JPH0757112B2 - Speed control motor drive - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a speed control motor drive as set forth in claim (1). Such a speed control motor drive is used, for example, in a magnetic tape recorder or the like in which a magnetic tape has to pass through a magnetic head at a predetermined speed. High precision speed control motor drives or turntable drives, especially needed to ensure high quality performance of electronic entertainment devices.

2. Description of the Related Art A video recorder equipped with a head drum motor and a capstan motor, both of which are adjusted by an adjusting circuit, is known from the periodical publication "Funkshiau", No. 13, pages 48 to 50, 1984. Each of the two motors is associated with a shaft angle encoder for indicating the motor position and a tachometer generator for indicating the motor speed, the output of each of these two devices being fed to the actual value input of the associated comparator. When the actual value deviates from the nominal value, the comparator produces a signal which maintains the speed and phase of the motor at predetermined values. The load moment applied to the motor by the tape drive reduces the motor speed. A regulation circuit modifies this speed reduction to maintain a constant speed.

Not all modes of operation of devices with such speed controlled motor drives require a given motor speed. For example, during winding, rewinding, and high-speed rotation of the tape, the magnetic tape is subjected to much higher distortion than in the normal recording and reproducing modes. Therefore, in these cases, the motor drive must not apply a tensile stress or a sudden high tensile force to the magnetic tape that exceeds a predetermined limit.

OBJECT AND SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to improve a motor drive as claimed in claim (1) so that it does not exceed a predetermined drive torque. According to the invention, this object is advantageously achieved by the method described in the characterizing part of claim (1).

The present invention takes advantage of the fact that the drive torque of a DC motor is a nearly linear function of the DC flowing through it. Further, the present invention uses the fact that the phase comparator used to control the speed of the DC motor produces an output signal that depends on the phase shift of the applied signals being compared. In this way, most of the speed control circuit can also be used for torque control of the DC motor. The only additional circuit required for torque control is the phase shifter. If the phase shifter is adjustable, as described in the dependent claims as another aspect of the invention, the drive torque of the motor drive according to the invention is adjusted in the form of a torque characteristic with a very strict precision. be able to.

〔Example〕

FIG. 1 is a block diagram of a motor drive having a DC motor 1 and a phase comparator 2 of a speed control circuit 3. A shaft angle encoder 4 that indicates the motor position and speed of the DC motor 1 is fixed in phase with respect to the DC motor 1. The output of the sensing head 6 of the shaft angle encoder 4 is connected to the first input 7 of the phase comparator 2. The phase comparator 2 outputs the signal from the shaft angle encoder 4 indicating the speed of the DC motor 1, and the output 9 is a reference signal generator 8 connected to the second input 10 of the phase comparator 2.
A voltage U ₀ is delivered at its output 11 in comparison with a reference signal from the drive, which drives a direct current to give the motor a predetermined speed.
If the frequency or phase of the signal output from the shaft angle encoder 4 deviates from the signal output from the reference signal generator 8, the phase comparator produces a correction pulse at its output 11, which causes the DC motor 1 The motor is set to a predetermined phase position and speed by being integrated by the armature mass of.

In front of the first input 7 of the phase comparator 2 is a switching switch 12, which completes the speed control circuit 3 including the phase comparator 2 at position 13 shown by the dashed line and phase comparator 2 at position 14 shown by the thick line. To complete the torque control circuit. In this control circuit, the first input 7 of the phase comparator 2 is connected to the output 16 of the phase shifter 17, and the input 18 of the phase shifter 17 is connected to the output 9 of the reference signal generator 8. This phase shifter shifts the phase of the signal U ₁ applied to the second input 10 of the phase comparator 2 by Δφ, which is adjusted, for example, by the control signal at the control input of the phase shifter 17.

