CROSS REFERENCE TO THE RELATED APPLICATIONS

This application is the national phase entry of International Application No. PCT/CN2020/080245, filed on Mar. 19, 2020, which is based upon and claims priority to Chinese Patent Application No. 201911183612.8, filed on Nov. 27, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an outer rotor direct drive motor with a position encoder.

BACKGROUND

It can be commonly seen in our daily life that some motors directly drive pulleys to work without using reducers to connect working machines and the motors. When these motors drive loads, they need to be driven through transmission devices (such as transmission belts, etc.). Then, there is actually a motor that can save the transmission device and directly drive loads. The motor is a direct drive motor that uses “direct drive technology”. As we all know, the transmission mechanism of the conventional motor is that the motor mover is connected to the load through the motor shaft and then through a series of mechanical transmission mechanisms such as couplings, screw rods, timing belts, racks, reducers, etc. In the process, from the mechanical point of view, the possibility of the existence of factors such as clearance, elastic deformation, friction damping, etc. has been increased, resulting in the reduction and loss of equipment rigidity and response characteristics.

Unlike the conventional motor, the direct drive motor directly couples the moving load and the motor mover together, thereby saving the connection mechanisms such as reducers, gear boxes, pulleys, etc., so that the entire system has the advantages of high efficiency, low consumption, high speed, high reliability, maintenance-free, high rigidity, fast response, no need for lubrication, quiet operation, etc.

At the same time, because the direct drive motor has a large output torque, it is also called a torque motor. In order to maximize the output torque, however, a design method of an outer rotor direct drive motor is generally adopted. The outer rotor motor means that the rotor is an outer permanent magnet pole and an inner coil part is fixed; and an inner rotor motor means that the rotor is an inner coil part and an outer permanent magnet pole is fixed. Under the same motor size, the output torque of the outer rotor motor is much larger than that of the inner rotor motor. Therefore, in order to maximize the output torque, many designers generally adopt the design method of the outer rotor direct drive motor.

However, in terms of position encoder selection as the most important part of the motor control system, there are many technical barriers to the outer rotor direct drive motor.

1) At present, many servo motor encoders use magnetic effect encoders or photoelectric encoders, wherein the magnetic effect encoder needs to be installed on a motor shaft end, a motor shaft of the outer rotor direct drive motor is connected to a motor housing at one end and directly connected to a moving load at the other end, and there is no space left for the installation of the magnetic effect encoder. Due to the harsh working environment, such as vibration, oil pollution, etc., the photoelectric encoder will be damaged. Also, the price is expensive. Therefore, the photoelectric encoder is also not the first choice for designers of the outer rotor direct drive motors.

2) The position encoders used in many outer rotor direct drive motors on the current market are simple three Hall switches, the most basic function of which is to collect position signals for three-phase current switching of the motor. However, the resolution of the position encoder is limited to the number of motor pole pairs. For example, the number of motor pole pairs is 1, and then the motor can only obtain 6 position signals for one revolution. The resolution is much lower than an ordinary servo motor. Thus, it can not accurately reflect the position information of the motor rotation so that the control system cannot effectively control the parameters such as motor efficiency, speed, output torque, etc., which causes energy waste.

SUMMARY

In view of the defects in the prior art, an objective of the present invention is to provide an outer rotor direct drive motor with a position encoder that solves the above technical problems.

To solve the above technical problems, the present invention provides an outer rotor direct drive motor with a position encoder, comprising an outer rotor and a stator disposed in the outer rotor, wherein the stator includes: a stator chassis; a stator printed circuit board disposed on a side of the stator chassis, at least an excitation coil and a receiving coil being printed at the stator printed circuit board; and a stator winding disposed on the stator printed circuit board; wherein the outer rotor changes a coupling strength between the excitation coil and the receiving coil.

Preferably, the outer rotor includes: a motor housing; a motor shaft, an end of the motor shaft extending into the motor housing and being connected to a bottom of the motor housing; permanent magnet steels disposed on an inner side wall of the motor housing; and an induction mechanism disposed on the motor housing, the induction mechanism corresponding to the excitation coil and the receiving coil; wherein the induction mechanism changes the coupling strength between the excitation coil and the receiving coil.

Preferably, the induction mechanism includes a rotor printed circuit board disposed on the motor housing, and a plurality of conductive material scale areas periodically repeated in a circumferential direction are printed on the rotor printed circuit board.

Preferably, the conductive material scale areas printed on the rotor printed circuit board are overlapped with the excitation coil and the receiving coil printed on the stator printed circuit board in a vertical direction.

Preferably, the induction mechanism includes sawtooth structures periodically repeated and disposed at a bottom of a side wall of the motor housing.

Preferably, the sawtooth structures at the bottom of the side wall of the motor housing are overlapped with the excitation coil and the receiving coil printed on the stator printed circuit board in a vertical direction.

Preferably, the permanent magnet steels are polarities alternately and evenly distributed along an inner wall of the motor housing.

Preferably, the number of pole pairs of the permanent magnetic steels is a positive integer greater than or equal to 1.

Preferably, a rotor bearing is provided on the motor shaft, and a stator bearing is provided on the stator chassis.

Preferably, a spring is provided between the outer rotor and the stator.

Compared with the prior art, the present invention differs from the conventional outer rotor direct drive motor in that it uses an electromagnetic induction position encoder. Compared with the Hall switch, the magnetic effect encoder and the photoelectric encoder, the electromagnetic induction position encoder has the following advantages.

a) The installation method is flexible, and it supports through-shaft installation without occupying too much space of the motor body.

b) The sensor structure is stable. The rotor scale area and the induction coil are all printed on the printed circuit board. Even in the case where the rotational speed is too fast, deformation or cracking will not be occurred. At the same time, its non-contact induction method is not affected by external environments such as oil pollution and electromagnetic interference.

c) The accuracy is high and the resolution is high. The receiving coil has one or more periodically repeated specific geometric figure structure characteristics. The more the number of repetition cycles, the more the number of signals obtained, and the higher the resolution of the output signal. It can not only speed up the circuit processing speed, but also improve the accuracy of the encoded signal. Unlike the conventional motors that increase the number of motor pole pairs to improve the resolution, in the embodiment, increasing the number of cycles of the receiving coil only requires drawing more receiving coils on the stator printed circuit board without adding additional cost.

d) The resolution of signal of the motor encoder is increased without adding additional cost or changing the motor structure.

