Abstract:
The system of present invention is intended for use with a bed having a drive system for moving at least one movable section of the bed and a weight meter which receives transducer signals from transducers in the legs of the bed and displays a patient weight. In the system of the present invention the weight meter is operably coupled to the drive system so that when the drive system is activated, the weight meter automatically enters a hold mode wherein the weight meter stores the most recent weight value as a hold weight value. When the bed drive system is deactivated, the weight meter automatically returns to the operating mode by converting changes in the signals from the transducers into a change in weight value that is added to or subtracted from the hold weight value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/154,712 filed Sep. 18, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a weighing system for a motorized hospital bed that has a drive system including motors and motor controls that are used to adjust the position of the bed. More particularly, the present invention relates to the coupling of the bed&#39;s drive system and the bed&#39;s weighing system so that the weighing system stores a last calculated hold weight value before any one of the bed&#39;s motors can begin operating and then continues calculating changes in measured weight in relation to the hold value after the bed&#39;s motors have stopped operating. 
     BACKGROUND OF THE INVENTION 
     Hospital beds that use weighing systems are known in the prior art. Generally, such weighing systems include transducers that produce signals in response to the magnitude of the loads transferred through the members supporting a bed. One common approach known within the art is to use load cells or force measurement type transducers. These load cells can, for example, be formed from a unitary block of metal machined into a parallelogram configuration to provide a pair of parallel flexible members known as flexures. Strain gauges secured to the flexures produce electrical signals responsive to the magnitude of the load applied to the flexures. The strain gages of a load cell are normally connected into a wheatstone bridge type circuit that can produce a voltage change in response to a change in the resistance of the strain gages. These voltage changes can be calibrated to known loads so that load cell signals can be displayed as weight values on a standard readout device known as a weight meter. 
     In some therapeutic situations, it is critical that the patient&#39;s weight be continuously tracked with a high level of precision. Beds that employ force transducer type weighing systems have a common disadvantage of measuring false changes in weight values when the bed position is changed, that is, when one section of the bed is moved relative to another section of the bed. Typically, patient weight will not change abruptly, however, the relatively abrupt movements that occur when the position of a bed is changed will cause sudden changes in the loads measured by the bed&#39;s transducers. This causes false indications that the weight of a patient has changed. Such erroneous indications of a weight change can interfere with patient care. 
     Many present bed weight measurement systems provide a “hold” function that causes a “hold” weight value to be stored while the bed is repositioned. After a bed having a hold function is repositioned, the hold function is manually released and the weight measurement system uses the hold weight value as a new baseline by resetting the value resulting from the next set of load cell signals after release of the hold function as equal to the hold weight value. From that point, the weight measurement system calculates changes in the patient&#39;s weight as a change in relation to the hold weight value and then as a change in the next weight value to continue producing weight values in an ongoing sequence. A manually operated hold function, however, must be activated every time a bed is repositioned. Present beds that have weighing systems and motorized systems for changing bed position do not have a means for automatically holding a weight value while a bed is repositioned. Since hospital personnel are often busy and distracted and since patients are often able to reposition their own beds, beds are often repositioned without activating a hold function. Consequently, false indications of changes in weight often occur when there is a change in bed position. What is needed is a bed having a position control system and a weight measurement system that are coupled so that the weight measurement system automatically enters into a hold mode while the position control system is changing the bed&#39;s position. 
     SUMMARY OF THE INVENTION 
     The system of the present invention satisfies this need because it has a position control system that is coupled with the weight measurement system via a logic control unit. The bed has a logic control unit that monitors and regulates the interaction between the weight measurement system and the position control system. The position control system includes motor units that are controlled by a position control unit. The weight measurement system includes load cells and a weight meter. The load cells are situated in the load paths of the members that support the bed and include strain gauges arranged in a wheatstone bridge circuit for producing signals for the weight meter. The weight meter converts strain gauge signals from the load cells to a weight value corresponding to the load supported by the bed. 
     In the system of the present invention, the weight measurement system is coupled to the position control unit via a logic control unit that monitors the position control unit and activates the weight meter to store a weight measurement. When a signal is given to the logic control unit to reposition the bed, the logic control unit will first activate the weight meter to initiate a hold function wherein the weight meter stores the most current weight measurement. Once the initiation of the weight meter hold function has been verified by a feedback signal to the logic control unit, the logic control unit will activate the position control unit to reposition the bed as desired. When the position control unit has completed repositioning the bed, a second feedback signal confirms to the logic control unit the deactivation of the position control unit. The logic control unit, upon receiving this second feedback signal, sends a signal to the weight meter to deactivate the hold function and restore the meter to display the last stored weight measurement. The weight measurement system then interprets subsequent sets of load cell signals as only producing changes in relation to the last stored weight value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and its many attendant objects and advantages will become better understood upon reading the following detailed description of the preferred embodiment in conjunction with the following drawings, wherein: 
     FIG. 1 is a plan view of a motorized hospital bed having the weighing system of the present invention. 
