JPH02255905A - Method and apparatus for stopping rotor at desired position of angle - Google Patents

Abstract

PURPOSE: To make it possible to completely stop the rotating body which is small in heat generation and noise generation by reducing the rotary body down to a specific speed and measuring the speed reduction time, and predicting a specific angular position and braking the rotating body so that it stops at the position. CONSTITUTION: A rotating load 1 is fitted onto the shaft of an electric motor 2 arranged on force sensors 4-6, and an optical disk 7 provided at the far end of the load 1 rotates inside optical sensors 8 and 9 which generate mutually 90 deg. out-of-phase quadrant signals; and the signals of both the sensors are inputted to a microcomputer 12, and the electric motor 2 is braked through a brake contact 15 with a direct current from a three-phase full-ware rectifying device 14. The electric motor 2 which rotates at a specific speed is braked and when the electric motor reaches a median speed, the electric supply is stopped, so that the electric motor 2 rotates inertially thereafter. A computer 12 measures the speed reduction time up to when the motor reaches the median speed and predicts the angular displacement up to the stop from the median speed, thereby braking and stopping the motor according to the angular displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for accurately stopping a rotating body in an angular position, and more specifically, for braking a rotating body driven by an asynchronous squirrel cage induction motor without using a mechanical brake. Concerning an economical method of stopping.

Among industrial processes, for example, in sewing machines and wheel balancing devices, it is necessary to accurately stop a rotating body at a desired angular position. Traditionally, this type of work has been performed by indexing work. After the rotating body is first stopped at a random position, the drive motor is braked for a short period of time. This operation is repeated several times to rotate the rotating body until it reaches the desired position.

This method is possible when using gear drives, belt transmissions, or mechanical brakes, since the inherent losses quickly absorb the angular momentum and bring it to a precise stop. However, repeated switching of high starting currents, typically six times the rated current of the motor, causes abnormal wear on the supply contacts of the motor. Additionally, when using mechanical brakes, the wear surface needs to be adjusted and renewed as wear progresses.
Also, harmful dust is generated during braking.

Recently, U.S. Patent Boxes 4,474,786 and 4.55
No. 8265 discloses a method for determining a braking start point using acceleration time and driving time.

U.S. Pat. No. 4,741,210 discloses a method and apparatus for reversing a motor to stop a load at a desired position using acceleration time as a measure of angular momentum.

These US patents do not disclose an accurate stopping method for automotive wheel balance Vi locations.

Direct Drive Motor for Wheel Balancing Devices (U.S. Patent Box 4)
, 423, 632) is not equipped with a mechanical brake. Furthermore, since the rotating wheel group has a large inertia, the above-mentioned indexing operation is unreliable and inaccurate. Therefore, AC reversal is used for electric braking. The disadvantage of using alternating current reversal for braking is that errors arise due to the inherent delay in opening and closing the contacts.When braking with alternating current, the current M can cause the wheel to move too far in the opposite direction. However, this is especially a problem when the load is small and the deceleration is high, i.e. when the load is completely stopped, residual motion of overshooting and overspreading is unavoidable, and when stopping exactly at a given angular position. It is impossible to do so.

Another thing to consider when using a wheel balancing device is that each rotating body to be balanced has a different rotational inertia, so it is necessary to compensate for this difference when applying the brake.

Another disadvantage of AC reversing is that motors in large equipment may experience high temperatures, resulting in changes in the motor's braking torque characteristics as the winding resistance changes.

The present invention provides a new braking method and device for stopping a rotating body at a desired angular position. Asynchronous squirrel cage induction motor for driving a rotating body (U.S. Patent Box 4,423,63
(Refer to No. 2), but since the braking work is done by direct current, it is faster and generates less heat than in the case of alternating current reversal, the noise level is low, and it is also possible to completely stop the rotating body. can.

The braking action in the present invention is performed in three stages. In the first step, the speed of the rotating body is reduced to a low speed (referred to as median speed) that allows accurate positioning, and the deceleration of the motor is measured under the conditions of load, voltage, and winding temperature. The second step is to coast the load at the median speed. In the third stage, braking direct current is applied again to stop the load at the desired position. The desired position is ascertained during the same braking cycle by the balancing functions of the balancing device.

Rotating load (wheel) (1) is directly driven induction motor (2)
) is attached to the shaft. The electric motor (2) is part of a typical direct drive wheel balancer and is placed above three force sensors (4), (5), (6). An optical disc (7) located at the remote end from the rotating load (1) is adapted to rotate within the two optical sensors (8), (9). These optical sensors (8), (9
) are quadrant signals (10) with a phase difference of 90°, (
11), and the signals (10) and (11) are input to the microcomputer (12).

Acceleration by three-phase alternating current of the electric VJ machine (2) is achieved through the forward contact (1).
Braking of the electric motor (2) is carried out via the brake contact (1) with direct current from the three-phase full-wave rectifier (14).
5).

When the forward contact (13) is closed and the motor (2) is energized, the motor (2) will eventually reach the desired maximum speed (360 revolutions per minute in this practical example), but any suitable equilibrium speed can be selected. After that, you can turn off the power. The rotating load (1) then rotates due to inertia and the unbalance can be measured as is well known in the prior art.

At the completion of this type of balance measurement, the brake contact (15
) is closed for the first time, direct current flows through the windings and braking torque is applied, so that the electric motor R(2) begins to decelerate. Part or all of the time the brakes are applied,
A microcomputer (12) measures the time it takes to decelerate from the initial speed to the median speed. This deceleration time indicates deceleration, and is expressed by the following relational expression among load inertia, braking torque, and speed difference. That is, where GD2 is the total moment of inertia (kgfm), nb is the speed difference, and bav is the average torque (kafm).

