GB2049300A

GB2049300A - Linear motor drive system for driving linear tracking system

Info

Publication number: GB2049300A
Application number: GB7913719A
Authority: GB
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1979-04-19
Filing date: 1979-04-19
Publication date: 1980-12-17
Also published as: DE2916153A1

Abstract

A linear motor system for driving a linear tracking tonearm (4) of a record player comprises a linearly moving element (3), e.g. including a magnet (7), and a stator (8/9) and a circuit (10) which detects the relative positional displacement of the tonearm in opposite directions and generates two outputs. A circuit (14) compares the outputs thus obtained by the circuit (10), and a drive circuit (15) energises the stator winding (9) to drive the moving element (3) in response to the output of the circuit (14). The detection circuit (10) includes two phototransistors (Q1, Q2) which receive light through an aperture (20) in a moving plate (13). In a further arrangement (Figure 4 not shown), two stators with corresponding windings (9a, 9b) receive drive signals from two transistors (Q3, Q4) for driving a tonearm in opposite directions, i.e. in accordance with the outputs of two detectors (Q1, Q2). <IMAGE>

Description

SPECIFICATION Linear motor drive system for driving linear tracking tonearm This invention relates to a linear motor drive system for driving a tonearm of a record player.

A linear tracking type tonearm driven by a linear motor comprises a horizontally secured stator around which a coil is wound. A magnet is disposed to confront the stator at spacing therefrom for applying magnetic flux thereto and a movable element comprises a sliding member slidably movable along a shaft in parallel to the stator when the movable element travels along the stator by flowing electric current in the coils of the stator. A linear tracking tonearm is constructed in such a manner that the tonearm is equipped to be horizontaly movable and vertically rotatable with respect to the sliding member of the linear motor. In the linear tracking tonearm, by varying the direction of the electric current flowing in the coil of the stator and the level thereof, the movement direction and the movement velocity of the tracking tonearm are controlled.However, due to the fact that the tracking tonearm at its playing is only driven to one direction, that is, to the central direction of a record disc, a disadvantage occurs since the tonearm does not accurately follow a record disc having an eccentric central aperture and thus a tracking error is produced.

Accordingly, an object of the present invention is to provide a linear motor drive system for driving a tonearm of a record player eliminating the aforementioned disadvantages by driving the tracking tonearm in horizontally opposite two directions during playing of the record disc.

Briefly, and in accordance with one aspect of the present invention, a displacement detection means is provided with which generates two outputs proportional to the relative positional displacement of the tonearm and the moving element in two opposite horizontal directions. The two outputs thus obtained are compared by a comparison circuit and the output of the comparison circuit is applied to a drive circuit which operates to drive the moving element in two opposite horizontal directions.

In accordance with another aspect of the invention there is provided in a linear motor drive system for driving a linear tracking tonearm of a record player including a linearly movable moving element on which the tonearm is supported to be horizontally movable and vertically rotatable and a first and a second statorfor driving said moving element in opposite two directions, the improvement comprising, displacement detection means generating two outputs proportional to the relative position displacement of said tonearm and said moving element in two opposite horizontal directions, and drive means for driving either said first or second stator in response to the outputs of said displacement detection means.

In the accompanying drawings, Figure 1 is a perspective view showing one example of the linear tracking tonearm mechanism, Figure 2 is a circuit diagram showing the first embodiment of the drive system according to the present invention, Figure 3(a) is a front cross-sectional view of the displaceent detection means shown in Figure 2, Figure 3(b) is a side cross-sectional view of the displacement detection means shown in Figure 2, and Figure 4 is a circuit diagram showing the second embodiment of the drive system according to the present invention.

A first preferred embodiment according to the present invention will now be described with reference to the accompanying drawings.

Figure 1 is a perspective view showing one example of a linear tracking arm mechanism where both ends of a guide member 1 are secured to a supporting stand 2 and a sliding member 3 is slidably disposed on the guide member 1. The sliding member 3 engages the guide member 1 via, for example, a bearing (not shown) so that a tonearm 4 is horizontally movable and vertically rotatable with respect to the guide member 1. In Figure 1, reference numerals 5 and 6 designate a balance weight and a heat shell for a cartridge respectively. A magnet 7 is fixedly mounted on the upper surface of the sliding member 3 wherein the magnet 7 is magnetized such that the upper surface thereof is the north pole and the lower surface thereof is the south pole.An elongated magnetic member 8 is secured to the supporting stand 2 in parallel to the guide member 1, which confronts the upper surface of the magnet 7 at a predetermined distance apart therefrom. A coil 9 is helically wound around the outer periphery of the magnetic member 8 over the entire length thereof. The magnetic member 8 and the coil 9 wound therearound constitute a linear stator while the sliding member 3 and the magnet 7 fixed thereto constitute a movable element.

Figure 2 is a circuit diagram of a drive system according to the first embodiment of the present invention. Reference numeral 10 designates a displacement detection circuit that generates two kinds of outputs proportional to relative positional displacement of the sliding member 3 and the tonearm 4 on a horizontal plane. Specifically, the displacement detection circuit 10 detects the rightward and leftward relative displacement of the sliding member 3 and the tonearm 4.

As shown in Figures 3(a) and 3(b), the displacement detection circuit comprises a pair of light receiving elements 12a and 12b, a light emitting element 11 and a light shielding plate 13 provided with a slit therein. The light receiving elements 12a and 12b are disposed in parallel to the direction of movement of the tonearm 4. The light emitting element 11 is disposed above the intermediate position ofthe light receiving elements 12a and 12b, and is adapted to confront with those light receiving elements. The light shielding plate 13 is disposed between the light emitting element 11 and the light receiving elements 12a and 12b, i.e., above the light receiving elements 12a and 12b but below the light emitting element 11.It is used to determine the amount of light received in the light receiving elements 12a and 12b in accordance with the horizontal movement of the tonearm 4.

