JPH03213227A - Screw tightening device - Google Patents

Abstract

PURPOSE:To correctly arrange a uniform length of fitting of screws by controlling a bit driving means being based on a number of angle signals from an angle signal generating means which generates the angle signal in accordance with a rotational angle of a bit. CONSTITUTION:When a bit 2 for holding a screw 1 is rotated, an angle signal is generated by a number in accordance with a rotational angle of the bit 2, by an angle signal generating means 4. This angle signal is counted by an angle signal counting means 5 to obtain the number of these signals. A driving means 3 is controlled being based on the number of the angle signals, obtained by the angle signal counting means 5, in a rotary angle control means 6. By a control of this means 6, for instance, a relationship to a rotary angle of the bit 2, related to the number of the angle signals, is left as previously obtained to obtain the rotary angle of the bit 2 from the number of the angle signals, and a length of fitting of the screw 1 can be arranged to almost a fixed value by controlling the driving means 3 so that the rotary angle of this bit 2 agrees with a target value in which the length of fitting of the screw 1, related to a screw tightening object, is converted into the rotary angle being based on a pitch of the screw 1.

Description

[Detailed Description of the Invention] (Summary) The present invention relates to a screw tightening device equipped with a driving means for rotating a bit holding a screw to attach the screw, and an object of the present invention is to align the fitting length of the screws. In the above-mentioned screw tightening device, there is provided an angle signal generating means for emitting angle signals in a number corresponding to the rotation angle, an angle signal counting means for counting the angle signals, and an angle signal generating means for counting the angle signals based on the number of angle signals counted by the angle signal counting means. and rotation angle control means for controlling the drive means.

[Industrial application field]

The present invention relates to a screw tightening device, and more particularly to a screw tightening device equipped with a driver that rotates a bit holding a screw and attaches the screw.

With the advancement of factory automation (FA),
Various tasks are being replaced by robots, and even the assembly of relatively sophisticated mechanical parts has come to be performed by robots.

In this assembly work, in addition to the work in which the robot installs another part at a specified position of one part, there is also a screw tightening work in which a mechanical part is fixed to another part by, for example, tightening screws. Screw tightening work is usually performed using a screw tightening device in which a driver such as an electric screwdriver or an air driver is attached to a robot or other drive mechanism, and reliable screw tightening is desired.

(Conventional technology) An example of a conventional screw tightening device will be explained with reference to FIG.

This screw tightening device uses negative pressure from a vacuum pump to adsorb a screw, moves it to a predetermined position, and tightens the object with the screw. A driver 11 which has a built-in drive means such as (not shown) and which tightens the screw 16 by rotation thereof, a driver control circuit 12 which controls the rotation of this motor, and a driver 1
A suction sleeve 13 is provided at the tip of the suction sleeve 13 and has a cylindrical shape so that the screw 16 can be suctioned by negative pressure. It has a bit 14 formed with a thread corresponding to the thread groove, and a vacuum pump 15 that makes the inside of the suction sleeve 13 a negative pressure.

As shown in the figure, the driver 11 is connected to the Z-direction movable section 20a via a pressing force sensor 17 having a parallel spring structure. The pressing force sensor 17 has strain gauges 19 attached to several places inside each of leaf springs 18a and 18b provided on both the upper and lower sides, and the deflection of the leaf springs 18a and 18b acts on the screw 16 in the Z direction, that is, in the vertical direction. The method is to measure the pressing force.

The driver 11, the pressing force sensor 17, and the two-direction movable part 20a are integrally moved in the Z-axis direction by the Z-direction drive mechanism 20, and an X-axis and a Y-axis perpendicular thereto are set in the horizontal direction. It is moved in the X-axis direction by an X-direction drive mechanism 21 and in the Y-axis direction by a Y-direction drive mechanism 22. The two-way drive mechanism 20 includes a motor 23
The driving force is utilized and is controlled by the Z direction control circuit 24. In other words, the Z-direction control circuit 24 receives the measured value of the pressing force acting on the screw 16 fed back from the pressing force sensor 17 and the input device (such as a keyboard).
(not shown) and compares the measured value with a previously set value, and controls the drive of the motor 23 so that the measured value approaches this set value, thereby controlling the elevation of the Z-direction movable part 20a. It is something.

