Patent Publication Number: US-2004051388-A1

Title: Power tool with replaceable power supply cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001] This application claims priority of Taiwanese application no. 091213672, filed on Aug. 30, 2002.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The invention relates to a power tool with a replaceable power supply cartridge, the power tool being operable in either a cordless mode using a self-contained rechargeable battery or a corded mode using a conventional AC or DC power source.  
       [0004] 2. Description of the Related Art  
       [0005] Power tools that function in a cordless mode, i.e., powered using a rechargeable battery cartridge, are well known. Cordless power tools have the advantage of not being constrained by electrical cords, which makes them easy to carry and safe to use. However, the lack of a connection to a power source is also the main disadvantage of cordless power tools. Due to the limited storage capacity of batteries, frequent recharging is needed.  
       [0006] To ensure uninterrupted use of the power tool, a corded counterpart can be employed. The main drawback of corded power tools, however, is that the range of movement is limited by the cord length. Further, corded power tools are useless in areas where a conventional AC power source is not available. As a result, both corded and cordless power tools have advantages and disadvantages that cannot be compensated in both aspects.  
       [0007] Dual-mode power tools are also available in the market and can be operated in either the cordless battery mode or the corded AC mode as needed. The dual-mode power tool includes a switch to select between the AC and DC modes. With the availability of such power tools, users can avail of the conveniences of both corded and cordless power tools.  
       [0008] However, the prior art design of a dual-mode power tool is constrained by the cost and complexity of circuit design. Particularly, AC/DC motors used in the prior art design are expensive in comparison with DC- or AC-only motors. Further, due to its inherent duality, the circuit design is relatively complicated.  
       SUMMARY OF THE INVENTION  
       [0009] Therefore, the object of the present invention is to provide a power tool with a replaceable power supply cartridge that is convenient to use and that can be fabricated at a relatively low cost.  
       [0010] According to the present invention, a power tool comprises:  
       [0011] a tool housing provided with a set of first electrical contacts;  
       [0012] an electric drive motor mounted in the tool housing and coupled electrically to the first electrical contacts;  
       [0013] a driver unit mounted in the tool housing and coupled to and driven rotatably by the electric drive motor;  
       [0014] a power supply cartridge including a casing connected removably to the tool housing, a set of second electrical contacts to connect electrically with the first electrical contacts when the casing is connected to the tool housing, and a power converter disposed in the casing and coupled electrically to the second electrical contacts; and  
       [0015] a power supply cable having a first end connected to the power supply cartridge to connect electrically with the power converter, and a second end adapted to be connected to an external power source. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016] Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which:  
     [0017]FIG. 1 is a perspective view of the first preferred embodiment of a power tool with a replaceable power supply cartridge according to the present invention;  
     [0018]FIG. 2 is a schematic circuit block diagram of the first preferred embodiment;  
     [0019]FIG. 3 is a schematic circuit block diagram of the second preferred embodiment of a power tool according to the present invention;  
     [0020]FIG. 4 is a schematic circuit block diagram of the third preferred embodiment of a power tool according to the present invention;  
     [0021]FIG. 5 is a schematic circuit block diagram of the fourth preferred embodiment of a power tool according to the present invention; and  
     [0022]FIG. 6 is a perspective view of a replaceable power supply cartridge of the fifth preferred embodiment of a power tool according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0023] Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure.  
     [0024] Referring to FIG. 1, the first preferred embodiment of a power tool  1  according to the present invention is shown to comprise a tool housing  2 , an electric drive motor  3 , a driver unit  4 , a power supply cartridge  5 , and a power supply cable  6 .  
     [0025] The tool housing  2  has a bottom portion  21 , in the form of a handle. The bottom portion  21  defines therein a cavity  22 , which has an open end  220  that faces downwardly. Located within the cavity is a set of first electrical contacts  8 . Adjacent to the open end  220 , the bottom portion  21  is formed with an outwardly extending skirt  211 . The bottom side of the skirt  211  is provided with fastening grooves  212 .  
     [0026] The electric drive motor  3  is mounted in the tool housing  2  and is coupled electrically to the first electrical contacts  8 . In this embodiment, the electric drive motor  3  is a direct current (DC) motor.  
     [0027] The driver unit  4  is mounted in the tool housing  2  and is coupled to and is driven by the electric drive motor  3 . In this embodiment, the driver unit  4  includes a trigger mechanism  41  for controlling actuation of the electric drive motor  3  in a conventional manner, and a driver element  42 , in the form of a conventional chuck for screw driving, driven by the electric drive motor  3  in a known manner.  
