Nabtesco RV series high-precision gearbox

2.3 Output Modes

The RV gearbox provides two basic output modes:

Fixed shell and rotating output shaft: the most common working mode, suitable for robot joints, turntables, etc.

Fixed output shaft, rotating housing: suitable for situations requiring large hollow holes or special installation methods.

Speed ratio calculation formula (taking shaft output as an example):

R=1+Z2Z1⋅Z4

R=1+ Z 1Z 2⋅Z 4

Among them, Z1Z1 is the number of input gear teeth, Z2Z2 is the number of spur gear teeth, and Z4Z4 is the number of needle teeth. Due to the large size of Z4Z 4, the overall speed ratio can be achieved very high (from tens to nearly 200).

RV-E series: the benchmark for universal precision reducers

3.1 Model and Specifications

The RV-E series covers a variety of specifications from small to large, including models such as RV-6E, RV-20E, RV-40E, RV-80E, RV-110E, RV-160E, RV-320E, and RV-450E. The rated torque, speed ratio range, and external dimensions of each model gradually increase.

Definition of rated torque: For RV-6E, the rated output speed is 30 r/min; For other models, the rated output speed is 15 r/min. The output torque at this speed is used as the benchmark for calculating the lifespan. At different speeds, the allowable output torque varies according to the principle of "N · T=constant".

3.2 Detailed Explanation of Performance Parameters

3.2.1 Torque and Capacity

Taking RV-160E as an example, under the condition of speed ratio 129 (shaft output):

At an output speed of 15 r/min, the rated output torque is 13887 in lb (approximately 1568 N · m).

As the speed increases to 30 r/min, the allowable output torque decreases to approximately 11894 in lb, and the input capacity increases accordingly.

The peak torque allowed during acceleration and deceleration is 250% of the rated torque (200% for RV-6E).

The instantaneous maximum allowable torque under emergency stop or impact conditions is 500% of the rated torque.

3.2.2 Main bearing capacity

The RV-E series has built-in angular contact ball bearings that can directly withstand external loads. The main parameters include:

Moment stiffness: The value of the bending moment (in lb/arc. min) required to deflect the output shaft by one degree. For example, the bending moment stiffness of RV-160E is 26038 in lb/arc.min, which means its ability to resist bending deformation is extremely strong.

Allowable moment: The maximum allowable moment applied to the output shaft during normal operation. The allowable bending moment of RV-160E is 34718 in lb (approximately 3920 N · m).

Instantaneous maximum allowable bending moment: usually twice the allowable bending moment, used to withstand unexpected impacts.

3.2.3 Stiffness and backlash

Torsional stiffness: Apply torque to the output shaft while fixing the input shaft, and measure the torsional angle. The higher the stiffness, the smaller the elastic deformation under the same torque.

Lost motion: The torsional angle corresponding to the midpoint of the hysteresis curve measured during reciprocating loading within the range of ± 3% of the rated torque. The typical hysteresis value of the RV-E series is 1 arc minute (1 arc. min), which means that the backlash during forward and reverse switching is extremely small, making it very suitable for high-precision positioning.

Backlash: The twisting angle at which the torque is zero. The RV series controls the backlash within 1 arcminute through precision assembly.

3.2.4 No load starting torque and low temperature characteristics

Idle starting torque: The torque required to rotate the gearbox from the input side under no-load conditions. This value is affected by the viscosity of the lubricating grease and assembly accuracy.

Backdriving torque: When a certain torque is applied to the output shaft, the input shaft is driven in the opposite direction to rotate. This feature requires special attention in certain applications such as force feedback and gravity balance.

Low temperature characteristics: In low temperature environments (such as below -10 ℃), the viscosity of lubricating grease increases, and the no-load starting torque significantly increases. The product information provides measured curves under different low temperature conditions.

3.2.5 Angular Transmission Accuracy

Angle transfer error is defined as the difference between the theoretical output angle and the actual output angle. The RV series controls the angular transmission error within a very small range (usually within ± 1 arcminute) through high-precision cycloidal profile and strict manufacturing tolerances, thereby ensuring the smoothness and repeatability of the robot trajectory.

3.3 Installation and Assembly

The RV-E series is not pre lubricated at the factory, and users need to inject the specified amount of lubricant (Nabtesco Molybdenum RE00) during installation. The required amount of oil varies depending on the installation direction (horizontal or vertical).

Installation accuracy is crucial:

The coaxiality tolerance requirement between the motor flange and the input side of the reducer is 0.03-0.05mm (depending on the model).

The flatness and verticality of the installation surface must be controlled within the recommended range, otherwise it may cause vibration, noise, and abnormal wear.