Next, referring to graphs a to c of FIG. 2, a torque control circuit
The operation of 15 will be described. In the first row of the graph, the signal 20 at the output 9 of the reference signal generator 8 is the second input of the phase comparator 2.
Shown as signal U ₁ applied to 10. Graph a ~
The second row of c shows the signal U ₂ at the first input 7 of the phase comparator 2. This signal U ₂ is obtained by shifting the signal 20 from the reference signal generator 8 by Δφ in the phase shifter 17 and appears as a signal 21 at the output 16 of the phase shifter 17. In the example of graph a), the signal at the first input 7 of the phase comparator 2 is shifted by -Δψ, in the example of graph c) it is shifted by + Δψ. There is no phase shift in the example of graph b). Graph a in Figure 2)
The third row of c) is a schematic diagram of the voltage U ₀ at the output 11 of the phase comparator. In the case where there is no phase shift as in the example of graph b), this voltage is a DC voltage that causes the DC motor 1 to drive a current and produces an average drive torque D _M as shown in the bottom row of the graph. In the case of a negative phase shift as shown in graph a), the phase comparator produces a DC voltage correction pulse at its output 11. The current pulse corresponding to the correction pulse is integrated by the armature mass of the DC motor 1 and increases the drive torque of the DC motor 1 according to the time domain share of the steady state DC. When the phase shifts by + Δψ in the positive direction as shown in the graph c, the DC voltage U ₀ of the output of the phase comparator 2 is interrupted for a time equal to the phase shift amount, the average motor current is reduced, and the drive torque is reduced. Will be reduced.

In the embodiment described above, the control signal for adjusting the phase shift Δψ of the phase shifter 17 is generated by the calculation circuit 23, which contains information for controlling the winding and rewinding process of the video tape on the video recorder, for example. 24 supplies. From this information, the calculation circuit 23 derives a control signal curve 25 corresponding to the winding and unwinding process. This curve is applied to the control input 19 of the phase shifter 17. The torque control circuit 15 derives the corresponding control signal of the DC motor 1 from this curve. This signal appears at the output 11 of the phase comparator 2 and controls the torque behavior adapted to the winding or unwinding process. For example, during winding or rewinding, the motor drive containing the DC motor 1 is connected as a reel drive for the magnetic tape to be wound or rewound. The phase shifter 17, the calculation circuit 23 and the control circuit 24 can, for example, be part of a microprocessor clocked by the reference signal generator 8.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a motor drive having a speed control circuit and a torque control circuit, and FIGS. 2a to 2c are graphs for explaining the operation of the torque control circuit of the motor drive of FIG. Is. Explanation of reference symbols 1 …… DC motor 2 …… Phase comparator 3 …… Speed control circuit 4 …… Axis angle encoder 6 …… Sensing head 8 …… Reference signal generator 12 …… Switching switch 15 …… Torque control circuit 17 …… Phaser 23 …… Calculation circuit 24 …… Control circuit

Claims (2)

[Claims] 1. A direct current motor (1); showing the position of said direct current motor (1), said direct current motor (1)
An axis angle encoder (4) coupled to the DC motor (1) in a fixed angular relationship of rotating by xα (x = constant) when rotating by a certain angle α; 8) and; a phase comparator (2), the first input (7) of which is connected to the axial angle encoder (4) and the second input (10) of which is the reference signal generator (8). ) Directly or via a frequency divider, the output (11) of which is connected to the DC motor (1) and drives the DC motor (1) to be compared by the phase comparator (2) 2 Canceling deviations between two quantities; the phase of the signal applied to the second input (10) of the phase comparator (2), which is connected to the output (9) of the reference signal generator (8). A phase shifter (17) for shifting the phase shifter; and the phase comparator (2) and the shaft angle encoder (4). And a phase changer (12) for controlling the constant speed and connecting the phase comparator (2) and the phase shifter (17) for constant torque control. Constant speed control of the DC motor (1) by switching the connection of the first input (7) of (2) from the output of the shaft angle encoder (4) to the output (16) of the phase shifter (17) Can be switched to a constant torque control, whereby a current flowing through the DC motor (1) is changed by the output (11) of the phase comparator (2) to control the driving torque thereof. Control motor drive. 2. The motor drive according to claim 1, wherein the phase shift (Δψ) generated from the phase shifter (17) is a control signal (25) at a control input (19) of the phase shifter. ) A speed control motor drive characterized by being adjustable by.