This application claims priority to Japanese patent application serial numbers 2000-350438 and 2000-356335, the contents of which are hereby incorporated by reference.
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.
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 has impacted or struck the anvil before the fastener has reached the seated position, e.g., due to a burr, the detected impact will not be utilized to determine when to stop the hammer drive source. Therefore, the fastener can be tightened to the desired tightening torque.
Optionally, a sensor may be provided to detect the impacts between the hammer and anvil. The sensor may communicate detected impacts to the control device and the control device may preferably utilize information concerning the detected impacts in order to control the operation of the drive source. If an oil pulse unit is utilize to generate elevated torque, instead of a hammer and anvil, the sensor may sense some characteristic (e.g., emitted sound) of the oil pulse unit that indicates the oil pulse unit is generating oil pulses. Again, this information may then be communicated to the control device and utilized
The type of sensor that can be utilized with the present teachings is not particularly limited and may be any type of sensor capable of detecting impacts between the hammer and anvil. For example, the present teachings contemplate the use of accelerometers, which detect the acceleration of the hammer, proximity sensors, which detect the position of the hammer, and/or sound sensors (e.g., condenser microphones, piezoelectric materials, etc.), which detect impact sounds generated by the hammer striking the anvil (or oil pulses generated by an oil pulse unit).
In another embodiment of the present teachings, methods are taught for programming the control device in order to determine whether a detected impact occurred before or after the fastener has reached the seated position. For example, one representative method determines whether an impact has occurred within a predetermined period of time after the tightening operation has started. The predetermined period of time may be, e.g., an average time between the art of the tightening operation and the fastener reaching the seated position. If the impact is detected before the predetermined period of time has expired, of control device determines that the fastener has not yet reached the seated position.
In another representative method, a determination is made by utilizing the time interval between impacts. For example, the time interval between impacts generally becomes shorter after the fastener reaches the seated position. Naturally, if the time intervals between impacts increase or do not become closer in time, it is likely that the fastener has not yet reached the seated position and an elevated torque is being generated to rotate a fastener having a burr or other imperfection.
Thus, in another representative method, the determination is made by utilizing or monitoring a change in the time intervals between impacts. For example, the intervals between impacts after the fastener has reached the seated position typically decrease linearly. On the other hand, if the intervals between impacts increase, the control device will determine that the previous impact(s) occurred before the fastener reached the seated position.
In another embodiment of the present teachings, the control device may start a timer each time that the sensor detects an impact between the hammer and anvil. When the timer reaches a preset or predetermined time, the control device will automatically stop the drive source. However, the timer is preferably re-set to zero if the control device determines that one or more impact(s) between the hammer and anvil occurred before the fastener has reached the seated position. Thus, the control device can effectively ignore impacts that occur before the fastener has reached the seated position, because such impacts may have been caused by the fastener having a burr or other imperfection. Preferably, the drive source may be stopped after driving the fastener for a predetermined period of time after the control device has identified the first occurrence of an impact between the hammer and anvil after the fastener has reached the seated position. Therefore, the fastener can be adequately and appropriately tightened.
In another embodiment of the present teachings, the control device is preferably programmed to count the number of detected impacts of the hammer striking the anvil. For example, when the number of detected impacts reaches a predetermined or preset number, the drive source is automatically stopped. Generally speaking, tho amount of torque increases as the number of impacts increases. Thus, a desired amount of tightening torque can be selected before the tightening operation begins by pre-selecting the number of impacts between the hammer and the anvil before stopping the drive source (e.g., motor).
On the other hand, when the control device determines that the hammer has begun to impact or strike the anvil before the fastener has reached the seated position, the impact counter is reset to zero. Thus, the drive source can be stopped after the hammer impacts or strikes the anvil a preset or predetermined number of times after the fastener has actually reached the seated position. Therefore, the fastener can be adequately and appropriately tightened
In another embodiment of the present teaching, power tools may have a drive source that is controlled according to a programmed operating mode. In one representative example, power tools may include a setting device that sets the operating mode. The setting device may be, e.g., one or more dials, which can be manually operated, or a remote control device. A selector switch may be provided to switch the operating mode, which was set by the setting device, to a predetermined operating mode. Further, the control device (e.g., a microprocessor) preferably can control the drive source according to the operating mode. For example, if the selector switch is set to a predetermined operating mode, the control device will drive the drive source according to the selected operating mode. On the other hand, if the selector switch is not set to a predetermined operating mode, the drive source will be driven according the operating mode that was set using the setting device.
Thus, such power tools may preferably include a selector switch, which switches the operating mode to a predetermined operating mode, and a setting device or setting means, which sets the operating mode. Further, the selector switch can be operated according to a predetermined condition or program in order to switch the operation of the power tool to one of the predetermined operating modes. Therefore, the power tools can be switched in a certain operating mode (e.g., manual mode) without having to change the operating mode set in the electric power tool (e.g., auto-stop mode). Consequently, if this technique is utilized in an impact tightening tool, the power tool can be temporarily switched to a manual mode by operating the selector switch if the drive source may possibly be stopped before the fastener has reached the seated position due to a burr or other imperfection of the fastener. Thereafter, the tightening operation can be continued in manual mode until the fastener reaches the seated position.
In another aspect of the present teachings, the control device preferably automatically returns to the operating mode set by the setting device as soon as the control device has finished driving the drive source in the operating mode selected by the selector switch. Thus, as soon as work in one selected operating mode is completed, the control device automatically returns to the operating mode set by the setting device. Therefore, continuation of work in the temporarily selected operating mode can be prevented.
In another embodiment of the present teachings, the selector switch may be a up switch that starts or energizes the drive source. Preferably, the control device switches to one operating mode when the start up switch is switched from the ON position to the OFF position in a predetermined condition, mode or program and then switched back again to the ON position within a predetermined time interval. If the start up switch is switched a the OFF position from the ON position, and if it is not then switched back to the ON position within the predetermined time interval, the operating mode set by the setting device will be utilized by the control device. Because the start up switch is used as the selector switch, an additional switch is not required to implement this function.
In addition, when the start up switch is switched to the OFF position and then switched back to the ON position within the predetermined time interval, the control device is switched to an operating mode stored in the control device (or in a memory that is in communication with the control device). If the start up switch is not switched back to the ON position within the predetermined time interval, the control device reverts to the operating mode set by the setting device. Consequently, if the start up switch is switched to the OFF position after the drive source has been driven in the pre-stored operating mode or program, tho control device reverts to the operating mode or program selected by the setting device. For example if the start up switch is not switched back to the ON position within a predetermined time interval, the control device will return to the operating mode or program selected by the setting device.
Preferably, the operating mode set by the setting device cannot be changed during normal operation. If the power tool is configured in this manner, accidental changes to the he mounted or installed in a location that can be accessed only after removing the battery pack. In the alternative, the operating mode can be set only by using special equipment (e.g., a radio control device or a remote control).
These aspects and features may be utilized singularly or in combination in order to make improved tightening tools, including but not limited to impact wrenches and impact screwdrivers. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above-described aspects and feature.