JPS581803B2 - Servo device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo device using a non-contact position feedback mechanism.

FIG. 1 is a schematic structural explanatory diagram of an example of a conventional servo device.

This device uses a rotor motor MO and a potentiometer Po as a position feedback mechanism, and the motor Mo rotates depending on the deviation between the input Ex and the output Vf of the potentiometer Po.
to move the position of brush B of potentiometer Po.

As described above, servo devices using a position feedback mechanism consisting of a rotor motor Mo and a potentiometer Po have been widely used.

However, the potentiometer Po used as a position feedback mechanism has a contact pressure of the plastic B, and this contact pressure causes a dead zone in the servo system.

The larger the dead zone of the servo system becomes, the less desirable it becomes.

Further, a flexible lead is required to connect the output of the brush B to the circuit, but it also requires sufficient force to bend this flexible lead.

Further, in this conventional servo device, the rotation of the motor Mo is transmitted to a movable part such as a recording pen or a pointer via a thread or the like, but the use of a thread or the like has the disadvantage that the structure becomes complicated.

The present invention has been made in view of these points, and uses a non-contact type linear motor in place of the rotor motor and a position feedback mechanism by using a differential inductor type displacement detector for position detection. Constructed in a non-contact manner,
This makes it possible to reduce the dead zone and realize a servo device with a simple configuration that does not use flexible leads or pull-through lines.

The present invention will be explained below with reference to the drawings.

FIG. 2 is a configuration explanatory diagram showing an embodiment of the device of the present invention.

In Figure 2, Ex is the input voltage, A is the differential amplifier,
Input Ex is applied to one input end of A via a resistor.

PF is composed of a linear motor LM used as a surf motor in a position feedback mechanism, a position detector PD of a differential inductor type, and a synchronous rectifier SR.

In the linear motor LM, reference numerals 11 and 12 denote a pair of rod-shaped cores arranged in parallel with a certain gap between them.A coil 13 is wound around the core 12 at a certain winding interval, and one end of this coil is connected to a differential amplifier. It is connected to the output end of A, and the other end is connected to common.

14 is a high coercive permanent magnet whose magnetic pole face is magnetized to <N, S as shown in the figure, and is held at an intermediate position within the interval between the cores I1 and 12 by, for example, an axle, and is held in the longitudinal direction of the cores 11 and 12. The town is moving to Noh.

Hereinafter, this permanent magnet 14 will be referred to as a movable magnet.

In the position detector PD, reference numeral 21 denotes an elongated core-shaped core disposed opposite to the motor LM, and 22 a short-circuiting ring made of copper.

This shorting ring is loosely fitted to one side 23 of the core 21 and is mechanically coupled to the movable magnet 14, so that it can freely move on the core 23 to the right or left in the figure.

24 is an excitation power source that outputs a constant alternating current voltage (or current) Er; 25 and 26 are coils; both coils are wound around both ends of the core 23;

One end of the coil 25 is connected to the common via the excitation power supply 24, and the other end is connected to the common via the coil 26, and is also connected to the other input terminal of the differential amplifier A via the synchronous rectifier SR. ing.

The operation of the servo device having such a configuration will be explained as follows.

The input voltage Ex is applied to the position feedback mechanism PF in the differential amplifier A.
is compared with the feedback voltage Vf obtained by the differential amplifier A.
outputs a DC voltage according to the deviation, and this voltage is applied to the coil 13 of the linear motor LM, so that a current Im flows through the coil 13.

In this case, if the current Im flows in the illustrated direction, the current Im flows from the front surface of the paper toward the back surface on the upper surface of the coil 13, that is, on the side facing the S pole of the movable magnet 14.

On the other hand, the magnetic flux coming out from the N pole of the movable magnet 14 is the core 11.1.
2 and return to the S pole.

Therefore, as evidenced by Fleming's law,
An electromagnetic force acting rightward in the figure acts on the coil 13 on the surface facing the movable magnet 14.

The coil 13 is fixed to the core 12.

Therefore, as a reaction to the force acting on the coil 13, the movable magnet 1
4 is given a force to the left.

Letting this force be F, F is expressed by the following equation.

However, N... Number of turns of the coil 13 t... Length of the coil 13 Φ - Magnetic flux due to the moving magnet 14 Due to the force F expressed by equation (1), the moving magnet 14 is moved within the gap between the cores 11 and 12. is moved to the left in the figure according to the magnitude of current Im.

When the magnitude of the human power voltage Ex and the feedback voltage Vf are reversed and the direction of the current Im is opposite to the arrow in the figure, the movable magnet 1
4 moves to the right in the figure.

Note that if a coil is also wound around the core 11, a force F will also be applied to the movable magnet 14 by the coil wound around the core 11, and therefore a force of 2F will act on the movable magnet 14.

Such movement of the movable magnet 14 is transmitted to the shorting ring 22 of the position detector PD connected to this magnet, thereby displacing it.

