Machine element or mechanism – Gearing – Directly cooperating gears
Patent
1988-03-22
1989-11-21
Braun, Leslie A.
Machine element or mechanism
Gearing
Directly cooperating gears
74426, 192 56R, 192 56L, 192150, 464 38, F16H 3510, F16H 2704
Patent
active
048814210
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a mechanical drive, especially stepping drives rotatable through a drive shaft for converting a rotary ddrive movement to an output rotary movement which follows a given law of motion and can be taken from an output shaft, in which a spring-biased safety coupling is disposed which is disengaged in the event of an overload.
The protection of rotary drives by safety couplings which disengage if a given maximum torque is exceeded is known. Safety couplings are also used to secure drives against damage by overload, and a great number of types of design have been developed. Such safety couplings can have, for example, coupling elements compressed into positive or frictional engagement by a biasing spring; one of them is coupled for co-rotation with the driving shaft and the other for co-rotation with the driven or output shaft of the rotary drive that is to be protected. The amount of the disengagement torque is determined by the bias of thespring forcing the coupling elements into engagement, i.e., it is substantially constant. The disengagement torque of the safety coupling is accordingly adjusted in such protected drives so as to be less than the designed maximum allowable torque calculated on the basis of strength. This is to assure that the drive can never be overloaded. But at the same time no consideration is given to the fact that, especially in the case of stepping drives with complex mechanical drives connected to their output, it is not the maximum load bearing capacity of the drive itself but the stress on the components of the following mechanism that can be critical, the allowable stress capacity depending on the position of the connected moving parts. In such applications the engagement torque of the safety coupling must be adjusted to the lowes torque allowed in the driven system, although the low disengagement torque determined in this manner is necessary only in quite specific conditions of operation. In certain applications it would also be desirable for the disengagement torque to be variable according to the output torque.
It is the object of the invention to create a drive, and especially a stepping drive, with a safety coupling whose disengagement torque automatically adapts itself to given operational requirements.
Setting out from a drive of the kind described above, this objec is achieved according to the invention by the fact that the spring biasing the safety clutch is supported on a biasing element held in the drive casing for movement toward an increase or reduction of the spring bias. The biasing element is part of the secondary part of a cam drive whose cam is coupled for co-rotation with the drive shaft or output shaft. By varying the shape of the control cam, therefore, the bias of the spring biasing the safety coupling and thus the disengagement torque of the coupling is variable according to the position of the rotor bearing the drive cam, i.e., of the driving or output shaft.
In one embodiment the drive to be protected is a stepping drive with a globoid wheel or cylindrical wheel disposed in the drive casing, on or in whose circumferential surface a drive control cam is provided in the form of crosspieces or grooves which mesh with output drive pins projecting at regular intervals radially from the circumference of a driven wheel, while the driven wheel is disposed on the output shaft mounted in the drive casaing at right angles to and at a distance from the driving shaft. The configuration is preferably such that the safety coupling disposed between the driven wheel and the output shaft has two coupling elements displaceable relative to one another and in positive engagement with one another or disengaged from one another depending on their relative position. One of these coupling elements is coupled co-rotationally with the driven wheel which in turn is journaled on the output shaft, and the other is coupled co-rotationally with the output shaft. One end of the biasing spring is supported directly or indirectly on the coupling element that is displ
REFERENCES:
patent: 2712246 (1955-07-01), Zakrajsek
patent: 3817116 (1974-06-01), Georgieff
patent: 3898816 (1975-08-01), Lindahl et al.
patent: 4044872 (1977-08-01), Punsmann et al.
Machine Design, Band 37, Jul. 1965, "Notched Latch Provides Torque Fuse", p. 128.
Anchell Scott
Braun Leslie A.
Elpatronic AG
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