Design of rack and pinion transmission for CNC machine tools

The rack and pinion transmission is divided into two types: single-motor mechanical anti-backlash rack and pinion transmission and dual-motor electric anti-backlash rack and pinion transmission. The former uses a single-motor drive with a mechanical anti-backlash gear box structure, and the transmission gap is through the mechanical structure. Adjustment, poor transmission accuracy retention, has been gradually eliminated; the current mainstream rack and pinion transmission method is dual-motor electric backlash-free rack and pinion transmission. Its working principle is as follows: adopt double gear drive on the same rack, in the normal feeding process of the machine tool (see Figure 1), the master and slave motors will work together, the rotation direction of the master and slave gears is the same, they all rotate clockwise, and can output 1.5 ～2 times the torque of a single motor. When the machine tool feeds in reverse (see Figure 2), the two output gears mesh with the opposite sides of the rack by applying torques in the opposite direction to the master-slave drive motor, and are kept The tension state, through this function, can eliminate the gear rack transmission gap, thereby improving the positioning accuracy of the machine tool and allowing it to be permanently maintained, and will not affect the positioning accuracy of the machine tool due to the wear of mechanical parts. Therefore, the dual-motor electric anti-backlash rack and pinion transmission is widely used in applications with relatively large strokes (strokes exceeding 6 500mm).

However, there is no complete and systematic literature for the theoretical calculation of rack and pinion transmission. Based on years of work experience, the author selects the rack and pinion, the reduction ratio of the reducer, the torque matching of the servo motor and the servo Several aspects of motor inertia matching have been introduced in detail, hoping to provide useful reference and help for readers. In order to make the problem more intuitive and clear, take the X-axis drive of a machine tool as an example to introduce the design process of the dual-motor electric anti-backlash rack and pinion transmission structure. This is an ordinary CNC metal cutting machine tool. Its X-axis transmission adopts a helical gear rack dual-motor electric anti-backlash transmission structure. The parameters of the X-axis drive are as follows: The carriage and the carriage load are 2 800kg, plus The deceleration time is 0.25s, the acceleration is 3.2m/s2, the fast forward speed is 48m/min, the stroke is 7 500mm, and the X-direction cutting resistance during machine cutting is 5 000N.

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