MXPA98000633A - Rotac detector - Google Patents

Abstract

A rotation detector 10 for a miniature permanent magnet direct current motor 20 comprising an induction coil 11 wound around a flow ring 15 for the motor. The flow ring 15 has a stepped portion 18 which accommodates the windings of the coil 11. The coil 11 produces electrical signals in response to changes in the magnetic field of the stator, caused by the rotation of the rot.

Description

"ROTATION DETECTOR" BACKGROUND OF THE INVENTION This invention relates to a rotation detector for use with an electric motor and in particular, with a rotation detector for a miniaturized permanent magnet direct current motor (PMDC). Many applications of PMDC motors require that the motor speed be monitored or that the number of revolutions made by the motor shaft be counted. This is often achieved by using a Hall sensor and a magnet fitted on the arrow or by using an encoder mounted on the arrow in cooperation with an optical sensor. Both of these methods involve relatively expensive parts, take time to assemble and require the engine to be designed to accommodate these parts since they occupy a considerable amount of space either inside the engine, increasing the size of the engine or outside of the engine, where they are vulnerable to harm. Recently, rotation detectors have been developed which use an induction coil to monitor changes in the magnetic flux of the motor, see, for example, Patent Number EP-A-0626748, wherein an inductor / capacitor circuit is adjusted within a separate box that is placed on the non-impeller end of the motor, snapped into the bearing flange. In this arrangement, the coil is detecting the exhaust flow and for efficient motors, the flow escape is expected to be reduced to a minimum to increase efficiency, reducing the reliability / sensitivity of this type of detector. See also Patent Number EP-A-0529131 using a coil mounted inside the motor.

COMPENDIUM OF THE INVENTION To provide a sensitive detector, the rotation detector according to the present invention uses an induction coil wound around a magnetic flux conducting means adapted to provide a return flow path for the motor stator. Ideally, this magnetic flux conducting means is a flow-adjusted ring in the motor housing or alternatively, it can be part of the motor housing. Flow rings are commonly used to provide a return path of low resistance magnetic flux between the magnetic poles of the stator. The use of a flow ring helps to concentrate the magnetic flux and reduce the flow escape, while allowing the motor housing to be made of a thinner material, without risks of saturation of the magnetic path. By winding the inductor coil around the flux ring, the flux ring acts as a core for the coil, simplifying the formation of the coil while ensuring that the magnetic flux passes through the coil, providing an intense signal to the coil circuit. rotation detection. At the same time, the flow ring mode allows the motor to be changed without affecting the detection circuit. Of course, the rotation detector can be adjusted in any motor, by appropriate adaptation of the flow ring and does not require that any specific characteristics be built into the motor. The scope of the invention is to provide a novel rotation detector for a permanent magnet direct current motor, using an induction coil. Since the rotation detection circuits are well known and do not form part of this invention, they will not be described yet when it should be remembered that the detector signal is fed to the detection circuit which will use this signal to achieve its designated function, which may include speed control, position control, overload detection and defective conditions such as a clogged operation.

Accordingly, the present invention provides the rotation detector for use with a direct current motor having a housing that houses a permanent magnet stator, the detector comprising: a magnetic flux conducting means adapted to provide a flow return path for the stator, and a detector means including a coil wound around the magnetic flux conducting medium whereby changes in the magnetic flux of the motor generate an electrical signal in the coil. Preferably, the magnetic flux conducting means is adapted to couple the motor housing. Alternatively, the magnetic flux conducting means may be at least a part of the motor case. Preferably, the magnetic flux conducting means is set on a printed circuit board and the coil is terminated at the terminals of the printed circuit board, and the printed circuit board has male terminals placed to match the female terminals of the motor. Preferably the printed circuit board has a circuit for interpreting the signals from the coil and for controlling the motor in response to those signals.

BRIEF DESCRIPTION OF THE DRAWINGS The preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a rotation detector according to a first embodiment; Figure 2 illustrates the rotation detector of Figure 1, fitted on a flat side motor; Figure 3 is the view similar to Figure 2 of a rotation detector mounted on a round motor; Figure 4 illustrates a rotation detector in accordance with another mode mounted on a motor; Figure 5 illustrates a rotation detector according to an alternative embodiment, mounted on a motor; Figure 6 illustrates the rotation detector of Figure 5, mounted on a printed circuit board; and Figure 7 illustrates a rotation detector according to yet another embodiment.

