Vogel phase shifting gearboxes provide mechanical adjustment of the phase angle between two rotating shafts. Adjustment can be made intermittently or continuously, leading to this type of transmission being widely used for print registration, wrapping on packaging machinery, and tensioning in papermaking plants. While many of these applications have transferred to servo technology in recent years, the use of phase-shifting gearboxes is once again gaining ground, as customers recognise the value of mechanical simplicity and low cost. Particularly in cases where adjustment is infrequent, for example made by manually turning a shaft, these gearboxes are a good option.
Phase-shifting gearboxes are a variation on a planetary design in which the outer ring can be rotated. It is turned by a shaft with a worm gear connection to the ring. Rotation of the worm shaft therefore superimposes a motion between the planetary input and output shafts, adding or subtracting a phase angle. Typically one turn of the worm shaft puts an increment of 3 degrees on the output shaft. This fine adjustment can be used to adjust the position of a driven part of a machine, for example flight bars to feed, print cylinders for registration or knives to achieve an accurate cut length. Continuous input to the worm shaft can be used for tensioning, for example webs of paper, and a speed trim of up to +/-24rpm is possible.
Two configurations of these phase-shifting gearboxes are available with details available and a catalogue downloadable from the Techdrives website. In-line gearboxes can be 1:1 or have a 3:1 reduction ratio and are available in five sizes for torques of 50 to 1500Nm. Right-angle gearboxes incorporate a bevel output stage with twin output shafts and gear ratios of 1, 2 or 3. An additional use for these gearboxes is found in emergency or pony drives. For example, with ovens and furnaces it is often necessary to remove products from the heated areas should the main drive fail, perhaps due to an mains supply fault. Here a manual input to the adjustment shaft, or perhaps an air motor, enables the output to be turned slowly and with a low power requirement. The main drive to the input shaft does not turn, as it may be locked against back-driving.
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