built-in sensor that transmits overload signals wirelessly to a receiver linked to a machine controller. The company says that this approach offers many advantages over conventional designs that rely on external limit switches and cables to send overload signals to controllers.

For example, the wireless design ensures reliable signal transmission in drive systems subject to vibration or horizontal motion. In conventional systems with external signal transmitters, the axial offset of clutches caused by thermal expansion of shafts can lead to false triggering.

In the case of drives with moving shafts – such as robot arms – the new EAS-Sensor system avoids the need to move brackets and cable guides along with the drives. This makes assemblies simpler and more reliable.

The system (shown above) is also said to be ideal for applications where there is not enough room to fit an external limit switch. Another attraction is that it is supplied ready to install, and does not need to be adjusted on site by skilled staff.

Safety clutches provide precise torque limiting to ensure that loads on machine components do not exceed allowable levels. When a clutch disengages due to excessive torque, its travel is measured in millimetres. This is all that is available to change the state of a built-in mechanical or contactless limit switch.

Traditionally, external limit switches have therefore been used and these need to be adjusted precisely to ensure that they will operate reliably. However, this precision can be in vain if, for example, the position of the clutch shifts during operation as a result of thermal expansion.

In the new system, the limit switch is integrated into the clutch. If there is an overload, it detects the disengagement motion of the clutch and sends a signal wirelessly to a base station connected to the machine controller. It is preset in the factory, eliminating the need for on-site assembly and adjustment.

The transmitter and its power supply are contained in the torque adjustment nut of one of Mayr’s EAS-compact safety clutches. The system reports the operating state of the clutch at regular intervals, along with information on the supply voltage. If the voltage drops, it triggers a warning signal, allowing the transmitter battery to be replaced before it fails, without needing to dismount the clutch.

The clutches are said to offer: high torsional stiffness; freedom from play; a rapid drop in torque when the overload limit is reached; accurately adjustable torque; long operating lives; and low lifecycle costs.

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