FIELD OF THE INVENTION
The present invention is directed to a permanent magnet direct current (d.c.) motor apparatus. Direct current motors as such are characterized by their simplicity of design and ability to convert electrical energy into mechanical rotary motion. They are normally used in engineering applications where continuous angular output shaft rotary motion is necessary. The output shaft rotates or moves through a specific angle as a result of an incoming electric pulse or exitation. The principle features of a conventional d.c. motor are a field winding, an armature winding and a commutator. The theory and operation of such motors is well known in the art of electromechanical energy conversion and need not be further explained here. The stators upon which the field windings are located generally consist of unlaminated ferromagnetic material. The flow of d.c. through the field windings establishes a magnetic field distribution along the periphery of an air gap maintained between the stators and the armature. The rotor upon which the armature winding is located is generally a laminated core. The rotor also contains the commutator which is basically a mechanical rectifier to serve the function of converting the induced alternating current voltage into a direct current voltage.
Another type of motor related to the present invention is the d.c. stepper motor. Stepper motors are generally used when incremental angular shaft rotary motion rather than continuous angular shaft rotary motion is needed. The principle features of a d.c. stepper motor are a field winding, an armature and a means for supplying an external pulse train to the field winding. The incremental angular shaft rotary motion is characterized by detent positions. Stepping angles may vary from 5 to 90 degrees, and the stepping rates may vary from about 100 steps per second for larger units to 350 steps per second for small motors. Generally, the rotor of a stepper motor has the ability to quickly stop after a given angle is traversed. The commonly available permanent magnet (pm) stepper motor has a wire wound stator with a pm rotor which delivers low torque. The direct current stepper motors are generally divided into three types, namely permanent magnet, variable reluctance, and permanent magnet-hybrid. The variable reluctance stepper motor is typically the most economical multipole soft iron rotor. The variable reluctance stepper is suited for low inertial loads, and small incremental angular movement.
The permanent magnet hybrid stepper motor is formed from a combination of the variable reluctance and permanent magnet stepper motors and is capable of the higher torque capacities at relatively small incremental angles ranging up to 15 degrees. Up to this time, and allowing for relatively high cost, the pm hybrid stepper motor has provided good performance in the appropriate applications.
As mentioned, the present application deals with a permanent magnet d.c. motor apparatus having a high torque capability and the ability to provide incremental angular motion ranging up to as much as 180 degrees, but preferably in the 45 degree to 90 degree range. The present disclosure describes a permanent magnet motor and apparatus which has the ability to provide constant high torque. Because of the inertia provided by the rotor the output shaft mechanically integrates any apparently incremental motion of the rotor and produces an effectual continuous output shaft rotation. The present disclosure describes a permanent magnet motor and apparatus which has the ability to provide constant high torque while employing a wound stator and a permanent magnet type rotor. Unlike the aforementioned pm stepper motors the pm d.c. motor described herein is used in applications where high output shaft power is a primary concern and not the control of discrete movement of the output shaft through a given angle. This is accomplished by the use of a novel arrangement of permanent magnets on the rotor of the d.c. motor which generate localized flux to act in association with solenoid style coils in the stator which are induced with a predetermined sequential flow of current from an electronic control device. The electronic control device provides electric current in response to a substantially high torque demand upon the rotor. In addition, the electronic control device provides a constant torque and speed relationship. Once the rotor is placed in motion its shaft output speed and torque is smooth and continuous and does not resemble the discrete motion that conventional pm stepper motors exhibit.