It is well known that the relationship 'bav'' (electric elliH (19! friction)) is obtained during acceleration, and the relationship 'bav-H (electric motor) + H (friction) is obtained during deceleration.

In this case, the braking torque 'bav is not always held constant, but is in a proportional relationship with the rotational speed, and is also in a proportional relationship with the braking current. The υ1 dynamic current is determined by the applied voltage and the motor winding resistance at the operating temperature.

For reasons of flow, simplicity and reliability, no device is provided to adjust the DC braking current. A simple full-wave silicon rectifier is used.

By directly measuring the deceleration time t during braking, the rotating body stopping device of the present invention eliminates the need to directly measure and evaluate each of the above-mentioned factors that affect the braking torque of the electric motor, and further improves the average torque. 'bay is directly measured, so υ
There is no need to control the 1-dynamic N flow.

In prior art U.S. Patent No. 4,741,210,
While the acceleration time is measured, the deceleration time is calculated using an approximate formula (a formula that subtracts H (friction) during acceleration and adds it during deceleration). In contrast, the present invention directly measures the deceleration time.

The measured deceleration time is used in a lookup table (see Figure 2) in the microcomputer (12) on which the program (see Appendix A) is executed to find the appropriate median speed. This median speed has been determined experimentally using test results of various wheels with different inertias. The median speed must be set at a speed that at least allows accurate positioning and provides sufficient angular momentum to the wheel (1) to make at least two rotations due to gravity. Diameter 30.48 cx (12”)
The median speed for small wheels is about 100rl
)l, the median speed for wheels with a larger diameter is approximately 8
Measure in rpm.

Another search table (see Figure 3), which was also determined experimentally, is
It shows the relationship between the deceleration time from the start of the braking operation until deceleration to the median speed and the amount of braking required at the final braking to stop the wheel at a desired position. This search table shows the angle at which the optical encoder rotates under conditions such as given load, current, and temperature from when the braking current switch is turned on until the wheel (1) stops. Therefore, the braking direct current is applied at the desired angle of the optical encoder until the desired stop position is reached.

As explained above, the method of stopping a rotating body according to the present invention, which uses two experimental lookup tables to determine the median speed and final braking angle, is an economical and simple method for accurately performing the final braking operation. .

It is not easy to calculate the median speed theoretically. In practice, this means that the median velocity is 11 for air and other brakes during wheel braking! This is because it is determined by to. The optimal median speed is set so that the wheel makes two revolutions under the action of gravity before coming to a stop due to friction.

The final braking angle (final braking time) can be calculated from the deceleration time by assuming that the braking torque is proportional to the rotational speed. The closer you get, the more inaccurate it becomes. The experimental lookup table was found to be more accurate.

[Brief explanation of drawings]

Fig. 1 is a side view showing an apparatus of the present invention for carrying out the stopping method of the present invention, Fig. 2 is a search table used in the stopping method of the present invention, and Fig. 3 is a side view showing a device used in the stopping method of the present invention. This is another search table. 1... Rotating load 4, 5.6... Sensor 8.9... Optical sensor 13... Forward direction contact 15... Braking contact 2... Direct drive induction 1j Electric motor 1... Optical disk 12...Microcomputer 14...Full-wave rectifier FIG, 1 Meji 2-in order J (: i-samu service: : Itokuchi G, 2 1C replacement splitter negative; Fukiri day G, 3

Claims (12)

[Claims] (1) A method for stopping a rotating body rotating at a first speed at a desired angular position, in which braking is performed only for a first period until the speed of the rotating body decreases to a speed lower than the first speed. A step of measuring the deceleration time, a step of calculating the deceleration from the measured deceleration time, and a step of calculating the angular displacement that occurs during braking from the low speed to the stop using the calculated value of the deceleration. calculating another angular position that differs from the desired angular position by an amount equal to the angular displacement; A method for stopping a rotating body, comprising the step of braking at the different angular position so that it comes to a complete standstill at a specific angular position. (2) The method for stopping a rotating body according to claim 1, further comprising the step of coasting the rotating body at the low speed at the same time as performing the predicting step. (3) The method for stopping a rotating body according to claim 1, characterized in that the low speed is selected using an experimental table in which the measured deceleration time is an independent variable. (4) A claim characterized in that the step of predicting the angular displacement that occurs during braking from the low speed to the stop is carried out using another experimental table in which the measured deceleration is used as an independent variable. The method for stopping a rotating body according to item 1. (5) The method for stopping a rotating body according to claim 1, wherein the brake is an induction motor. (6) The method for stopping a rotating body according to claim 5, wherein the induction motor is directly connected to a load. (7) The method for stopping a rotating body according to claim 6, wherein the exciting current during braking of the induction motor is direct current. (8) The method for stopping a rotating body according to claim 7, wherein the direct current is supplied from an alternating current power source through a full-wave rectifier. (9) The method for stopping a rotating body according to claim 1, wherein the measurement of the deceleration time is performed during a part of the first period. (10) A device for stopping a rotating body rotating at a first speed at a desired specific angular position, the device braking only for a first period until the speed of the rotating body decreases to a speed lower than the first speed. a device for measuring deceleration time; a device for calculating deceleration from the measured deceleration time; and a device for calculating deceleration from the measured deceleration time; a device for predicting using a calculated value; a device for calculating another angular position that differs from the desired predetermined position by an amount equal to the angular displacement; and a device for braking at said different angular position so as to completely stop at said desired specific angular position after rotation due to movement. (11) The device for stopping a rotating body according to claim 10, wherein the braking device includes a direct current supplied to an induction motor. (12) The device for stopping a rotating body according to claim 11, wherein the DC current is supplied from an AC power source.