JPH0655384A - Screw fastening device - Google Patents

Abstract

PURPOSE:To provide a screw fastening device high in safety while performing rapid screw fastening using speed control. CONSTITUTION:A servo amplifier 300 for controlling the speed of a motor 420 includes a current output part 310 and an overload detecting part 330. The setting input part of the current output part 310 converts the rating, switched by a rating switching part 290, into the maximum current value, and the setting input part of the overload detecting part 330 holds the rating switched by the rating switching part 290. Accordingly, even if the speed control feedback of the motor 420 is interrupted by an accident, the overloaded state is detected by the overload detecting part 330, so that excessive torque is not generated from the motor 420 to reduce the fear of twisting off a screw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called screw tightening device for tightening a screw by power. In particular, the present invention relates to a screw tightening device that applies a speed servo to an electric motor to tighten a screw.

[0002]

2. Description of the Related Art Conventionally, a so-called screw tightening device has been widely used in which an electric motor rotates a driver socket to automatically tighten a screw. In the operation of this screw tightening device, various techniques have been used to tighten the screw with its predetermined torque.

A stall method has been used for a long time for tightening with a predetermined torque. In this stall type, the maximum value of the output torque of the motor is set to the tightening torque of the screw, and when the predetermined tightening torque is reached, the motor stops (so-called stall). is there. This method has been widely used since ancient times because it is simple and there is little risk of screwing.

However, this stall type has a drawback that the screw tightening speed is slow because no speed control is performed. That is, as the screw tightening progresses and the torque increases, the speed of the motor gradually decreases. Therefore, in recent years, a screw tightening device in which the motor current is controlled to control the speed is exclusively used.

FIG. 7 is a block diagram showing the configuration of a typical screw tightening device that controls the motor current as described above. As shown in FIG. 7, the main screw tightening device 500 performs screw tightening according to a start command and an end command from an external equipment PC (programmable controller) 100. Then, the screw tightening device 500
Is the screw tightening controller 200 and the servo amplifier 30.
0 and a motor unit 400.

The screw tightening controller 200 has a CPU 2
10, a ROM 220, a RAM 210, and the like.
The program started by the command from C100 is stored. This program specifies the motor speed and torque. The speed designated by this program is sent to the speed command generating section 250, and the speed command generating section 2
Reference numeral 50 supplies a specific speed command value to the servo amplifier 300. This command value may be an analog signal or a digital signal.

The command value supplied to the servo amplifier 300 is converted into a current command by the speed control section 340 and then supplied to the current output section 310. Current output section 3
10 determines the output current from the current command and the current feedback from the current detection unit 320, and the motor unit 400
Supply this current to. The current output unit 310 includes
Current is supplied from the external drive power supply.

The motor section 400 comprises a motor 420, a rotary encoder (hereinafter, simply referred to as an encoder) 410 mounted coaxially with the motor 420, and a torque sensor 430. A speed signal such as a pulse train output from the encoder 420 is input to the speed detection unit 260 of the screw tightening controller 200. Accordingly, the screw tightening controller 200 can detect the rotation speed of the motor 420. In addition, the torque sensor 43
The torque signal from 0 is input to the A / D conversion unit of the screw tightening controller 200. As a result, the screw tightening controller 200 can detect the rotation torque of the motor 420.

In addition to such current control, motor overload control is also performed. The overload detection is performed by the overload detection unit 330 constantly monitoring the current from the current detection unit 320. Whether or not there is an overload is determined by the current value and the time during which the current flows, as shown in the graph of FIG. That is,
The longer the time is and the larger the current is, the more overload is determined. When the overload is detected in this way, the overload detector 330 sends an overload signal to the CPU 210. Then, CPU2
10 stops the execution of the program and sends an abnormal signal to the equipment PC 100 via the input / output unit 240. Thereby, the operator can grasp the overload state via the equipment PC 100.

The tightening operation of such a conventional screw tightening device will be described with reference to FIGS. 8 and 9. FIG. 8 shows a graph showing the rotation speed and the tightening torque of the motor 420 when the screw is tightened by the screw tightening device. The horizontal axis of this graph is time, and the vertical axis is rotation speed and tightening torque. The rotational speed scale is shown on the left and the tightening torque scale is shown on the right. The graph of the rotation speed is indicated by S in the figure, and the graph of the tightening torque is indicated by T in the figure.

