Abstract:
A video camera includes a processor that is operable to obtain a capacity value of a battery by communicating over a communications line with a battery pack that contains the battery and which provides power to the video camera. The capacity value indicates a number of cell structures in the battery. The processor is also operable to set a correction value based on the capacity value, to correct a low power warning voltage value by subtracting the correction value from the low power warning voltage value, to generate a low power warning when a detected battery voltage is less than or equal to the corrected low power warning voltage value, and to generate a residual power indication when the detected battery voltage is greater than the corrected low power warning voltage value. A display is operable to display the low power warning or the residual power indication.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. application Ser. No. 09/510,856, filed on Feb. 23, 2000, which claims priority from Japanese Application No. P11-051871, filed Feb. 26, 1999, all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a video camera which displays a warning when a battery becomes near empty, and a warning method thereof.  
         [0003]     A conventionally known power source of a video camera is, for example, a battery pack including a lithium ion battery, NiCd battery, nickel hydrogen battery, or the like as a secondary battery cell. The battery pack is constructed to be detachable from a battery attachment section provided in the video camera apparatus body.  
         [0004]     Normally, in an electric apparatus such as a video camera using this battery pack as a power source, the battery end voltage is determined depending on the terminal voltage of the battery pack. Also, a display of a warning prior to end of the battery is determined depending on the terminal voltage of the battery pack. The battery end voltage and the voltage for displaying a warning prior to end of battery are generally fixed.  
         [0005]     Meanwhile, the discharge characteristics (defined by subtracting a discharge time from a between terminal voltage) of battery packs differs depending on the type of the battery cell. Even the same cell may have different discharge characteristics, depending on the cell structure method. Therefore, if the battery end voltage Ve and the warning display voltage Vp prior to end of the battery are both fixed, there is a problem that the time from when a warning is displayed to when the battery actually ends greatly varies depending on the type of the battery pack. For example, suppose three types of cell structures, e.g., a one-stage cell structure in which two battery cells C 1  and C 2  are connected in series as shown in  FIG. 1 (A), a two-stage cell structure in which two stages each consisting of two battery cells C 1  and C 2  connected in series are connected in parallel as shown in  FIG. 1 (B), and a three-stage cell structure in which three stages each consisting of two battery cells C 1  and C 2  are connected in series are connected in parallel as shown in  FIG. 1 (C). Between these three cell structures types, the times T 1 , T 2 , and T 2  at which warnings prior to end are displayed are greatly different from each other as indicated by the relationships between the battery discharge characteristics F 1 , F 2 , and F 3  and the warning display times T 1 , T 2 , and T 3  in  FIG. 2 .  
         [0006]     This problem means lowered reliability with respect to warning display near the battery end of the electric apparatus, and the influence therefrom increases as the consumption power of the apparatus decreases.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The present invention hence has an object of providing a video camera and a warning display method thereof which enable warning display with high reliability.  
         [0008]     According to an aspect of the invention, a video camera includes a processor operable to obtain a capacity value of a battery by communicating via a communications line with a battery pack that contains the battery, the battery providing power to the video camera, the capacity value indicating a number of cell structures in the battery, to set a correction value based on the capacity value, to correct a low power warning voltage value by subtracting the correction value from the low power warning voltage value, to generate a low power warning when a detected battery voltage is less than or equal to the corrected low power warning voltage value, and to generate a residual power indication when the detected battery voltage is greater than the corrected low power warning voltage value. A display is operable to display the low power warning or the residual power indication.  
         [0009]     According to another aspect of the invention, a video system includes a video camera body, a battery pack including a battery having at least one battery cell, and a communications line connected to the video camera body and said battery pack. The video camera body includes a processor operable to obtain a capacity value of said battery by communicating with said battery pack via said communications line, the capacity value indicating a number of cell structures in the battery, to set a correction value based on the capacity value, to correct a low power warning voltage value by subtracting the correction value from the low power warning voltage value, to generate a low power warning when a detected battery voltage is less than or equal to the corrected low power warning voltage value, and to generate a residual power indication when the detected battery voltage is greater than the corrected low power warning voltage value. A display is operable to display the low power warning or the residual power indication.  
         [0010]     According to yet another aspect of the invention, a battery pack for a video system includes a cell structure section including at least one battery cell and having at least one stage, a power terminal operable to supply power to a video camera body of the video system over a power source line, a memory operable to store a capacity value of said battery, the capacity value indicating a number of battery cells in said battery, a communications terminal operable to provide a connection to a communications line connected between said battery pack and the video camera body, and a processor operable to provide the capacity value stored in said memory to the video camera body using said communications terminal and the communications line. The video camera body thereby sets a correction value based on the provided capacity value, corrects a low power warning voltage value by subtracting the correction value from a low power warning voltage value, detects a battery voltage of said at least one battery cell, generates a low power warning when the detected battery voltage is less than or equal to the corrected low power warning voltage value, generates a residual power indication when the detected battery voltage is greater than the corrected low power warning voltage value, and displays the low power warning or the residual power indication.  