Next, the operation of this screw tightening device will be explained as shown in Figs. 4 and 5, taking screw tightening of a disk of a magnetic disk device as an example.
This will be explained using figures.

First, the driver 11 is moved to the automatic screw supply u&25 by the X-direction moving mechanism 21 and the Y-direction moving mechanism 22, and is then lowered by the Z-direction driving mechanism 20 to pick up the screw 16a.

Next, the driver 11 moves above the screw hole 28a of the clamper 27 on the disk 26, descends, and partially tightens the screw 16a as shown in FIG. This is called temporary tightening, and the temporary tightening work up to this point is also performed for the other screw holes 28b and 28c.

Next, the driver 11 moves to the screw hole 28a again and screws l.
Tighten ea to the specified torque. This is called final tightening, and this final tightening operation is also performed for the other screw holes 28b and 28c.

Finally, when tightening the three screws, in order to balance the torque, the rotation speed is lowered than during temporary tightening and final tightening.

28c, the screws are tightened again, that is, retightened, using the specified torque in the same manner as the above-mentioned final tightening.

The above shows how to tighten screws in three general stages, but in order to finally tighten the screws in a well-balanced manner in each screw hole, when temporarily tightening the screws, tighten the screws as shown in Figure 5.
6 into the screw hole of the spindle 29, that is, the fitting length S needs to be uniform in each screw hole. The fitting length S is determined by looking at the distance between the lower end of the screw head and the surface of the screw tightening part of the clamper 27, as shown in the same figure.
If the nominal length is 6 and the thickness of the screwed part of the clamper 27 is d, then 5=L-d-vertical.

[Problem to be solved by the invention]

By the way, in such conventional screw tightening devices,
There are two ways to align the fitting lengths of the screws in the screw holes during temporary tightening, such as by detecting the position of the Z-direction movable part 20a and by detecting the operation time of the driver 11. Ta.

However, in the method of detecting the position of the Z-direction movable part 20a, the position of the Z-direction movable part 20a and the position of the driver 11 do not match due to changes in the amount of deflection of the leaf springs 18a, 18b of the pressing force sensor 17 during that time. , and also screw bit 14 into screw 16
Since minute vibrations are generated in the Z-direction movable part 20a when the driver 11 is pressed and screwed, the position of the driver 11 cannot be detected accurately and the fitting lengths cannot be accurately aligned. Moreover, according to the latter method of detecting the operating time of the driver 11, since the rotation speed changes when the driver 11 starts and stops rotating, an error occurs in the rotation angle of the bit even if the operating time of the driver 11 is constant. There was a problem in that it was not possible to accurately control the length of the screws fitted into each screw hole.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a screw tightening device that can accurately align the fitting lengths of screws.

(Means for Solving the Problem) As shown in FIG. 1, the means for solving the above problems in the present invention is a drive means for rotating a bit 2 holding a screw 1 and attaching the screw. 3, the angle signal generating means 4 generates a number of angle signals corresponding to the rotation angle of the bit 2, the angle signal counting means 5 counts the angle signals, and the angle signal counting means 5 performs counting. A rotation angle control means 6 is provided for controlling the drive means 3 based on the number of angle signals obtained.

(Operation) In FIG. 1, when the bit 2 holding the screw 1 rotates, the angle signal generating means 4 generates angle signals corresponding to the rotation angle of the bit 2. This angle signal is counted by the angle signal counting means 5 to obtain the number of signals. Then, the rotation angle control means 5 controls the drive means 3 based on the number of angle signals obtained by the angle signal counting means 5. In this control, for example, the relationship between the rotation angle of bit 2 and the number of angle signals is determined in advance, the rotation angle of bit 2 is determined from the number of angle signals, and this rotation angle is determined based on the pitch of screw 1. By controlling the driving means 3 so that the length of the screw 1 fitted into the object to be tightened corresponds to a target value converted into a rotation angle, the length of the screw 1 fitted to the object to be tightened can be made substantially constant.

