The selection of the motor (usually referring to the motor itself, especially the servo motor) and reducer of a laser cutting machine directly affects cutting accuracy, speed, stability, and equipment lifespan. A systematic approach is required; the following is a detailed selection guide:
Core Principle: Matching
The motor, reducer, and load (laser head or moving parts) must be selected as a system, not individually. The ultimate goal is to meet the dynamic performance requirements (speed, acceleration, positioning accuracy) and load requirements of the laser cutting machine.
Step 1: Determine the Type and Requirements of the Laser Cutting Machine
Equipment Type:
High-precision, high-speed type (e.g., fiber laser cutting machine, precision 3D cutting): Requires extremely high dynamic response and positioning accuracy.
High-power, heavy-duty sheet metal cutting type: Requires high torque and rigidity, with speed requirements being relatively less critical.
Core Performance Indicators:
Maximum speed (m/min)
Maximum acceleration (m/s²): High acceleration means the motor needs to be able to quickly output high torque.
Positioning accuracy and repeatability (mm or μm)
Load mass: The total mass of all moving parts, including the laser head, fixture, guide rails, and sliders.
Transmission method: Typically uses synchronous belts, rack and pinion gears, or ball screws. Different methods have different load characteristics, friction, and inertia.
Step Two: Motor Selection (usually a servo motor)
Laser cutting machines almost exclusively use AC servo motors because of their high control precision, fast response, and strong overload capacity.
Key selection parameters:
Torque:
Continuous torque: Must be greater than the torque required for the load to run at a constant speed.
Peak torque: Must be able to meet the instantaneous torque required for the load at maximum acceleration. This is the most important factor in selection. Laser cutting machines require frequent starts, stops, accelerations, and decelerations during rapid idle movement and at complex corners.
Calculation formula (simplified):
Required peak torque = (Load inertia + Motor's own inertia) × Maximum angular acceleration + Load friction torque
Where, angular acceleration is related to linear acceleration and needs to be calculated based on the transmission mechanism.
Rotational Speed: The rated motor speed must meet the maximum design speed requirements of the equipment, with a certain margin (usually 10-20%).
Calculation Formula: Motor Speed (rpm) = Maximum Linear Speed (m/min) / Transmission Mechanism Lead (m/revolution)
Inertia Matching: This is crucial for the stability and response speed of the servo system. It is generally recommended that: Load Inertia / Motor Rotor Inertia ≤ Recommended Ratio. For laser cutting machines with high dynamic response, the recommended ratio is typically within 3 to 10 times. The smaller the ratio, the faster the system response and the easier it is to control, but this may mean needing to select a motor with a larger inertia, resulting in higher costs.
Load inertia needs to be calculated precisely, including the rotational inertia of the worktable, workpiece, lead screw/rack and pinion, etc.
Encoder Resolution: Directly affects positioning accuracy. High-precision cutting requires a high-resolution encoder (such as a 23-bit or higher absolute encoder).
Brand and Reliability: Mainstream brands include: Yaskawa, Mitsubishi, Fanuc, and Panasonic from Japan; Siemens and Bosch Rexroth from Germany. Domestic brands such as Huichuan and Estun are also developing rapidly.
Step 3: Gearbox Selection
The main functions of a gearbox are: increasing output torque, reducing speed, and matching inertia.
When is a gearbox needed?
When the motor's rated speed is much higher than the required operating speed, and the torque is insufficient.
When the load inertia is too large, far exceeding the recommended inertia matching ratio of the motor, using a gearbox can significantly reduce the load inertia referred to the motor side (the reduction ratio is the square of the reduction ratio), thereby improving system response.
Key Selection Parameters:
Reduction Ratio (i): This is the most crucial parameter.
Speed Selection: i ≈ Rated Motor Speed / Required Output Speed
Inertia Matching Selection: To match the load inertia to the ideal range, the required reduction ratio i ≈ sqrt(Load Inertia / (Recommended Inertia Ratio × Motor Rotor Inertia)). The final determined reduction ratio must simultaneously meet the speed and torque requirements and use standard values.
Output Torque: The rated output torque of the reducer must be greater than the maximum load torque of the laser cutting machine during operation, and a safety factor (usually ≥2) must be considered.
Accuracy (Backlash): Backlash is the return clearance of the reducer, directly affecting the contour accuracy and corner accuracy of the cut.
High-precision laser cutting requires low-backlash or zero-backlash products.
Planetary Reducer: The most commonly used choice for laser cutting machines, with a backlash typically between 1-10 arcmin, and precision models can be less than 1 arcmin.
Harmonic Reducer: Extremely small backlash (<1 arcmin), but relatively small torque capacity, mostly used in precision 3D cutting heads or small equipment.
Cycloidal pinwheel reducer: High rigidity, but backlash is typically greater than that of planetary reducers, mostly used in heavy-duty, low-precision applications.
Rigidity: The reducer needs high torsional rigidity to minimize deformation under varying cutting forces, ensuring accurate cutting trajectories.
Installation Dimensions and Form: Must be compatible with the motor and mechanical structure. Common forms include shaft output and flange output.
Step 4: Selection Process Summary
Determine mechanical parameters: load mass, maximum speed, maximum acceleration, transmission mechanism parameters (lead screw lead, gear diameter, etc.), and working cycle.
Calculate load requirements:
Calculate the load inertia J_load.
Calculate the maximum load torque T_load (including friction, cutting force, etc.).
Determine the required output speed N_out.
Pre-select reducer: Pre-select the reduction ratio i based on the required N_out and the motor's common speed range.
Based on T_load and a safety factor, initially select the reducer model.
Reflecting to the motor side:
Reflected load inertia: J_load_reflected = J_load / i²
Required motor torque: T_motor = (T_load / i) + (J_motor + J_load_reflected) × α (α is angular acceleration)
Motor selection:
Find a motor that meets the following requirements: Peak torque > T_motor, Rated speed > N_out × i.
Inertia matching verification: Check if J_load_reflected / J_motor is within the ideal range of 3-10. If it exceeds this range, it may be necessary to adjust the reduction ratio i or the motor model, returning to step 3 for iteration.
Final verification:
Verify that the speed-torque characteristic curve of the entire system covers all operating points.
Consider heat dissipation, installation space, brand budget, and after-sales service.
Practical Advice
Consult Suppliers: Provide your equipment parameters (speed, acceleration, load capacity, transmission method) to reputable motor and gearbox suppliers (such as Sumitomo, Shinpo, Newcatel, etc.). They typically offer professional selection software and technical support.
Refer to Similar Models: Investigate the configurations used by successful laser cutting machine brands of the same type and specifications on the market.
Prioritize Precision: For laser cutting, to ensure cutting quality and sharp corners, choose high-response servo motors and low-backlash precision planetary gearboxes within your budget.
This is a typical mechatronics system design problem, requiring rigorous calculations and potential iterations. Hopefully, this guide will provide you with a clear selection strategy.