         [0011]     As described above, according to the present invention, a voltage correction value, which is determined based on information concerning the capacity of the cell in the battery pack, is subtracted from a prior-to-end warning voltage value to obtain a reference voltage value, and the obtained reference voltage value is compared with the voltage value of the battery pack. A warning is displayed when the voltage value of the battery pack becomes smaller than the reference voltage value. As a result, the time when the warning is displayed can be constant with respect to any of battery packs having various kinds of cell structures so that a warning display can be achieved with high reliability. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0012]      FIG. 1  is a view schematically showing the cell structure in a battery pack.  
         [0013]      FIG. 2  is a view schematically showing the relationships between the battery discharge characteristics and the warning display times of the battery packs respectively having a one-stage structure, two-stage structure, and three-stage structure in a conventional electronic apparatus.  
         [0014]      FIG. 3  is a block diagram showing the structure of a battery power source control system of a camera-integrated video recorder to which the present invention is applied.  
         [0015]      FIG. 4  is a flowchart showing processing of power source control in the camera-integrated video recorder.  
         [0016]      FIG. 5  is a flowchart showing correction value decision processing in the processing procedure of power source control.  
         [0017]      FIG. 6  is a view schematically showing the relationships between the battery discharge characteristics and the warning display times of the battery packs respectively having a one-stage structure, two-stage structure, and three-stage structure in the camera-integrated video recorder. 
     
    
       [0018]     In the followings, embodiments of the present invention will be explained specifically with reference to the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The present invention is practiced as a camera-integrated video recorder mounting a battery power source control system having a structure as shown in  FIG. 3 . This camera-integrated video recorder is constructed by connecting a video camera recorder body  10  with a battery pack  20  over a power source line  40  and a communication line  30 .  
         [0020]     The video camera recorder body  10  is provided with a positive terminal  12  and a negative terminal  13  connected with the power source line  40 , and a communication terminal  11  connected with the communication line  30 . Also, the video camera recorder body  10  is provided with a microcomputer  14  that transmits data to and receives data from the outside through the communication terminal  11 , a display section  15  controlled by the microcomputer  14 , a power control section  16 , and the like.  
         [0021]     The video camera recorder body  10  is supplied with power from the battery pack  20  through the positive and negative terminal  12  and  13 , and the microcomputer  14  receives internal information concerning the battery pack  20  through the communication terminal  11 . Also, the microcomputer  14  includes an internal voltage detector section  17  and detects the voltage of the power source supplied through the positive and negative terminals  12  and  13  as will be described later. Based on the detection result therefrom, the microcomputer  14  controls the display section and the power control section  16 .  
         [0022]     Also, the battery pack  20  is provided with positive and negative terminals  22  and  23 , respectively, for inputting power, which are connected with the power source line  40 , and a communication terminal  21  connected with the communication line  30 . This battery pack  20  comprises a microcomputer  24  which functions to transmit and receive data to and from the outside through the communication terminal  11 , and a cell structure section  25  internally including a battery cell which supplies the video camera recorder body  10  with power through the positive and negative terminals  22  and  23 , and the like. The cell structure section  25  internally includes a plurality of battery cells which are constructed in a two-stage or three-stage structure. The status of the battery cells in the cell structure section  25  is monitored by the microcomputer  24 .  
         [0023]     Further, in this camera-integrated video recorder, power source control is carried out in accordance with a procedure as shown in  FIG. 4 .  
         [0024]     Specifically, the microcomputer  14  of the video camera recorder body  10  detects the voltage of the power source supplied through the positive and negative terminals  12  and  13 , i.e., the battery voltage Vb of the battery pack  20 , by the voltage detector section  17  (step S 8 ), to determine whether communication with the microcomputer  24  in the battery pack  20  side is possible (step S 2 ).  
         [0025]     If the determination in the step S 2  is “NO”, which means that communication is not possible, e.g., in case where the microcomputer  24  of the battery pack  20  does not work normally or the battery pack  20  is not connected, the microcomputer  14  in the video camera recorder body  10  then ends the processing.  
         [0026]     Otherwise, if the determination in the step S 2  is “YES”, i.e., if communication with the microcomputer  24  in the battery pack  20  side is possible, the microcomputer  14  in the video camera recorder body  10  obtains a standard capacity as one of the property information items (such as a voltage, current, and a residual battery amount) inherent to the battery pack  20  (step S 3 ) and further carries out a residual amount calculation (step S 4 ).  
         [0027]     Next, the microcomputer  14  of the video camera recorder body  10  determines the type of the battery pack  20  (e.g., the cell structure of the cell structure section  25  in this example) based on the standard capacity obtained as a property information item inherent to the battery pack  20 , and decides a prior warning display voltage correction value ΔVp prior to end of the battery life, corresponding to the battery type (step S 5 ).  
         [0028]     The correction value decision processing in the step S 5  will now be explained specifically with reference to  FIG. 5 .  
         [0029]     That is, in this correction value decision processing, the microcomputer  14  in the video camera recorder body  10  determines whether the standard capacity obtained by communication is larger than the battery capacity of the battery pack having a cell structure section constructed in the two-stage structure (step S 21 ).  
