I. Miniature Stepper Motor and its Structure
Miniature stepper motors are key actuators in microelectromechanical systems (MEMS). With the deepening research in electronic technology and precision machining technology, micromotors are developing towards miniaturization, diversification, and modularization. Meanwhile, the materials used in micromotors are no longer limited to silicon, commonly used in microelectronics, but also include ceramics, metals, and composite materials. How to reliably assemble these tiny parts with varying materials and properties into complete micromotor products is a crucial process in micromotor manufacturing. Besides the necessary assembly robots and operators, connection technology is the core of the entire assembly process.
Micro stepper motor bonding is a process that uses adhesives to connect parts without melting the surface of the parts. Compared to micro-welding, solid-state bonding, and other micro-connection methods, micro-bonding has the following advantages: ① Wide range of applications, capable of bonding parts made of the same or different materials; ② Low curing temperature, avoiding the effects of high-temperature environments on the dimensional changes, uneven stress, and even performance degradation of micro-parts; ③ High curing strength and uniform stress distribution; ④ Easy to implement additional gear reducers for sealing, conduction, or insulation.
A miniature stepper motor mainly consists of a base, a mover, and a linear guide. The base also functions as the stator, with magnetic poles, stator teeth, coils, and control circuitry on its surface. The mover is located above the stator, with mover teeth on its lower surface. The guide acts like a linear bearing (12GA), holding the mover in the correct position. A sealing housing is located above the guide and mover, and the mover is separated from surrounding components by an air gap. The base dimensions are 10mm x 4mm x 1mm, and the guide dimensions are 8mm x 1mm x 1mm. The base and guide are made of monocrystalline silicon and are assembled together using adhesive bonding.
The requirements for the quality of the adhesive bonding assembly are as follows: ① The two guide rails must remain parallel in the direction of movement of the mover; ② Due to the presence of adhesive, the increase in guide rail height should not exceed 10 mm; ③ The guide rails must remain parallel to the substrate surface; ④ The surface of the long-life reducer area must not be contaminated by adhesive. Therefore, an adhesive bonding area is defined on the substrate surface for dispensing adhesive, with a dimension of 900 mm × 900 mm.
II. Working Principle of Miniature Stepper Motor
When an electromagnetic coil in the stator is energized, it generates a magnetic field. The magnetic poles on the rotor are attracted to this magnetic field, causing the rotor to rotate by a fixed angle. When the current in the electromagnetic coil in the stator changes direction, the rotor also changes direction. By gradually changing the direction and magnitude of the electromagnetic field, precise rotation control can be achieved.
The step angle of a miniature stepper motor is related to the number of electromagnetic coils and the number of magnetic poles. Typically, the step angle is 1.8 degrees or 0.9 degrees, but other step angles are also available. The speed of a stepper motor is related to the voltage and current; the speed is usually low, making it suitable for applications requiring precise control of angle and speed, such as digital printers, CNC machine tools, and medical equipment.
The advantages of micro-stepping motors are twofold: firstly, they allow for precise control of minute angular positions; secondly, they reduce vibration and noise in the low-speed range. Each step of a stepper motor is accompanied by damped vibration, eventually stopping at the predetermined position. In other words, it moves forward and backward several times relative to the stopping position before finally coming to a complete stop. If the stepper motor rotates at low speeds, this damped vibration can cause vibration and noise. Reducing the step angle can decrease damped vibration, and micro-stepping can further reduce vibration and noise in the low-speed range.
Driven by the above working principle, the operation of a miniature stepper motor can be divided into the following steps:
The circuit inputs pulse signals. The controller or driver sends pulse signals to the stepper motor, and each pulse signal corresponds to the stepper motor rotating by a fixed angle.
The motor rotates. When a pulse signal is input to the circuit, the stepper motor will rotate a fixed angle, typically 1.8 degrees or 0.9 degrees. The direction of rotation depends on whether the pulse signal input to the circuit is a positive or negative pulse.
Stepper motor control. The stepper motor control system adjusts the frequency and direction of the pulse signal as needed to precisely control the angle and speed of the motor's rotation.
Stop. The stepper motor stops rotating when no more pulse signals are input.
In general, stepper motors work by continuously inputting electrical pulse signals to control the angle and speed of the motor's rotation, thereby achieving precise position and motion control.