     [0028] With further reference to FIG. 2, the power supply cartridge  5  includes a casing  511  to be connected removably to the tool housing  2 , a set of second electrical contacts  52 , a power converter  53 , a motor control circuit  55 , and a motor protection circuit  56 . The casing  511  includes a base portion  513 , and an insert portion  512  that protrudes integrally and upwardly-from the base portion  513  and that is inserted removably into the insert cavity  22  through the open end  220 . The base portion  513  is provided with a pair of hook fasteners  57  that are associated operably with the fastening grooves  212  in the tool housing  2 . The fastening grooves  212  and the hook fasteners  57  constitute a releasable fastener unit for-fastening releasably the casing  511  on the tool housing  2 .  
     [0029] The second electrical contacts  52  are mounted on the insert portion  512  and are configured to connect electrically with the first electrical contacts  8  when the casing  511  is connected to the tool housing  2 . In this embodiment, the power converter  53 , the motor control circuit  55 , and the motor protection circuit  56  are connected in series and are disposed in the casing  511 . The power converter  53  is coupled electrically to the second electrical contacts  52  through the motor control circuit  55  and the motor protection circuit  56 . In the case that the motor control circuit  55  and the motor protection circuit  56  are disposed in the tool housing  2  instead of the casing  511 , the power converter  53  can be connected directly to the second electrical contacts  52 . The power converter  53  of this embodiment is a DC-to-DC power converter. Since the structures of the motor control circuit  55  and the motor protection circuit  56  are known to those skilled in the art, a detailed description of the same will be dispensed with herein for the sake of brevity. In this embodiment, a socket  54  is mounted on the base portion  513  and is connected electrically to the power converter  53 .  
     [0030] Therefore, when the casing  511  is connected to the tool housing  2 , the second electrical contacts  52  will establish electrical connection with the first electrical contacts  8 , thereby permitting electrical coupling between the power converter  53  and the electric drive motor  3 .  
     [0031] In this embodiment, the power supply cable  6  has a first end provided with a connector  62  to connect removably with the socket  54  of the power supply cartridge  5 , thereby connecting the power supply cable  6  to the power converter  53 . The power supply cable  6  further has a second end provided with a plug  61  to connect removably with an external power source  7 , in the form of a DC power source, such as a lithium battery. When the power supply cable  6  connects the power supply cartridge  5  to the external power source  7 , electric power for operating the electric drive motor  5  can be supplied accordingly.  
     [0032]FIG. 3 illustrates the second preferred embodiment of a power tool according to the present invention. Unlike the previous embodiment, the power converter  53 ′ is an AC-to-DC power converter, and the external power source  7 ′ is a commercial AC power source.  
     [0033]FIG. 4 illustrates the third preferred embodiment of a power tool according to the present invention. When compared to the first preferred embodiment, the power supply cartridge further includes a rechargeable power supply device  58  coupled electrically to the power converter  53  and to the second electrical contacts (not shown) through the motor control circuit  55  and the motor protection circuit  56 . In the case that the motor control circuit  55  and the motor protection circuit  56  are disposed in the tool housing instead of the power supply cartridge, the rechargeable power supply device  58  can be connected directly to the second electrical contacts. The rechargeable power supply device  58  is a known device that includes a rechargeable battery and associated charging circuit, and is disposed within the casing  511 . During operation, when connected to the external power source  7 , concurrent with providing DC power to the electric drive motor  3 , the power converter  53  also supplies charging power for charging the rechargeable power supply device  58 . Thereafter, when the power supply cartridge is disconnected from the external power source  7 , the rechargeable power supply device  58  can operate to supply DC power to the electric drive motor  3 .  
     [0034]FIG. 5 illustrates the fourth preferred embodiment of a power tool according to the present invention. When compared to the second preferred embodiment, the power supply cartridge further includes a rechargeable power supply device  58  coupled electrically to the power converter  53 ′ and to the second electrical contacts (not shown) through the motor control circuit  55  and the motor protection circuit  56 . Since the rechargeable power supply device  58  operates in a manner similar to that in the third preferred embodiment, a detailed description of the same will be dispensed with herein for the sake of brevity.  
     [0035] Referring to FIG. 6, in the sixth preferred embodiment of a power tool according to this invention, the first end  63  of the power supply cable  6 ′ is connected fixedly to the power supply cartridge  5 . The second end of the power supply cable  6 ″ is provided with the plug  61  to connect removably with the external power source (not shown).  
     [0036] The power tool according to this invention is connectable to either a commercial AC power source or a DC power source. Moreover, the power tool can also be powered by a rechargeable power supply device of the power supply cartridge that can be charged by the commercial AC power source or the DC power source. Thus, operation of the power tool in either a cordless mode using a self-contained rechargeable battery or a corded mode using a conventional AC power source or DC power source is possible in the power tool of this invention by merely replacing the power supply cartridge that is connected to the tool housing. The replaceable power supply cartridge also simplifies the implementation of circuit designs. It is also noted that the power tool of this invention employs a DC motor, which is much cheaper than conventional AC/DC motors.  
     [0037] While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.