Design and application of double motor drive to eliminate rack and pinion clearance

The CNC floor-standing milling and boring machine features a long X-axis stroke, typically ranging from 8 to 30 meters. Its transmission system commonly uses a gear-rack mechanism. However, due to the mechanical play between the motor and the moving part, this backlash can significantly affect the machine's positioning accuracy, repeatability, and overall system stability. Traditional methods to address this issue often involve using a single motor to drive multiple gear pairs with pre-tensioning or other mechanical adjustments. While these approaches help reduce static errors caused by backlash, they fall short in high-speed, high-precision systems where rapid direction changes occur frequently. Even with mechanical compensation, transient errors caused by the gap remain challenging to eliminate. Moreover, the limitations of traditional backlash compensation mechanisms result in longer manufacturing cycles, higher maintenance demands, and increased costs. As electrical technology continues to advance, a more efficient solution has emerged: dual-motor anti-backlash technology. This innovative approach employs two motors, two reducers, and two gear-rack systems, all synchronized by a numerical control system. By applying an electric preload torque, it dynamically eliminates the transmission gap between the gears and rack, improving both static and dynamic accuracy of the machine tool. One key advantage of the dual-motor system is its enhanced driving force during acceleration and deceleration. Since both motors work together at the start and end of movement, the machine’s feed axis achieves better acceleration performance compared to a single-motor setup. This allows for the use of smaller, more cost-effective motors, reducers, and racks. Additionally, the dual-motor structure reduces the need for complex mechanical adjustments, lowering maintenance and operational costs. The dual-motor drive system operates by having each motor control a separate set of gear pairs. These gear pairs engage with the same rack, ensuring continuous contact and eliminating any gap when the direction changes. The numerical control system applies a controlled tension to the motors near the zero-torque point, allowing them to compensate for the backlash effectively. Once the direction change is complete, both motors work in unison to maintain smooth and precise motion. This method not only improves accuracy but also enhances the machine’s responsiveness and reliability, making it ideal for high-speed, precision machining applications. Overall, the dual-motor anti-backlash system represents a significant advancement in CNC machine design, offering a more efficient and effective solution to the age-old problem of mechanical backlash.

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