When the screw tightening is started at time t1, the rotation speed of the motor 420 is initially set to the maximum value. At this time, the tightening torque has a low value.

When the screw tightening progresses, the screw is seated, but from this time, the tightening torque starts to increase. Then, a predetermined tightening torque (for example, 100 kg · c
When it reaches m), the screw tightening controller 200 detects that it is in a seated state (indicated by time t2 in the figure) and reduces the speed command value. In the example shown in FIG. p. It has been lowered to m. In this way, the screw is tightened slowly after the seat is seated, and the screw can be tightened with an accurate tightening torque.

Finally, at time t3, when the desired tightening torque is reached, the rotation of the motor 420 is stopped to finish the screw tightening. Generally, the screw tightening action from time t1 to time tt2 is called "temporary tightening", and the screw tightening action from time t2 to time t3 is called "final tightening".

Thus, the screw tightening by the conventional screw tightening device has been performed. Further, an example of a screw tightening device that controls the motor current as described above is disclosed in Japanese Patent Laid-Open No. 63-63.
-212425. The screw tightening device described here is, in particular, a screw tightening device characterized by being provided with means for detecting a screw tightening failure.

[0015]

The conventional screw tightening device has been constructed and operated as described above. Therefore, there is no problem when screwing close to the rating. However, in recent years, it has been desired to perform many types of screw tightening with one screw tightening device. There are various types of screw tightening devices used for such applications, such as those that manually change the tightening torque, and those that are controlled by a program to automatically change the tightening torque and replace the socket. The basic structure is the same as that of the screw tightening device described above.

In such a screw tightening device,
Since it has to cope with various tightening torques,
Occasionally, a motor with a large system rating must be used to perform screw tightening that requires a relatively small tightening torque.

The above case can be dealt with by changing the maximum value of the tightening torque by changing the normal program. However, since the motor itself has not been changed, the overload state detected by the overload detection unit is (even if the specified tightening torque is changed by the screw, the motor rating does not change. ) Only the overload condition was detected with the same threshold value.

Therefore, when a screw having a small maximum tightening torque is being tightened, if the torque feedback system fails, there is a possibility that the screw may be screwed off by an excessive torque. In addition, even if it is screwed off, if the excessive torque causes a defect in the metal connection state of the screw,
There was a problem that it was almost impossible to detect the defect with the naked eye.

The present invention has been made to solve the above problems, and an object thereof is a screw tightening device using a motor whose speed is controlled by a current control device, in which an abnormality occurs in a feedback system. Even if it occurs, an excessive torque exceeding the tightening torque of the screw will not be applied to the screw, and it can prevent damage to the screw or change in the metal connection state inside the screw that cannot be visually discerned. Is to get.

[0020]

In order to solve the above problems, the present invention outputs a rotation speed signal of a motor that generates power for tightening a screw, rotates in conjunction with the motor, and outputs a rotation speed signal of the motor. An encoder, a speed command unit that outputs a speed command that commands the rotation speed of the motor, and the speed command and the rotation speed signal are compared, and the motor is controlled to rotate at a speed that matches the speed command. A current control unit for supplying the motor with the generated current, and monitoring the motor current flowing through the motor, and the magnitude of the motor current,
From the flowing time and the rated torque of the motor, an overload detection unit that detects an overload state and outputs an overload signal, and, when the overload signal is received, from the current control unit In a screw tightening device provided with an overload stopping means for stopping the supply of current to the motor, a setting means for setting a maximum torque for tightening the screw, and a current supplied by the current control unit to the motor are set as described above. A maximum current limiting unit for limiting the maximum torque set by the means to a current value or less for generating the maximum torque, and a rated torque setting for supplying the maximum torque set by the setting means as the rated torque to the overload detection means. The overload detection means detects an overload state based on the rated torque supplied by the setting means, and if the overload state is present, The load signal is supplied to the overload stop means, wherein the motor is a screw clamping device which is characterized in that stop.

