Abstract:
Power control systems and methods are provided to control when and how power is removed from devices. A power control system includes a sensing module that detects an output voltage level of a battery pack. A shutoff module initiates a shutoff routine when the output voltage level decreases to a device shutoff voltage level. The device shutoff voltage level is greater than the battery pack shutoff voltage level. A bypass module prevents the initiation of the shutoff routine when the device performs one or more operations that are known to cause high battery current spikes that will resultant in significant voltage drops from the battery pack.

Description:
FIELD OF THE INVENTION  
       [0001]     Aspects of the present invention relate to battery protection circuits. More specifically, aspects of the present invention provide battery protection circuits that may bypass shutoff procedures during known high demand conditions.  
       BACKGROUND  
       [0002]     It is common for existing battery packs, such as lithium ion battery packs, to have a low voltage protection circuits integrated into the battery packs. When the battery voltage drops below a predetermined voltage the low voltage protection circuit turns off the battery pack. The low voltage protection circuit then will not let the battery pack resume providing power until the voltage exceeds a predetermined voltage and the battery pack is removed from the circuit and reinserted into the host device. For example, a battery pack having a low voltage protection circuit having a threshold voltage of 6.0 volts will be shutoff by the low voltage protection circuit when the battery pack generates an output voltage of less than 6.0 volts. Even after the battery pack has been removed and reinserted, the low voltage protection circuit will not allow the battery to provide power until the voltage generated by the battery pack exceeds 6.5 volts.  
         [0003]     There are several drawbacks associated with such conventional battery packs. Existing devices that use conventional battery packs are forced to stop operating when the conventional low voltage protection circuit removes power. This can be problematic in many situations, such as when data is stored in a volatile memory or when a device shutdown procedure is desired for proper operations.  
         [0004]     Another drawback associated with conventional battery packs that include low voltage protection circuits is that the low voltage protection circuits do not account for predictable and momentary high current drain conditions. For example, a printing device may have a high current drain and produce a low output voltage during a printing operation. This momentary low voltage condition may cause the low voltage protection circuit to shut off power, even though the battery pack does not need to be recharged.  
         [0005]     Therefore, there is a need in the art for systems and methods that provide better control over how and when power is removed from battery packs during low voltage conditions.  
       BRIEF SUMMARY  
       [0006]     Aspects of the present invention address one or more of the issues mentioned above, thereby providing device power control systems that better control when and how power is removed from devices. In one embodiment of the invention a power control system includes a sensing module, a shutoff module and a bypass module. The sensing module may be used to detect an output voltage level of a battery pack. The shutoff module initiates a shutoff routine when the output voltage level decreases to a device shutoff voltage level. The device shutoff voltage level is greater than the battery pack shutoff voltage level. The bypass module prevents the initiation of the shutoff routine when the device performs one or more operations that are known to cause high battery current spikes. The shutoff routine may include removing power from all components or may include additional steps such as saving data stored in volatile memory, removing power from components in a predetermined sequence, alerting the user that the device will be shutdown, etc.  
         [0007]     In a second embodiment a power control system includes a sensing module and a shutoff module. The sensing module detects output voltage levels of a battery pack and generates an average voltage level that represents a voltage level that is between a current output voltage level and an output voltage level that existed at a previous time. The shutoff module initiates a shutoff routine when the average voltage level decreases to a device shutoff voltage level. The device shutoff voltage level is greater than a battery pack shutoff voltage level.  
         [0008]     In other embodiments of the invention, computer-executable instructions for implementing the disclosed methods are stored as control logic or computer-readable instructions on computer-readable media, such as an optical or magnetic disk. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Aspects of the present invention are described with respect to the accompanying figures, in which like reference numerals identify like elements, and in which:  
         [0010]      FIG. 1  shows a functional block diagram of a device having a power control system in accordance with an embodiment of the invention;  
         [0011]      FIG. 2  shows a functional block diagram of a handheld printer implementation that includes a power control module in accordance with an embodiment of the invention;  
         [0012]      FIG. 3  shows a conventional handheld printer device that may be used in connection with various embodiments of the invention;  
         [0013]      FIG. 4  is a circuit diagram of an analog embodiment of the invention;  
         [0014]      FIG. 5  is a circuit diagram of a digital embodiment of the invention; and  
         [0015]      FIG. 6  illustrates a method of controlling power delivered to a device, in accordance with an embodiment of the invention 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  shows a functional block diagram of a device  102  having a power control system  104 , in accordance with an embodiment of the invention. A rechargeable battery pack  106  includes battery element  108  and a low voltage protection circuit  110 . Battery pack  106  may be implemented with a conventional battery pack, such as a lithium ion battery pack. Low voltage protection circuit  110  shuts off power when an output voltage produced by battery element  108  drops below a battery pack shutoff voltage level.  
