CA1337076C - Hospital bed for weighing patients - Google Patents

Abstract

A hospital bed has a support frame and a weigh frame mounted on the support frame by load cells. The output of the load cells is summed to provide a reading of the total weight on the weigh frame. The tare weight is subtracted to provide the patient's weight.

Description

Hospital Bed for Weiqhing Patients Background of the Invention This application is a division of co-pending Canadian Application Serial No. 569,320 filed June 13, 1988.
This invention relates to a hospital bed, and more particularly, to a hospital bed having the capability of measuring and maintaining a record of a patient's weight as well as changes in the patient's weight.
The bed of the present invention has its principal use in intensive care or critical care units of a hospital. There, it is necessary to monitor vital functions of a patient on a r~gular basis. Some must be monitored continuously. One of the vital functions that must be measured on a regular basis is the patient's weight.
Since the patient's health is in such a state that the patient is required to be in intensive or critical care, it is highly likely that the patient cannot leave the bed for a weight measurement and that the patient probably should not be subjected to the trauma attending moving the patient to some sort of scale.
Patient weighing has been done in various ways.
A cumbersome sling overlying the bed has been provided, and it has been necessary to move the patient onto the sling and to lift the patient, by means of the sling, off the bed to effect the weighing operation.
Thin weighing scales adapted to be slid under the patient have been disclosed. See U.S. Patents Nos.
3,217,818 and 3,463,368.
A weigh system forming part of a bed assembly has been disclosed in U.S. Patent No. 4,015,677. Since - 1 337n76 there is practically no bed structure disclosed, it is assumed that the total bed and patient are weighed.
It is known that Stryker Corp. of Kalamazoo, Michigan is marketing a bed having a weight monitoring capability, but not much is known about how the weighing is accomplished. The literature indicates that there are provisions for changing tare to accommodate things added or taken from the bed. Aside from the background art heretofore disclosed, there is little art relating to weigh beds.

Summary of the Invention In accordance with an embodiment of the present invention there is provided in a hospital bed having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus connected to the load cell comprising: a display for weigh data; control means including keys for entering weigh units connected between the load cell and the display; the control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs, and for displaying the patient's weight; and means for initiating an alarm at a central station when a patient leaves the bed.
In accordance with another embodiment of the present invention there is provided, in a hospital bed having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus connected to the load cell comprising: a display for weigh data;
control means including keys for entering weigh units connected between the load cell and the display; the control means for entering and displaying tare weigh~ and changing tare when an unknown change in tare occurs, and for displaying the patient's weight; a SET switch for activating the display to show alarm weight and to activate keys for setting or changing existing a'arm weight value;
and a MODE switch for sequencing the control means through "exit" weight, "over" weight, and "under" weight; and an _ 3 _ 1 3 3 7 07 6 alarm that is activated when any of the preset mode conditions occur.
In accordance with a further embodiment of the present invention there is provided, in a hospital bed having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus connected to the load cell comprising: a display for weigh data;
control means including keys for entering weigh units connected between the load cell and the display; the control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs, and for displaying the patient's weight; and means for initiating an alarm at a central station when a patient leaves the bed; an ALARM switch for programming the following alarm types: Silent - flashing LED on readout unit; Local - flashing LED plus audio beep on readout unit;
REMOTE - audio beep transmitted to central station.
In accordance with yet another embodiment of the present invention there is provided, in a weigh apparatus having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus operatively connected to the load cell and comprising: a display for weigh data;.control means including keys for entering weigh units connected between the load cell and the display; the control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs; and for displaying the weight of a load supported by the weigh frame; and means for initiating an alarm at a central station when a load is removed from the weigh frame.
In another embodiment of the present invention there is provided, in a weigh apparatus having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus operatively connected to the load cell and comprising: a display for weigh data;
control means including keys for entering weigh units connected between the load cell and the display; the control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs; and for displaying the weight of a load supported by the weigh frame; a SET switch for activating the display to show alarm weight and to activate keys for setting or changing existing alarm weight value; a MODE switch for sequencing the control means through "exit" weight, "over" weight, and "under" weight; and an alarm that is activated when any of the preset mode conditions occur.
In accordance with yet another embodiment of the present invention there is provided, in a weigh apparatus having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus operatively connected to the load cell and comprising: a display for weigh data; control means including keys for entering weigh units connected between the load cell and the display; the control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs; and for displaying the weight of a load supported by the weigh frame; means for initiating an alarm at a central station when a load is removed from the weigh frame; and an ALARM
switch for programming the following alarm types: Silent -flashing LED on readout unit; Local - flashing LED plus audio beep on readout unit; Remote - audio beep transmitted to central station.
In a preferred embodiment, a weigh frame that contains the patient supporting surface is mounted at its four corners by load cells to a bed support frame. The weight from the four load cells is summed, as will ~e described below.
Each load cell may be fixed at one end to the support frame and at the other to the weigh frame by universal swivels having upper and lower ball joints.
Thus, the weigh frame "floats" with respect to the support frame and does not bind, thereby eliminating possible error _ 5 _ 1337076 in the weighing function.
In a preferred feature, the weigh frame is an inverted U that telescopes over a support frame that is preferably formed of a hollow rectangular section tube.
The depending legs of the inverted U provide points of attachment for the connection of the weigh frame to the swivel joint and thus to the support frame. The relationship of inverted U weigh frame and the rectangular tube support frame provides freedom of vertical movement of the weigh frame while restricting horizontal or lateral movement, thus providing a stable support of the weighing assembly with respect to the support frame and lower bed structure.
In another preferred feature, a four panel patient support surface is mounted entirely on the weigh frame. Pistons and cylinders connect the support surface to the weigh frame to permit normal articulation of the four panels to permit the patient to assume the conventional reclining and sitting attitudes associated with hospital beds. The system for providing pressure to the pistons and cylinders is mounted on the lower base frame and does not form a part of the weight applied to the load cells, with flexible hoses being provided to connect the pressure system to the pistons and cylinders that operate the patient support surface In another preferred embodiment, the support frame projects at both of its ends beyond the weigh frame.
The projecting portions of the support frame carry accessories such as infusion pumps, I.V. bags, drainage bags, head and foot-boards and the like. By mounting those accessories on the support frame, the adjustments of tare are minimized and the monitoring of the patient's weight is more accurate. For example, with the drainage bag off the weigh frame, the loss of fluids by discharge from the patient into the drainage bag is accurately reflected in loss of patient's weight. Similarly, by mounting the I.V.

