Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-15
2001-05-29
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S236000
Reexamination Certificate
active
06239531
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electric motors and, more particularly, to an apparatus and method for mechanically commutating electric motors.
BACKGROUND OF THE INVENTION
Electric motors are nearly ubiquitous today and range from very small in size, such as those found in compact disk players, to very large such as those found in industrial applications. The type of motor, its size, power and control requirements all depend on the particular implementation.
In general, electric motors include a shaft, a rotor and a stator. Driving a workpiece may be as simple as connecting the shaft to a platen for spinning an object such as a compact disk in a compact disk player. Alternatively, the shaft may drive the workpiece through one or more gears or transmissions for imparting rotational force under desired torque conditions or for imparting translational force.
There are several different types of DC electric motors, including brush and brushless motors. In brush motors, the rotor includes coils called the armature which must be connected to a power source to create torque on the rotor. The connection of the rotor coils to the power source is made through brushes, typically carbon, which slide over a metal cylindrical surface that is part of the rotor. The stator includes either a fixed permanent magnet or fixed coils which exert torque on the rotor via the armature.
There are several problems associated with brush motors, most of which relate to application of power to the rotor through the brush itself. These problems include wear of the brush and rotor contact during use, arcing, resistance and heating at the brush-contact interface, and burning of the brush during temperature extremes.
In brushless motors, permanent magnets are implemented in the rotor instead of coils. The stator includes fixed coils that may be selectively energized to create torque on the rotor. Because the permanent magnets do not require connection to a power source, no brush is required. Thus, the problems associated with the brush-rotor contact interface are avoided. Brushless motors tend to be more reliable over time than brush motors and are ideal for aerospace applications.
All brushless electric motors must be commutated in order to create torque and rotation on the shaft. During commutation, one or more coils of the stator are momentarily energized in a rotating fashion around the axis of rotation of the rotor. Each energized coil creates a magnetic field which imparts electromotive force (“EMF”) between the energized coil and a magnetic pole of the rotor. It is the selective energizing of the coils which imparts torque on the motor shaft.
Traditionally, commutation has been done electronically using electronic components. Electronic commutation is accomplished by using position sensors on the motor which determine the position of the rotor relative to the stator and a series of switches which energize the stator coils based on the rotor position. Electronic commutation is reliable but expensive and is difficult to implement when stator coil currents are high.
There is a need for a new commutation technique for brushless electric motors which does not require expensive electronics and which can handle high coil excitation currents. The technique needs to be inexpensive and reliable and should avoid problems associated with a brush-rotor contact interface.
SUMMARY OF THE INVENTION
According to the present invention, problems associated with sliding brush contacts, expensive electronics and current limited switches for exciting stator coils are avoided by mechanically commutating a brushless motor.
To accomplish mechanical commutation of the motor, one end of the stator coils is connected to a series of distinct contact elements arranged to have an inner cylindrical surface which makes electrical contact to achieve commutation. The electrical contact is made with a flexible cylindrical ring. Its outer diameter is slightly smaller than the diameter of the inner cylindrical surface of the stator contact elements. The electrical contact is made at two discreet points (180 degrees apart) by deforming the ring outward so that it contacts the stator elements. This is shown and described with reference to
FIGS. 3A & 3B
. Connected to the motor shaft is an arm with rollers at each end which deforms the flexible ring outward. The arm with the rollers is aligned with the permanent magnetic polls of the rotor.
The flexible ring is restrained by, for example, keys on the stator. These keys and the two rollers are to be electrically insulated to completely isolate the flexible ring. Because the flexible ring does not rotate, it can be connected to the external power source. Consequently, the stator coils are sequentially activated at the desired time to achieve commutation. Commutation is thus accomplished without electronically controlled switches and without reliability problems associated with a sliding electrical interface like a brush-contact interface.
In one embodiment, a commutation assembly for mechanically commutating a brushless electric motor includes a plurality of distinct electrical contacts forming a circular surface around a motor shaft. At least some of the electrical contacts are electrically coupled to distinct coils within the motor. The assembly further includes a conductive flexible ring and an arm. The conductive flexible ring has a circumference that is less than the circumference of the circular surface. The arm is for rigid attachment to the motor shaft and has a roller disposed at a distal end for forcing an electrical connection between the flexible ring and some of the electrical contacts during rotation of the arm. The electrical connection causes at least one of the distinct coils to be selectively energized.
The roller may make substantially non-sliding contact with the flexible ring. In some embodiments it may be a bearing assembly while in others it may be a pin and wheel assembly such as a bushing. The conductive flexible ring may be made of beryllium copper and may be coupled to a source of electrical power.
A method of commutating a brushless electric motor according to one embodiment of the invention includes the steps of providing, coupling and attaching. In a providing step, a plurality of distinct electrical contacts are provided to form a circular surface around a motor shaft. In the coupling step at least some of the electrical contacts are coupled to distinct coils within the motor. In another providing step, a conductive flexible ring is provided having a circumference that is less than the circumference of the circular surface. In the attaching step an arm is attached to the motor shaft. The arm has a roller disposed at a distal end for forcing an electrical connection between the flexible ring and some of the electrical contacts during rotation of the arm. This causes at least one of the distinct coils to be selectively energized during motor operation and therefore commutation of the motor.
REFERENCES:
patent: 5382889 (1995-01-01), Peters et al.
patent: 5534763 (1996-07-01), Williams et al.
patent: 5600218 (1997-02-01), Holling et al.
patent: 5783917 (1998-07-01), Takekawa
patent: 5796248 (1998-08-01), Weber
Lockheed Martin Corporation
Nguyen Tran
Ramirez Nestor
Swidler Berlin Shereff & Friedman, LLP
LandOfFree
Apparatus and method of mechanically commutating a brushless... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method of mechanically commutating a brushless..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method of mechanically commutating a brushless... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2511766