What type of planetary gearbox is used for servo/stepper motors?

What type of planetary gearbox is used for servo/stepper motors?
In automation equipment, motors and planetary gearboxes are like a pair of partners, and only with good coordination can the equipment operate efficiently.

But there are many types of reducers on the market, how to find suitable "partners" for servo motors and stepper motors? Don't worry, let's combine 5 real industry cases and explain the selection method in a simple and easy to understand way. After reading it, you can learn

What is the difference between choosing a reducer for servo motors and stepper motors?

The servo motor has high precision, as delicate as embroidery. When paired with a reducer, emphasis is placed on "fast response" and "no deviation". For example, for machines that apply protective film to mobile phone screens, if the precision of the reducer is not enough, the film will be applied incorrectly. So when choosing a servo motor reducer, you should choose one with "small clearance" (professionally called backlash, fortunately within 15 arc minutes) and "sufficiently stiff" (torsional stiffness of at least 50N · m/arcmin).

Stepper motors excel in their affordable price and are commonly used in places where precision requirements are not as high. It needs a gearbox to help amplify torque, just like adding power to a small horse pulling a large car.

When choosing a reducer for a stepper motor, attention should be paid to high efficiency (at least 90%) and sufficiently hard gears (with a tooth surface hardness of HRC58), otherwise it is easy to encounter situations where "a small horse cannot pull a large car", such as 3D printers printing half of the casing.

3 key formulas to teach you how to calculate the appropriate reducer

Formula 1: Calculate torque, don't let the gearbox get tired out

The formula is: rated torque of the reducer ≥ rated torque of the motor × reduction ratio × safety factor ÷ transmission efficiency.

For example, a Panasonic servo motor used in a 3C product placement machine has a power of 100W, a speed of 3000 revolutions per minute, and requires a torque of 0.8N · m during operation. If a reduction ratio of 10:1 is chosen, with a safety factor of 2.0, and the transmission efficiency of the reducer is calculated at 96%, then the required rated torque of the reducer is at least 6.875N · m.

After selecting a helical planetary gearbox with a rated torque of 10N · m, the precision of the surface mounting machine has been improved from ± 0.15mm to ± 0.05mm, and there will be no more misaligned parts attached.

Formula 2: Calculate inertia to make the equipment run more stably

The formula is simple: load inertia ÷ motor rotor inertia ≤ 10 (servo motor) or ≤ 5 (stepper motor).

For example, in the joints of collaborative robots, the previously used gearbox achieved an inertia ratio of 15:1, causing the robot to shake like motion sickness.

By replacing it with a hollow shaft planetary gearbox, the inertia has been reduced by 30%, the inertia ratio has decreased to 8:1, the vibration frequency has been reduced from 120Hz to 200Hz, the movement is smoother, and the work efficiency is also higher.

Formula 3: Calculate speed ratio, balance speed and force

The formula is: reduction ratio=rated motor speed x transmission efficiency ÷ required load speed, or reduction ratio=load torque ÷ (rated motor torque x transmission efficiency).

On the lithium battery equipment coating machine, the stepper motor speed is 1500 revolutions per minute, and I want to reduce it to 75 revolutions per minute with a load torque of 5N · m.

By calculation, the reduction ratio is 20:1. After choosing a reducer with overload protection, the efficiency has increased from 75% to 95% compared to the original worm gear reducer. It can save 3000 kWh of electricity per year and also solve the problem of uneven coating thickness.