What Is a Motor Shaft?
A motor shaft is a linear servo motor that moves in a linear motion by means of electricity.
The first means of obtaining linear motion by electricity is a ball screw. Motor shafts have advantages over ball screws, such as high positional accuracy, high speed operation, and high quietness, as well as the ability to control multiple actuators on a single shaft, called multi-drive.
Another major difference between a motor shaft and a flat type linear motor that performs the same linear motion as a shaft motor is the coreless structure. Shaft motors do not suffer from cogging, which is a drawback of linear motors that use an iron core called a core.
Uses of Motor Shafts
Motor shafts are used in mechanisms to control linear motion. Motor shafts can be roughly divided into two categories: processing and manufacturing equipment as well as measuring and inspection equipment.
1. Processing and Manufacturing Equipment
Examples of applications in processing and manufacturing equipment include metal processing equipment, electrical discharge machining tools, laser cutting machines, precision XY stages, steppers, and coater/developers.
2. Measurement and Inspection Equipment
Examples of measuring and inspection equipment include inspection equipment for liquid crystal applications and semiconductor applications, microscopes for living organisms, spectroscopic and optical measuring instruments, as well as inspection equipment for printed circuit boards, surface inspection equipment, three-dimensional measuring equipment, probers, and scanners.
In addition to the above, motor shafts are also used when multiple mover units are required on the same shaft, when two shafts are used to move large, heavy objects, or when high environmental performance is required.
Principle of Motor Shafts
A motor shaft consists of a shaft section and a coil section. The shaft section consists of several cylindrical magnets arranged so that their N and S poles face each other and are housed in a stainless steel cylinder.
The feature of the shaft is that the magnets are arranged so that they are facing each other with the same poles, thus generating a strong magnetic force. The coil part is the component that functions as a mover, and the coil is wound to cover the shaft part. When a magnetic field is generated by passing an electric current through the coil, a thrust force is generated according to Fleming’s left-hand rule. The operating principle of the motor shaft is to control the position and moving speed of the mover by controlling the electric current.
Characteristics of Motor Shafts
Motor shafts have four main features:
1. Simple Structure
The structure of a motor shaft consists only of a shaft and a coil. The shaft part is a permanent magnet and the coil part is a wound coil. Therefore, there are no complicated mechanical parts. Since the parts do not come into contact with each other, there is no friction. Another advantage of motor shafts is that they are easy to maintain and do not generate noise or wear powder.
2. High Positional Accuracy
Ball screws are contact mechanisms, and errors due to gaps between parts, known as backlash, are inevitable. The coreless structure of a motor shaft, however, has the advantage of eliminating cogging, or uneven motion, because the coil and shaft do not have an adsorption force.
3. Compatible With Various Drive Systems
Motor shafts can be used in parallel, tandem, and multi-shaft drive systems in addition to single-shaft drive, which is a linear motion of one shaft. Parallel drive is a method in which two parallel motor shafts are driven simultaneously, and is used to drive large and heavy objects.
Tandem drive is a method in which two motors are driven side by side on the same axis, and a large thrust force can be obtained. Multi-drive is a drive method in which two mover units are driven separately on the same axis.
4. Easy Installation
Motor shafts can be installed by centering them within the clearance between the shaft and mover. Poor centering accuracy for ball screws can greatly affect the life of the equipment. In addition, flat-type linear motors with cores require that the mounting gap between the mover and stator be uniform over the entire length of the motor.