JPH0373231A - Screw tightening device - Google Patents

Abstract

PURPOSE:To control the presence of a bit with a high accuracy without any influence by the friction and twisting of an absorbing sleeve by detecting and controlling only the force at which the bit presses a screw actually. CONSTITUTION:The force Fb at which a bit 3 presses a screw 91 actually, not the force at which a screwdriver 1 presses, is fed back to a moving command circuit 81. To control precisely the force at which the bit 3 presses the screw 91, a force detection means 31 for detecting the force Fb applied to Z-axis direction of the bit 3 is provided so that the force Fb applied to the bit actually is detected and is fed back to the moving command circuit 81. As a result, the moving command circuit 81 generates a moving command value to make the force applied to the bit coincide with a force command value, taking the force signal Fb applied to the bit actually as a feed-back value and outputs it to a servo control circuit 82, and the servo control circuit 82 servo-controls the motor of a Z-axis drive mechanism 6 according to the moving command value.

Description

[Detailed Description of the Invention] [Summary] Regarding a screw tightening device using an electric screwdriver or an air screwdriver, the purpose of this invention is to precisely control the force with which the bit actually presses the screw, and the screw is held by suction at the tip of the bit. a screwdriver that rotates the bit; a Z-axis drive mechanism that drives the driver in the direction of the rotation axis of the driver; and a Z-axis control circuit that controls the Z-axis drive mechanism; The force detecting means detects an external force applied to the force detecting means, and the Z-axis drive mechanism is configured to be driven and controlled by the Z-axis control circuit so that the output value of the force detecting means coincides with the force command value.

[Industrial application field]

The present invention relates to a screw tightening device using an electric screwdriver or an air screwdriver, and more particularly to a screw tightening device that brings the bit of the screwdriver into contact with the head of the screw with a weak force.

With the advancement of factory automation (FA), various tasks are being replaced by robots, and robots are also being used to assemble relatively sophisticated mechanical parts.

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 the mechanical part is fixed to another device by screw fastening.

The screw tightening work is performed using a screw tightening device in which a driver such as an electric screwdriver 1 or an air driver is attached to a robot or other drive mechanism.

When automatically tightening screws with a screw tightening device, insert the screwdriver's tip into the groove of the screw head (hexagonal hole, cross groove, slotted groove, etc.) and press it with a constant force. A function is required to lower the bit in accordance with the speed of screw advancement.

[Conventional technology]

FIG. 5 is a diagram showing the configuration of a conventional screw tightening device.

In the figure, ■ is a screwdriver that tightens screws, and the driver l is controlled by a driver control circuit (not shown).
The start/stop of the motor inside the motor is controlled.

Reference numeral 2 denotes a suction sleeve, which suctions and holds the screw 91 on the tip of the bit 3 by suctioning the air inside the sleeve with a vacuum pump 22.

The driver 1 includes an X-axis drive mechanism 4, a Y-axis drive mechanism 5, an
It is moved in the XYZ directions by the shaft drive mechanism 6. The driver 1 is connected to the Z-axis rotation unit 7 via a force sensor 71 having a parallel plate spring structure. A strain gauge 73 is attached to the plate spring 72 of the force sensor 71 to detect an external force acting on the driver 1 in the Z-axis direction.

8 is a control circuit that controls the X-axis drive mechanism 6.

The movement command circuit 81 compares the force command value instructing the pressing force of the driver 1 in the Z-axis direction with the force signal 16 from the force sensor 71 indicating the actual pressing force of the driver 1, and determines whether the force signal is a force. A Z-axis movement command value is generated to match the command value and output to the servo control circuit 82. The servo control circuit 82 servo-controls the motor 61 of the X-axis drive mechanism 6 according to the movement command value.

FIG. 6 is a diagram showing an example of screw tightening work using the screw tightening device described above. The example shown in FIG. 6 is a work in which a magnetic disk disk 100 of a magnetic disk device is fixed to a shaft (not shown) located at the center of the disk 100 using a clamper 101.

