Machine element or mechanism – Mechanical movements – Oscillation or reciprocation to intermittent unidirectional...
Patent
1987-02-11
1988-03-08
Staab, Lawrence
Machine element or mechanism
Mechanical movements
Oscillation or reciprocation to intermittent unidirectional...
74 88, 74161, F16H 2702, F16H 3100
Patent
active
047292512
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a stepping mechanism. Such stepping mechanisms serve to rotate a toothed wheel in a stepwise manner; a machine element, for example, a parts magazine or the like, which is to be positioned, is in a drive connection with the shaft of the toothed wheel by way of a gear unit. The publication of "Constructional Elements of Precision Mechanics", Richter and Voss, 1959, page 477, discloses stepping mechanisms comprising two wheels whose axes intersect. The driving wheel carries two parallel ribs at its outer surface area, which are connected by means of an inclined intermediate piece. These ribs engage in corresponding gaps of the driven toothed wheel. During the rotation of the driving wheel, the toothed wheel is only shifted further when the inclined intermediate piece is engaged. The shifting distance corresponds to the distance between two parallel ribs. After shifting, the toothed wheel is locked again. Such stepping mechanisms are used predominantly in motion picture technology for shifting the film strip by one frame in each instance. They require a relatively narrow tooth pitch, which sharply restricts their range of application.
In addition, there are single-tooth gear units, of which the Geneva movement star wheels are the most well-known. In this case, the driving wheel carries a peg, instead of a tooth, while the driven wheel, the so-called star wheel, comprises four slots. In order to secure the catch position the driving wheel is provided with a cylindrical projection which engages in a recess of the star wheel in each catch position. Such gear units require very accurate manufacturing. The wheels consist, as a rule, of precision-cut parts whose surfaces, which contact one another, are subjected to fine machining in order to reduce the friction.
Finally, tooth ratchet mechanisms are known, in which the stepwise shifting of a toothed wheel is effected by means of an oscillating member which engages in the teeth of the toothed wheel with a pawl. Since the toothed wheel is not secured when the member swings back, a special stop pawl must be applied which engages in corresponding tooth gaps of the toothed wheel. Whereas in ratchet mechanisms with a shifting pawl and a stop pawl the oscillating shifting member carries along and accordingly shifts the toothed wheel by means of the shifting pawl during forward movement, but, during reverse movement, runs idle and while the toothed wheel is at rest, the toothed wheel is shifted further in both oscillating directions of the shifting member in ratchet mechanisms with two pawls. A shifting pawl shifts in each instance, while the other runs idle.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a stepping mechanism, which would require only a shifting pawl in order to shift the toothed wheel further by one tooth pitch in each instance in both movement directions of the slide. The stepping mechanism according to the invention has a simple, sturdy construction which requires no fine-machined precision structural component parts and is uncritical with respect to tolerances. Another advantage of the invention resides in that the stepping mechanism is easily adaptable to toothed wheels with different tooth pitches by means of a corresponding inclination and/or length of the tooth guiding face of the shifting pawl.
In accordance with further modifications of the invention it is particularly advantageous for the presetting of the pawl position that the slide have two stops which define the swiveling path of the shifting pawl and determine the angle of inclination of the tooth guiding surface and which are arranged in the movement path of a lever arm, which is connected with the shifting pawl so as to be fixed with respect to rotation relative to it. The conveyance of the shifting pawl into its two working positions can be achieved in a simple manner in that two stops, which are integral with the device, are provided in the movement path of another lever arm of the shifting pa
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Robert & Bosch GmbH
Staab Lawrence
Striker Michael J.
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