Machine element or mechanism – Gearing – Backlash take-up
Reexamination Certificate
2000-07-14
2002-05-14
Hannon, Thomas R. (Department: 3682)
Machine element or mechanism
Gearing
Backlash take-up
C074S400000, C074S425000
Reexamination Certificate
active
06386059
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is generally directed to a an improved adjustable speed reducer assembly. More particularly, the invention contemplates a speed reducer assembly which implements a split worm whose spring force can be easily adjusted.
Speed reducers have been used to transmit motion and power between non-intersecting shafts generally at right angles to one another. A typical speed reducer consists of an input shaft with threads and a toothed wheel or circular gear. The threaded input shaft, which is referred to as the worm is aligned to mesh with the teeth on the circular gear. A transfer of power occurs as the threads on the worm slide into contact with the teeth of the circular gear causing the circular gear to turn.
A common form of speed reducer uses a cylindrically shaped worm. The thread of the cylindrically shaped worm is of uniform diameter and generally contacts only a few wheel teeth. The number of teeth which the worm contacts can be significantly increased if the shape of the worm is modified from a cylindrical to conical. The conical worm is narrower at its center where it meets the top of the circular gear and wider at its ends conforming to the arc of the circular gear. The conical worm is sometimes referred to as a “double-enveloping” worm. Because the “double-enveloping” worm conforms to the arc of the circular gear, the worm thread contacts many more teeth on the circular gear. This additional contact between the worm thread and the circular gear's teeth increases the torque throughput allowing for higher load capacities, improved accuracy and reduced stress levels in the contact area thus extending the operating life of the speed reducer assembly.
A common problem encountered with the use of speed reducers is backlash. Backlash is generally defined as the play between the worm thread and the mating teeth. Backlash results in imprecise angular positioning of the speed reducer output shaft. Use of a double enveloping worm, rather than a cylindrically shaped worm, can reduce the backlash in a speed reducer.
The reduction of backlash in the speed reducer allows for the speed reducer to be used in industries which require precise positioning and increased throughput. For example, metal cutting and forming machinery requires accuracy in the position of a work piece even if the work piece is heavy and repeated starting and stopping is necessary. In machinery used in printing and packaging applications, double enveloping worm gearing helps printing press rolls maintain precise print registration at very high speeds.
The backlash can be further reduced by using a split worm. A split worm is a worm which is formed with two worm segments placed together at the axial center of the worm thread. One segment of the worm is fixed in its bearing set, while the other segment is positioned laterally and is capable of reciprocal movement along the worm's axis and thus is referred to as the floating worm segment. Springs are implemented to manipulate the position of the floating worm segment so that a consistent clamping force is maintained on both sides of the gear. Half of the worm contacts the drive side of the gear while the other half of the worm makes continuous contact with the opposing side of the gear. The result of this split worm gear design is the elimination of backlash, making it ideal for applications which require extremely accurate positioning.
With this split worm arrangement, the spring force requirement on the floating worm segment is unique for each application. If the spring force is too light to resist the torque on the loaded gear, the worm will move out of position, misalign the gear mesh and destroy the gearset. If the spring force is too great, the system will require excessive force to turn, and will rapidly wear the gear.
The process of determining the proper spring force begins by determining output torque requirement. Using the output torque requirement, the spring force required to resist that output torque is then calculated. Springs are then selected and spacers are either added or removed to achieve the desired spring force. Removing additional spacers increases the spring force by incrementally compressing the spring within a fixed space. The spacers are provided in a variety of widths so as to allow for controlled incremental compression of the spring.
Setting the spring force on the split worm gear in this manner results in a number of difficulties. One such difficulty is that the measurement given for the desired output torque is often inaccurate. The inaccurate torque measurement often is not discovered until the spring force has been set, the housing has been reassembled and the speed reducer has been implemented. To adjust the spring force at this point requires first that the housing be opened and then requires that springs and/or spacers are added or removed to achieve the proper spring force. Often the spring force is set by the manufacturer and the speed reducer assembly is then shipped to a customer. The manufacturer sets the spring force based upon the customer provided measurement and calculation of the required spring force. Depending upon the accuracy of the measurements and calculations and how the speed reducer has been implemented, it may be necessary for a technician to travel to the site where the speed reducer assembly has been implemented to make the spring force adjustments. This, of course, adds to the cost of the speed reducer.
Another problem with the current method of setting the spring force is that springs are selected and implemented based upon their theoretical spring force ratings. However, there are high tolerances within these spring force ratings and inaccurate spring force settings result.
The present invention provides an adjustable speed reducer assembly which overcomes the problems presented in the prior art and which provides additional advantages over the prior art, such advantages will become clear upon a reading of the attached specification in combination with a study of the drawings.
OBJECTS AND SUMMARY OF THE INVENTION
A general object of the present invention is to provide a speed reducer assembly with a minimal amount of backlash.
An object of the present invention is to provide a speed reducer assembly whose spring force can be easily adjusted.
Another object of the present invention is to provide a speed reducer assembly whose spring force can be accurately measured.
A further object of the present invention is to provide a device for measuring the spring force within a speed reducer assembly.
Briefly, and in accordance with the foregoing, the present invention discloses an improved speed reducer assembly and a method and apparatus for accurately setting the spring force within the speed reducer assembly. The spring force within the speed reducer assembly is adjusted by rotating an adjuster which extends beyond the speed reducer housing, thus allowing adjustments to be made without disassembling the speed reducer.
REFERENCES:
patent: 2786360 (1957-03-01), Cameron
patent: 4261218 (1981-04-01), Eagan
patent: 4739671 (1988-04-01), Nelson
patent: 6050557 (2000-04-01), Shimoseki
patent: 33 44 133 (1985-06-01), None
patent: 0 527 121 (1993-02-01), None
patent: 3-61751 (1991-03-01), None
patent: 4-29664 (1992-01-01), None
patent: 5-118409 (1993-05-01), None
WhisperDrive Servo Precision Gearhead Product Catalog by Cone Drive Operations, Inc. p. 6.
Cone Drive Operations Inc.
Hannon Thomas R.
Joyce William C
Trexler, Bushnell Giangiorgi, Blackstone & Marr, Ltd.
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