[0021]

The rated torque setting unit in the present invention supplies the maximum torque set by the setting means to the overload detection unit as the rated torque. Therefore, when the maximum torque is changed, the overload detection unit detects the overload state based on the changed rated torque. Therefore, even if a failure occurs in the feedback of the rotation speed signal from the encoder, if an excessive current tries to flow, an overload state is detected, and the overload stopping means suppresses the supply of current to the motor. Does not generate excessive torque.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the construction of the screw tightening device of this embodiment. This screw tightening device has substantially the same structure as the conventional screw tightening device shown in FIG. 7, and is a device for tightening a screw by a start command and an end command from an external equipment PC (personal computer). In FIG. 1, the screw tightening device 500 is
It is composed of a screw tightening controller 200, a servo amplifier 300, and a motor unit 400.

The screw tightening controller 200 is a microcomputer including a CPU 210, a ROM 220, a RAM 210 and the like as in the conventional case. The RAM 230 stores a program activated by a command from the equipment PC. This program specifies the motor speed. The speed designated by this program is sent to the speed command generating section 250, and the speed command generating section 2
Reference numeral 50 supplies a specific speed command value to the servo amplifier 300. This command value is an analog signal, for example, 1
Volt / 100r. p. It is defined to represent m. Further, the speed is detected by inputting a pulse signal from the encoder 410 of the motor unit 400 to the speed detecting unit 260. The speed signal from this speed detector is also supplied to the speed controller 340 of the servo amplifier 300.

Further, the screw tightening controller 200 has a rating switching section 290. A feature of this embodiment is that the rating switching unit 290 is provided. This rating switching unit sets the rating of the motor 420 to an optimum value according to the screw that is the object of tightening. This makes it possible to prevent damage or the like due to erroneous application of a large torque even to a screw having a small tightening torque.

The command value supplied to the servo amplifier 300 is converted into a current command by the speed control unit 340 and then supplied to the current output unit 310, as in the conventional case. The current output unit 310 outputs the current value according to the current command using the current feedback from the current detection unit 320. This current is supplied to the motor unit 400. A current is supplied to the current output unit 310 from an external drive power source (not shown).

A detailed block diagram of the current output section 310 and the overload detection section 330 of the servo amplifier 300 is shown in FIG. As shown in FIG. 2, the current control unit 312 converts the current command from the speed control unit 340 into a current value. This current value is amplified by the current amplification unit 313 and then supplied to the motor unit 400. In addition, the current control unit 312 uses the maximum value control unit 3 that determines the maximum value of the current value.
12A is included. This maximum value is set and held by the setting input unit 311, but the setting input unit 311
This value is generated from the rating supplied by the rating switching unit 290 described above.

A feature of this embodiment is that the setting input section 311 converts the rating supplied by the rating switching section 290 into the maximum value of the current value output by the current control section 312. The rating is set according to the type of screw to be tightened. What is the rating?
Since it is the maximum value of the current that is constantly supplied to the two, it is possible to convert the two into one-to-one.

Further, the overload judging section 332 monitors the current value from the current detecting section 320 and detects the overload state from the magnitude and the flowing time. If it is in the overload state, an overload signal is output to the overload transmission unit 333,
The overload transmission unit 333 supplies this overload signal to the CPU 210 in the screw tightening controller 200, as shown in FIG. The overload determination unit 332 determines whether or not it is in an overload state based on the currently supplied rating, and the rating which is the basis of this determination is set and held by the setting input unit 331. The setting input unit 331 generates this value from the rating supplied by the rating switching unit 290 described above.

The feature of this embodiment is that the setting input section 331 holds the rating supplied by the rating switching section 290, and the overload judging section 332 judges overload based on this rating. It is that you are. This makes it possible to accurately detect overload even when the maximum tightening torque of the screw is small, that is, when the rating is small.

As described above, in this embodiment, the output of the rating switching unit 290 is supplied to the setting input units 311 and 331 of the current output unit 310 and the overload detection unit 330, respectively, so that the output is adjusted according to the rating. At the same time that the maximum value of the current output is limited, the reference value (threshold value) for detecting the overload condition is also changed according to the rating.

