JPS6327955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC servo motor device comprising an automatic control system for rotating a first DC motor following a second DC motor.

For example, in an electric sewing machine, a single motor rotates an upper shaft for driving a needle bar and a lower shaft for driving an outer hook. However, especially in large industrial sewing machines that have long arms and long upper and lower shafts, the needle bar and outer hook may not be properly aligned due to distortion caused by twisting of the upper and lower shafts. There is a risk that the upper shaft and
There is a problem in that the lower shaft and the power transmission mechanism therebetween must have an extremely rigid structure. In order to solve this problem, the upper and lower shafts are each rotated by a dedicated motor, and the lower shaft motor is automatically controlled to endlessly rotate in synchronization with the upper shaft motor. The idea is to set up a system. In such an automatic control system, a position detector is required to detect the rotational position of the upper shaft motor. In this case, position detectors include synchronizers such as so-called celsyn, DC synchronizers, and optical synchronizers. An incremental encoder of Eq. However, when using a synchro, there is a drawback that the transmitting side synchro receives reverse transmission due to the reaction of torque at the receiving side synchro, which causes inconvenience in control. Moreover, in this case, since the synchro is assembled with extremely high precision, there is a drawback that it is difficult to disassemble and repair it. Furthermore, when a configuration is adopted in which torque is extracted directly from the rotor shaft of the receiving side synchronizer, there is a drawback that the generated torque is small compared to its weight.

On the other hand, when using DC synchronization, the rotor made of permanent magnets on the receiving side rotates once for every change of one rotation in the command signal output from the transmitting side corresponding to the rotational position of the upper shaft motor. However, since the rotor is limited to a two-pole type, the generated torque is small, and in order to solve this problem, a new feedback loop must be provided.

Furthermore, when using an optical incremental encoder, various problems arise due to quantization errors that occur when the rotation angle of the upper shaft motor is converted into a pulse train. In other words, it cannot be confirmed whether or not the upper shaft motor is rotating during the period when the pulse from the encoder is falling. Therefore, when the lower shaft motor is stopped or rotating at low speed, the lower shaft motor is at least There is a drawback that hunting occurs with an angular width equivalent to one pulse. In order to overcome these drawbacks, if the number of divisions of the encoder is increased to improve the resolution, the rotational speed of the upper shaft motor will be reduced due to the response speed constraints of the optical detection element in the encoder. The upper limit becomes low, which is extremely inconvenient in actual use. As described above, it is difficult to increase the response speed in an automatic control system using an optical incremental encoder.

The present invention has been made to solve the above-mentioned problems, and its purpose is to increase the torque obtained by each motor when the first and second DC motors are rotated synchronously, and to improve the torque when the motors are stopped and when the motors are stopped. It is an object of the present invention to provide a DC servo motor device that can prevent hunting during low speed rotation and increase response speed.

An embodiment in which the present invention is applied to a sewing machine will be described below with reference to the drawings.

In Figure 1, 1 is the sewing machine bed, 2 is the arm, 3 is the bobbin case, 4 is the inner hook, 5 is the outer hook, and 6
A lower shaft 7 has one end connected to the outer hook 5, and a first DC motor 7 for driving the outer hook 5 is connected to the other end of the lower shaft 6 via a coupling ring 8. Also, 9
1 is a needle bar, 10 is a needle, 11 is a needle bar holder, 12 is a needle bar crank rod, 13 is a counterbalance cranker, 14 is an upper shaft whose one end is connected to the counterbalance crank 13, 1
Reference numeral 5 designates a second DC motor connected to the other end of the upper shaft 14 via a coupling ring 16.

Next, in FIG. 2, 17 is a first position signal generator for detecting the rotational position of the first DC motor 7, particularly the rotational position of the lower shaft 6; 7, a detection shaft 19 is rotated via a pair of gears 18 to reduce the rotation speed to 1/2, and a coupling 2 is attached to this detection shaft 19.
It comprises a sine/cosine potentiometer 21 connected through 0. That is, the first position signal generator 17 generates a first sine wave signal SINx from the sine/cosine potentiometer 21 (where x is the detection axis 19
rotation angle from the reference position) and the first cosine wave signal
Output COSx. On the other hand, 22 is a second position signal generator for detecting the rotational position of the second DC motor 15, particularly the rotational position of the upper shaft 14, which is directly rotated by the second DC motor 15. It has a sine/cosine potentiometer 23,
As the DC motor 15 rotates, a second sine wave signal SINy (where y is the rotation angle from the reference position of the upper shaft 14) and a second cosine wave signal COSy are output. By the way, in order to function as a sewing machine, both DC motors 7 and 15 are operated so that the needle 10 driven by the second DC motor 15 and the outer hook 5 driven by the first DC motor 7 meet at the optimum timing. must be synchronized. Therefore, needle 1
If the sine/cosine potentiometer 23 of the second position signal generator 22 is set to the reference position (i.e., the position of y=0) when 0 is at a predetermined position, then the optimum outer hook 5 for the position of the needle 10 is determined. The position of the sine/cosine potentiometer 21 of the first position signal generator 17 corresponding to the position of the outer hook 5 is determined as a reference position (that is, the position where x=0). Now, 24 is an arithmetic circuit that calculates each output from the first and second position signal generators 17 and 22 to generate a feedback voltage V _F.
Specifically, the first and second sine wave signals SINx,
SINy and first and second cosine wave signals COSx,
Based on COSy, SINxCOSy-SINyCOSx=-SIN(y-x) is calculated, and the thus synthesized sine wave signal is output as a feedback voltage _VF . Therefore, this feedback voltage V _F exhibits a waveform as shown in FIG. And 25 is the feedback voltage
This is a driver circuit that amplifies _VF , and the first DC motor 7 is driven by its amplified output. Further, 26 is the second DC motor 1
This is a driver circuit for 5 drive. Note that each of the rotation angles x and y described above is, for example, the upper axis 14 and the detection axis 1.
9 assumes a positive value when rotated in the directions of arrows X and Y in the figure, respectively.