         [0017]     Power control system  104  may be configured to sense the voltage level generated by battery pack  106  and initiate a shutdown routine when the sensed voltage reaches a device shutoff voltage level. The device shutoff voltage level exceeds the battery pack shutoff voltage level. As is described below, the shutoff routine may include saving data stored in volatile memory and shutting down electronic circuits  112  in a predetermined order. In some embodiments of the invention, power control system  104  enables the resumption of power to electronic circuits  112  when the output voltage of battery pack  106  increases to a turn-on voltage that exceeds the device shutoff voltage level.  
         [0018]      FIG. 2  shows a functional block diagram of a handheld printer implementation that includes a power control module in accordance with an embodiment of the invention. A battery pack  202  provides power to a power control module  204  and a power module  206 . Power control module  204  may include a sensing module  208 , a bypass module  210  and a shutdown module  212 . Sensing module  208  detects an output voltage level generated by battery pack  202  and may compare the detected voltage level to a predetermined device shutoff off voltage level. Shutdown module  212  may initiate a shutdown routine when the detected voltage level falls below the device shutoff voltage level. In one embodiment of the invention, shutdown module  212  receives a signal from sensing module  208  when the detected voltage level falls below the device shutoff voltage level and the received signal causes shutdown module  212  to initiate the shutdown routine. In various embodiments of the invention the shutdown routine may be performed by shutdown module  212 , power module  206  or a central processing unit (CPU)  216 . The shutdown routine may be as simple as removing power from all components or may include additional steps such as saving data stored in volatile memory, removing power from components in a predetermined sequence, etc.  
         [0019]     Bypass module  210  may be coupled to sensing module  208  and/or shutdown module  212  to prevent the initiation of the shutdown routine during operations that are known to cause high battery current spikes, such as during printing operations. High battery current spikes result in reduced battery output voltage levels. Power module  206  receives power from battery pack  202  and may regulate, filter or otherwise process the power delivered by battery pack  202  before delivering the power to printer components. A backup battery pack  214  may be included to provide power when battery pack  202  fails or produces an output voltage that falls below the device shutoff voltage level. Power module  206  may provide power to CPU  216 , a volatile random access memory (RAM)  218 , a print head  220  and a motor  222 .  
         [0020]     CPU  216  may retrieve computer executable instructions from RAM  218  or a read only memory (ROM)  224  and process those instructions in a conventional manner. RAM  218  may include label data and/or other volatile data. ROM  224  may include firmware, the shutdown routine and/or other nonvolatile data. Print head  220  may be implemented with a thermal print head, inkjet print head or another type of print head for printing on a web or label. Print head  220  may receive print commands from a print module  226 . Print module  226  may also provide a signal to bypass module  210  to indicate that the printer is performing a print operation. Various embodiments of the invention may also include conventional handheld printer components, such as those shown in  FIG. 3 .  
         [0021]      FIG. 3  shows a handheld printer  300  described in U.S. Pat. No. 5,486,259, the entire disclosure of which is hereby incorporated by reference. Printer  300  that has a movable housing section or cover  302  which carries a scanner  304  and a lens  306  mounted at the front end of the scanner  304 . Cover  302  is movable between a closed position shown in  FIG. 3  and an open position by pivoting the cover  302  about a pivot  308 . A movable housing section  310  mounts a keyboard  312  and a display  314  about pivot  308  so that housing section  310  can be moved between its closed position and an open position for servicing the electronic components (not shown) housed in a chamber  316  defined in part by a wall  318 .  
         [0022]     Printer  300  mounts a roll R of a composite web C of record members illustrated to be a series of labels L releasably adhered to a carrier web W. Roll R is mounted within the housing  320  and the composite web C passes from the roll R into guided relationship with a guide roll  322  and from there to between a print head  324  and a platen  326 . Platen  326  is shown to include a platen roll  328 . Adjacent print head  324  is a delaminator  340  about which the carrier web W passes. A label L is delaminated from the carrier web W as the web W is advanced. The label L is advanced following printing into label applying relationship to and under an applicator  330  which is shown to comprise a roll  332 . Carrier web W passes from delaminator  340  into contact with platen roll  328 , about a guide roller  342  into the nip of a feed roll  344  and a back-up roll  334  and through a chute generally indicated at  336  from which the carrier web W exits housing  320 . A motor  338  may be included for advancing composite web C through printer  300 .  
