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Gearhead Construction and Use

  • Spur Gear Type Gearheads
  • Direction of Rotation
  • Planetary Gears

Spur Gear Type Gearheads

Spur gear type gearheads are probably the best possible choice for relatively low torque applications. They tend to be quieter in operation and have a relatively low amount of internal friction as well. Engineers designing high accuracy positioning servos are occasionally surprised to find that many of the small gearhead series supplied by MICROMO use non-integer gear ratios. This fact is often discovered after the engineer has repeatedly tried to reconcile motor encoder counts with gearhead shaft position only to find a small but persistent position error. At first glance, the use of non-integer gear ratios appears to have no apparent purpose (with the possible exception of frustrating servo designers). There is a fundamentally sound reason for designing gearheads with such gear ratios, however, and the servo designer who has sufficient information will generally have no problems using them.
In the process of cutting gears, there is a small but inevitable error in tooth profile that is introduced by such process parameters as tool-wear. The profile error usually manifests itself in the last tooth cut on a particular gear blank. Depending upon the machine set-up and extent of tool wear, the material remaining on the gear blank for last tooth may be more or less than required to form a perfect tooth profile. As a result, an error may be introduced in the profile of the
last tooth.