(Example) Hereinafter, an example of the screw tightening device according to the present invention will be described based on FIG. 2.

Fig. 2 shows the main parts of the screw tightening device of this embodiment, and the members not shown in the figure in this embodiment are the same as those in the conventional example, and the parts shown in Fig. 3 in the same figure are the same as those in the conventional example. Components that are the same as those in the conventional example are given the same reference numerals as those in the conventional example, and detailed explanations thereof will be omitted.

As shown in FIG.
An encoder 42 as an angle signal generating means for generating an angle signal corresponding to the rotation angle of the bit 14 is provided in parallel with the rotation angle of the bit 14, and the shaft of the encoder 42 and the shaft of the motor 41 are connected to a gear 43a.

43b. In this embodiment, the gear 43a,
The number of teeth ratio of 43b is set to l:1, and the screw 3 to be used is
6 is an M3 coarse screw with a pitch P of 0.5 mm. Further, in this embodiment, the number of angle signals generated by the encoder 42 per one rotation of the bit 14, that is, the resolution R is set to 360. Therefore, when the bit 14 rotates by the rotation angle θ0, the distance Z that the screw 36 advances is z=p・(θ/R)=0.5・θ/36
0=0.0014θ, IIrm. Therefore, the distance that the screw 36 travels through the screw hole, that is, the length of the screw 36 fitted can be directly measured from the rotational speed of the bit 14.

Further, in this embodiment, the driver control circuit 32 controls the rotation of the motor 41. In other words, the driver control circuit 32
An angle signal counting section 61 as an angle signal counting means;
It has a rotation angle control section 62 as a rotation angle control means.

The angle signal counting section 61 is composed of a counter or the like, and counts by inputting a pulse signal generated by the encoder 42 when the motor 41 rotates. On the other hand, the rotation angle control unit 62 controls the screw 3 held by the bit 14 when the driver 31 descends.
When the object to be screwed is a magnetic disk as shown in FIG. 2, the tip of the spindle 5 at the center of the disk 51
When it comes into contact with the opening periphery of the tap hole 54 of No. 2, a change in the signal output by the pressing force sensor 17 is detected, and control is performed so that current is supplied based on this change in signal and the rotation of the motor 41 is started. It is something. Also, the rotation angle control section 62
The number of angle signals counted by the angle signal counting section 61 is converted into a rotation angle based on the resolution R of the encoder 42, and this rotation angle is calculated in advance by the fitting length of the screw 1 based on the pitch P of the screw 36. When the rotation angle matches the set target value, the rotation of the motor 41 is controlled to be stopped, and at the same time, a screw tightening completion signal is sent to the Z direction control circuit 24 to pull up the driver 31. .

Next, the operation of the screw tightening device according to this embodiment will be explained using FIG. 2, taking screw tightening of a disk device as an example.

First, the driver 31 moves to the screw feeder, picks up the screw 36, and moves above the screw hole 55 of the clamper 53, as in the conventional example. next.

When the driver 31 descends and the tip of the screw 36 held by the bit 14 comes into contact with the opening periphery of the tapped hole 54 of the spindle 52, a pressing force is applied to the bit 14, and the pressing force is transmitted via the driver 31 to the pressing force sensor 17. It is transmitted to At this time, in the pressing force sensor 17, the strain gauge 19 expands and contracts due to the bending of the plate springs 18a and 18b, so the pressing force sensor 17 changes the value of the signal and sends this signal to the driver control circuit 32 and Z direction control. The signal is sent to circuit 24.

