B = Bc + Bv (49)
where:
Bc = constant backlash
Bv = variable backlash
12.2 Transmission Error
The sources of transmission error originate both from the gears and their installation. Some of these are also sources of backlash. The list of usual sources is as follows:
| I. II. |
Position error in the individual
gears 1. Total composite error a. Single-cycle errors (pitch-line runout) b. High-frequency tooth-to-tooth composite errors (TTCE) Installation errors 1. Runout sources a. Clearance between gear bore and shaft b. Runoutat point of gear mounting c. Eccentricity of rotating race of ball bearing d. Miscellaneous runouts: component shaft composite gear assembly 2. Miscellaneous error sources a. Shaft couplings b. Material creep of shaft and bearings |
The above errors are converted to angular-position error in the same manner as TCE is converted by equation 46. Thus, the total transmission error for each mesh is proportional to the sum of all eccentricity error sources:
a(ET)mesh = ± 3440 SEi (arc minutes)
(50)
R
where:
Ei = eccentricity
(one half runout value) of error contributors
A more detailed explanation and analysis of transmission error can be obtained from Reference 5.
12.3 Integrated Position Error
Backlash and transmission error should be distinguished from functional considerations which are not necessarily related to gear performance. For example, in a servomotor gear train, backlash may be very important, whereas position error may be immaterial. Alternatively, in a unidirectional position sensor gear-train, backlash may be of little concern, while transmission error might be critical. Often however, positional accuracy is most important in the overall accuracy of gear trains. In such cases, backlash combines with transmission error to yield an integrated position error (IPE). In essence the
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