As shown in FIG. 1, the motor unit 40
Reference numeral 0 denotes a motor 420, and an encoder 410 and a torque sensor 43 that are mounted coaxially with the motor 420.
It is composed of 0 and 0. A speed signal such as a pulse train output from the encoder 410 is supplied to the screw tightening controller 20.
0 is input to the speed detection unit 260. Accordingly, the screw tightening controller 200 can detect the rotation speed of the motor 420. The torque signal from the torque sensor 430 is the A / D of the screw tightening controller 200.
It is input to the converter. As a result, the screw tightening controller 200 can detect the rotation torque of the motor 420.

Next, the operation of this embodiment will be described in detail using a flow chart.

FIG. 3 shows a flow chart of the operation of the screw tightening controller 200, FIG. 4 shows a flow chart of the operation of the overload detection section 330, and FIG. 5 shows a current output section. A flowchart of the operation of 310 is shown.

As shown in FIG. 3, when the screw tightening controller 200 is powered on, first, step 6 is performed.
00 self-diagnosis.

Then, in step 610, the system torque rated value is sent to the servo amplifier section 300. The system torque rated value is the rating of the motor 420 itself. That is, it is the maximum rating of the main screw tightening device. Overload detection unit 330 that has received this system torque rated value
The operation of the current output unit 310 and the current output unit 310 is shown in the section X of the flowcharts shown in FIGS.

In step 620, all the final torque setting values (the tightening torque at the end of the final tightening described above, that is, the maximum tightening torque) specified for each block in the work program written in advance in the RAM 230 are all set. Read / Rating switching unit 290
To the setting input units 311 and 331 in the servo amplifier. The rating switching unit receives this value and stores it for each block.

The work program is a program showing the procedure of the screw tightening work, and the screw type, the socket type to be used, the screw position, the screw tightening torque, etc. are defined for each work unit. . Further, such a work unit is referred to as a block in the text.

At step 630, a start command from the equipment PC is waited, and if there is a start command, the process proceeds to the next step 640.

In step 640, the program starts.

At step 650, the block number to be executed is sent to the servo amplifier. The block number is a number assigned to each block, and each block is identified by this block number. This block number is sent out via the rating switching unit 290 via the setting input unit 311 in the servo amplifier.
331.

In this way, the characteristic feature of this embodiment is that both the final tightening torque set value and the rating used to detect an overload state are updated for each screw to be tightened. That is. Conventionally, the rating of the motor 420 itself is used as the rating used for detecting the overload state, and even if the block changes (that is, even if the type of screw and the final torque setting value change), the overload state is detected. The ratings used for the were not updated. Therefore, according to the present embodiment, the rating for detecting the overload state is also updated according to the update of the final torque value for tightening, so that the feedback loop of the current control may have a failure or the like.
Even if there is a break, there is little risk that the screw will be damaged due to an excessive current flowing to the motor 420.

In this step 650, when the block number is sent to the setting input units 311, 331 in the servo amplifier, each setting input unit sets the maximum current value and the rating according to the block number. Update. This is possible because the block number and the final torque setting value for the block number are previously received by the respective setting input sections as described above. The operations of the overload detection unit 330 and the current output unit 310 at this time are shown in the Y portion of the flowcharts of FIGS. 4 and 5, and the description thereof will be given later.

In step 660, the actual screw tightening operation is performed.

In step 670, it is checked whether there is a next block to process, and if there is a block, step 650 is entered. On the contrary, when there is no next block, that is, when the screw tightening process is completed, all the processes are ended.

As described above, the screw tightening controller 200 sends the block number of each block to the servo amplifier. Therefore, the maximum current amount and rating are set based on the final torque value as described later.

Next, the operation of the overload detector 330 will be described with reference to the flowchart of FIG. First step 70
As indicated by 0, self-diagnosis is performed when the power is turned on.

Then, in step 705, a state of waiting for an input from the screw tightening controller 200 is entered. And
If there is an input, the process proceeds to the next step 710.

In step 710, the system rated torque value from the screw tightening controller is set to the setting input unit 3
It is transferred to the overload judging unit 332 via 31. The overload determination unit 332 stores and holds the transferred value as a system rated torque value, that is, a rated torque value of the motor 420 itself. This step corresponds to the X part in FIG. 4, as can be understood from the symbol of the X part.

In step 720, it waits for the block number to be sent from the screw tightening controller 200. If the block number is transmitted, the process proceeds to the next step 740. The reception of this block number corresponds to the Y part in FIG.

In step 740, the setting input section 3
31 transfers the final torque value corresponding to the received block number to the overload determination unit 332.

In step 750, the overload determination unit 332 divides the final torque value by the system rated value.
The result of this calculation is the ratio of the rated value, which is the basis for determining the overload condition, to the system rated value.

In step 760, the previous step 75
The value calculated at 0 is stored and held in the overload judging unit as it is, and thereafter, it is judged using this value whether or not it is in the overload state. After this step 760, the process proceeds to step 720 and the block number is input and repeated.

As described above, the overload detector 330
Selects the final torque value corresponding to the block number sent from the screw tightening controller 200, and thereafter detects the overload state using the final torque value.

As a result, the area detected as the overload state changes as shown in the graph of FIG. Similar to the conventional graph shown in FIG. 9, the graph shown in FIG. 6 shows the motor current on the horizontal axis and the time when the current flows on the vertical axis. As shown in the figure, the change in rating causes the boundary of the region considered as overload to be different. What is indicated by P in the drawing is a boundary line for identifying an overload state when the rating is equal to the rating of the motor 420 itself. That is, the boundary line indicated by P is the same as the conventional boundary line. As indicated by hatching in the figure, the area on the right side of this boundary line is the area determined to be in the overload state.

In the figure, Q is a boundary line for identifying an overload condition when the set rating is 80% of the rating of the motor 420 itself. As understood from the figure, in this embodiment, the boundary line Q at 80% is 100.
It is a curve obtained by translating the boundary line P at the time of% to the left. In this embodiment, the boundary line indicating whether or not the vehicle is in the overload state is a curve obtained by moving the 100% curve P, which is the same as the conventional one, in parallel to the left side. That is, the rating is 60
When%, the boundary line is represented by the curve R and the rating is 4
At 0%, the boundary line is represented by the curve S. In each boundary line, the hatched area on the right side is the area considered to be in the overload state.

Next, the operation of the current output section 310 will be described with reference to the flowchart of FIG. First step 800
When the power is turned on, self-diagnosis is performed as indicated by.

Then, in step 805, a state of waiting for an input from the screw tightening controller 200 is entered. And
If there is an input, the process proceeds to the next step 810.

In step 810, the system rated torque value from the screw tightening controller is set to the setting input unit 3
The data is transferred to the current control unit 312 via 11. The current control unit 312 stores and holds the transferred value in the maximum value limiting unit 312A as the system rated torque value, that is, the rated torque value of the motor 420 itself. This step corresponds to the X part in FIG. 4, as can be understood from the symbol of the X part.

In step 820, the process waits until the block number is sent from the screw tightening controller 200. If the block number is transmitted, the process proceeds to the next step 840. The reception of this block number corresponds to the Y part in FIG.

In step 840, the setting input section 3
11 is the final torque value corresponding to the received block number (maximum current value (since torque is proportional to current,
The torque value is synonymous with the current value)), and the maximum value limiting unit 3
Transfer to 12A.

In step 850, maximum value limiting unit 312A divides the final torque value by the system rated value. The result of this calculation is the ratio of the maximum current in the current control unit 312 to the system rated value.

In step 855, the previous step 85
The calculation result at 0 is multiplied by 1.5. In this embodiment, the speed control of the motor 420 is performed. However, if the maximum value of the current is completely the same as the value that generates the maximum torque value of the screw, the speed control cannot be performed. Therefore, in this embodiment, the maximum value of the flowing current is set to 1.5 times the maximum torque value. It should be noted that this value may be 1.2 times or 1.3 times, depending on the applied system.

In step 860, the previous step 85
The value calculated 1.5 times in 5 is the maximum value control unit 312.
It is stored and held in A as it is, and thereafter, the current control is performed with this value as the maximum value of the current. Note that this step 860
After that, the process proceeds to step 820, and the block number is repeated from the input.

As described above, according to this embodiment, the block number is sent to the setting input sections 311 and 331 via the rating switching section 290. Then, the setting input sections 311 and 331 set the maximum current value and the rating corresponding to the block number. Therefore, since only the maximum current value was set and updated in the past, the rating was also updated. Therefore, even if the feedback loop of the speed control is interrupted due to an unexpected situation, an excessive current is supplied to the motor 420. It is possible to effectively prevent the screw from being damaged and the like due to the application of excessive torque.

Therefore, according to the present embodiment, in the screw tightening device in which the speed is controlled by controlling the motor current, the reference value for detecting the overload state of the motor according to the type of screw to be tightened. Since the rating that is the (threshold value) is changed, even if the feedback from the speed control or the signal from the torque sensor is interrupted, a large current flows to the motor, and excessive torque may damage the screw or It is possible to effectively prevent abnormalities in the internal connection state.

[0067]

As described above, according to the present invention, the maximum current set by the setting means is changed so that the maximum current of the current control section is regulated by the maximum current limiting section, and the rated torque is set. The unit supplies the overload detection unit with the rated torque changed according to the above change. Therefore, the rated torque, which is the basis for detecting the overload condition, is changed according to the change of the set maximum torque.Therefore, even if the feedback loop of the current control unit is abnormal, the motor may generate an excessive torque. There is no.

Therefore, according to the present invention, in the screw tightening device for quickly tightening the screw by using the speed control, even if the feedback control is abnormal, the screw is screwed by an excessive torque, or the screw is screwed. It is possible to obtain a screw tightening device that does not cause an abnormality in the internal connection state of the. As a result, the effect that the screw tightening can be performed quickly and safely is obtained.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a screw tightening device according to a preferred embodiment of the present invention.

FIG. 2 is a detailed configuration block diagram of a current output unit 310 and an overload detection unit 330.

FIG. 3 is a flowchart of the operation of the screw tightening controller.

FIG. 4 is a flowchart of the operation of the overload detection unit 330.

FIG. 5 is a flowchart of the operation of current output 310.

FIG. 6 is a diagram showing a graph showing a region detected as an overload state.

FIG. 7 is a configuration block diagram of a conventional screw tightening device.

FIG. 8 is a diagram showing a graph showing a region detected as an overload state by a conventional screw tightening device.

FIG. 9 is an explanatory diagram of a screw tightening operation performed by a conventional screw tightening device.

[Explanation of symbols]

 200 screw tightening controller 210 CPU 220 ROM 250 speed command generation unit 260 speed detection unit 290 rating switching unit 300 servo amplifier 310 current output unit 311 setting input unit 312 current control unit 312A maximum value control unit 313 current amplification unit 320 current detection unit 330 Overload detection unit 331 Setting input unit 332 Overload determination unit 333 Overload transmission unit 340 Speed control unit 400 Motor unit 410 Encoder 420 Motor 430 Torque sensor 500 Screw tightening device

Claims (1)

[Claims] 1. A motor that generates power for tightening a screw, an encoder that rotates in conjunction with the motor and that outputs a rotation speed signal of the motor, and a speed command that commands the rotation speed of the motor. A speed control unit, a speed control unit, a current control unit that compares the speed command and the rotation speed signal, and supplies to the motor a current that is controlled so that the motor rotates at a speed matching the speed command; An overload detection unit that monitors a motor current flowing in the motor, detects the overload state from the magnitude of the motor current, its flowing time, and the rated torque of the motor, and outputs an overload signal, A screw tightening device comprising: an overload stopping means for stopping the supply of the current from the current control unit to the motor when the overload signal is received. Setting means for setting a maximum torque, a maximum current limiting section for limiting a current supplied to the motor by the current control section to a current value or less for generating the maximum torque set by the setting means, and the setting means And a rated torque setting unit that supplies the maximum torque set by the above as the rated torque to the overload detection unit, wherein the overload detection unit is based on the rated torque supplied by the setting unit. The screw tightening device is characterized in that an overload state is detected by an overload signal, and if it is in an overload state, an overload signal is supplied to the overload stopping means to stop the motor.