JPH09108963A - Offset type nut runner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the conspicuous phenomenon of peak torque to perform accurate fastening, by interposing the odd number of intermediate gears between prime driving and driven gears. SOLUTION: The odd number of intermediate gears 12 is arranged between prime driving and driven gears 11 and 13. A servomotor 2 is driven to rotate the gears 11 and 13 in a same direction via the intermediate gear 12. This reverses the direction of fastening reaction force to the rotating direction of the gear 11 to cancel both force with each other. Consequently, at final engaging time, the momentary loading of a moment load to the nut runner main body can be eliminated to prevent the jumping up of a torque curve (conspicuous phenomenon) when an engaging member is fastened, thereby performing accurate fastenning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an offset type nut runner in which an output shaft (driving shaft) of a drive unit and a tightening shaft (driven shaft) are arranged in an offset manner.

[0002]

2. Description of the Related Art In various assembly processes including the automobile industry, automatic screw tightening machines (nutrunners) are often used for the purpose of improving productivity when screwing two members together and reducing production cost by labor saving. ing. This nut runner automatically controls the tightening member such as a screw with a predetermined tightening force by feedback controlling the servo motor based on the detection signals from various sensors, and most of them detect the tightening torque with a torque sensor sequentially. The tightening axial force is managed based on this detected value.

As the nut runner, as shown in FIG. 3 (a), an output shaft (25) of a drive section (24) comprising a servo motor (22) and a speed reducer (23) and a socket (27) at the tip. It is common to arrange the tightening shaft (26) having the same axis coaxially. However, in the case of this coaxial type, when the nut runners are arranged side by side in the fastening work at two or more places, the distance between the fastening places is the drive part (24). Must be larger than the diameter (L1), and may not be placed in a space smaller than that. Therefore, under such a condition, as shown in FIG. 3B, the output shaft (25) and the tightening shaft (26) are offset (eccentric arrangement).
The offset type nutrunner is used. In the case of such an offset type, the tightening shaft (26) can be arranged closer to each other as compared with the coaxial type described above, and tightening can be performed even at tightening points having a narrow pitch (L2) of two or more points.

[0004]

The torque curve (torque-time t curve) of the coaxial type nutrunner shown in FIG. 3 (a) has the shape shown in FIG. 4 (a). In the case of the coaxial type as described above, the torque curve draws a gentle slope even at the final stage of tightening (immediately before reaching the set torque T), so that the peak torque can be accurately determined, and therefore, precise tightening can be performed. Become.

On the other hand, in the torque-time curve of the offset type shown in FIG. 3 (b), as shown in FIG. 4 (b), a sharp protrusion (P) is generated in the torque curve at the end of tightening (protrusion). phenomenon). Therefore, it becomes difficult to determine the peak torque, and there is a problem that the tightening accuracy is reduced.

Incidentally, these tendencies similarly occur not only when the torque-time curve is taken but also when the torque-rotation angle θ curve is taken. Therefore, it is an object of the present invention to eliminate the phenomenon of peak torque protrusion in an offset type nut runner and enable more accurate tightening.

[0007]

Although the exact cause of the above-mentioned protrusion phenomenon is not always clear, it is presumed as follows. In the coaxial type, as shown in FIG. 5A, the rotation direction of the output shaft (25) of the drive unit and the direction of the reaction force from the fastening member are opposite to each other. In contrast,
In the offset type, as shown in Fig. 5 (b), the driving gear (28) attached to the output shaft (25) and the tightening shaft (27).
Because the torque is transmitted by meshing with the driven gear (29) attached to the, the rotation direction of the output shaft (25) and the direction of the tightening reaction force are the same. From such a difference, it is considered that there is a difference in the appearance of the peak torque of both. That is, in the offset type, the tightening reaction force and the rotational force of the output shaft (25) are momentarily weighted when the screw is completely tightened, so the nut runner body receives a moment load in the same direction as these, and as a result, It is estimated that the peak torque jumps (P).

From the above consideration, it is considered that the peak torque protrusion phenomenon can be prevented by reversing the rotation direction of the output shaft and the direction of the tightening reaction force as in the coaxial type. In order to realize this in the offset type nut runner, the driving gear attached to the output shaft (driving shaft) of the drive unit and the driven gear attached to the tightening shaft (driven shaft) may be rotated in the same direction.

Therefore, according to the present invention, in the nut runner for transmitting torque between the driving shaft and the driven shaft, which are arranged offset, by the driving gear and the driven gear, the odd number of intermediate gears are provided between the two gears. It was decided to interpose a gear.

