Pneumatic tooth clutches offer the advantage of high torque capacity in small dimensions, which can bring significant cost savings to machine designs. Techdrives offers tooth clutches from Mönninghoff, which manufactures a range of six basic models and their variants covering torques from 100-2200Nm. A clutch with rated torque of 500Nm has an outside diameter of only 166mm, which can be compared with pneumatic friction clutches with diameters typically twice the size. Pneumatic tooth clutches can be run in wet or dry conditions, and variable toothforms allow them to be used in different types of application.
Pneumatic tooth clutches work by applying an air pressure of 4-6bar onto an internal piston. Very small volumes of air are required, so the response is rapid. The piston pushes one set of sliding teeth into engagement with a set of fixed teeth, which transmits the torque. Engagement needs to be at static or low speeds, but disengagement can be at any speed. The torque-transmitting teeth can be cut in different forms. Standard is a 20-degree flank angle that suits torque transmissions in either direction. Saw-tooth forms transmit different torques clockwise and counter-clockwise. Irregular toothforms can synchronise input to output at 360 degrees or at several fixed intervals per revolution if required. Shallower tooth forms can be used for torque limiting, with the release point being proportional to the pressure applied.
The most popular clutch models have a stationary piston mounted either on a flange or bearing, with the axial force transmitted to the teeth by a ball bearing. The axial movement of the teeth can be detected by using a proximity switch onto an integrated switch plate. Consequently the clutch status and any overload can be monitored. Simpler and lower-cost clutches are also available using a rotating union to feed the air supply in through the shaft; this can halve the length of the clutch.
Mönninghoff clutches also include tooth brakes available from 80-1000Nm, and spring-applied tooth brakes in the same torque range. Tooth brakes are best suited to low-speed applications where accidental engagement will not cause tooth damage. Spring-applied tooth brakes give a true holding torque until air pressure is applied. Applications include holding barrier arms, and the toothform can be set so that in an emergency the barrier can be forced open manually.
Mönninghoff pneumatic tooth clutches, together with electromagnetic clutches, are available in the UK through Lenze Ltd, whose engineers can also provide technical advice. A brochure is available on request.
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