Coils 25 and 26 constituting the position detector are connected in series, and the output Er of the excitation power source 24 is applied to this series circuit.

Therefore, the inductance of the coil 25 is L1, the inductance of the coil 26 is L2, and the coils 25 and 26 are
Letting Ef be the voltage taken out from the connection point k, Ef is expressed as.

In this case, two magnetic paths are formed in the core 21 by the shorting ring 22 as shown by dotted lines, but the magnetic resistance of the core of both magnetic paths is greater than the magnetic resistance of the respective air gaps of both magnetic paths. If it is so small that it can be ignored, then holds true.

However, N1, N2...Number of turns W of coils 25, 26
...Thickness t1, l2 of the core 21 in the direction perpendicular to the plane of the paper in FIG. 3... From the coils 25, 26 to the shorting ring 22
Each distance tg...Air gap length μ0...Vacuum permeability As is clear from equations (3) and (4), the inductances L1 and L2 of the coils 25 and 26 are short-circuited rings. 2
It changes differentially in proportion to the moving distances t1 and t2 of 2.

Therefore, equation (2) is expressed by the following equation. The movement of the shorting ring 22 is controlled by a linear motor LM connected thereto.
This is done by moving the movable magnet 14 that constitutes the.

The amount of movement of the movable magnet 14 depends on the magnitude of the output current Im of the differential amplifier A, as shown in equation (1), where Im is the input voltage E.
It is proportional to the deviation between x and the feedback voltage Vf.

Therefore, if the gain of differential amplifier A is sufficiently large, E
x=Vf, and the system is in equilibrium.

As described above, in the servo device of the present invention, a non-contact type linear motor is used as the servo motor constituting the position feedback mechanism PF, and the linear motor is still connected to the movable magnet 14 of the linear motor LM as the position detector PD for movement. It is constructed using a pair of coils whose inductance changes differentially according to the position of the shorting ring 22. This position feedback mechanism PF is a non-contact type, and as shown in FIG. Compared to conventional devices that use a potentiometer PO as a mechanism, there is no contact pressure caused by the brush B, and there is no need to add a flexible lead wire to the movable body.

Furthermore, since the recording pen or finger index can be directly attached to the movable magnet 14 or the shorting ring 22, there is no need to connect the rotation of the motor Mo to the pen or index using a pulley or the like as in conventional devices. Therefore, according to the present invention, a servo device with a simple configuration can be obtained.

Note that a known circuit as shown in FIG. 3 may be used as the electric circuit of the differential inductor portion constituting the position detector PD.

In FIG. 3, 31 to 34 are diodes, 35 is an operational amplifier having a resistor 36 and a capacitor 37 in its feedback circuit, and 25 and 26 are coils wound around the core 21 shown in FIG. The inductance is Ll,
The inductance of the coil 26 is L2, and the excitation power source 38
Let Ir be the output current of Ir, and let the current flowing through the coil 25 during one cycle of Ir be 11, and the current flowing through the coil 26 be 12, then I1 will be 25→31 and 36→34→25.
2 flows from 26 to 32 to 36 and from 33 to 26.

Therefore, it is expressed as.

The operational amplifier 35 is given 1 and 12 with opposite polarity in the half period when Ir is positive and the half period when Ir is negative, respectively, and the value of half of the difference current multiplied by the resistance value of 36 is given. A voltage Vf is taken out from the output of this operational amplifier.

The voltage Vf is fed back to the differential amplifier A shown in FIG. 2 as a feedback voltage Vf.

(2) The difference current between 1 and 12 is expressed by the following equation. As described above, since L1711 L212, equation (6) becomes as follows.

Since t, +t2 are constant, I1 and 1 shown in equation (7)
The difference current between the two is the inductance L1 of the coils 25 and 26,
This value corresponds to the amount of movement of the shorting ring 22, that is, the output current Im of the differential amplifier A.

Even if such a differential inductor circuit shown in FIG. 3 is used, a servo device having the same effect as that described in connection with the device in FIG. 2 can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an example of a conventional servo device, FIG. 2 is a configuration explanatory diagram of an embodiment of the servo device of the present invention, and FIG. 3 is a differential inductor portion used in the device of FIG. 2. FIG. 3 is a circuit diagram of another example. PF...Position feedback mechanism, PD...Position detector, LM
... Linear meter, 11, 12.21 ... Core, 1
3, 25, 26... Coil, 14... Town motion magnet, 2
2...Short ring.

Claims (1)

[Claims] 1. A position detector that has a pair of coils whose inductance differentially changes according to the displacement of a shorting ring that is loosely fitted to the core, and a pair of cores that have a coil wound around one or both of them. a linear motor having movable magnets arranged opposite to each other with a gap therebetween and provided within the gap so as to be mechanically connected to a shorting ring in the position detector and movable in the length direction of the pair of cores; What is claimed is: 1. A servo device comprising: a position return mechanism; the output of the position return mechanism is compared with an input signal; and a deviation signal thereof is applied to a coil of the linear motor.