Tool driving or impacting – Automatic control of power operated means
Reexamination Certificate
2001-11-16
2003-07-29
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Automatic control of power operated means
C173S176000, C318S281000, C073S862230
Reexamination Certificate
active
06598684
ABSTRACT:
This application claims priority to Japanese patent application serial numbers 2000-350438 and 2000-356335, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power tools and more particularly, relates to power tools, such as impact wrenches and impact screwdrivers, having a drive source that is controlled by a pre-set operating program (operating mode).
2. Description of the Related Art
Known impact power tools have a drive source that is controlled by a pre-set or predetermined operating program (operating mode) in order to facilitate the tightening operation and to provide uniform work quality. For example, known impact wrenches and impact screwdrivers can be operated according to such operating programs.
Further, known impact tightening tools generally include a drive sou such as an electric motor or a pneumatic motor, that rotates a hammer in order to strike an anvil and generate an elevated torque. This elevated torque may be utilized to securely tighten a fastener, such as a screw, a nut or a bolt. Generally speaking the hammer is allowed to slip and freely rotate with respect to the anvil when a predetermined amount of torque is exerted.
Thus, the fastener can be driven with a relatively light load until a head potion of the fastener contacts the workpiece (i.e., before the fastener becomes seated against workpiece), because the hammer will continuously rotate the anvil in order to continuously tighten the fastener using a relatively low torque. However, as the fastener is driven further and the hammer exerts more than a predetermined amount of force against anvil, because the head of the fastener has contacted the workpiece (i.e., after the fastener has become seated against the workpiece), the hammer will begin to slip and rotate freely. Therefore, the hammer will impact the anvil after rotating by a predetermined angle. By the repetition of the slipping and impacting action, the anvil will rotate a small amount each time the hammer impacts the anvil and the fastener can be tightened to an appropriate torque.
In this type of impact tightening tool, the tightening torque may be determined based upon the number of times that hammer impacts or strikes the anvil. Therefore, if the number of impacts between the hammer and anvil is too high the tightening torque applied to the fastener will be too great and may possibly damage the fastener. In order to prevent and anvil, and automatically stops the drive source of the hammer when a pre-determined number of impacts have been detected (i.e., the tightening torque is determined by the number of impacts). Thus, a sensor is utilized to detect impacts between the hammer and anvil and a microprocessor counts the number of impacts. When the number of counted impacts reaches a preset number, the drive source is automatically stopped to prevent the fastener from being overtightened.
In the alternatives the drive source can be automatically stopped after a predetermined time interval or period has elapsed after the detection of the first impact of the hammer striking the anvil. Therefore, application of excessive torque is avoided and damage to the fastener can be prevented.
SUMMARY OF THE INVENTION
However, if the fastener has a burr in its threads, it may be necessary to utilize a tightening force that exceeds the predetermined amount of torque in order for the fastener to reach the seated position. As a result, if the known tightening techniques are utilized, the drive source may be prematurely stopped before, the fastener has reached the seated portion. Consequently, if a burr is present, insufficient tightening torque may be applied to the fastener and/or the drive source may be stopped before the fastener reaches the seated position. Thus, known tightening techniques may not adequately tighten a fastener having a burr or other imperfection within the fastener threads.
It is, accordingly, one object of the present teachings to provide improved power tools that can adequately and appropriately tighten fasteners having a burr or other imperfection according to a desired tightening torque.
For example, in one aspect of the present teachings, impact tightening tools are taught that are capable of tightening fasteners using a sufficient or adequate tightening torque, even if a burr is present on the fastener. Therefore, even if the hammer impacts or strikes the anvil before the fastener has reached the seated position, the power tool can adequately compensate for this additional torque that is applied to the fastener without applied an excessive torque to the fastener.
Thus, in one embodiment of the present teachings, impact tightening tools may include a hammer that is allowed to slip and rotate freely with respect to an anvil when a force exceeding a predetermined magnitude is applied between the hammer and anvil. Preferably, the hammer may impact or strike the anvil after the hammer has slipped or rotated by a predetermined angle. The impact then causes the anvil to rotate by a small amount and tighten the fastener. Such impact tightening tools may also include a drive source, such as an electric or pneumatic motor, and a control device, such as a microprocessor, for controlling the operation of the drive source. The control device preferably determines whether the hammer has begun to impact the anvil either before or after the fastener has reached the seated position. If the control device determines that the impacts have began after the fastener has reached the seated position, the control device will automatically stop the drive source when the pre-determined torque has been applied.
On the other hand, if the control device determines that one or more impacts (i.e., the hammer striking the anvil) have occurred before tho fastener is seated against the workpiece, the control device will ignore such impacts for the purpose of determining the amount of torque that has been applied to the fastener. Instead, the control device will begin to count the number of impacts (i.e., the hammer striking the anvil) after the control device determines that the fastener has reached the seated position against tho workpiece. Thereafter, the fastener can be tightened with the desired (or predetermined) torque, even if a burr or other imperfection is present on the fastener.
In the alternative, the control device can also determine or identify the first impact of the hammer striking the anvil after the fastener has reached the seated position and then start a clock or timer. If the control device determines that an impact (i.e., the hammer striking the anvil) occurred before the fastener is seated against the workpiece, the control device will not start the clock or timer. Thereafter, the control device can automatically stop the motor after a predetermined amount (or period) of time has elapsed in this mode, the predetermined amount of time corresponds to a predetermined amount of torque and the predetermined amount of torque can be set by an operator (or other individual) before a particular tightening operation is begun. Thus, the control device may be programmed, such that a desired amount of torque is centered into the control device before the tightening operation. The control device then converts the desired (or predetermined) amount of torque into an amount or period of time that the drive source (e.g., a motor) will continue to drive or rotate the hammer from the time that the first impact of the hammer striking the anvil has occurred after the fastener has reached the seated position.
In another aspect of the present teachings, when an impact between the hammer and anvil is detected, the control device preferably determines whether the impact has occurred before or after the fastener has reached the seated position. The drive source will be stopped at an appropriate timing when the first impact is identified that occurred after the fastener his reached the seated position. On the other hand, if the control device determines that the hammer ha
Makita Corporation
Orrick Herrington & Sutcliffe LLP
Smith Scott A.
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