Duplex screw
In contrast to normal gears (also called simplex worm drives ), the tooth flanks of duplex worms are manufactured with slightly different modules or numbers of shapes. This results in different helix angles for the two tooth flanks, so that the tooth thickness or tooth gap changes continuously over the worm tooth width. The different modules on the worm wheel lead to different profile shift factors and pitch circle diameters and thus to different flank shapes for the leading and trailing flanks. The tooth thicknesses and gaps remain constant on the circumference of the wheel. The backlash is adjusted by axially shifting the worm so that the area of the worm toothing with the tooth thickness that matches the tooth flank backlash meshes with the worm wheel (Fig. 1).
The tooth flank backlash can be set to any value and can be readjusted sensitively and continuously at any time without changing the meshing conditions of the gearing.
Other ways of setting the game
In addition to the duplex method, there are basically the following options for setting or adjusting the backlash of a worm drive:
- Change the center distance by turning the eccentric bushings in which the worm shaft and / or the worm gear shaft are mounted in the housing.
- Axial displacement of a conical screw (Fig.2a)
- Division of the screw into two halves (Fig. 2b), which are rotated or shifted relative to each other (Ott system)
- Division of the wheel into two disks (Figure 2c), which are rotated relative to each other.
However, all of these methods have significant disadvantages:
- Clearance adjustments and readjustments falsify the geometrically exact tooth engagement.
- They shift the contact pattern and change its shape and size.
- As a result, they reduce the load-bearing capacity and decrease the efficiency.
- Every adjustment results in a large amount of wear in the inlet.
- The risk of incorrect adjustment and destruction of the worm drive is great.
Duplex gears do not have these problems.
They allow a geometrically exact and, moreover, very sensitive clearance setting. Neither the contact pattern that has been developed, nor the load-bearing capacity or the degree of efficiency are affected. In addition, the duplex toothing, designed as involute toothing , is relatively insensitive to changes in the center distance, e.g. B. as a result of screw deflections.
Setting the game
When installing and adjusting a DUPLEX wheel set, proceed as follows:
- The shaft and wheel are assembled one after the other. The arrows for the adjustment direction on both parts point in the same direction (Fig. 1)
- The shaft is to be mounted with bearings in an axial position before the zero position. In this position she has play on the wheel.
- The wheel is mounted in its bearing, but is still axial, i.e. H. transversely to the worm shaft axis, movable.
- Both worm shaft flanks are spotted and the shaft is rotated by hand in both directions by at least 2 × 360 ° so that the spotting color is transferred from the worm flanks in the contact area (contact pattern) to the wheel flanks.
- The wheel must now be moved along its axis of rotation (axially) until the front and rear flanks of the wheel show contact patterns that are approximately evenly removed from the center.
- The wheel is fixed in this optimally achievable central position of the contact patterns.
- The shaft can now be screwed in down to the zero position (notch at the height of the wheel axle) or up to any other desired play.
- Now the shaft is axially fixed in this position.
Applications
Duplex gears are used wherever backlash between the shaft and gear teeth is undesirable or harmful,
- to achieve high positioning accuracy in both directions of travel
- in order to avoid a damaging, pulsed contact edge change when the load direction changes
For example:
- as a drive in rotary and swivel tables
- as adjustment drive in milling heads
- in press adjustments
Web links
- HENSCHEL MUTAX®-DUPLEX worm gear with backlash-adjustable toothing (PDF file; 1.52 MB)