GB2025703A - Vibration motor - Google Patents

Abstract

A vibration motor comprises a concentrator of torsional vibrations 13 whose end face is in close contact with a rotor 1. The concentrator is driven by a piezoelectric cell 14 energised by an oscillator 22. A feedback piezoelectric cell 15 is disposed beneath the cell 14. A magnetic field source (as shown a magnet 6), holds the rotor (1) firmly against the end face of the concentrator 13, and forms a magnetic circuit with a disc 2 on the rotor and a stationary part 10. These have complementary teeth 3, 11, so that on rotation the attractive force varies periodically dependent on rotary speed. This rotary speed pick up modulates the output of the feedback cell 15 with a low frequency signal dependent on speed. The high and low frequency components of this output are separated at 24. The i.f. signal is fed to a unit 25 which provides a d.c. signal indicative of speed, this being used to regulate the output of oscillator 22. Modifications are disclosed whereby the magnet has a different position or is replaced by a coil. <IMAGE>

Description

SPECIFICATION Vibration motor The present invention relates to electric motors and relates more particularly to vibration motors in tended for use in high4idelity sound-recording and reproducing devices.

The invention resides in that in a vibration motor comprising a concentrator of torsional vibrations whose end face is in close contact with a rotor provided with marks equispaced along a circumfer ence and intended for operation in conjunction with a rotor speed pickup connected with a unit of piezoelectric cells adjoining the concentrator of torsional vibrations, via a frequency detector, a d-c power supply source and a high-frequency electric oscillator put in series, according to the invention, the rotor speed pickup is made in the form of a magnetic system comprising a magnetic field source, arranged under the rotor at the side of the concentrator of torsional vibrations and having a power sufficient to hold the rotor firmly against the concentrator end face, and an open magnetic circuit, one part of which is movable, rigidly attached to the rotor and fashioned as a disk with circumferentially spaced slots serving as rotor marks, and the other part separated from the first one by an air gap is stationary, encloses the magnetic field source and is provided with peripheral slots identical to those of the movable disk and arranged opposite to them.

Use can be made of a ring-shaped permanent magnet enclosing the concentrator as a magnetic field source. The magnetic field source can also be represented by an electromagnet whose coil form encircles the concentrator.

In the latter case it is expedient to provide the coil form with two windings and connect one of the windings to an adjustable d-c power supply source and the other winding a frequency detector.

A vibration motor constructed in accordance with the present invention is characterized by a high output power and a high degree of rotor speed stability. Moreover, the construction of the vibration motor is markedly simplified owing to a structural combination of the means of discrimination of the signal proportional to the rotor speed and the means of holding down the rotor against the concentrator end face. The control of the vibration motor rotation al speed is made easier and wider in range both by way of acting on the amplitude of oscillations and by ~controlling the rotor hold-down force through the utilization of a single magnetic system.

Given below is a detailed description of exemplary embodiments of the present invention, in which reference will be made to the accompanying draw ings, wherein according to the invention: Figure 1 shows a vibration motor with a magnetic system based on a permanent magnet, longitudinal elevation; Figure 2 is a fragmental view of a similar vibration motor in which the permanent magnet adjoins the rotor, longitudinal section; Figure 3 shows a vibration motor with a magnetic system based on an electromagnet, longitudinal elevation; Figure 4 shows another embodiment of the vibration motor provided with an additional electromagnet coil, longitudinal elevation.

The vibration motor comprises a rotor 1 (Figure 1) carrying a movable part 2 of the magnetic circuit, which is made in the form of a disk with slots 3 equally spaced along a circumference and serving as marks of the rotor 1. The rotor 1 and the part 2 of the magnetic circuit are secured to the disk 4 of an electric playback device, being fitted on a shaft 5.

Located under the movable part 2 of the magnetic circuit is a magnetic field source - a ring-shaped permanent magnet 6. The upper end face 7 of the magnet 6 is separated from the part 2 of the magnetic circuit by a distance (gap) 8, the lower end face 9 thereof rests on the magnetic circuit stationary part 10, encircling the magnet 6. The power of the magnet 6 is sufficient to hold the rotor 1 firmly against the end face of the concentrator 13. The upper peripheral end face of the magnetic circuit part 10 is provided with equispaced slots 11 identical to the slots 3 of the magnetic circuit part 2 and arranged opposite to the slots 3.

Inserted through the central hole of the ringshaped magnet 6 is the driving stage 12 of the concentrator 13 of torsional vibrations. The concentrator 13 adjoins the piezoelectric cell unit consisting of a working piezoelectric cell 14 and a feed-back piezoelectric cell 15. The piezoelectric cells 14 and 15 are insulated from each other by gaskets 16 and 17 separated by a thin attachment flange 18. The piezoelectric cells 14 and 15, gaskets 16 and 17 and attachmentflange 18 are held tight against the concentrator 13 by a bolt 15 and a washer (cover disk) 20 to provide a reliable acoustic joint.

The end face of the driving stage 12 of the concentrator 13 makes contact with the rotor 1 for instance, through a tapered joint serving both driving and bearing functions, as shown in Figure 1. It is obvious that vibration motors of other designs are possible with the shaft 5 installed on bearings.

The concentrator 13 (through the medium of the attachment flange 18) and the stationary part 10 of the magnetic circuit are rigidly secured within a vibration motor housing 21.

The working piezoelectric cell 14 is connected with the output of an adjustable high-frequency oscillator 22 whose one input is coupled to an adjustable d-c power supply source 23 and the other to a frequency separator 24.