     FIG. 2 is a side view of a motorized hospital bed having the weighing system of the present invention. 
     FIG. 3 is an exploded front view of a caster wheel assembly shown in FIG.  2 . 
     FIG. 3A is an exploded side view of a caster wheel assembly shown in FIG.  2 . 
     FIG. 4 is a block diagram of the logic steps employed by the logic control unit of the weighing system of the present invention. 
     FIG. 4A is a block diagram of an alternate set of logic steps employed by the logic control unit of the weighing system in a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG.  1  and FIG. 2 show a motorized hospital bed  10  that includes a frame  20 , caster wheel assemblies  22 A,  22 B,  22 C and  22 D, load cells  24 A,  24 B,  24 C and  24 D, motor units  30 A and  30 B, a position control unit  34 , a logic control unit  40  and a weight meter  50 . 
     As shown in FIG.  1  and FIG. 2, frame  20  of motorized bed  10  is supported by load cells  24 A,  24 B,  24 C and  24 D which are in turn supported by caster wheel assemblies  22 A,  22 B,  22 C and  22 D. Each of the load cells  24 A,  24 B,  24 C and  24 D are force measurement type transducers that produce signals which are carried by data transmission lines  25 A,  25 B,  25 C and  25 D and a single cable bundle  52  to weight meter  50 . Weight meter  50  integrates the inputs from each of the load cells  24 A,  24 B,  24 C and  24 D and displays the weight supported by bed  10 . The weight of bed  10  displayed by weight meter  50  can be normalized at zero when bed  10  is empty and in a pre-selected standard position so that weight meter  50  can display only the weight of the patient supported by bed  10 . 
     FIG.  3  and FIG. 3A provide detailed, exploded views of caster wheel assembly  22 A, load cell mount  324 , and load cell  24 A. Caster wheel assemblies  22 A,  22 B,  22 C and  22 D together with load cells  24 A,  24 B,  24 C and  24 D provide support members that support bed  10 . Caster wheel assembly  22 A includes a securing pin  322 , a lock nut  323 , a caster  320  and a wheel  321 . Load cells  24 A,  24 B,  24 C and  24 D are transducers that are placed in the load paths of the support members supporting bed  10  which can produce signals in response to the amount of load transmitted through the load paths of the support members. In this preferred embodiment, load cell  24 A like the other three load cells includes a strain gage force measurement transducer  326  and a signal cable  325 . Load cell mount  324  provides a mounting for load cell  24 A. Load cell mount  324  includes a caster wheel axle  328 , a bed mounting bracket  328 A, a spacer  327 , bolts  332 A and  332 B, and securing nuts  333 A and  333 B. One end of the load cell  326  is secured to the load cell mount  324  by a pair of bolts  332 A and  332 B. Spacer  327  is placed between the load cell  326  and load cell mount  324  to allow the opposite end of the load cell  326  to deflect in response to changing loads. The caster wheel assembly  22 A is secured to load cell  326  by pin  322  at the end of load cell  326  opposite the end where load cell  326  is secured to the load cell mount  324 . 
     Caster wheel assembly  22 A, load cell mount  324 , and load cell  24 A, when assembled complete a support member for supporting bed  10 . Because of the presence of load cell  24 A which produces signals that vary in response to the magnitude of the load carried by that support member, loads transmitted through this completed support member can be measured- As a load is transmitted from wheel axle  328 , through load cell mount  324 . through load cell  326  and finally to caster wheel assembly  22 A, load cell  24 A deflects and produces a variable electrical signal proportional to the applied load By using load cells such as load cell  24 A signals can be provided to a weigh meter such as weight meter  50  shown in FIG.  1  and FIG. 2 Weight meter  50  can respond to those signals by continuously providing a weight value that corresponds to the total load being supported by the bed. 