Follow the steps below to tighten the screws.

■The driver 1 moves to the screw feeder 9 and picks up one screw 91.

■Move the screwdriver l to the screw hole 101a of the clamper 101 and tighten the screw 91 halfway. (Temporary tightening) ■Repeat ■■ for screw holes 101b and 101c to temporarily tighten.

■Move the screwdriver 1 to the screw hole Iota and tighten the screw 91 to the specified torque. (Final tightening) ■Screw hole 101
b. Repeat step (■) for 101c as well to fully tighten.

■In order to balance the tightening torque of the three screws 91, repeat ■ for the screw holes 101a, 101b, and 101c and tighten the screws again. (Retightening) In order to perform stable screw tightening with a screw tightening device, it is necessary to accurately control the force with which the bit 3 presses the screw 91.

An example of tightening an M3+ screw will be explained.

Figure 7 shows the shape of the bit tip for the + screw, and Figure 8 shows the shape of the head of the + screw. When performing final tightening and additional tightening in the above steps
1, lower the screwdriver 1, apply the bit 3, and tighten the screw, but when the bit 3 contacts the screw 91,
Since the direction of the crest 3a of the bit and the direction of the cross groove 91a are random, the bit 3 may not fit into the cross groove 91a.

When the bit 3 is rotated in this state, the ridges 3a of the bit and the ridges 91b of the cross groove rub against each other, causing scratches 91c.

The size of the scratch 91c is approximately 0.111 in the case of M3+ screws.
It is so small as 11 to 0.31 Im that it is almost invisible to the naked eye.

However, in the case of precision machines such as magnetic disk drives, which are extremely dust-free, 0.1 m + * - 0,3 + am (7) If Neshino debris is inside the magnetic disk drive, there is a risk of serious problems such as head crashes. However, the occurrence of scratches is an important problem when trying to automate screw tightening.

In this example, in order to avoid damaging the screw 27, it is necessary to bring the bit 3 into contact with the head of the screw with a force of about 200 gf or less.

Next, when the bit 3 is fitted into the cross groove 91a and the screw is being rotated, the screw 91 advances into the part. It is necessary to press it against the screw 91 with a force of 500 gf to 1 kgfO.

Further, when tightening the screw 91, it is necessary to press the bit 3 against the screw 91 with a force of approximately 1 kgf to 1.5 kgf so that the bit 3 does not rise from the cross groove 91a due to the rotational torque of the bit 3.

[Problem to be solved by the invention]

FIG. 9 is a diagram showing the state of the tip of the driver 1 during a screw tightening operation.

When the pressing force of the screwdriver 1 is F, F is the force Fb with which the bit 3 presses the screw 91, as shown in the figure.
, and a force Fs+ opposing the frictional force between the suction sleeve 2 and the sleeve guide 21.

As mentioned above, in order to perform screw tightening stably, it is necessary to be able to control the force Fb with which the bit 3 presses the screw 91. In the conventional example, as shown in FIG. 5, the pressing force of the driver 1 is detected by a force sensor 71, and the force signal is
The pressing force is controlled by feedback to the axis control circuit. However, since the force sensor 71 is located between the driver 1 and the Z-axis rotating part 7, the force detected by the force sensor 71 is the resultant force of Fb+ and Fs, that is, Fl.
It is not possible to separate and detect only Fb+. Therefore, Fl is controlled to a constant value, but depending on the degree of friction or stiffness between the sleeve 2 and the sleeve guide 21, Fs+
When this changes, the pressing force Fb of the bit 3 also changes, making it impossible to stably tighten the screws.

Further, for example, as shown in FIG. 10, when the sleeve 2 is in contact with a component and the bit 3 is not yet in contact with the screw 91, the sleeve 2 is tilted and the friction between it and the sleeve guide 21 becomes large. Or if it is broken, Fsz=
When the screwdriver 1 reaches Fz, the downward movement of the screwdriver 1 is stopped, causing a problem that the screw tightening operation is interrupted before the bit 3 contacts the screw 91.

