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Power toolPower tool description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080061742, Power tool. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This application is based on and claims the benefit of priority from the prior Japanese Patent Application No.2006-243168, filed on Sep. 7, 2006; the entire contents of which are incorporated herein by reference. Technical Field [0002]The present invention relates to a power tool, and particularly to a power tool which prevents overcurrent and overdischarge of a battery pack. BACKGROUND Description of the Related Art [0003]Heretofore, there has been known a codeless power tool (hereinafter referred to as a power tool) such as a driver or a circular saw which can operate by supply of electric power from a battery pack. Large electric power is necessary to operate such the power tool. Therefore, recently, in addition to a nickel-cadmium battery and a nickel-hydride battery, a lithium-ion battery is used widely as a charging battery of the battery pack. [0004]The lithium-ion battery has an advantage that large electric power can be supplied and size/weight reduction of a tool can be realized. On the other, the lithium-ion battery must strictly cope with the ignition of the battery and the life lowering thereof due to overcharge, overcurrent and overdischarge. For example, in the lithium-ion battery, it is thought that: when the overdischarge is produced or the over current flows in a load, a battery temperature increases thereby to cause lowering of the battery life or to cause breakdown of a motor of a power tool; or when overcharge is produced, the ignition of the battery is produced. For the above problems, there has been known a battery pack which includes a braking unit that interrupts supply of the electric power to the power tool (for example, refer to Japanese Patent No. 3,222,951). Japanese Patent No. 3,222,951 discloses FET (Field-Effect Transistor) as a breaking unit. SUMMARY [0005]There is a battery pack in which plural FET's are provided as a braking unit in order to prevent the overcurrent and the overdischarge. Herein, also in case that the current larger than permissible maximum current of the FET flows in the power tool, the power supply to the power tool can be surely interrupted by the plural FET's. Further, there is also a battery pack which is not used exclusively for a specified power tool but can be used for various kinds of power tools in common. Therefore, depending on the used power tool, the number of the FET's included in the battery pack cannot make the interruption of the overcurrent possible. Namely, in case that the number of the FET's included in the battery pack is small, and the current flowing in the power tool connected to the battery pack is large, the current flows in the FET's excessively, and the FET's break down. To the contrary, in case that the number of the FET's included in the battery pack is large, and the current flowing in the power tool connected to the battery pack is small, the FET's become useless. [0006]Therefore, the invention has an object to provide a power tool which includes the necessary number of braking units which interrupts the flow of the current when the overcurrent or the overdischarge is produced. [0007]In order to solve the above problems, according to a first aspect of the invention, a power tool connected to a battery pack including a battery and a battery state monitoring unit which detects overcurrent or overdischarge of the battery and outputs a detection signal, includes: a drive part driven by electric power supplied from the battery; a first switch unit for setting arbitrarily power supply from the battery to the drive part in ON/OFF state; and a second switch unit for setting the power supply to the drive part in ON/OFF state on the basis of the detection signal. [0008]Further, according to a second aspect of the invention, the power tool includes a retaining unit which retains, in case that the first switch unit is in ON state and the power supply to the drive part is interrupted by the second switch unit, the interruption state of power supply to the drive part by the second switch unit while the first switch unit is in the ON state. [0009]According to a third aspect of the invention, the power tool includes a first signal output unit which outputs a first signal for turning on the second switch unit, and a second signal output unit which outputs a second signal for turning off the second switch unit. Herein, in case that the battery and the drive part are connected in the state where the first switch unit is turned on, the second signal is input into the second switch unit. [0010]According to a fourth aspect of the invention, in the power tool, the first signal output unit includes a resistor and a condenser, the second signal output unit includes at least a resistor and a condenser, and time constant by the resistor and the condenser is larger in the second signal output unit than that in the first signal output unit. [0011]According to a fifth aspect of the invention, the power tool further includes an informative unit which informs a state of the second switch unit of a user. [0012]According to a sixth aspect of the invention, a power tool connected to a battery pack including a battery includes a drive part driven by electric power supplied from the battery; a first switch unit for setting arbitrarily power supply from the battery to the drive part in ON/OFF state; a second switch unit for setting the power supply to the drive part in ON/OFF state on the basis of a detection signal according to a state of the battery pack; a first signal output unit