The cycloidal gearbox is a compact actuator that is used in applications where a permanent magnet synchronous motor is used. It is made up of a cycloidal disc and a number of outer rollers that are stacked to transmit torque. This type of cycloidal gearbox is commonly found in servo drives. There are a few companies that manufacture cycloidal gearboxes. However, there are less than ten that have become the leaders in the industry.
Cycloid gearboxes are designed to provide high efficiency and low mechanical service factors. They also offer a large output shaft bearing span and shock load capacity.
To build the cycloidal gearbox, it is first important to create the base and output hole for the gear. The center of the cycloid should be at the center of the output hole. In order to do this, the radius of the pin circle should be equal to the Desmos R and C values. Also, the base should be at least five millimeters thick.
A cycloidal gearbox is usually made with a small number of teeth. It is therefore recommended that the total number of teeth be no less than twice the thickness of the gear. Besides, the overall diameter of the gearbox should be no less than 45 millimeters. As shown in the figure below, the input shaft bearing should be at least five millimeters in diameter.
The outer rollers are placed on a pair of 2mm shafts. These rollers are connected to the outer cylinders by an eccentric roller bearing. An eccentric roller bearing helps to keep rotational inertia low and reduces vibration.
The cycloidal design also introduces compression forces that help to stabilize the output shaft. Because of this, the input torque must be greater than the stiction to start movement. If the stiction is not overcome, the motor will chatter at standstill. On the other hand, if the input torque is greater than the stiction, the output torque will rise as the speed increases.
Since the cycloidal design provides minimal friction, it allows the system to operate at lower mechanical service factors. However, since there is no constant coefficient of friction, the efficiency of a cycloidal gearbox will vary from quadrant to quadrant. Although the average efficiency varies in each quadrant, the maximum efficiency is usually above 100% in generator mode.
Several studies have been conducted to analyze static problems of the gears. The main reason for the variation in efficiency is the presence of static friction. While it is possible to simulate stiction in a single gear by using a ring gear, the friction coefficient in a cycloidal gearbox is not constant. Therefore, to calculate the maximum efficiency of the gearbox, the contact stress should be studied.
For this purpose, the VonMises stress contour is used. The stress contour is obtained by calculating the corresponding stress contours of the outer rollers and housing rollers. Using this method, the cycloidal gearbox efficiency can be calculated.
The output angular velocity is then calculated to the motor side. Based on the characteristics of the gearbox, the stiction breakaway speed is selected.