JP4022164B2 - Automatic screwing machine and screwing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic screw tightening machine and a screw tightening method for tightening a screw on a workpiece.
[0002]
[Prior art]
Conventionally, as one of automatic screw tightening machines, a screw tightening device disclosed in patent literature is known. The screw tightening device has a screw tightening bit that can be engaged with a drive hole formed in the head of the screw, and has a structure in which the screw tightening bit is connected to an electric driver via a bit drive shaft. When a screw is tightened on a workpiece with this screw tightening device, the electric driver is driven in a state where a screw tightening bit is engaged with a drive hole of the screw. Thereby, a rotational force is transmitted from the screw tightening bit to the screw, and the screw is tightened into a predetermined screw hole of the workpiece. In this screw tightening, whether or not the screw has been tightened normally depending on whether or not the load torque acting on the screw tightening bit reaches the preset final target tightening torque as the screw is screwed in. Has been determined. The screw tightening torque is generally obtained from a load current value of an electric driver, a signal value of a torque sensor, and the like.
[0003]
[Patent Literature]
JP-A-6-39653 [0004]
[Problems to be solved by the invention]
However, in the conventional torque management type automatic screw tightening machine, it is difficult to properly tighten the self-tapping screw with respect to a workpiece having different hardness depending on the screwing position. As an example, consider the case where a wood screw is fastened to wood. In this case, the hardness of the wood differs depending on the density of the tissue, the presence or absence of nodes, etc., and the wood screw is a kind of self-tapping screw that forms a female screw on the wood as it is screwed. When tightening wood screws to wood in this way, if a certain target tightening torque is set in advance and the screws are tightened, the screws will be excessively tightened in the soft part and the female screw will be damaged. There is a problem that a screw tightening failure frequently occurs in each part of the workpiece, for example, the target tightening torque is reached before the screw is seated and the tightening is completed early.
[0005]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an automatic screw tightening machine that can securely tighten a screw even on a workpiece having different hardness at each screwing position.
[0006]
In order to achieve the above object, the present invention provides a screwdriver bit that can be engaged with a screw, rotational drive means that can rotationally drive the screw fastener bit, and the screwing bit and the rotational drive source of the screw fastening bit. In an automatic screw tightening machine equipped with a reciprocating means for reciprocating in the axial direction, a height detecting means capable of detecting the screwing height of the screw and a load torque generated when the screw is screwed into the workpiece can be detected. Load torque from the start of screwing the screw into the workpiece to immediately before the screw is seated by the detecting unit, and accumulating these, and finally, based on the accumulated data And a control means for determining a desired target tightening torque .
[0007]
Further, the present invention relates to a screw tightening method in which a screw tightening bit is engaged with a screw, the screw tightening bit is rotated by driving a rotation driving means to transmit rotation to the screw, and the screw is screwed into the work. The load torque during the period from the start of screwing to immediately before seating of the screw is continuously acquired by the detection means, these are accumulated, and the final target tightening torque is determined based on the accumulated data , The screw is tightened until the load torque detected by the torque detecting means reaches the target tightening torque.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes an automatic screw tightening machine, which includes an electric driver 2 that is an example of a rotation driving unit, and a screw tightening bit 3 that rotates by receiving the driving of the electric driver 2. The electric driver 2 includes an AC servo motor 21, a speed reducer 22 that decelerates the rotation output of the AC servo motor 21 at a predetermined gear ratio, and transmits the output shaft 23 to the output shaft 23. And a torque sensor 24 as torque detecting means capable of detecting the load torque transmitted to the motor. Further, the screw tightening bit 3 is formed so that its tip can be engaged with a cross-shaped drive hole formed in the screw head.
[0009]
The electric driver 2 is installed on a table 41 of a ball screw mechanism 4 which is an example of a reciprocating means. Thereby, the electric screwdriver 2 and the screw tightening bit 3 are configured to be reciprocally movable in the axial direction of the screw tightening bit 3 upon receiving the operation of the ball screw mechanism 4.