Next, the operation of the above configuration will be explained. Now, when the second DC motor 15 is driven by the driver circuit 26 and the upper shaft 14 is rotated in the direction of arrow Y in the figure,
At this moment, the state becomes y>x, and the second sine wave signal SINy and second cosine wave signal COSy corresponding to the rotation angle of the upper shaft 14 are output from the sine/cosine potentiometer 23 as command signals. Ru. Then, the arithmetic circuit 24 receives the command signal and the position signal (SINx,
outputs the feedback voltage _VF based on the output voltage (COSx). At this time, since y>x, that is, y-x>o, the feedback voltage V _F
exhibits a negative voltage, and this voltage V _F is applied to the first DC motor 7 via the driver circuit 25 to drive it, thereby causing the lower shaft 6 to move in the direction opposite to the arrow X direction at y=
It is rotated until x. By continuously performing such operations, the lower shaft 6 moves to the upper shaft 14.
At this time, the rotation angle of the lower shaft 6 is 2x with respect to the rotation angle x of the detection shaft 19, so as a result, the lower shaft 6
is rotated at twice the speed of the upper shaft 14. In this embodiment, the rotation direction of the first DC motor shaft and the detection shaft 19 is reversed by the pair of gears 18, so that the output V _F of the arithmetic circuit 24 is
As shown in the figure, V _F = -SIN (y-x), but if the rotation directions of both are the same, V _F =
Of course, SIN(y-x) should be fed back. For example, if the sewing machine is in a state where y≠x when the power is turned on, the lower shaft 6 is rotated to the position where y=x by the same operation as described above, and then the synchronous rotation described above is performed. will be carried out.

Therefore, the range in which the lower shaft 6 follows the rotation of the upper shaft 14 as described above is guaranteed within the range -180°<y-x<+180°, and therefore has a sufficient feedback effect against external disturbances. In particular, y−x=0
(that is, the point where the feedback voltage V _F becomes zero), the slope of the V _F curve is steep, and the number of poles of the first DC motor 7 can be arbitrarily selected, so that the DC motor 7 has sufficient follow-up torque. We can expect this to occur.
Furthermore, in the above configuration, if the arithmetic circuit 24 is configured with an analog arithmetic unit, the feedback voltage V _F
The calculation speed of the first DC motor 7 can be made extremely high, and the resolution is infinitesimal, which together with the response speed of the automatic control system can be sufficiently increased. can be prevented.

It goes without saying that the present invention is applicable not only to sewing machines but also to other devices.

According to the present invention, as is clear from the above description, in a DC servo motor device that rotates the first and second DC motors synchronously, the torque obtained by each DC motor can be increased, and the It is possible to prevent hunting and increase response speed. Moreover, according to the present invention, the first and second sine/cosine potentiometers are configured to obtain a signal for synchronizing the first and second DC motors, so that high-precision parts such as synchronizers can be used. This can be done at low cost, and there is no possibility that the disassembly and repair will be complicated. Also, there is no reverse transmission due to torque reaction, so there is no possibility of inconvenience in control. Further, according to the present invention, only a DC power source is required, and an AC power source is not required as in the case of using a synchronizer, thereby making it possible to downsize the entire device.

[Brief explanation of the drawing]

The drawings relate to one embodiment of the present invention.
2 is a diagram showing a schematic configuration of the sewing machine, FIG. 2 is an explanatory diagram of the configuration of an automatic control system, and FIG. 3 is an output waveform diagram of an arithmetic circuit. In the figure, 6 is the lower shaft, 7 is the first DC motor, 14
is an upper shaft, 15 is a second DC motor, 17 is a first position signal generator, 21 and 23 are sine/cosine potentiometers, 22 is a second position signal generator,
24 is an analog arithmetic circuit, and 25 is a driver circuit.

Claims (1)

[Claims] 1. A first DC motor 7, and a first sine wave signal SINx (x is a rotation angle from a reference position) and a first cosine wave as the first DC motor 7 rotates. signal
COSx, the first sine/cosine potentiometer 21, the second DC motor 15, and the second sine wave signal SINy (y is from the reference position) as the second DC motor 15 rotates. rotation angle) and the second
a second sine/cosine potentiometer 23 that generates a cosine wave signal COSy, and signals from the first and second sine/cosine potentiometers 21, 23;
Sine wave signal from SINx, COSx, SINy, COSy
An analog arithmetic circuit 24 that synthesizes and outputs SIN(y-x) and an output signal of the analog arithmetic circuit 24
A driver circuit 25 for amplifying SIN(y-x) is provided, and by supplying the output signal of the driver circuit 25 to the first DC motor 7, the rotation of the second DC motor 15 is controlled by the first DC motor 7. A DC servo motor device characterized in that a DC motor 7 follows and rotates. 2 The second DC motor 15 is connected to the upper shaft 1 of the sewing machine.
4, the first DC motor 7 is connected to the lower shaft 6 of the sewing machine.
2. The DC servo motor device according to claim 1, wherein the DC servo motor device is for rotationally driving each of the servo motors.