- - 5a -bag off the weigh frame, increases in the patient's weight by virtue of the introduction of the I.V. fluids is accurately monitored.
The invention provides for changes in tare even when the incremental change in tare is unknown. In a particularly preferred embodiment, alarm options may be provided including an alarm at a remote location such as a nurse's station, an illuminated alarm, an audible alarm and no alarm. The alarms provide notification of the patient's exit from the bed, which is particularly useful for patient's whose acuity is impaired. The patient's loss or gain of a predetermined amount of weight can be programmed to operate the alarm. The invention provides for displaying of weight in either pound units or kilogram units. All of the controls for the scale may be battery-operated and the weight control system provides, on its display, an indicator for low battery supply.
Brief DescriPtion of the Drawinqs The several features of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Fig. 1 is a perspective view of a bed employing the present invention;
Fig. 2 is a perspective view of the support frame and weigh frame combination;
Fig. 3 is a cross-sectional view taken along lines 3-3 of Fig. 2;
Fig 4 is a cross-sectional view taken along lines 4-4 of Fig. 2; and Fig. 5 is a plan view of the display for the control/readout unit associated with the weigh scale.
The bed to which the present invention is applied is shown in Fig. 1. That bed is more fully described and claimed in U.S. Patent No. 4,751,754, issued June 21, 1988.

1 3370~6 The bed has a base frame 10 that is suppor'-ed on casters 11. Bosses 1 fixed to the base frame pivotally support the ends of a cantilevered support - arm 13 and a stabilizer arm 14. The ends of the cantilevered support arms 13 and the stabilizer arm 14 are pivotally connected to a bracket 15, thereby providing a parallelogram linkage support ~or the bed.
The bracket 15 is bolted to support frame 16. A
piston and cylinder 20 driving a piston rod 21 is mounted on the base frame 10 with the piston rod 21 being connected to the support arm 13 by ~eans of a clevis mount 22. Actuation of the piston and cylinder 20 causes the piston rod 21 to extend and contract, thereby raising and lowering the parallelogram linkage and the support frame 16 of the bed.
Referring to Figs. 1-4, the support frame 16 consists of two tubular rectangular section beams 25 joined together by transverse bars 26 mounted at each end of the beams 25. A weigh frame 30 is ~.ounted on the support frame 16. The weigh frame consists of two inverted U-shaped beams 31 that are shorte_ than the rectangular beams of the support frame. The rectangu-lar beams of the support frame are nested within theU-shaped beams of the weigh frame with front and rear portions 33 and 34 of the support beam projecting beyond the weigh frame 30.