DESCRIPTION OF THE PREFERRED MODALITIES In the rotation detector 10 of the first embodiment shown in Figures 1 and 2, the magnetic flux conducting means is a flow ring 15 and the coil 11 is wound around the flow ring. The flow ring 15 is of the full shell type, implying that the ring essentially surrounds the box 22 of the motor in use. In practice, the inner diameter of the flow ring in its relaxed state is smaller than the diameter of the motor housing so that the flow ring 15 is lengthened to fit in the motor housing 22, with the resilience of the ring used to secure the ring in the motor. Additional seals can be provided. The shape of the ring essentially matches the shape of the motor housing to provide good contact between the housing and the ring, in order to minimize the resistance of the magnetic flux path. The motor 20 shown in a flat-sided motor means that the box has two arcuate portions 41 or in circular portions, connected by two straight portions 42, the straight portions being parallel to each other. The stator has two arched permanent magnets 23 mounted on the circular portions 41 of the box 22. The flow ring 15 is similarly formed with a slit 19 in a position corresponding to a plane passing through the poles of the magnets of the stator. The coil 11 is wound around one of the straight portions 42. This is where the concentration of the magnetic flux during the use is greater. The flow ring 15 is deformed to provide a stepped portion 18 in the position where the coil 11 is wound to produce a gap or clearance between the flow ring 15 and the motor housing 22 for the coil, since the ring 11 flow is otherwise contiguous to the motor housing. The coil 11 can be terminated at the terminals 12 mounted on the flow ring 15 as shown in Figure 1, or it can have flying conductors 13 as shown in Figure 2, to connect directly with the detection circuit. Figure 3 illustrates a similar rotary sensor 10 mounted on a round motor 20 (a motor with a box having a circular cross section). The detents (not shown) ensure that the flow ring 15 (likewise with an essentially circular cross-section) is mounted in the motor housing 22, with the slot 19 aligned with a plane passing through the magnetic poles of the stator and the coil 11 is placed in a stepped portion 18, between two adjacent poles of the stator. These motors usually have two permanent arched individual magnets or a rubber ring magnet formed with two or more poles. Figure 4 shows a detector 10 of rotation similar in construction to the rotation detector of Figures 1 and 2, mounted on a motor 20 of flat sides with the variation that the magnetic flux conducting means is an average flow ring 16 shell, implying that the flow ring 16 extends circumferentially around the engine case 22 only about half. In practice, the flow ring 16 extends slightly more than half in order to provide a self-supporting tie in the box. In all other respects, the detector is the same as in the embodiment of Figure 1. Figure 5 is a view similar to Figures 2 and 4 of a rotation detector 10, incorporating the magnetic flux conducting means in the form of a flow ring 16 of the quarter shell type. The fourth part conha flow ring 17 extends between the magnets along the flat side of the motor housing and extends the flow path provided by the housing 22. Again, the flow ring 17 has a portion 18 stepped in a position between the poles or the magnets to accommodate the winding of the coil. The quarter-shell flow ring 17 allows for interesting mounting arrangements, such as the arrangement shown in Figure 6, where the flow ring 17 is mounted on a printed circuit board (PCB) 30. The PCB 30 has a connector 33 for connecting the board 30 with a power supply for the motor, and for control signals for the operation of the motor.

The PCB 30 also has an electronic circuit 32 for interpreting the signals from the rotation detector 10, and for controlling the motor 20 in response to the signals of the rotation detector and the input control signals. The control signals may be simple on / off signals or may be more complicated, including specifying the condition to be maintained, e.g., the speed or position. In the embodiment shown, the motor has female terminals (not visible) and the PCB 30 has male 31 terminals to match the female terminals of the motor. The male terminals 31 also provide positioning assistance and support assistance even when in most applications, the additional support for retaining the motor 20 in the flow ring 17 and / or the PCB 30 would require preventing accidental displacement of the motor with with respect to the PCB due to vibration, shaking, etc. Even though a flat-sided motor has been shown, the quarter-part shell flow ring can be used with a round motor, taking care to ensure correct alignment of the flow ring with the stator poles. The embodiment of Figure 7 dispenses with the separate flow ring and uses the motor case 22 as the magnetic flux conducting medium. The box 22 which is of flat-side type is manufactured in two halves 25, 26 and is colloquially known as a clam shell box. The two halves 25, 26 are joined together by dovetail connections 27. The connections 27 are formed along the straight sides of the box and are placed between the pair of magnets 23 forming the stator. Each half accommodates a single arched magnet. One of the connections has a straight finger 28 in the first half 25, and is received in a recess 29 in the other half 26. Around this finger 28, the induction coil 11 is wound or placed to monitor changes in the magnetic field as the rotor rotates. While the coil 11 may be a coil wound to help hold the coil terminals 12, it is preferably encapsulated in epoxy or a resin that provides a sturdy, stable and insulated coil of minimum dimensions. As an alternative, the motor housing could be a can deep drawn with the finger being a cut and raised portion that is placed in the coil and bent or deforms back towards the recess formed by the finger creation with the distal end of the finger bumping or staying closely adjacent to the edge of the recess from where it is cut to minimize the resistance of the flow path through the finger.

Although several preferred embodiments have been described, it will be appreciated by those skilled in the art that modifications and changes may be made in the described embodiments without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (8)

R E I V I N D I C A C I O N E S:

1. A rotation detector for use with a direct current motor having a housing that houses a permanent magnet stator, the detector comprises: a magnetic flux conducting means adapted to provide a return flow path for the stator; and a detector means including a coil wound around the magnetic flux conducting means whereby changes in the magnetic flux of the motor generate an electrical signal in the coil.

2. A rotation detector according to claim 1, wherein the magnetic flux conducting means is at least part of the motor case.

3. A rotation detector according to claim 1, wherein the magnetic flux conducting means is adapted to couple the motor housing.

A rotation detector according to claim 3, wherein the magnetic flux conducting means is mounted on a printed circuit board and the printed circuit board has male terminals positioned to match the female terminals of the motor.

5. A rotation detector according to claim 4, wherein the printed circuit board has a circuit for interpreting the signals from the coil and for controlling the motor in response to those signals.

6. A rotation detector according to claim 1, wherein the magnetic flux conducting means is a flow ring mounted on the motor housing.

7. A rotation detector according to claim 6, wherein the flow ring has a stepped portion to accommodate the windings of the coil.

8. A permanent magnet direct current motor incorporating a rotation detector, the motor comprises: a permanent magnet stator comprising two permanent arched magnets, a magnetically conductive box that forms a return flow path for the stator that holds the magnets, a rotor mounted on the arrow in confronting relationship with the stator, two end brackets mounted on the respective axial ends of the box and supporting the bearings, on which the arrow hinges, a coil of the rotation detector , wherein the box has a first piece and a second piece joined together by intertwining projections, the first piece has a finger extending through a recess in the second piece and abutting against the second piece, the detector coil rotation is placed within the recess and around the finger, whereby changes in the magnetic flux of the engine caused s by rotating the rotor, they generate an electrical signal in the coil.