     As shown in FIG.  1  and FIG. 2, motor units  30 A and  30 B are mounted to frame  20 . Position control unit  34  controls motor units  30 A and  30 B. Position control unit  34  has a control input device which in this preferred embodiment is a hand held switch unit  35 . Switch unit  35  is used to initiate various functions within position control unit  34  that cause The motors within motor units  30 A and  30 B to actuate mechanisms that change the positions of sections of bed  1   0  relative to other sections of bed  10 . Typically, each of the switches  35 A of switch unit  35  closes a low voltage direct current circuit that causes a high voltage alternating current relay to close within position control unit  35  to provide motive power to one of the motors in motor unit  30 A or motor unit  30 B. The motors in unit  30 A and  30 B are preferably reversible AC motors that can be activated at either a forward or reverse contact to run in a forward or a reverse direction. 
     Logic control unit  40  is used to monitor and to initiate various functions within position control unit  34  and weight meter  50 . Logic control unit  40  controls and manages the sequencing of operations as motors are engaged and as the weight meter  50  moves between the hold mode and the operating mode. Logic control unit  40  can be programmable or it can be a set of analog circuits that accomplish the functions described below. When a switch  35 A in switch unit  35  is depressed, logic control unit  40  receives a signal via cable  36  from switch unit  35  to activate a motor within motor units  30 A and  30 B and change the positioning of bed  10 . Logic control unit  40  responds to this signal by sending to weight meter  50  via cable  45  a hold signal that causes weight meter  50  to enter into a “hold” function. When entering the hold function, weight meter  50  takes a weight reading and stores or holds that value. After entering the hold function, weight meter  50  sends a feedback signal to logic control unit  40  indicating that it has entered the hold function. In response to the feedback signal from weight meter  50 , logic control unit  40  relays the motor activating signal from switch unit  35  to position control unit  34  via line  36 A for the length of time switch  35 A of switch unit  35  is depressed. 
     Once repositioning of bed  10  is completed as indicated by a releasing of switch  35 A of switch unit  35 , logic control unit  40  sends a signal to position control unit  34  to deactivate. After receiving a feedback signal from position control unit  34  indicating that it has deactivated and that all of the motors have ceased operating, logic control unit  40  then sends a resume signal to weight meter  50  causing it to leave the hold function and resume interpreting signals from load cells  24 A,  24 B,  24 C and  24 D in relation to the last stored hold weight value. 
     As those skilled in the art can readily appreciate, the above described functions of switch unit  35 , logic control unit  40 , position control unit  34  and weight meter  50  can be accomplished in a number of ways. In the preferred embodiment, switch unit  35  includes switches that independently close a number of low voltage circuits. Logic control unit  40  includes a relay arrangement that detects the closing of any one of those circuits and then produces a hold signal for weight meter  50  in the form of a low voltage current in a closed circuit. Upon receiving a feedback signal from weight meter  50 , confirming that weight meter  50  is in the hold mode, logic control unit  40  closes a second relay that allows the low voltage current initiated at switch unit  35  to proceed on through the selected circuit or circuits to position control unit  34 . Position control unit  34  responds to low voltage currents in a selected circuit or in a combination of selected circuits by closing the appropriate high voltage AC circuit or circuits to turn appropriate motors in either a forward or reverse direction as dictated by the signals originating in switch unit  35 . Position control unit  34  also includes a relay arrangement that produces a low voltage current whenever any one of the motors is operating. This low voltage current indicating that one of the motors is running is also conveyed to logic control unit  40 . Logic control unit  40  is programmed to respond to the presence of this feedback by continuing to send the hold signal to weight meter  50 . When all of the motors stop, the low voltage current indicating that one of the motors is running will also stop. Logic control unit  40  is programmed to respond to this voltage drop by sending a resume operation signal to weight meter  50 . 
     FIG. 4 illustrates the logic controlling operation of the various elements of the invention system. In FIG. 4, signals passing between switch unit  35 , logic control unit  40 , weight meter  50  and position control unit  34  can be merely low voltage currents in a selected circuits as described above or signals that are coded to convey information such as a command to activate a motor or a commend to enter a mode of operation. FIG. 4 is intended to present the logic of the invention system rather than the actual mechanisms employed to accomplish system functions. 