The feed-back piezoelectric cell 15 is connected with the input of the said adjustable d-c power supply source 23 via the frequency separator 24 and frequency detector 25, thereby forming the following closed circuit for stabilization of rotational speed of the rotor 1: 17 < 24 < 25 < 23 < 22 < 14.

It is worth while mentioning that the ring-shaped permanent magnet 6 can be arranged on the movable part 2 of the magnetic circuit, as shown in Figure 2.

There are certain versions of vibration motors in which the force holding down the rotor 1 against the concentrator 13 must be controlled.

To provide the possibility of an electric control of the hold-down force, use can be made of an electromagnet as a magnetic field source.

The vibration motor shown in Figure 3 features a coil form 26 with a winding 27 arranged inside the movable part 10 of the magnetic circuit and forming in conjunction with the movable part 2 thereof an integral plane tachogenerator. To make up a control circuit for speed regulation of the rotor 1 by varying the rotor-to-concentrator hold-down force, the winding 27 is connected with the output of the adjustable d-c power supply source 23. In all other respects the rotor speed stabilization circuit is similar to that shown in Figure 1.

Figure 4 shows another vibration motor version distinguished from that shown in Figure 3 by an additional winding 28 in the coil form 26 to provide one more independent signal proportional to the rotational speed of the rotor 1.

In this case the feed-back piezoelectric cell 15 is connected directly to the high-frequency electric oscillator 22, while the input of the frequency detector 25 is coupled to the other (signaling) wuinding 28. The first (working) winding 27 is connected with the output of the adjustable d-c power supply source 23 in the manner shown in Figure 3.

The vibration motor operates as follows.

The oscillator 22 produces high-frequency electric oscillations fed to the working piezoelectric cell 14.

The piezoelectric cell 14 converts the electricoscilla- tions into mechanical ones, thereby exciting the concentrator 13 of torsional vibrations. The concentrator 13 changes the longitudinal vibrations of the piezoelectric cell 14to longitudinal-torsional ones which are concentrated in the driving zone of the stage 12 due to proper selection of the shape and size of the concentrator 13 to rotate the rotor 1. The magnetic circuit (parts 2 and 10) and the magnet 6 make up a magnetic system. The force holding down the rotor 1 against the concentrator 13 varies periodically (pulsates) during rotation of the rotor 1 due to the presence of the slots 3 and 11 made respectively in the parts 2 and 10 of the magnetic circuit, which results in a periodic variation of the load on the concentrator representing a high-Q oscillating system.The frequency separator 24 re chives the high-frequency oscillations of the feedback piezoelectric cell 15, which are amplitudemodulated due to the periodic variation of the load by a low-frequency signal whose frequency is proportional to the rotational speed of the rotor 1. The high-frequency oscillations discriminated by the frequency separator 24 are fed to the ocillator 22 to synchornize it and then supplied from the output of the oscillator 22 to the working piezoelectric cell 14.

The piezoelectric cells 14 and 15 and units 24 and 22 make up a feed-back loop whose function is to maintain the natural frequency of oscillations of the concentrator 13.

The low-frequency oscillations are fed to the frequency detector 25 which converts any frequency change into a voltage change. The voltage change is applied to the regulating element of the due power supply source to produce an output voltage in accordance with the deviation of the rotational speed of the rotor 1.

The vibration motor presented in Figure 2 operates in a similar way. The only difference consists in the fact that a smaller electromagnetic force is needed to hold down the rotor 1 against the concentrator 13 of this vibration motor.

The vibration motor version shown in Figure 3 offers a possibility of electrically controlling the force holding down the rotor 1 against the concentrator 13 by means of the winding 27. This aim is achieved by making the following additional feed-back loop to control the rotor speed: 15 < 24 < 25 < 23 < 27. In the case under consideration any change in the rotational speed of the rotor 1 is counteracted (with a resultant compensation for the speed change) by an increase or decrease of the amplitude of electric oscillations at the output of the oscillator 22 and by a change of current flow through the winding 27.

The vibration motor shown in Figure 4 also comprises a feed-back loop to maintain the natural frequency of oscillations of the oscillator 13: 1 #22#1 4. As the rotor 1 revolves, the magnetic flux of the winding 27 changes; the periodic variation of the magnetic flux is sensed by the additional winding 28 (the magnetic flux variation frequency is proportional to the rotor rotational speed). The signals proportional to the rotor speed are fed to the frequency detector 25. In all other respects this version ofthevibration motorfunctions identically with the operation of the vibration motor presented in Figure 3.

Claims (5)

CLAIMS:

1. A vibrator motor including a concentrator of torsional vibrations, a rotor held firmly against the end face of the concentrator, a magnetic field source located under the rotor at the side of the concentrator and having a power sufficient to hold the rotor tight against the concentrator end face, a magnetic circuit whose one part is movable, rigidly attached to the rotor and fashioned as a disk with slots equispaced along a circumference, and whose other part separated from the first one by an air gap is stationary, encircles the magnetic field source and is provided with peripheral slots identical to whose of the movable disk and arranged opposite to them; said magnetic field source and magnetic circuit forming a rotor speed pickup connected with the piezoelectric cell unit, adjoining the concentrator of torsional vibrations, through a frequency detector, an adjustable d-c power supply source and a high frequency electric oscillator put up in series.

2. A vibration motor according to claims 1, including a ringshaped permanent magnet encircling the concentrator and serving as a magnetic field source.

3. A vibration motor according to claim 1, including an electromagnet with its coil form surrounding the concentrator and utilized as a magnetic field source.

4. A vibration motor according to claim 3, wherein the electromagnet coil form comprises two windings, the first one being connected with the adjustable d-c power supply source and the other with the frequency detector.

5. A vibration motor substantially as described hereinbefore with reference to the accompanying drawings.