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Posted on Jan 3, 2019
In modern machinery, the direct drive motor can be a rotary or linear motor type, whose load is directly connected to the motor without any other mechanical transmission elements, such as gearboxes, belts, and pulley systems.
In modern machinery, direct drive motors can be rotary or linear format, the load is directly connected to the motor without the need for mechanical transmission elements such as gearboxes, belts, and pulley systems. Here, we will discuss these two main categories of direct drive motor which are rotary motors and linear motors.
The advantage of the rotary direct drive motor is that it can provide high torque at low speed even when it is stalling, so it is also called a torque motor. In terms of its design, torque motors are usually brushless and permanent magnet synchronous motors. They are usually frameless designs, which mean they have no housing, bearings or other feedback devices.
Another type of rotary direct drive motor is the pancake motor. Unlike the torque motor described above, the pancake motor is a brushed DC motor in which the armature winding is printed on a set of insulating and non-magnetic materials.
The armature set is located between two stator groups, which contain permanent magnets arranged alternately in north and south. At the same time, the magnetic flux runs along the length of the motor, and the current runs in the radial direction, causing torque around the motor axis. Pancake motors and torque motors are used in different industrial fields. Although both belong to the category of rotary motors, they are essentially different. Torque motors are widely used in tape recorders, and can work well with wheel winding mechanisms to achieve smooth operation.
The other type is the linear direct drive motor, usually referred to as a linear motor in the field of machine tools. This category includes ironless and iron core types, depending on the structure of the frame assembly related to the winding.
In ironless core linear direct drive motors, there is a primary tendency that is made of windings embedded in an epoxy resin. In the iron core type, the winding is installed on an iron-laminated stack.
Read More: What is a Linear Motor?
Linear motors also have another distinguishing feature: flat or tubular structures. In the ironless flat linear motor, there is a flat magnet with a primary forcer, which consists of a coil mounted on an aluminum plate. These motors have excellent speed control, but compared to other motors, their force is smaller. Another configuration of the ironless motor is to use two magnetic tracks facing each other to achieve a better magnetic effect, thereby achieving the disc effect. The second primary component (the forcer) runs between the tracks. Therefore, these motors have no cogging and can achieve very agile acceleration and deceleration ratios.
For flat iron core linear motors, there are two types of slotted or slot-less designs. Slotted iron core type is more common in the market because of its practicality and reasonable cost. The second part of the slotted iron core linear motor is composed of a back iron plate and an iron teeth set, and the coil is tightly wound on the iron teeth set to prevent the magnetic reverse effect. They have the greatest force competence, but may have a huge cogging effect.
On the other hand, the slot-less design of the linear DD motors is considered to be a structure that integrates the ironless and the traditional slotted iron core structure. They have coils wound with no iron lamination, but are installed on the back iron plate. The second part is usually contained in aluminum housing. Compared to slotted iron core types, these motors have lower cogging and lower inertia.
There is another variant of the structure, which contains the magnet in a cylindrical tube that contains the winding in the thrust block surrounding the tube. Similar to the linear flat motor, the second part of the tubular linear motor can be made with or without iron core. The main advantage of the tubular linear motor is that its precise symmetrical design allows all magnetic flux to be used to generate thrust. This feature makes this DD motor very suitable for servo robotic arms in the assembly line, thus showing the best assembly and disassembly capabilities.
The design advantage of the DD motors is that it eliminates mechanical components that can cause backlash issues and reduce positioning accuracy, and has high repeatability. Whether in linear or rotary format, DD motors are widely used in industrial fields, but not in the manufacture of household goods, such as robot components, machine tools, defense products, etc.
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