.
, At each corner of the weigh frzme 30, the weigh frame is supported on the supporl fr~me by a load cell 35. The load cell is an elongated element 36, containing a strain gauge, not shown, and having a boss 37 connected by bolts 38 to the inside of the - rectangular beam 25. Thus, the major portion of the load cell is cantilevered from the boss 37 presenting a free end 39. The free end 39 is connected to a swivel 40 by means of a bolt 41 threaded into the free end 39 of the load cell. The projecting end or head of the bolt 4, is a ball 42. The ball sits in a housing 43 to form a ball joint. The housing has a female thread 44 that is connected to a male thread 45 on a second housing 46. The second housing 46 re-ceives a ball 47 to form a second ball joint. Theball 47 is mounted on a pin 48 that is secured to a clevis mount 49 on a bracket 50.
At each corner of the weigh frame flanges 55 project laterally. The brackets 50 are bolted to said flanges 55 across the open end of the U-shaped beams 31. Thus, each swivel mounting securely connects the ~ree end of the load cell to the weigh beam 31. The swivel connection permits limited universal movement of the weigh frame in the horizontal dlrection, thereby preventing any binding of the weigh frame with respect to the support frame. Preferably, a set screw 56 is provided in free end 39 to limit the movement of the load cell in a downward direction while permittin.s 1 337~`7~

the load cell to be stressed to the point or reflect-ing a weigh level well beyorld ~he e~pected loading of the corner of the weiah frzme, thereby preventing damage to the load cell. The lcad cell is provided with suitable strain gauces configurated into a ~heatstone bridge as is conventional. The strain gauges~~ are connected to a computerized control 58 -~ which in turn is connected to a control/readout unit 60, to be described more fully below. The output of the strain gauges are read seauentially and then summed to provide the total weight on the weigh frame_ The weigh frame has two laterally-projecting brackets 65. A patient support 66 having a head panel 67, a seat panel 68, a thigh panel 69 and a foot panel is secured by means of the seat panel to the brackets 65 and, hence, to the weigh frame. The head panel 67 is hinged to the seat panel 68 and is con-- nected by a bracket 71 to a piston and cylinder 72 ~~ which is secured to a bracket 73 on the weigh frame.
Thus, the piston and cylinder 72 on the weigh frame causes the raising and lowering of the head panel 67.
The foot panel 70 is pivotally connected to a bracket 75 which is pivoted to the weigh frame. The foot panel is hinged to the thigh panel 69 which is in turn pivoted to the seat panel. A piston and cylinder 76 connects the thigh panel to the weigh frame. The pistons and cylinders 72 and 76 are connected by hoses, diagrammatically indicatea at 77 and 78, to 2 hydraulic system 79 mounted on the base frame. The ~anipulation of the panels of the patlent support and manipulation of the support frame are all performed in a manner as described in U-S- Patent ~ro. 4,751,754 issued June 2~, 1988 and forms no part of the present -- - invention except to note the pistons and cylinders for operating the patient support panels are mounted on the weigh frame and become a part of its tare whereas the hydraulic system including pump and fluid reser-voir is mounted on the main frame with only hoses beir.g connected between the two. It should b~
understood that the manipulation of said panels could be performed using electric motors mounted on the weigh frame and a power source mounted on the base, with conductors connecting the power source to the weigh frame.
The portions 33 and 34 of the support frame that project beyond the weigh frame provide elements directly connected to the main frame for supporting accessories such as infusion pumps, I.~. bags, drain-- age bags, headboards and the like. All of those accessory elements are thus supported separately from the weigh frame and the weighing system.
The bed as thus described will be outfitted with a mattress, sheets, pillows, blankets, and the like. These items become part of the tare. When these are varied, as by addinq a blan~et or removing pillow, the tare can be chansed, whether the weight of the items be known or unknown, by followir.g an easy sequence of ste~s on the control/readout unit 60.
Further, an attendant can set the controls to provide an alarm, visual or audible, to warn an attendant that the patient has lost or gained weight beyond prede-termined limit, or that the patient has left the bed.
Since---lV bags and drainage bags are supported on the - support frame 16 and/or bracket 15 and are thus out of the weighing system, losses from the IV bags and sains in the drainage bag do not influence the determination of the patient's true weight.
The alarm is adapted to be connected to a central nurse station 74 so as to initiate an immedi-ate response to an emergency situation such as a patient's falling or climbing out of bed; or a delayed response for weight gain or loss beyond the pre-set limit.
The control/readout unit 60 is preferably -- mounted on the front or foot end of the bed convenient for reading and manipulating by the attendant.
The panel has a liquid crystal display 80 that will display the nu~bers indicating the weight and will display the weight units as KG or LB. The units, KG or LB, are set by the units key 81. The display will also show one of four modes: OFF, EXIT, WEIGHT (+), WEIGHT (-). The monitoring mode is selected by mode key 82. The display will also show the alarm which is one of three alternatives: silent, local, remote. The alarm concit,on is determined by the alarm key 83. Four digits are displayed to reflect weight. These digits are controlled by four digit stepping ke~s: 85 for tenths, 8 6 for units, 8 7 for tens and 8~ for hundreds. The hundreds key - - sequences the display through 0, 100, 200, 300, 400, -400, -300, -200, -100, -0, ~0. Thus, by proper sequencing of the hundreds key, the units can be changed from plus to minus.
10A read key 90 is provided to activate a weight reading. A zero key 91 is provided to activat~
a tare reading or effect tare adjustments and a set key 92 is provided to activate monitoring controls.
The key functions are set forth more particularly as lS follows:
READ Initiates 5 to 8 sec weight measurement upon release.
Causes display "+" and preset units, either LB or KG, as previously set, to blink upon closure and while measurement is in process.
Signa]s measurement display with a chime.