     As shown in FIG. 4, when one or more switches  35 A in hand held switch unit  35  are depressed, a signal goes to logic control unit  40 . When logic control unit  40  receives the signal from switch unit  35  indicating that one or more switches  35 A have been depressed, it sends a “hold” signal to weight meter  50 . When weight meter  50  receives the “hold” signal from logic control unit  40 , weight meter  50  enters the “hold” mode by calculating and storing the current weight value. This step could be accomplished by one of two methods. In a first method, when weight meter  50  receives a hold signal, weight meter  50  employ a constantly updated memory containing the last weight value which it could then instantly identify as the hold value. In a second method, weight meter  50 , if it had no memory, could upon receiving a hold signal, sample signals from load cells  24 A,  24 B,  24 C and  24 D and calculate a hold value. Once weight meter  50  enters the hold mode and after it has stored the hold weight value, weight meter  50  ignores any changes in signals coming from load cells  24 A,  24 B,  24 C and  24 D. 
     As shown in FIG. 4, when one or ore switches  35 A in hand held switch unit  35  are depressed, a signal goes to log c control unit  40 . When logic control unit  40  receives the signal from switch unit  35  indicating that one or more switches  35 A have been depressed, it sends a “hold” signal to weight meter  50 . When weight meter  50  receives the “hold” signal from logic control unit  40 , weight meter  50  enters the “hold” mode by determining and storing the current weight value. This step could be accomplished by one of two methods. In a first method, when weight meter  50  receives a hold signal, weight meter  50  employ a constantly updated memory containing the last weight value which it could then instantly identify as the hold value. In a second method, weight meter  50 , if it had no memory, could upon receiving a hold signal, sample signals from load cells  24 A,  24 B,  24 C and  24 D and determine a hold value. Once weight meter  50  enters the hold mode and after it has stored the hold weight value, weight meter  50  ignores any changes in signals coming from load cells  24 A,  24 B,  24 C and  24 D. 
     The system of the present invention therefore has a weight meter  50  that ignores load cell inputs when bed  10  is moving. Because changes in signals from load cells  24 A,  24 B,  24 C and  24 D are ignored while bed  10  is in motion, apparent changes in patient weight that are actually caused by changes in the positions of sections of bed  10  relative to other sections of bed  10  are ignored. 
     FIG. 4A illustrates a second approach for initiating a hold function in weight meter  50  when a motor is activated. This second method uses timing instead of feedback signals between the various components to insure the proper sequencing of operations in the various components of the system. In FIG. 4A, when a switch in switch unit  35  is closed, the signal to activate position control unit  34  is routed to position control unit  34  and weight meter  50 . However, the signal routed to position control unit  34  is delayed “x” amount of time to allow weight meter  50  to store and hold a weight value before position control unit  34  activates the bed motors. This sequence including a delay of “x” amount of time insures that the hold function is completely initiated in weight meter  50  before a motor is activated. If weight meter  50  includes a constantly updated memory capable of instantly providing a hold weight value for the hold mode, the amount of time “x” could be very short. When the previously closed switch in switch unit  35  is opened, the signal to position control unit  34  and weight meter  50  ceases. However, the signal drop off is allowed to lag “y” amount of time to weight meter  50  to allow position control unit  34  to completely deactivate motor operations before weight meter  50  resumes normal operation. This delay insures that the hold function in weight meter  50  continues for “y” amount of time after all of the switches in switch unit  34  are open and all of the motors have completely stopped. This gives the time for the movement in the bed to stop before weight meter  50  resumes normal operation. 
     As can be seen from the forgoing descriptions, any one of a number of methods can be used to initiate a hold state within weight meter  50 . A logic control unit similar to logic control unit  40  could be placed exclusively in communication with position control unit  34  and weight meter  50  so that any operation of position control unit  34  would initiate a hold function in weight meter  50 . A logic control unit similar to logic control unit  40  could be placed exclusively in communication with hand held switch unit  35  and weight meter  50  so that any operation of switch unit  35  would initiate a hold function in weight meter  50 . 
     Although many ways can be selected to accomplish the functions of the present invention system. the present invention system is a system for suspending the operation of the weight meter of an adjustable hospital bed when the position of the hospital bed is being adjusted where the weight meter would normally receive inputs from load transducers placed in the load paths of the bed support members and constantly or periodically update the weight value based on changes in those inputs. What is necessary to the present invention is that a system of the present invention have a way detect the activation of any motor used to adjust the position of a bed and that upon the detection of such activation, a hold signal is sent to the weight meter which responds by holding the last calculated hold weight value while any of the motors are operating and until after they have all ceased operating. When the motors cease operating, a system of the present invention must have the second capability of either ceasing to send a hold signal or sending a second signal to the weight meter so that the weight meter can respond by continuing to calculate changes in weight in relation to the hold weight value based on changes in signals coming from the load transducers.