Combined clutch and brake mechanisms are used for driving power presses in which the movement of a crank or eccentric shaft must be stopped immediately after the clutch is disengaged. Combined clutch and brake mechanisms are designed such that, when the clutch is engaged, the brake is automatically disengaged, and, when the brake is engaged, the clutch is automatically disengaged.
Combined clutch and brake mechanisms utilize friction linings or friction elements which are engageable with a clutch disk and a brake disk. Friction elements undergo extensive wear during use and frequently must be replaced. Friction element wear is particularly problematic because any variation in the clearance between the friction element and the clutch disk seriously affects the proper functioning of the clutch. Similarly, any variation in the clearance between the friction element and the brake disk seriously affects the proper functioning of the brake. As a consequence, a prescribed clearance between the linings and the disks must be maintained to enable the combined clutch and brake mechanism to operate properly.
Existing combined clutch and brake mechanisms are difficult to service. Adjusting the clearances between the friction elements and the brake and clutch disks on those mechanisms requires numerous time-consuming steps. Replacing worn friction elements is also a time-consuming process. To replace a friction elements, the entire mechanism must be completely disassembled, the friction elements replaced, and the mechanism must then be reassembled. Consequently, existing combined clutch and brake mechanisms are subject to significant down time.
A need therefore exists for a combined clutch and brake mechanism that permits the clearances between the friction elements and the clutch and brake disks to be quickly and easily adjusted and allows worn friction elements to be efficiently replaced.
In addition, existing combined clutch and brake mechanisms are prone to mechanical failure as the difficulties in accessing the friction elements unduly delays their replacement. This is particularly problematic where one of the sealing collars which secure the piston in the casing of the pneumatic cylinder fails and the piston is no longer able to move the clutch into an engagement position.
A need exists for a combined clutch and brake mechanism that allows for easy maintenance of parts requiring replacement.
During operation, frequent adjustments must be made to the length of the piston stroke in the pneumatic cylinder of a combined clutch and brake mechanism. Existing combined clutch and brake mechanisms require that the entire mechanism be disassembled before the stroke length can be adjusted and reassembled after the adjustment is made. This also is time-consuming and subjects existing clutch and brake mechanisms to significant down-time.
Therefore, a need exists for a combined clutch and brake mechanism having an increased service life and having improved performance, particularly under emergency conditions.