The driver control circuit 32 controls the motor 4 by inputting this signal.
Start the rotation of 1. At the same time, in the driver control circuit 32, the angle signal counting section 61 inputs a pulse signal corresponding to the rotation speed generated by the encoder 42 due to the rotation of the motor 41 transmitted through the gears 43a and 43b, and counts the number of pulses. The rotation angle control unit 62 determines the rotation angle of the bit 14 based on the resolution R of the encoder 42 from the number of pulses determined by the angle signal counting unit 61.

The rotation angle control unit 62 is configured to stop the rotation of the motor 41 when the rotation angle of the bit 14 matches a preset target value, that is, the rotation angle calculated from the fitting length during temporary tightening. A control signal is sent to the driver 31, and a screw tightening completion signal is also sent to the Z direction control circuit 24 to pull up the driver 31.

As a result, in this embodiment, as described above, the distance Z that the screw 36 advances is Z=0.00140. , "?' Therefore, when the encoder 42 generates one pulse, that is, when the bit 14 rotates by 10, the screw 36 becomes △Z=
It will advance by 0.0014-. Also, screw 36
The screw rotates an average of 180' until it engages with the tapped hole 54, and the screw does not advance during this time, but the M3 coarse screw used in this example has a pitch P of 0.5. ,,,． 1, the average error in the advancing distance of the screw at the same rotation angle is 0.25-. Therefore, in this example, the error in the fitting length can be considered to be approximately 0.25-, and this value is sufficient accuracy for practical use with the M3 coarse thread screw used in this example, and the error of the bit in this example is sufficient for practical use. By directly detecting the rotation angle, it has become possible to control the fitting length with high precision, which was not possible with conventional methods.

Then, the temporary tightening work up to this point is performed for other screw holes, that is, tapped holes, and final tightening and additional tightening are sequentially performed for each tapped hole as in the conventional example. If the rotation angle of the bit 14 is detected during this final tightening and additional tightening, more accurate screw tightening can be performed.

Therefore, according to this embodiment, since the screw fitting length is controlled by directly detecting the rotation angle of the bit, the fitting length is adjusted for each screw hole when temporarily tightening the screw. For example, when attaching the clamper of a magnetic disk drive to the spindle, the discs will not be unbalanced due to the difference in fitting length during temporary tightening, making it easier to tighten screws in precision devices. Effective for work. Further, during final tightening and additional tightening, more accurate screw tightening can be achieved by detecting the rotation angle of the bit at the same time as tightening with a constant torque.

In this embodiment, the resolution R of the encoder 42 has been described as 360 by taking an M3 coarse screw as an example, but in the present invention, it is of course possible to use screws other than M3 coarse screw and to change the resolution appropriately. Further, in this embodiment, the idle rotation portion of the screw 36 was not corrected, but in the present invention, the screw 36
In order to compensate for the idle rotation of
You may rotate it extra.

〔Effect of the invention〕

As explained above, according to the present invention, the screw fitting length is controlled by directly detecting the rotation angle of the bit, so the screw fitting length can be accurately determined for each screw hole. They can be aligned and are effective for tightening screws on precision equipment.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing the configuration of a screw tightening device according to this embodiment, FIG. 3 is a diagram showing a conventional example, FIG. 4 is a diagram showing a screw tightening operation, and FIG. FIG. 5 is a sectional view showing the state when the screws are temporarily tightened. 1.36...Screw 2.34...Bit 3.41...Driving means (motor) 4.42...Angle signal generating means (encoder) 5.6
1... Angle signal counting means (angle signal counting section) 6.62
...Rotation angle control means (rotation angle control unit) has not yet been invented (Fig. 1!II!

Claims (1)

[Claims] A screw tightening device comprising a driving means (3) for rotating a bit (2) holding a screw (1) and attaching the screw (1), according to the rotation angle of the bit (2). angle signal generating means (4) for emitting angle signals for the same number of angle signals; angle signal counting means (5) for counting the angle signals; and said driving means based on the number of angle signals counted by the angle signal counting means (5). (3) Rotation angle control means (6) for controlling
A screw tightening device characterized by being provided with.