The problem to be solved by the present invention is to solve these conventional problems and provide a screw tightening device that can accurately control the force with which a bit presses a screw.

[Means to solve the problem]

FIG. 1 is a diagram showing the configuration and principle of the present invention.

In the figure, 1 is the driver and 3 is the driver 1
It is a bit attached to a chuck.

2 is a suction sleeve, which holds the screw by suction.

21 is a sleeve guide.

Reference numeral 31 denotes a force detection means, which detects an external force Fl applied to the bit 3 in the direction of the rotation axis.

8 is a Z-axis control circuit, which consists of a movement command circuit 81 and a servo control circuit 82.

A movement command circuit 81 generates and outputs a movement command value so that the detected force signal matches a force command value given from a main control section (not shown).

A servo control circuit 82 servo-controls the motor of the Z-axis drive mechanism according to a given movement command value.

[For production]

In the present invention, the force Fb with which the bit 3 truly presses the screw 91 is fed back to the movement command circuit 81, not the force with which the driver 1 presses, but the force with which the bit 3 presses the screw 91 is precisely controlled.

Therefore, in the present invention, a force detection means 31 is provided to detect the force Fb applied to the bit 3 in the Z-axis direction, and the force Fb truly applied to the bit is detected and fed back to the movement command circuit 81.

As a result, the movement command circuit 81 uses the force signal Fb that is truly applied to the bit as a feedback value, generates a movement command value so that the force applied to the bit matches the force command value, outputs it to the servo control circuit 82, and outputs it to the servo control circuit 82. The control circuit servo-controls the motor of the Z-axis drive mechanism 6 based on this movement command value.

In this way, by controlling the force Fb that is truly applied to the bit 3 by feeding back, it becomes possible to control the pressing force of the bit 3 with high precision.

[Embodiment] FIG. 2 is a diagram showing the configuration of a first embodiment of the present invention.

In this embodiment, force sensors detect the pushing force of the driver and the pushing force of the sleeve and sleeve guide, and subtract the latter from the former to find the pushing force of the bit, thereby controlling the pushing force of the bit. It is.

The difference between FIG. 2 and FIG. 5 is that a force sensor B23 is attached to the connecting portion between the sleeve guide 21 and the driver 1, and the part 100 of the sleeve 2 is generated by g-vibration force or prying between the sleeve 2 and the sleeve guide 21. Detecting the pressing force and feeding back the force signal to the Z-axis control circuit 8, and controlling the force signal by subtracting the force signal output from the force sensor B23 from the force signal output from the force sensor A71 in the Z-axis control circuit 8. The difference lies in the provision of a difference circuit 83 that generates a signal.

Here, if the pressing force of the driver 1 is F and the pressing force of the sleeve 2 is Fs, then the value of the force control signal is F-F
s, which is equal to the force Fb with which the bit 3 truly presses the screw 91. Therefore, this force control signal is manually input to the movement command circuit 81, and the movement command circuit 81 compares it with the force command value that instructs the pressing force of bit 3, and adjusts the Z-axis command value so that the force control signal matches the command value. generate. and,
If the servo control circuit 82 servo-controls the motor of the Z-axis drive mechanism 6 based on this movement command value, the pressing force of the bit can be accurately controlled.

FIG. 3 is a diagram showing the main part configuration of the first embodiment of the present invention.

Reference numeral 23 denotes a force sensor B, which has a structure in which a strain gauge 25 is attached to each of the parallel plate springs 24.

One end of the force sensor B23 is fixed to the driver 1, and the other end is fixed to the sleeve guide 21.

A pair of force sensors B23 are arranged in the X direction and a pair in the Y direction (not shown), and detect the pressing force of the sleeve 2 at four locations in the XY directions. The force sensor B23 also serves to hold the sleeve guide 21 in a fixed position by means of a parallel plate spring structure.