As a result, the driving gear and the driven gear rotate in the same direction, so that it is possible to avoid the peak torque jump by reversing the rotation direction of the driving gear and the direction of the tightening reaction force. As a result of actual experiments, it was confirmed that no protrusion phenomenon occurred even at the final stage of tightening, and the torque curve had a shape similar to that of the coaxial type.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A specific structure of an offset type nut runner according to the present invention will be described below with reference to FIGS. 1 and 2. As shown in Figure 1, this nut runner (1)
Is a drive unit (4) including a servo motor (2) and a speed reducer (3), a gear device (5) for ensuring a predetermined offset amount, a tightening shaft (6) and a socket head (7). The tightening part (8) is a main component.

In the gear device (5), three gears (11), (12) and (13), which are meshed with each other, a driving gear (11), an intermediate gear (12) and a driven gear (13) are parallel to each other in the rotating shaft. And stored rotatably. Of these gears, the drive gear (11) located on the drive section (4) side is the drive section (4) that serves as the drive shaft.
The driven gear (13) attached to the output shaft (14) and located on the tightening portion (8) side is attached to the tightening shaft (6) serving as a driven shaft. The gear device (5) offsets the output shaft (14) and the tightening shaft (6) to obtain a desired offset amount (L). The offset amount (L) can be changed to an arbitrary value by changing the diameter of each gear. Further, in the drawing, the pitch circles of the gears (11), (12) and (13) have the same diameter, but they may have different diameters.

The socket head (7) is fitted with a socket (not shown) for tightening fastening members (screws, bolts, nuts, etc.). The socket head (7) and the connecting portion of the socket have a detachable structure so that the socket head (7) can be replaced with a socket matching the head size of the fastening member to be used.

A torque sensor (15) is mounted on the outer peripheral portion of the tightening shaft (6) as shown by a chain double-dashed line. The detected value of the torque sensor (15) is transmitted to the driver that drives the servo motor (2) of the drive unit (4), and the feedback control of the servo motor (2) is thereby performed.

In the above structure, the servo motor (2)
When is driven, the driving gear (11) and the driven gear (13) rotate in the same direction as shown in FIG. As a result, the tightening reaction force is opposite to the rotation direction of the driving gear (11),
Both forces cancel each other out. Therefore, the moment load is not momentarily applied to the nut runner main body at the final stage of fastening, and even when the fastening member is closed, the torque curve can be prevented from jumping up (protrusion phenomenon) and high-precision fastening can be performed. Becomes

In FIG. 1, only one intermediate gear (12) is arranged, but the number is arbitrary as long as it is an odd number. If there is an odd number of intermediate gears (12), drive gear (11)
This is because it is possible to rotate the driven gear (13) and the driven gear (13) in the same direction.

[0017]

As described above, according to the present invention, since the rotation direction of the driving gear and the tightening reaction force are made opposite to each other to cancel each other, the torque curve does not remarkably jump up even at the end of tightening. The phenomenon can be reliably avoided. Therefore, it is possible to provide an offset type nut runner having high tightening accuracy.

Further, since the intermediate gear is interposed, a large offset amount can be obtained, and the tightening work can be performed even when the working space is limited. Conventional 2
In the gear type (see FIG. 3 (b)), when increasing the offset amount, each gear has to have a large diameter, which has the drawback that the width dimension of the nut runner increases, but the nut runner of the present invention has the same offset. Since the amount can be realized by a gear having a smaller diameter, an increase in width dimension can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of an offset type nut runner according to the present invention.

FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG.

3A is a sectional view of a coaxial type nut runner, and FIG. 3B is a sectional view of a conventional offset type nut runner.

FIG. 4 (a) is a torque curve of a coaxial type nut runner, and FIG. 4 (b) is a torque curve of a conventional offset type nut runner.

5A is a sectional view taken along line BB of FIG. 3A,
FIG. 3B is a sectional view taken along the line CC of FIG.

[Explanation of symbols]

 1 offset type nutrunner 2 servo motor 3 speed reducer 4 drive unit 5 gear device 6 tightening shaft 7 socket head 8 tightening unit 11 driving gear 12 intermediate gear 13 driven gear 14 output shaft 15 torque sensor

Claims (1)

[Claims] 1. A nut runner for transmitting torque between a driving shaft and a driven shaft, which are arranged offset, by a driving gear and a driven gear, wherein an odd number of intermediate gears are interposed between the two gears. Offset type nutrunner characterized by