Service Life: Service Life of Gearheads

The gearhead life is reached mainly when power can no longer be transmitted because the bearing mechanical life has ended. Therefore, the actual life of a gearhead varies depending on the load, how the load is applied, and the rotation speed used. Oriental Motor defines life under certain conditions as rated life, based on which the life under actual operation is calculated according to load conditions and other factors. The tooth surface of Oriental Motor's gearheads is lubricated by a grease lubrication mechanism. Lubrication is not required.

Rated Life of Parallel Shaft and Right-Angle Shaft Types

The rated life of parallel shaft and right-angle shaft types is determined by the load applied to the bearing by the transmission torque and the load applied to the bearing by the radial and axial loads on the output shaft.
Oriental Motor defines the rated life as the life of a gearhead under the following operating conditions:

Conditions

Torque
Permissible torque
Load Type
Uniform load
Input Rotation Speed
Reference input rotation speed
Radial Load
Permissible radial load
Axial Load
Permissible axial load

Table 1: Rated Life Time of Parallel Shaft and Right-Angle Shaft Types

Motor Type Series Gearhead Type Reference Input Rotation Speed
[r/min]		 Rated Life
[Hours]
AC Motors KIIS Series
KII Series		 Parallel Shaft Gearhead 1500 10000
Right-Angle Hollow Shaft Hypoid GV Gearhead
JH Gearhead, JL Gearhead 5000
BH Series Parallel Shaft Gearhead 5000
Right-Angle Gearhead 10000
World K Series
K Series		 Parallel Shaft Gearhead 5000
Right-Angle Gearhead
TM Series Parallel Shaft Gearhead 10000
Torque Motors
SMK Series		 Parallel Shaft Gearhead 5000
FPW Series Parallel Shaft Gearhead 5000
AC Speed Control Motors
 		 US2 Series
DSC Series		 Parallel Shaft Gearhead 10000
JH Gearhead, JL Gearhead 5000
US Series Parallel Shaft Gearhead 5000
Right-Angle Gearhead
Brushless Motors BMU Series
BLE2 Series		 Parallel Shaft Gearhead 3000 10000
Parallel Shaft Gearhead
H1 Food-Grade Lubricant		 5000
Hollow Shaft Flat Gearhead 10000
JH Gearhead, JB Gearhead, JV Gearhead 5000
BXII Series
BLE Series
BLV Series		 Parallel Shaft Gearhead 10000
Hollow Shaft Flat Gearhead
BLH Series Parallel Shaft Gearhead* 10000
CS Geared Type
Hollow Shaft Flat Gearhead
αSTEP/
Stepper Motors		 AZ Series
RKII Series		 TS Geared Type 1500 10000
FC Geared Type 5000
AR Series TH Geared Type 5000
FC Geared Type
CRK Series TH Geared Type 5000
2-Phase PK Series SH Geared Type
(□90 mm)		 5000
2-Phase PKP Series SH Geared Type 10000
CS Geared Type
5-Phase PKP Series TS Geared Type 10000
  • *15 W has a rated life of 5000 [hours].

Planetary Geared Type Rated Life

The rated life of the planetary geared type is determined by the load applied to the bearing due to the radial or axial load applied to the output shaft.
Oriental Motor defines the rated life as the life of a gearhead under the following operating conditions:

Conditions

Torque
Permissible torque
Load Type
Uniform load
Input Rotation Speed
Reference input rotation speed
Radial Load
Permissible radial load
Axial Load
Permissible axial load
  • *Value when either radial load or axial load is applied

Table 2: Rated Life Time of Planetary Geared Type

Motor Type Series Gearhead Type Reference input rotation speed
[r/min]		 Rated Life
[Hours]
αSTEP/
Stepper Motors		 AZ Series
RKII Series		 PS Geared Type 1500 20000
AR Series
CRK Series		 PS Geared Type 20000
PN Geared Type
Servo Motors AZX Series
NX Series
 PS Geared Type 3000 10000

Rated Life of Harmonic Geared Type and HPG Geared Type

The rated life of the harmonic geared type and the HPG geared type is determined by the load applied to the gears and bearings by the transmission torque, and the load applied to the bearings due to the radial and axial load applied to the output shaft.
Oriental Motor defines the rated life as the life of a gearhead under the following operating conditions:

Conditions

Torque
Permissible torque
Load Type
Uniform load
Input Rotation Speed
Reference input rotation speed
Radial Load
Permissible radial load
Axial Load
Permissible axial load
  • *The HPG geared type represents the value when either radial load or axial load is applied

Table 3: Rated Life Time of Harmonic Geared Type and HPG Geared Type

Motor Type Series Gearhead Type Reference input rotation speed
[r/min]		 Rated Life
[Hours]
αSTEP/
Stepper Motors		 AZ Series HPG Geared Type 1500 20000
Harmonic Geared Type
(□30 mm, □42 mm)		 7000
Harmonic Geared Type
(□60 mm、□90 mm)		 10000
AR Series
CRK Series		 Harmonic Geared Type 5000
RKII Series Harmonic Geared Type
(□42 mm)		 7000
Harmonic Geared Type
(□60 mm、□90 mm)		 10000
2-Phase PKP Series With flat harmonic gearhead
(□51 mm)		 5000
With flat harmonic gearhead
(□61 mm)		 7000

Estimating Lifetime

Lifetime under actual conditions of use is calculated based on the rotation speed, load and load type, using the following formula. The calculated lifetime represents the actual driven hours.