[0010]
As is well known, the ball screw mechanism 4 is configured by screwing a nut member 44 to a screw shaft 43 that rotates in response to driving of an AC servo motor 42 and connecting the table 41 to the nut member 44. is there. As a result, the AC servo motor 42 is driven to rotate the screw shaft 43 so that the table 41 can reciprocate in the direction of arrow Y in the figure. The AC servo motor 41 includes a rotary encoder 45 (hereinafter simply referred to as an encoder 45) that outputs a signal corresponding to the rotation of the screw shaft 43 as an example of the height detection means. Thus, the movement amount in the axial direction of the screw tightening bit 3 can be determined with high accuracy in the control unit 51 described later.
[0011]
Reference numeral 5 denotes control means. The control means 5 processes and controls signals from the control unit 51, motor drive units 52 and 53 that drive and control the AC servomotors 21 and 42, respectively, in response to a command from the control unit 51, and the encoder 45. A height signal processing unit 54 to be sent to the unit 51, a torque signal processing unit 55 to process the signal of the torque sensor 24 and send it to the control unit 51, various programs necessary for controlling the automatic screw tightening machine, and target tightening A storage unit 56 that stores various parameters such as torque, an input unit 57 for performing input setting of various parameters, and a display unit 58 that displays various types of information such as tightening torque when tightening is completed. .
[0012]
Next, the operation of the automatic screw tightening machine 1 will be described along with an example in which a wood screw is screwed into a workpiece made of wood and tightened.
When the wood screw is tightened by the automatic screw tightening machine 1, the tip of the screw tightening bit 3 is engaged with the drive hole of the wood screw head to hold the wood screw. In the present embodiment, the screwing bit 3 is magnetized so that the wood screw can be held in this way. When the wood screw is held at the tip of the screw tightening bit 3, the control unit 51 gives a drive command to the motor drive units 52 and 53. In response to this, the AC servo motor 21 is driven to rotate the screw tightening bit 3 or the wood screw, and the AC servo motor 42 is driven to lower the table 41. As a result, the wood screw is screwed into contact with the workpiece.
[0013]
The control unit 51 acquires the signal of the encoder 45 continuously from the start of the operation of the ball screw mechanism 4 through the height signal processing unit 54, and determines the moving position of the screw tightening bit 3 obtained from that, that is, the screwing height of the wood screw. To check. Further, the control unit 51 continuously acquires the signal of the torque sensor 24 through the torque signal processing unit 55 and stores the load torque in the storage unit 56 in time series.
[0014]
When the screw is screwed up to the screwing height immediately before the wood screw is seated (hereinafter referred to as the pre-sitting position), this is detected by the control unit 51 from the signal of the encoder 45. In response to this, the control unit 51 calculates the load torque accumulated in the storage unit 56 so far and determines the final target tightening torque related to the screwing. Specifically, the maximum value in the accumulated load torque is obtained, and a torque about 1.5 to 2.5 times this value is set as the target tightening torque.
[0015]
When a self-tapping screw such as a wood screw is tightened on a workpiece having different hardness at each part such as wood, the contact area between the screw and the workpiece increases as the screwing amount of the screw increases. Therefore, the load torque acting on the screw tightening bit 3 as the screw is screwed has a shape as shown in FIG. FIG. 2 shows a load torque curve (solid line) when the screw is screwed into a hard part and a load torque curve (dotted line) when the screw is screwed into a soft part. As shown in FIG. 2, the magnitude of the load torque generated until the screw is seated varies greatly depending on the hardness of the work, and when the screw is screwed into the hard part of the work, the load torque generated until the seat is high. When the screw is tightened to the soft part of the workpiece, the load torque generated until the seating changes at a relatively low level. This is a result of different frictional resistance against screws due to the density of the wood structure. From this, the load torque up to the pre-sitting position is acquired and accumulated as described above, and by setting the target tightening torque from the maximum value among these, the workpiece at the screwed position is set for each screw tightening cycle. The target tightening torque can be set according to the properties.
