Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2001-09-14
2003-04-15
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06546815
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of controlling tools designed to provided a torque to a screw member such as a bolt and a nut, including hand-held powered wrenches, such as an impact wrench and an impulse wrench, and hand-held nut runners, when tightening or loosening the bolt and nut by use of the tool.
BACKGROUND ART
In general, when a screw tightening work for tightening a number of screw members such as bolts and nuts is performed in an automobile factory and the like, there is a need for tightening all screw members with a uniform screw torque. To meet this need, a hand-held powered wrench was developed, as described by Japanese Patent Publication No. Hei 6-16990, which is structured so that a rotary member that rotates with a driving shaft is driven to rotate around a driven shaft so that a torque of the rotary member can be transmitted to the driven shaft through a hammer to tighten a screw member. Further, a screw tightening angle (a screwing angle) of the screw member is detected by a rotary detecting member to rotate together with the driving shaft and a detecting sensor disposed at a non-revolving part of a wrench body.
In this type of hand-held powered wrench, in order to detect the screw tightening angle of the screw member via the rotary detecting member and the detecting sensor, a number of pulses R
1
generated when the rotary member rebounds in the opposite rotation direction after colliding with the driven shaft through the hammer and a number of pulses F
1
generated during the time during which the rotary member runs freely in the normal rotation direction after the rebound until it collides with the driven shaft again to apply a hammering force to it are detected. From these numbers of pulses R
1
and F, a number of pulses&thgr;
1
equivalent to the screwing angle at a hammering is determined. For an impact wrench wherein the rotary member provides one hammering per rotation of the same, the number of pulses&thgr;
1
is calculated from the following Equation:
&thgr;
1
=F
1
−(the number of pulses equivalent to 360°)−
R
1
(Eq. 1).
Then, the number of pulses equivalent to the screwing angle is calculated and converted into an angle every time the hammering is provided. When the cumulative total of angles reaches a predetermined screw tightening angle, the driving shaft is stopped.
On the other hand, in order to reduce a hammering sound that is one of the problems of the impact wrench of the type mentioned above, an impulse wrench was developed as a type of hand-held powered wrench, which is structured so that the torque of the rotary member is transmitted to the driven shaft by means of oil.
However, in the method for controlling the screw tightening of the hand-held powered wrench of the conventional type mentioned above, since the number of pulses at the rebound and the number of pulses at the normal rotation are detected and then the number of pulses&thgr;
1
equivalent to the screwing angle is determined from Equation (1) by using the detected number of pulses, if a wobbling, as will be mentioned later, is caused by a worker operating the impact wrench in the course of tightening the screw member seated on a bearing surface to a predetermined screw tightening angle, then the wobbling angle is detected and considered as a large error in screw tightening angle by the detecting sensor arranged at the wrench body side. Because of this, the method of controlling the screw tightening by using the hand-held powered wrench did not come into wide use.
It should be noted that the term “wobbling” referred to in the specification is intended to cover the following three different types of movements:
1. The movement of the thread center of the screw member not moving or moving linearly and the powered wrench turning with respect to the thread center;
2. The movement of the screw member turning around a point different from the thread center of the screw member (e.g. a fastening bolt of a car wheel), and as such, causing the powered wrench to infectiously move in parallel; and
3. The movement of the screw member turning around a point different from the thread center of the screw member and the powered wrench turning with respect to the thread center.
However, the movement of the thread center of the screw member moving linearly, and as such, causing the powered wrench to infectiously move in parallel is not included in the definition of the wobbling in the specification.
It should also be noted that no adequate ways of controlling the loosening, as well as the tightening have been proposed. This can cause following problems. For example, when a nut is loosened excessively in the loosening direction, the nut can fall down to the floor or ground from the bolt and allowing grit in the nut, so that when the nut is tightened at a later time, it cannot be tightened properly. In addition, when the nut is not loosened enough with a power tool to be loosened further by hand, some tool must again be used to loosen the nut, thus presenting poor workability. Further, when the nut is loosened excessively at an overhead location, the nut can fall from the bolt and put a person under that location in danger.
The inventors have gained knowledge in that since the time for the impact to be actually provided is very short (in the order of a millisecond), an angle of the wobbling that can be produced within such a very short time cannot help but be very limited or minute. As a result, and they have derived from this knowledge the method of the present invention for enabling a screwing angle to be measured with necessary and sufficient accuracy even when some wobbling is caused. Also, through the use of this method, the inventors have devised a method on the screw tightening control and on the screw loosening control.
Further, the inventors propose herein the technique of examining the degree of error included in measurement results caused by the wobbling, to evaluate the screw tightening on the basis of the degree of the wobbling.
SUMMARY OF THE INVENTION
The present invention provides a method for reading a screwing angle of a hand-held powered wrench comprising a rotary member which, after running freely, starts decelerating when it provides a hammering force or torque to a driven shaft side and, after the end of deceleration, rebounds and runs freely again, wherein a rotation angle formed throughout deceleration of the rotary member in a tightening direction from the start of deceleration to the end of deceleration is accumulated, so that when a sum total of the accumulated rotation angle reaches a preset angle, a controlled stoppage of tightening can be provided.
The present invention provides a method for reading a screwing angle of a hand-held powered wrench comprising a rotary member which, after running freely, starts decelerating when it provides a hammering force or torque to a driven shaft side and, after the end of deceleration, runs freely again, wherein an angle obtained by subtracting a certain angle from a rotation angle formed throughout deceleration of the rotary member in the tightening direction from the start of deceleration to the end of deceleration is accumulated, so that when a sum total of the accumulated angle reaches a preset angle, a controlled stoppage of tightening can be provided.
Also, the present invention provides a method for controlling a hand-held powered wrench comprising a rotary member which, after running freely, starts decelerating when it provides a hammering force or torque to a driven shaft side and, after the end of deceleration, rebounds and runs freely again, wherein there is provided detecting means to detect variation in rotation velocity or rotational frequency of the rotary member and a rotation angle of the same, wherein on the basis of the variation in the rotation velocity and the rotation angle detected by the detecting means, an angle obtained by subtracting a cumulative total of the rotation angle in the rebounding direction from a cumulative total of the rotation angle in
Nagare Yoshihiko
Shibata Ryoichi
Yamada Masakazu
Kuken Co., Ltd.
Noori Max
Wenderoth , Lind & Ponack, L.L.P.
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