\(\begin{aligned}& L(\text { Lifetime })=L_1 \frac{K_1}{\left(K_2\right)^3 \cdot f}[\mathrm{h}] \end{aligned}\)
L1
Rated life time [hours]
Determined by each gearhead type from Table 1~3.
K1

Rotation speed coefficient
The speed coefficient K1 is calculated based on the reference input rotation speed listed in Table 1~3 and the actual input rotation speed.

\(\begin{align}K_1=\frac{\text{Reference input rotation speed}}{\text{Actual Input Rotation Speed}}\end{align}\)
K2

Load factor
The load factor K2 is calculated based on the actual operating torque and the permissible torque for each gearhead.

\(\begin{align}K_2=\frac{\text{Operating Torque}}{\text{Permissible torque}}\end{align}\)

The average torque may be considered operating torque if the gearhead is subject to load while starting and stopping only, such as when driving an inertial load. For the calculation method, refer to How to Obtain the Average Torque. Permissible torque represents the specification values listed in the product catalog.

f
Load-Type Coefficient f
The load-type coefficient f is determined based on load type, using the following drive examples as a reference:
Load Type Example Load-Type Coefficient f
Uniform Load
  • Unidirectional continuous operation
  • For driving belt conveyors and film rollers that are subject to minimal load fluctuation
 1.0
Slight Impact
  • Frequent starting and stopping
  • Cam drive and inertial body positioning control via stepper motor
 1.5
Medium Impact
  • Frequent instantaneous bi-directional operation, starting and stopping of reversible motors
  • Frequent instantaneous stopping by brake pack of AC motors
  • Frequent instantaneous starting and stopping by brushless motors and servo motors
 2.0

Note

Regarding the Effects of Radial Load and Axial Load

  • The above estimated lifetime is calculated according to the radial load and axial load, which are in proportion to a given load factor. For example, if the load factor is 50 %, the life is calculated using 50 % radial load and axial load.
  • The actual life of a gearhead having a low load factor and a large radial load or axial load will be shorter than the value determined through the previous formula.

How to Obtain the Average Torque

The stepper motor or servo motor is used for intermittent operation of an inertial load, such as driving an index table and arm. In this case, the average torque shall be considered the operating torque, as described below. The load factor for driving an inertial load using an AC motor or brushless motor shall be 1.0.

Driving an Inertia Body Only ①

The graph below shows torque generated when driving only an inertial load over a long operating cycle. Frictional load caused by bearings and other parts during constant speed operation is negligible and therefore omitted.

Driving an Inertia Body Only ①
$$\begin{align}P_a= \root 3 \of {\frac{({P_1}^3 \times n_1 \times t_1) + ({P_3}^3 \times n_3 \times t_3)}{(n_1 \times t_1) + (n_2 \times t_2) + (n_3 \times t_3)}}\end{align}$$

n1 and n3 represent the average rotation speed in the t1 and t3 area.

In the above example: \(\begin{align}n_1= n_3 =\frac{1}{2}n_2\end{align}\)

Driving an Inertia Body Only ②: Driving an arm or similar object

When driving an arm or similar object, the gearhead may be subjected to load fluctuation as shown in the following graph. For example, such load fluctuation will occur when driving a double-joint arm or moving an arm in the vertical direction. In such an application, the average torque shall be 75 % of the max. acceleration/deceleration torque, as shown in the following formula.

Driving an Arm, etc

Operating Temperature

An increase in gearhead temperature affects the lubrication of the bearing.
However, the effect of temperature on gearhead life varies according to the condition of the load applied to the gearhead bearings, frame size and many other factors. This makes it difficult to include temperature effects in the formula to estimate the lifetime.
The following data shows the temperature effect on the gearhead bearings. The gearhead life is affected when the gear case's surface temperature is 55 °C min.

Gear Case Temperature Factor

Note

In some cases, a lifetime of several tens of thousands of hours may be obtained from the calculation under certain conditions. Use the estimated life as a reference only.
The above life estimation is based on the bearing life.
An application in excess of the specification values may adversely affect parts other than the bearings. Use the product within the range of specified values listed in the product catalog.

Technical Reference