which outputs a first detection signal for permitting the power supply from the battery to the drive part to the second switch unit; and a second signal output unit which outputs a second detection signal for interrupting the power supply from the battery to the drive part to the second switch unit. Herein, in case that the battery and the drive part are connected in the state where the first switch unit is turned on, the second detection signal is input to the second switch unit. [0013]According to the power tool in the first aspect of the invention, the second switch unit which sets the power supply to the drive part in ON/OFF state on the basis of the detection signal is provided not for the battery pack but for the power tool. When the power supply to the drive part is set in ON state, the current flows into the second switch unit. However, in case of a power tool in which large current flows, plural second switch units must be provided in parallel to disperse the current. According to the power tool in the first aspect of the invention, since the second switch unit is provided for the power tool, the necessary number of second switch units may be provided correspondingly to the current which its power tool requires. Hereby, it can be prevented that: Due to a small number of the second switch units, the current amount per a second switch unit becomes excessive, so that the second switch unit breaks down. Further, since it is not necessary to provide the unnecessary number of second switch units, cost can be reduced. [0014]Further, according to the power tool in the second aspect of the invention, there is provided the retaining unit which retains, in case that the power supply to the drive part is interrupted by the second switch unit in the state where the first switch unit is turned on, the interruption state of power supply to the drive part by the second switch unit while the first switch unit is in the ON state. Therefore, it is possible to prevent the power supply and the power interruption from being repeated in a short period. Namely, though the OFF state of the second switch unit solves the overcurrent state, and thereafter the ON state of the second switch unit restarts the power supply, the overcurrent state is soon produced again, so that the second switch unit is turned off again. The repeat of this ON/OFF of the second switch can be prevented by the retaining unit. Also, while the first switch unit is in the ON state, the interruption state is retained in case that the second switch unit is interrupted so as to present the power tool from being driven again when overcurrent is removed by taking the power tool away from the object. Accordingly, safety improvement can be made. [0015]According to the power tool in the third aspect of the invention, there are the first signal output unit which outputs the first signal for turning on the second switch unit, and the second signal output unit which outputs the second signal for turning off the second switch unit. Herein, in case that the battery and the drive part are connected in the state where the first switch unit is turned on, the second signal is input into the second switch unit. Therefore, once the second switch unit is turned off, while the first switch unit is turned on, it is possible to prevent the electric power from being supplied again to the drive part. [0016]According to the power tool in the fourth aspect of the invention, the first signal output unit includes the resistor and the condenser, the second signal output unit includes at least the resistor and the condenser, and time constant by the resistor and the condenser is larger in the second signal output unit than that in the first signal output unit. Therefore, once the second switch unit is turned off, while the first switch unit is turned on, it is possible to prevent the electric power from being supplied again to the drive part by simple construction. [0017]According to the power tool in the fifth aspect of the invention, there is the informative unit which informs the state of the second switch unit of the user. Therefore, the user can recognize that the second switch unit is turned off and the power tool cannot be operated. [0018]According to the power tool in the sixth aspect of the invention, there are provided the first signal output unit which outputs the first detection signal for permitting the power supply from the battery to the drive part to the second switch unit, and the second signal output unit which outputs the second detection signal for interrupting the power supply from the battery to the drive part to the second switch unit. Herein, in case that the battery and the drive part are connected in the state where the first switch unit is turned on, the second detection signal is input to the second switch unit. Therefore, once the second switch unit is turned off, while the first switch unit is turned on, it is possible to prevent the electric power from being supplied again to the drive part. BRIEF DESCRIPTION OF THE DRAWINGS Continue reading about Power tool... Full patent description for Power tool Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Power tool patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Power tool or other areas of interest. ### Previous Patent Application: Power supply device Next Patent Application: Delay time generation circuit, semiconductor device for protecting secondary batteries using delay time generation circuit, battery pack, and electronic device Industry Class: Electricity: battery or capacitor charging or discharging ### FreshPatents.com Support Thank you for viewing the Power tool patent info. 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