UNITS Always comes up in previously set units.
Alternately displays in LB or KG upon contact closure.
Freezes displav when activated and held during weight display.

~ 1 337076 Resets 10 sec. displa~--hold-timer upon contact openins.

ZERO *Initiates automatic zero-tare o~ empty bed when held while touching READ.
- - *Activates digit stepping keys for entry of known tare change, plus or minus, when held.
*Increments total tare value by difference between display and memory, when activated and held during display while then touching READ.
Recalls total system tare value when acti-vated and held; displays for 10 sec after release, or until cancelled by READ or SET.
*All tare operations are protected from accidental change by dual-key or sequenced operation.

SET Activates display when held, to show exist-ing alarm weight value for monitoring modes.
Activates digit stepping keys when held, to allow settin~ or changing existing alarm weight value.
Facilitates MODE and ALAR~ setup when held, by activating display when display is otherwise inactive. Releasing SET causes display to clear.

PrGvides memory recall cf last weight when held while activating READ.

MODE/OFF Selects monitoring mode, shown in display, and as described:
OFF: Automatically timed monitoring ~-~ functions inactive.
-`- EXIT: Rough weight measurement (+ 0, -10~ accuracy) taken every 3 to 4 seconds.
Places EXIT alarm if weight falls below existing alarm-weight value for two successive readings.
WT-: Precise weight measurement (+1%
accuracy, +0.1% repeatability) taken every 10 minutes. Places weight-loss alarm if weight falls ~- below existing alarm- weight value for two successive readings. Last weight value is stored in memory for recall.
WT+: Precise weight measurement (+1%
accuracy, +0.1% repeatability) taken every 10 minutes. Places weight-gain alarm if weight exceeds existing alarm-weight value for two successive re2dinss.
Last weight value is stcred in memorv for recall.
Cancels alarm with single touch; requires resetting, as before, to re-arm monitoring - - mode.

-~ Sequences through available settings in rotation with each touch, or rolls at a l/2 sec. rate if held for l sec.
Skips settings that are not available due t~
hard-wire inhibit or programmed inhibit.
Settable any time a full display is present, that is, during weight display holding time, during total tare display holding tlme, or any time SET is held act,ivated.

ALARM Selects alarm type, shown in the display, ~~ and as described:
SILENT: Flashing yellow LED on Nurse Panel Facade.
LOCAL: Flashing yellow LED plus audio beep from Nurse Panel.
REMOTE: Flashing yellow LED plus room-cancellable call with identifying audio beep transmitted through SIDECOM to nurse station.

During all alarms the preset monitoring condition (EXIT, WT-, or WT+) flashes in the display to identify the type of alarm placed.
Audio tone for EXIT is 400 Hz gated ON for ~
sec., OFF for ~ sec., for WT+ and WT-, a 400 ~~ Hz tone gated ON for 2 sec., OFF for 12 sec.
-~ The LED and DISPLAY flash at the same ON/OFF
rate as the audio.
Yellow alarm LED burns steadily anytime a monitoring mode has been set; then flashes upon alarm.
Sequences through rotation from SILENT to LOCAL to REMOTE to SILENT with each touch of the key, or rolls at a ~ second rate if held for l second.
Settable any time a full display is present, that is, during weight display holding time, ~ during total tare display holding time, or anytime SET is held activated.
Alarm placement occurs within ten seconds if the set weight, when entered, is already in the alarm condition when the SET key is released. This alerts the staff while still in the room.