[0016]
After the seating position, the control unit 51 compares the set target tightening torque with the load torque obtained from the signal from the torque sensor 24. When the load torque reaches the target tightening torque, the control unit 51 gives a stop command to the motor drive units 52 and 53 to temporarily stop the driving of the electric driver 2 and the ball screw mechanism 4, and from the signal of the encoder 45. It is confirmed whether or not the obtained screwing height has reached the screwing completion height. The control unit 51 determines whether or not the screw tightening is normally completed from the comparison results of the load torque and the screw-in height, and displays the result on the display unit 58. After determining whether the screw tightening is good or bad, the control unit 51 sends a reverse drive command to the motor drive unit 53 to drive the ball screw mechanism 4 in the reverse direction. As a result, the table 41 rises, and the electric driver 2 or the screwing bit 3 returns to the original position. It should be noted that the tightening torque accumulated in the storage unit 56 is cleared after determining whether the screw tightening is good or bad.
[0017]
As described above, the target tightening torque is determined based on the load torque in the screwing process at the screwing position. For this reason, even if it tightens the screw by torque management from the position before seating, it is possible to securely tighten the screw.
[0018]
In the embodiment of the present invention, the maximum value is selected from the tightening torques obtained up to the position immediately before the seating, and the target tightening torque is set based on the maximum value. Various statistical values such as an average value, a variance value, and a standard deviation value of the obtained tightening torque may be used. Further, any of the above statistical values of the tightening torque is obtained and accumulated every minute time Δt, and the target tightening is performed based on the maximum value, average value, variance value, standard deviation value, etc. obtained from the accumulated data. A torque may be set. In this way, for example, even when a large tightening torque is momentarily generated, this tightening torque can be prevented from being directly reflected in the target tightening torque.
[0019]
In the above description, the ball screw mechanism 4 is adopted as the reciprocating means and the rotary encoder 45 is adopted as the height detecting means. For example, as shown in Japanese Patent Laid-Open No. 2000-343347, the reciprocating means is used. An air cylinder may be employed, and a sensor that detects the moving position of the screw tightening bit 3 may be employed as the height detection means. This also provides the same effect.
[0020]
【The invention's effect】
The automatic screw tightening machine of the present invention performs screwing by the height detection method to the position before sitting, acquires load torque information during that time, determines the final target tightening torque from this load torque information, and determines the position before sitting Until the target tightening torque is reached. For this reason, even when tightening self-tapping screws such as wood screws to workpieces with different hardness at each part such as wood, an appropriate target tightening torque can be set corresponding to each of the hard part and soft part There is an advantage that the screw can be accurately tightened by preventing the occurrence of problems such as breakage of the female screw and screw floating that occur when the screw tightening is performed with a certain target tightening torque.
[Brief description of the drawings]
FIG. 1 is a block diagram of a pendant unit in a robot controller of the present invention.
FIG. 2 is an overall perspective view of a screw tightening robot system including a robot controller of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Automatic screwing machine 2 Electric driver 21 AC servo motor 22 Reduction gear 23 Output shaft 24 Torque sensor 3 Screw fastening bit 4 Ball screw mechanism 41 Table 42 AC servo motor 43 Screw shaft 44 Nut member 45 Encoder 5 Control means 51 Control part 52 Motor drive unit 53 Motor drive unit 54 Height signal processing unit 55 Torque signal processing unit 56 Storage unit 57 Input unit 58 Display unit

Claims (2)

A screw tightening driver bit engageable with a screw, rotational drive means capable of rotationally driving the screw tightening bit, and reciprocating means for reciprocating the screw tightening bit and the rotational drive source in the axial direction of the screw tightening bit. In the automatic screw tightening machine provided,
A height detection means capable of detecting the screwing height of the screw;
A torque detecting means capable of detecting a load torque generated when the screw is screwed into the workpiece;
The detection means continuously obtains the load torque from the start of screwing into the workpiece to immediately before the screw is seated, accumulates them, and determines the final target tightening torque based on the accumulated data. An automatic screw tightening machine comprising a control means for determining . In a screw tightening method in which a screw tightening bit is engaged with a screw, this screw tightening bit is rotated by driving a rotation driving means to transmit rotation to the screw, and a screw is screwed into a workpiece.
The detection means continuously obtains the load torque from the start of screwing into the workpiece to immediately before the screw is seated, accumulates them, and determines the final target tightening torque based on the accumulated data. It determined, screwing method characterized by tightening the screw until the load torque detected by said torque detecting means reaches a torque with the target tightening.

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