         [0030]     Further, if the determination result in the step S 21  is “YES”, which means that the standard capacity obtained by communication is larger than the battery capacity of the battery pack whose a cell structure section has a two-stage structure, the microcomputer  14  in the video camera recorder body  10  sets the prior warning display voltage correction value ΔVp to a correction value ΔVp3 corresponding to the battery capacity of the battery pack whose cell structure section has a three-stage structure (step S 22 ).  
         [0031]     Otherwise, if the determination result in the step S 21  is “NO”, which means that the standard capacity obtained by communication is smaller than the battery capacity of the battery pack of the battery pack whose cell structure section has a two-stage structure, the microcomputer  14  in the video camera recorder body  10  further determines whether or not the standard capacity obtained by communication is larger than the battery capacity of the battery pack whose cell structure section has a one-stage structure (step S 23 ).  
         [0032]     Further, if the determination result in the step S 23  is “YES”, which means that the standard capacity obtained by communication is larger than the battery capacity of the battery pack whose cell structure section has a one-stage structure, the microcomputer  14  in the video camera recorder body  10  sets the prior warning display voltage correction value ΔVp to a correction value ΔVp2 corresponding to the battery capacity of the battery pack whose cell structure section has a two-stage structure (step S 24 ).  
         [0033]     Further, if the determination result in the step S 21  is “NO”, which means that the standard capacity obtained by communication is smaller than the battery capacity of the battery pack whose cell structure section has a two-stage structure, the microcomputer  14  in the video camera recorder body  10  sets the prior warning display voltage correction value ΔVp to a correction value ΔVp1=0 (step S 25 ).  
         [0034]     At this time, the warning display voltage correction value ΔVpn corresponding to the cell structure of the battery pack (where n=1, 2, 3) is stored together with a standard prior warning voltage value Vp in the memory of the microcomputer  14  of the video camera recorder body  10 .  
         [0035]     After the prior warning display voltage correction value ΔVp is thus decided, the microcomputer  14  of the video camera recorder body  10  subtracts the prior warning display voltage correction value ΔVp from the standard prior warning voltage value Vp thereby to obtain a corrected prior warning display voltage value Vpn in correspondence with the type of the battery pack  20  (step S 6 ). 
 
 Vpn=Vp−ΔVpn  (where n=1, 2, 3) 
 
         [0036]     Then, whether the battery voltage value Vb of the battery pack  20  detected by the voltage detector section  17  in the step S 1  is larger than the corrected prior warning voltage value Vpn is determined (step S 6 ).  
         [0037]     Also, if the determination result in the step S 7  is “YES”, which means that the battery voltage Vb of the battery pack  20  is higher than the corrected prior warning display voltage value Vp, the microcomputer  14  of the video camera recorder body  10  controls the display section  15  to display the residual amount calculated by the step S 4 , so residual amount display is thus carried out (step S 8 ). Thereafter, the microcomputer returns to the step S 1  and performs repeatedly the above-described processing.  
         [0038]     Otherwise, if the determination result in the step S 7  is “NO”, which means that the battery voltage Vb of the battery pack  20  is lower than the corrected prior warning display voltage value Vp, the microcomputer  14  of the video camera recorder body  10  determines whether the battery voltage value Vb of the battery pack  20  is higher than the end voltage value Ve (step S 9 ).  
         [0039]     If the determination result in the step S 9  is “YES”, which means that the battery voltage value Vb of the battery pack  20  is higher than the end voltage Ve, the microcomputer  14  of the video camera recorder body  10  controls the display section  15  to display a prior warning (step S 10 ), and then returns to the step S 1  and repeatedly performs the processing described above.  
         [0040]     Further, if the determination result in the step S 9  is “NO”, which means that the battery voltage value Vb of the battery pack  20  is smaller than the end voltage value Ve, the microcomputer  14  of the video camera recorder body  10  ends the processing for power source control.  
         [0041]     At this time, the battery end voltage value Ve is stored in the memory of the microcomputer  14  in the video camera recorder body  10  or the memory of the microcomputer  24  in the battery pack  20 .  
         [0042]     In this kind of camera-integrated video recorder, the microcomputer  14  of the video camera recorder body  10  obtains a corrected prior warning display voltage Vpn which is corrected with a voltage correction value ΔVpn decided in accordance with the type of the battery pack  20  based on information concerning the capacity of the cell in the battery pack which is obtained from the battery pack  20 . Display of a warning is started when the battery voltage value Vb of the battery pack  20  becomes equal to or lower than the prior warning display voltage value Vpn. The display of the warning ends when the battery voltage value Vb reaches the end voltage value Ve at which use of battery should be ended. Therefore, the prior warning display time prior to end of battery life can be constant with respect to any battery pack having any cell structure, as schematically indicated by the relationships between the battery discharge characteristics F 1 , F 2 , and F 3  and the warning display times T 1 , T 2 , and T 3 .  
         [0043]     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.