DIGIT Four (4) digit stepping keys, each KEYS associated with a single decade numerai of the display, are used to increment the display for ZERO and SET, when either of the latter keys are held.
Dual key activation reduces the opportunity for accidental changes in tare resulting from touching a wrong key.
~~ ~undreds sequence is +0, +1, +2, +3, +4, -4, ~ -3, -2, -1, -0, etc; tens, units and tenths step incrementally from 0 to 9 and then jump back to zero without a carryover into the next decade.
Digits step with each touch of the key, or roll at a ~ second rate if held more than 1 second.
BAT Annunciator flashes in display when charge is within 5 to 15% of depletion. Scale is fully functional yet with this reserve, and meets all accuracy requirements. Automatic-ally places a nurse call every 10 minutes when BAT display is activated.

NOTE: In tare or recall operations involving holding ZERO or SET while momentarily activating READ, there will be a tendency to release simultaneously. To prevent activation of an unintentional function when READ is released last, controls are designed such that if READ opens last, bu~ wit;~in -1 3~7076 sec. of ZERO or SET opening, the operation will not be affected.
The steps in the various procedures for weighing the patient, changing the tare, changing the alarm, etc., are as follows:

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- - It will be appreciated that while the preferred embodiment of the invention is described in connection with hospital beds, the invention may be adapted for use in connection with other forms of weigh apparatus, such as patient supporting wheel-chairs, livestock scales, or the like.
From the above disclosure of the general principles of the present invention and the preceding detailed descript~on of a preferred embodiment, those skilled in the art will readily comprehend the various modifications to which the present invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof:

Claims (6)

1. In a hospital-bed having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus connected to said load cell comprising:
a display for weigh data;
control means including keys for entering weigh units connected between said load cell and said display;
said control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs, and for displaying the patient's weight; and means for initiating an alarm at a central station when a patient leaves said bed.

2. In a hospital bed having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus connected to said load cell comprising:
a display for weigh data;
a control means including keys for entering weigh units connected between said load cell and said display;
said control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs, and for displaying the patient's weight:
a SET switch for activating said display to show alarm weight and to activate keys for setting or changing existing alarm weight value; and a MODE switch for sequencing said control means through "exit" weight, "over" weight, and "under" weight;
and an alarm that is activated when any of said preset mode conditions occur.

3. In a hospital bed having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus connected to said load cell comprising:
a display for weigh data;
control means including keys for entering weigh units connected between said load cell and said display;
said control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs, and for displaying the patient's weight; and means for initiating an alarm at a central station when a patient leaves said bed;
an ALARM switch for programming the following alarm types:
Silent: flashing LED on readout unit Local: flashing LED plus audio beep on readout unit Remote: audio beep transmitted to central station.

4. In a weigh apparatus having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus operatively connected to said load cell and comprising:
a display for weigh data;
control means including keys for entering weigh units connected between said load cell and said display;
said control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs; and for displaying the weight of a load supported by said weigh frame; and means for initiating an alarm at a central station when a load is removed from said weigh frame.

5. In a weigh apparatus having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus operatively connected to said load cell and comprising:
a display for weigh data;

control means including keys for entering weigh units connected between said load cell and said display;
said control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs; and for displaying the weight of a load supported by said weigh frame;
a SET switch for activating said display to show alarm weight and to activate keys for setting or changing existing alarm weight value;
a MODE switch for sequencing said control means through "exit" weight, "over" weight, and "under" weight, and an alarm that is activated when any of said preset mode conditions occur.

6. In a weigh apparatus having a weigh frame supported by at least one load cell on a support frame, a control/readout apparatus operatively connected to said load cell and comprising:
a display for weigh data;
control means including keys for entering weigh units connected between said load cell and said display;
said control means for entering and displaying tare weight and changing tare when an unknown change in tare occurs; and for displaying the weight of a load supported by said weigh frame;
means for initiating an alarm at a central station when a load is removed from said weigh frame; and an ALARM switch for programming the following alarm types:
Silent: flashing LED on readout unit Local: flashing LED plus audio beep on readout unit Remote: audio beep transmitted to central station.