The sleeve guide 21 and the sleeve 2 are connected to the force sensor-B.
Since it is connected to driver 1 only through 23,
The force that the sleeve 2 applies to the component 100 during screw tightening is all detected by the force sensor B23.

FIG. 4 is a diagram showing the main part configuration of a second embodiment of the present invention.

In this embodiment, the force sensor 71 in the conventional example shown in FIG. 5 is unnecessary, and the Z-axis control circuit S is the same as that in the conventional example shown in FIG. is unnecessary), so only the specific configuration of the part that detects the force applied to bit 3 will be shown.

31 is a force sensor C, which has a structure in which a strain gauge 33 is attached to a parallel plate spring 32. Since the bit 3 rotates and the force sensor C31 is fixed to the driver 1 side, the bit 3 and the force sensor C31 are connected via the bearing 34. As the bearing 34, a thrust bearing was used.

The other end of the force sensor C31 is connected to the driver 1 by a member 35. A pair of force sensors C31 are arranged in the X direction and a pair in the Y direction (though not shown), support the bit 3 at four locations in the X and Y directions, and detect the pressing force of the bit 3. With this configuration, bit 3 is a force sensor.
It is stably supported from the driver 1 via C31 in a double-sided structure.

When a load is applied to the bit 3, the bit 3 is slightly displaced in the Z-axis direction, so the chuck part 11 that connects the bit 2 to the driver 1 has a gap 12 that absorbs the displacement of the bit 3.
has been established.

In this way, in this embodiment, it is possible to detect only the force that truly acts on the bit 3 using only the force sensor C31.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, only the force with which the bit actually presses the screw is detected and controlled, so the pressing force of the bit can be controlled accurately without being affected by the friction or prying of the suction sleeve. This has a remarkable industrial effect in that it can provide a screw tightening device that tightens screws extremely stably.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration and principle of the present invention, Fig. 2 is a diagram showing the configuration of a first embodiment of the present invention, and Fig. 3 is a diagram showing the main part configuration of the first embodiment of the present invention. Figure 4 is a diagram showing the main part configuration of the second embodiment of the present invention, Figure 5 is a diagram showing a conventional example of a screw tightening device, and Figure 6 is a diagram showing an example of screw tightening work using the screw tightening device. Figure 7 shows the shape of the tip of the bit, Figure 8 shows the shape of the head of the + screw, Figure 9 shows the state of the tip of the screwdriver during screw tightening, and Figure 10 FIG. 2 is a diagram showing an abnormal state during a screw tightening operation. In the figure, 1 is a driver, 2 is a suction sleeve, 3 is a bit, 4 is an X-axis drive mechanism, 5 is a Y-axis drive mechanism, 6 is a Z-axis drive mechanism, 7 is a Z-axis movable part,
8 is a Z-axis control circuit, 9 is a screw feeder, 11 is a chunk portion, 12 is a gap, 21 is a sleeve guide, 22 is a vacuum pump, 23, 31.71 is a force sensor (force detection means), 24 ,
32.72 is a parallel plate spring, 25, 33.73 is a strain gauge, 3a is a bit ridge, 34 is a bearing, 35
are members, 61 is a motor, 81 is a movement command circuit, 82 is a servo control circuit, 83 is a subtraction means (difference circuit), 91 is a screw, 91a is a cross groove,
91b is the peak of the cross groove, 91c is the scratch, 10
0 indicates a component (disk), 101 indicates a clamper, and 101a, 101b, and 101c indicate screw holes. Figure 1 p--

Claims (1)

[Claims] A driver (1) that rotates a screw (91) held by suction at the tip of a bit (3), and a Z-axis drive that drives the driver (1) in the direction of the rotation axis of the driver (1). mechanism(
6) and a Z-axis control circuit (8) that controls the Z-axis drive mechanism (6),
3) force detection means (
31), the Z-axis control circuit (8) causes the force detection means (3
A screw tightening device characterized in that the Z-axis drive mechanism (6) is drive-controlled so that the output value of 1) matches the force command value.