For example, photo-transistors Q1 and Q2 are employed as the light receiving elements 12a and 12b, where the collectors of the photo-transistors Qi and Q2 are connected to a power souce #B and the emitters thereof are grounded via resistors R1 and R2 respectively. It is assumed that the moving direction of the tonearm 4 at its playing condition and the lead-in time is positive (leftward in figure) and the moving direction thereof at its returning condition is negative (rightward in figure). Also, it is set so that the photo-transistor Q1 produces an output proportional to the relative positional displacement of the sliding member 3 and the tonearm 4 in the case of the tonearm movement in the positve direction.

When the relative positional displacement is zero, neither of the photo-transistors Q1 nor Q2 produce outputs.

When the tonearm is moved in the positive direction, the photo-transistor Q2 does not produce an output but the photo-transistor Q1 is rendered conductive. The outputs of the photo-transistors Q1 and Q2 are supplied to a comparison circuit 14 which comprises a differential amplifier. The comparison circuit 14 is constructed to produce zero, positive and negative level outputs when the relative positional displacement is zero, positive and negative, respectively. A drive circuit 15 operates to actuate the coil 9 controlling the direction of a current flowing in the coil 9 and the level thereof in accordance with the input level of the drive circuit 15.As a result, the sliding member 3 is driven to move rightward when the output of the comparison circuit 14 is a positive level and to move leftward when the output thereof is a negative level. By changing the width of the slit so formed on the light shielding plate 13, the drive characteristics of the sliding member 3 can be adjusted.

Figure 4 is a circuit diagram showing a second embodiment of the drive system according to the present invention, in which like numerals in Figures 1 to 3 refer to like elements. In this embodiment, the magnet is mounted on the upper surface of the sliding member 3 with the north pole at the side of the sliding member 3 and the south pole at the opposite side thereof. A second stator, around which a coil is wound, is disposed to confront the upper surface of the magnet at a predetermined distance apart therefrom. The linear tracking arm according to this embodiment is constituted so that the movable element is moved in horizontally rightward and leftward directions by the first and the second stators.

The structure and the operation of the displacement detection means 10 are identical with respect to those of the first embodiment. Coils 9a and 9b operate to move the sliding member 3 in the two opposite directions when electric currents are supplied thereto. For example, the coil 9a is employed to move the sliding member 3 in the negative direction.

A drive circuit 16 supplies currents with the coils 9a and 9b in accordance with the two outputs of the displacement detection circuit comprising NPN transistors Q3 and Q4 and resistors R1, R2, R3 and R4. If the tonearm 4 is moved in the positive direction, the photo-transistor Q1 produces an output proportional to the relative position displacement of the sliding member 3 and the tonearm 4 in the positive direction due to the movement of the shielding plate 13 coupled to the tonearm 4. Accordingly, the transistor Q3 supplies the coil 9a with a current corresponding to the output of the transistor Q1, thereby causing the sliding member 3 to move in the positive direction. Likewise, when the tonearm 4 is moved in the negative direction, the transistor Q4 supplies the coil 9b with a current corresponding to the output of the transistor Q2, thereby causing the sliding member 3 to move in the negative direction.

As described, in the drive system according to the present invention, since the tracking arm can be easily driven horizonally two opposite directions during play, the tonearm can be advanced corresponding with a record disc having an eccentric central aperture. Accordingly, a linear tracking arm of high performance can be obtained which has little trackin errors.

It is apparent that other modifications can be made without departing from the essential scope of this invention.

Claims

1. In a linear motor drive system for driving a lineartracking tonearm of a record player including a linearly movable moving element on which the tonearm is supported to be horizontally movable and vertically rotatable and a stator for driving said moving element, the improvement comprising; displacement detection means generating two outputs proportional to the relative positional dispacement of said tonearm and said moving element in two opposite horizontal directions, comparison means for comparing the two outputs obtained by said displacement detection means and drive means for driving said moving element in two opposite horizontal directions in response to the output of said comparison means.

2. In a linear motor drive system for driving a lineartracking tonearm of a record player including a linearly movable moving element on which the tonearm is supported to be horizontally movable and vertically rotatable and a first and second stator for driving said moving element in opposite two directions, the improvement comprising; displacement detection means generating two outputs proportional to the relative position displacement of said tonearm and said moving element in two opposite horizontal directions, and drive means for driving either said first or second stator in response to the outputs of said displacement detection means.

3. The linear motor drive system as claimed in claims 1 or 2, wherein said displacement detection means comprises a pair of light receiving elements disposed parallel to the direction of movement of said tonearm, a light emitting element disposed above the intermediate position of said light receiving elements, said light emitting element being adapted to confront said light receiving elements, a light shielding plate provided with a slit therein and disposed between said light emitting element and said light receiving elements, said light shielding plate being horizontally moved in accordance with the movment of said tonearm, and signal generating means for generating an electrical signal in accordance with the output of said light receiving elements.

4. The linear motor drive system of claim 3, wherein said signal generating means comprises a pair of photo-transistors, each photo-transistor producing an output associated with one direction of travel of said moving element.

5. The linear motor drive system of claim 2, wherein said drive means comprises first and second drive transistors coupled to said detection means and first and second coils coupled respectively to said first and second drive transistors.

6. A linear motor drive system for driving linar tracking tonearm of a record player substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

7. A linear motor drive system for driving linar tracking tonearm of a record player substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.