         [0023]      FIG. 4  is a circuit diagram that illustrates an analog embodiment of the invention. A sensing circuit  402  detects an output voltage level of a battery pack. In one embodiment of the invention, an averaging capacitor  404  is included to generate an average voltage level that represents a voltage level between a current output voltage level and an output voltage level that existed at a previous time. With this embodiment, high battery current spikes initially do not result shutdown, but will result in shutdown if they exist for a long enough time period. Sensing circuit  402  may also include a solid state comparator circuit  406  to detect voltage levels. A shutoff circuit  408  may be used to shutdown one or more power supplies included within a device, such as a printer. An external shutdown circuit  410  may be used by an operator to shutoff the device during routine or regular shutoffs. A bypass circuit  412  may be used to bypass sensing circuit  402  during operations that are known to cause high battery current spikes. In the embodiment shown, bypass circuit  412  applies a bypass signal to a field effect transistor  414  during bypass operations. Bypass circuit  412  may alternatively bypass shutoff circuit  408  during operations that are known to cause high battery current spikes. As shown in  FIG. 4 , sensing circuit  402 , shutoff circuit  408 , external shutoff circuit  410  and bypass circuit  412  may include solid state amplifier and switching elements, such as operational amplifiers. Bypass circuit  412  receives a bypass input  416 , which may be from a microprocessor, and disables sensing circuit  402  which, in turn disables shutoff circuit  408  during known high current spikes.  
         [0024]      FIG. 5  is a circuit diagram that illustrates a digital embodiment of the invention. A battery pack  502  is shown coupled to a device  504 . Device  504  may be a portable handheld printer device, a motor or some other device that causes high battery current spikes. A sensing circuit  506  may be used to sense the output voltage level from battery pack  502 . Sensing circuit  506  may be implemented with a conventional analog voltage sensing circuit. In one embodiment of the invention, sensing circuit  506  may include an averaging capacitor, such as averaging capacitor  404  (shown in  FIG. 4 ) or another element that performs a function similar to that of averaging capacitor  404 . Sensing circuit  506  may also provide a shutdown signal to power supply module  518  when it is desired to remove power, such as when battery pack  502  operates continuously for a predetermined time or just prior to reaching a shutoff limit of battery pack  502 .  
         [0025]     The output of sensing circuit  506  may be in the form of an analog voltage signal that is transmitted to an analog-to-digital converter  508 . Analog-to-digital converter  508  converts the analog voltage signal into a digital signal that is then provided to a central processing unit (CPU)  510 . In some embodiments of the invention, the output of battery pack  502  may be provided directly to analog-to-digital converter  508 . CPU  510  may access shutdown parameters  512  stored in a memory  514  and determine when to shutoff operational circuits  516 . Operational circuits  516  represent the circuits used to perform the operations of device  504  and may include a motor, a print head, a scanner or other elements. Shutdown parameters may include a minimum voltage level, time period at a minimum voltage level, minimum current amount, a voltage spread between a peak voltage and a current voltage or any other parameters that may be used to determine when to shutoff prior to battery pack  502  shutting off. Memory  514  may be implemented with a nonvolatile memory, such as a read only memory.  
         [0026]     CPU  510  may also receive data from operational circuits  516  to determine when to bypass a shutdown routine. For example, a signal that indicates that a print head is operating may be used by CPU  510  to bypass a shutoff routine that would otherwise take place. When a shutoff routine is executed, CPU  510  may shutoff certain components in a predetermined order, save data to a nonvolatile memory and/or shutoff a power supply module  518 .  
         [0027]      FIG. 6  illustrates a method of controlling power delivered to a device in accordance with an embodiment of the invention. First, in step  602  the output voltage of a battery pack is detected. Then it is determined whether the output voltage level is less than a device shutoff voltage level in step  604 . As described above, the device shutoff voltage level is selected to be higher than a battery pack shutoff voltage level. When the output voltage level is not less than a device shutoff voltage level, the process returns to step  602 . Of course a delay period may be included before performing step  602  again. When the output voltage is less than a device shutoff voltage level it is next determined whether the device is performing one or more operations that are known to cause high battery current spikes in step  606 . When the device is performing one or more operations that are known to cause high battery current spikes the shutoff routine is bypassed by returning to step  602 . Again, a delay period may be included before performing step  602  again. When the device is not performing one or more operations that are known to cause high battery current spikes, in step  608  a shutoff routine is initiated.  
         [0028]     After the device has been shut down, in step  610  the output voltage of a battery pack is detected. Then it is determined whether the output voltage is greater than a device turn-on voltage level in step  612 . The device turn-on voltage level may be greater than the device shutoff voltage level. When the output voltage is not greater than a device turn-on voltage level the process returns to step  610  after an optional delay. When the output voltage is greater than a device turn-on voltage level a turn-on routine is initiated in step  614 . The turn-on routine may include providing power to components in a predetermined order, loading data into a volatile memory or performing other steps that precede operating the device.  
         [0029]     It should be noted that the term module used herein refers to functionality of physical structure. Thus, various physical components, such as analog and/or digital circuits, may be combined as desired and appropriate to form the various modules. In addition, the same hardware may be used to provide the functionality of one or more modules. A module may also be broken up or combined and does not have to be a discrete unit. For example, two or more of the circuits shown in  FIG. 4  may be modified to have some common circuit elements and each circuit may still be an example of a module.  
         [0030]     The present invention has been described in terms of preferred and exemplary embodiments thereof. Numerous other embodiments, modifications and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure.