Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1999-11-05
2001-02-20
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S162000, C324S427000, C702S063000, C600S513000
Reexamination Certificate
active
06191557
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to portable battery-powered equipment. In particular, the invention relates to methods and apparatus for displaying a fuel gauge icon representing the state of a battery in battery-powered equipment.
BACKGROUND OF THE INVENTION
When providing medical care to patients, it is frequently necessary to monitor the patient using medical diagnostic instruments. One type of instrument, the patient monitor, is capable of monitoring the patient to acquire electrocardiogram data, cardiac output data, respiration data, pulse oximetry data, blood pressure data, temperature data and other parameter data. In particular, lightweight portable monitors exist which can be moved with the patient, allowing continuous monitoring during patient transport.
To facilitate monitoring at remote locations or during patient transport, modern portable patient monitors are powered by rechargeable batteries. Extended-use batteries, with quick recharge times, help maximize monitor availability. Advanced monitors have a smart battery management system which maximizes battery life, reducing maintenance and replacement. Such monitors use smart batteries which can be interrogated to obtain data representing the ongoing state of the battery, e.g., the current charge capacity and battery terminal voltage.
Portable patient monitors with integral battery power supply are commercially available in a compact, ergonomic package which allows easy handling. The compact design is achieved in part through the use of flat display panels. The color or monochrome screen accommodates all numerics and multiple waveforms.
In addition to displaying waveforms and numerics representing the data being acquired, advanced patient monitors are able to display a battery fuel gauge icon representing the current charge capacity of a battery. For example, the battery fuel gauge may display a rectangle of pixels having a width proportional to the percentage of the full charge capacity (assumed to be equal to the design capacity) which remains in the battery. If the full width of the displayed fuel gauge is 75 pixels and the charge remaining is 20% of the full charge capacity, then the current charge state can be depicted by displaying a rectangle on the gauge having a width equal to 15 pixels (i.e., 20% of 75 pixels).
Users of portable battery-powered equipment need to have a dependable means of determining the present condition (state of charge) of the batteries installed in the system. Portable equipment with high-capacity batteries can be capable of very long run times. Some users of the equipment frequently use only a small percentage of this capability, but occasionally can require the equipment to deliver the full run time capability. This type of use profile, along with other contributing factors, such as transient pulsatile loads and electronic circuit errors (circuit tolerances), can cause the electronic charge capacity gauging internal to the smart battery to become inaccurate. This error can result in the smart battery reporting a remaining charge capacity to the host system which is higher than the charge which the battery can actually deliver.
The foregoing problem is most apparent and critical to the user when the actual remaining battery charge capacity is low. With no additional correction means, the charge capacity gauging internal to the smart battery can lead the user to believe that charge remains in the battery when in reality the battery is fully depleted. In this case, the equipment will automatically and unexpectedly shut down. In addition, the charge capacity gauging internal to the smart battery is a very poor indicator of both run time remaining and the rate of decline in the capacity of the battery to power the host system when the battery is nearing a fully discharged condition. The error in the battery charge capacity gauging is relatively small when the battery has a relatively large remaining charge capacity; however, this error becomes unacceptably large as the percentage of the battery charge capacity remaining approaches the percentage of accumulated error in the charge capacity gauging.
Thus there is a need for a method of giving the system user a relative “feel” for the rate of decline in a battery's capability to power a system when the battery is near the fully discharged condition. There is also a need for a method of giving the user a positive point at the end of the fuel gauge where the unit will dependably shut down.
SUMMARY OF THE INVENTION
The present invention is a method and an apparatus for changing the mode of operation of the bar graph fuel gauge icon when the battery crosses a predetermined threshold preceding a fully discharged state. From the time when the battery crosses that predetermined threshold until the time of full discharge, the battery will herein be deemed to be in a so-called “soft” condition. A battery entering the soft condition can be identified by detecting that the battery terminal voltage has declined to a battery soft voltage threshold that is on the so-called “knee” of the battery discharge voltage characteristic curve. This point also has an approximate equipment remaining run time value associated with it. At the point corresponding to the predetermined voltage threshold, the fuel gauge icon mode of operation is seamlessly changed so that the pixels displayed represent the proportional battery terminal voltage instead of the remaining charge capacity as a percentage of the full charge capacity. In particular, the voltage range from the predetermined voltage threshold down to the battery full discharge cutoff (shutdown) voltage is scaled into the remaining charge capacity active pixel space. This display mode gives the user a relative “feel” for the rate of decline in the battery's capability to power the system as well as a positive point at the end of the fuel gauge where the unit will dependably shut down.
In accordance with the preferred embodiment of the invention, the bar graph fuel gauge icon is displayed as two overlapping rectangles which are left (or right) justified. The first layer is a solid outline, always the same width, representing the full charge capacity of the battery. The second layer is a filled-in rectangle representing the present (actual) charge capacity in the charge depletion mode or the battery terminal voltage in the voltage mode. The charge depletion mode is active when the battery has significant charge capacity remaining and the battery discharge voltage characteristic is very flat. Under these circumstances, accumulated errors in the charge depletion mode fuel gauging are less significant while the voltage mode fuel gauging is impractical.
It should be appreciated that the invention is not limited to a particular voltage threshold. It is only necessary to select a voltage threshold for a particular battery that will cause the voltage mode to be activated at the desired point on the battery discharge voltage characteristic curve. That curve will vary from battery to battery, as will the voltage threshold level.
In accordance with the preferred embodiment, a central processing unit (CPU) of a patient monitor interrogates a microprocessor of a smart battery via a serial data bus to obtain feedback concerning the full and current charge capacities and the terminal voltage of that battery. The charge capacity and terminal voltage values are stored in respective registers in the smart battery microprocessor. Using the polled information, the host system CPU constructs a fuel gauge having an indicator representing the battery current charge capacity when the fuel gauging is in the charge depletion mode and constructs a fuel gauge having an indicator representing the battery terminal voltage when the fuel gauging is in the voltage mode. The newly constructed fuel gauge is then sent to the display controller, which causes the desired fuel gauge icon to be displayed on the display panel.
The invention is preferably implemented completely in software. However, the person skilled in
Gray James M.
Schieble David L.
Cabou Christian G.
Flaherty Dennis M.
GE Marquette Medical Systems, Inc.
Price Phyllis Y.
Toatley , Jr. Gregory J.
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