JP2001179646A - Automatic thread fastening apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic thread fastening apparatus capable of remarkably increasing the reliability of thread fastening results. SOLUTION: This automatic thread fastening apparatus is provided with a driver bit 3 receiving the driving of a motor 2 so as to rotate, and engaging with the head of a thread, a torque sensor 4 for detecting the fastening torque of the thread, and an angle detecting means for detecting the rotational angle of the thread, and involves a control unit 10 for comparing the fastening torque of the thread detected by the torque sensor 4 with predetermined reference torque, measuring the rotational angle of the thread from the time when the fastening torque has reached the reference torque, determining whether the rotational angle is included between an angle upper limit and an angle lower limit which are predetermined when the fastening torque has reached the predetermined final fastening torque, and judging whether thread fastening is good or bad.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic screwing machine used for tightening a screw on a work.

[0002]

2. Description of the Related Art In a conventional automatic screw tightening machine, when tightening a screw, the tightening torque of the screw is monitored, and the rotation angle of a driver bit from a predetermined position is read and stored. Is reached, it is checked whether or not the rotation angle falls between a preset angle upper limit value and a preset angle lower limit value, thereby making a final judgment on screw tightening.

[0003]

However, in the above-mentioned conventional automatic screw tightening machine, in order to determine the detection start position of the rotation angle, the identification member is integrated with a driver bit or the like which descends following the screwing of the screw. In many cases, a configuration is adopted in which the sensor is read by a sensor arranged at a predetermined position. For this reason, the measurement start point of the rotation angle changes every time according to the sensitivity of the sensor, and there has been a problem that the reliability of the final rotation angle is lowered.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a driver bit rotatable and engageable with a screw head, driven by a motor, and a screw tightening device. An automatic screw tightening machine having a torque detecting means capable of detecting a torque and an angle detecting means capable of detecting a rotation angle of a screw, wherein a tightening torque of the screw detected by the torque detecting means is set to a predetermined reference. Compared with the torque, the rotation angle of the screw is measured from the time when the tightening torque has reached the reference torque, and when the tightening torque has reached the preset screw tightening set torque, the rotation angle is set to the preset angle upper limit value. It is characterized by including a control unit that determines whether or not the angle falls within the angle lower limit value, and thereby determines whether screw tightening is appropriate.

A plurality of the reference torque, the screw tightening set torque, the angle upper limit value and the angle lower limit value are set in advance in accordance with the characteristics of the workpiece and the screw, and are preferably selected and used at the time of work. It is desirable to check whether the tightening torque has reached the screw tightening set torque before reaching the reference torque.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an automatic screw tightening machine used for tightening a screw on a work, a motor 2 as an example of a rotary drive source, a driver bit 3 rotatable by driving the motor 2, and a driver The control unit 10 includes a torque sensor 4, which is an example of a torque detecting unit capable of detecting a screw tightening torque by detecting an axial torque acting on the bit 3. The torque sensor 4 is disclosed in Japanese Patent Application Laid-Open No. 4-135131.
A reaction force detection type known in the art, for example, is suitable.

The motor 2 is an AC servomotor, which can keep the rotation speed constant even if the load on the output shaft fluctuates, and can detect the rotation angle by a built-in encoder (not shown). It is configured as follows. The driver bit 3 is configured to be able to engage with a driving hole formed in the head of the screw, and the vicinity of the tip is magnetized so that the screw can be held by suction.

The control unit 10 includes a main controller 11 electrically connected to the motor 2, an operation unit 12 capable of manually inputting various setting parameters, a setting parameter input from the operation unit 12, Storage unit 13 for storing a screw tightening program and the like for performing a predetermined screw tightening operation using these parameters, a display unit 14 for displaying various information, and for raising and lowering the driver bits 3 and the like. Input / output unit 15 for inputting / outputting a signal to / from an external device such as a lifting / lowering means (not shown), and an amplification unit 16 for amplifying a signal of the torque sensor 4
And an A / D converter 17 for digitally converting the torque signal amplified by the amplifier 16.

The set parameters include a reference torque serving as a reference for starting the measurement of the rotation angle, a screw tightening set torque used for comparison with the screw tightening torque (hereinafter, simply referred to as a set torque), and a normal tightening of the screw. The upper limit value and the lower limit value of the rotation angle in the case of being set can be set, and the set torque includes a temporary tightening torque generated when the screw is screwed into the work and seated, and a final tightening of the screw. Two torques (hereinafter, referred to as final tightening torque) are set. A plurality of values are set in advance for these setting parameters according to the material of the work and the screw, and the optimum value is obtained by manually inputting by the operator before the screw tightening work or automatically identifying the work and the screw. Is selected and used.

The main controller 11 includes a control unit 2
1 and the torque detected by the torque sensor 4 are obtained, and the obtained torque is compared with a reference torque, a temporary tightening torque, or a final tightening torque selectively sent from the control unit 21 as necessary. A torque processing unit 22 for returning the motor, a motor driving unit 23 for controlling the driving of the motor 2 in response to a command signal from the control unit 21, and a rotation angle from a position obtained by analyzing an encoder signal. And a position control unit 24 for sending the data to the control unit 21.

When the main controller 11 tightens a screw, as shown in FIGS. 2 to 4, 1) When a wait for a screw tightening start command signal is input, the control section 21 sends an input / output section to the input / output section. It outputs a descending command signal and outputs a motor high-speed driving command signal to the motor drive unit 23. Further, the control unit 21 resets the actual rotation angle at the time of the previous work stored in the storage unit 13. (S00
1, S002) 2) The torque processing unit 22 acquires the detected torque of the torque sensor 4. (S003) 3) The detected torque is compared with the temporary tightening torque. If the detected torque has reached the temporary tightening torque, the control unit 21 outputs a motor stop command signal to the motor drive unit 23, and jumps to 15).
(S004, S101) 4) The detected torque is compared with the reference torque, and if the reference torque is not reached, the process jumps to 2). (S005) 5) The control unit 21 acquires the actual rotation angle read by the position control unit 24, and sends this to the storage unit 13. (Storage unit 13
(S006) 6) The torque processing unit 22 acquires the detected torque of the torque sensor 4. (S007) 7) The detected torque is compared with the temporary tightening torque. If the temporary tightening torque has not been reached, jump to 5). (S00
8) 8) The control unit 21 outputs a motor low-speed drive signal to the motor drive unit 23. (S009) 9) The control unit 21 acquires the actual rotation angle read by the position control unit 24, and sends this to the storage unit 13. (Storage unit 13
(S010) 10) The torque processing unit 22 acquires the detected torque of the torque sensor 4. (S011) 11) The detected torque is compared with the final tightening torque. If the detected torque does not reach the final tightening torque, the process jumps to 9).
(S012) 12) The controller 21 outputs a motor stop command signal to the motor driver 23. (S013) 13) The actual rotation angle stored in the storage unit 13 is
And checks whether it is between the upper limit and the lower limit. If not, jump to 15). (S0
14) 14) The tightening completion display command signal and the torque display command signal are output from the control unit 21 to the display unit 14, respectively.
Jump to 6). (S015) 15) The control unit 21 outputs an abnormality display command signal to the display unit 14. (S102) 16) The controller 21 outputs a lift command signal of the lifting means to the input / output unit. (S016) 17) End. (S017) It is configured to perform the screw tightening control as follows.

In the automatic screw tightening machine 1, when a screw tightening start signal is input after the screw is sucked and held at the tip of the driver bit 3, the control unit 21 instructs the lifting / lowering means (not shown) to lower. A signal is output, and a motor high-speed drive command signal is output to the motor drive unit 23. As a result, the elevating means moves down, and the motor 2 is driven to rotate at high speed. Therefore, the screw held by the driver bit 3 starts to be screwed into the tightening point of the work.
At this time, the shaft torque acting on the driver bit corresponding to the screw tightening torque is detected by the torque sensor 4 and sent to the torque processing unit 22 via the amplifier 16 and the A / D converter 17. The torque processing unit 22 compares the detected torque with a reference torque sent from the control unit 21.

When the torque detected by the torque sensor 4 becomes substantially equal to the reference torque, the actual rotation angle of the motor 2, that is, the rotation angle of the screw is obtained by the position control unit 24, and this is stored in the storage unit 13. Go. The control unit 21 reads the temporary tightening torque and the final tightening torque stored in the storage unit 13 and sends them to the torque processing unit 22. The torque processing unit 22 performs a comparison determination between the set torque sent from the control unit 21 and the detected torque detected by the torque sensor 4. At this time, if the detected torque does not reach the final tightening torque via the temporary tightening torque within the predetermined time, the control unit 21 determines that the screw tightening is abnormal, and the display unit 14 displays the screw tightening abnormality.

When the detected torque reaches the temporary tightening torque, the control section 21 outputs a motor low-speed drive command signal to the motor drive section 23. As a result, the motor 2 is switched to the low-speed rotation drive. When the detected torque reaches the final tightening torque under the low-speed driving of the motor, the control unit 21 outputs a motor stop command signal to the motor driving unit 23, and
Stop driving.

Subsequently, the control unit 21 reads the rotation angle stored in the storage unit and the upper limit value and the lower limit value of the angle, and checks whether the rotation angle falls between the upper limit value and the lower limit value of the angle. Check whether or not. At this time, if the actual rotation angle falls between the angle upper limit value and the angle lower limit value, it means that the screw has been tightened to the correct height with the correct torque. A display command signal and a torque display command signal are output. As a result, the display section 14 displays the completion of screw tightening and the tightening torque display.

If the actual rotation angle does not fall between the angle upper limit value and the angle lower limit value, the screw is not properly seated on the work due to oblique tightening, biting of foreign matter, etc., so-called screw floating has occurred. Or the screws are over-tightened. For this reason, the control unit 21 outputs an abnormality display command signal to the display unit 14, and in response thereto, the display unit 14 displays an abnormality. After that, the driver bit and the like return to the original position as the elevating means moves upward by the ascending command signal, thereby completing a series of screw tightening operations.

In the above description, the torque sensor 4 detects the shaft torque acting on the driver bit 3 to detect the screw tightening torque. However, the torque sensor 4 is proportional to the screw tightening torque. Alternatively, the tightening torque of the screw may be detected from the load current of the motor that increases.

[0018]

According to the automatic screw tightening machine of the present invention, since the measurement start point of the actual rotation angle is set by the reference torque, the actual rotation angle is always changed from a fixed position according to the characteristics of the work and the screw. The measurement can be started, and there is an advantage that the reliability of the tightening result of the screw can be remarkably improved as compared with the related art. Looking at the relationship between the generation of the reference torque and the generation of the temporary tightening torque (or final tightening torque), the temporary tightening torque (or final tightening torque) is generated at an extremely early stage due to damage to the thread. For example, it is possible to detect an abnormality before the rotation angle is detected.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an automatic screw tightening machine according to the present invention.

FIG. 2 is a flowchart showing a first part of a control process of the automatic screw tightening machine according to the present invention.

FIG. 3 is a flowchart illustrating a middle part of a control process of the automatic screw tightening machine according to the present invention.

FIG. 4 is a flowchart showing a latter part of the control process of the automatic screw tightening machine according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Automatic screwdriver 2 Motor 3 Driver bit 4 Torque sensor 10 Control unit 11 Main controller 12 Operation part 13 Storage part 14 Display part 15 Input / output part 21 Main control part 22 Torque processing part 23 Motor drive part 24 Position control part

Claims (3)

[Claims] 1. A driver bit rotatable and engageable with a head of a screw when driven by a motor, torque detection means capable of detecting a tightening torque of the screw, and angle detection capable of detecting a rotation angle of the screw. Means and an automatic screw tightening machine having a means, wherein the tightening torque of the screw detected by the torque detecting means is compared with a preset reference torque, and the rotation angle of the screw is changed from the time when the tightening torque reaches the reference torque. Measurement, when the tightening torque reaches a preset screw tightening set torque, it is determined whether the rotation angle falls between a preset angle upper limit value and a preset angle lower limit value, and thereby, the screw An automatic screw tightening machine comprising a control unit for judging the quality of tightening. 2. The method according to claim 1, wherein the reference torque, the screw tightening set torque, the angle upper limit value and the angle lower limit value are set in advance in accordance with the characteristics of the workpiece and the screw, and are selectively used during the operation. Automatic screw tightening machine according to 1. 3. The automatic screw tightening machine according to claim 1, wherein the control unit checks whether the tightening torque has reached a screw tightening set torque before the tightening torque has reached a reference torque. .