GB1595947A - Electronic apparatus for monitoring movement of bed patients - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRONIC APPARATUS FOR MONITORING MOVEMENT OF BED PATIENTS (71) I, ROBERT BERNARD GAL LIPEAU of 23, Potters Croft, Horsham, Sussex, RH13 5LR a citizen of the U.S.A.

and JOSEPH GERARD GUILMETTE of 4167 W 172 nd. Street., Torrance, Califor nia, U.S.A. 90504 a citizen of the U.S.A. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to electronic apparatus which is responsive to the movement of a patient out of bed.

Electrical apparatus which provide a warning to hospital staff of movement of patients out of bed are already known, for example B.P. spec. No. 1484332. However, such known apparatus require either individual wiring systems for each bed to be monitored or the provision of radio signals which could cause interference with other hospital equipment.

An object of the present invention is to avoid the use of costly installations and wiring systems by the provision of a transmitter which is responsive to the out of bed condition of one or more patients and which transmits a series of impulses via the mains power line to a single receiver located remote from the patients being monitored.

The receiver is capable of receiving impulses from a number of transmitters, one transmitter for example monitoring two beds. The transmitter emits impulses only when an out of bed condition of a patient is detected, the impulses being converted by the receiver to give a visual indication to hospital staff of the room number where the incident has occured. The impulses can also trigger via the receiver an audible alarm system to give warning of the out of bed condition of the patient.

The invention is particularly suited to use in hospitals and nursing homes where the movement of a patient out of bed could cause the patient considerable danger and where such a condition might not be readily apparent to nursing staff.

According to the present invention, an electronic apparatus for monitoring the condition of a patient comprises at least one sensor for sensing the movement of a patient out of bed, a transmitter electrically connected to said sensor and responsive to a signal from said sensor and capable of emitting impulses corresponding to the location of said sensor, the impulses being fed to a mains power line and received by a receiver located remote from the transmitter.

Various features and advantages of the present invention will appear from the following description of a particular embodiment thereof, given by way of example only with reference to the accompanying drawings in which: Figure 1 is a plan view of a bed provided with pressure sensors.

Figure 2 is a side elevation of a crosssection of a pressure sensor.

Figure 3 is a schematic circuit diagram of the transmitter logic.

Figure 4 is a circuit diagram of a power supply of the transmitter and/or receiver.

Figure 5 is a circuit diagram of a power amplifier.

Figure 6 is a circuit diagram of a controlled oscillator having an optional tank circuit.

Figure 7 is a circuit diagram of the tone decoder and reset arrangement of Figure 3.

Figure 8a is a circuit diagram of the clock of Figure 3.

Figure 8b is a circuit diagram of the clock inhibit control arrangement.

Figure 9 is a circuit diagram of a 1 second hold circuit. Figure 10 is a circuit diagram of the switch logic of Figure 3.

Figure 11 is a circuit diagram of the state counter of Figure 3.

Figure 12. is a circuit diagram of an input from the sensors of two beds.

Figure 13 is a circuit diagram of the receiver logic.

Figure 14 is a circuit diagram of the automatic reset arrangement of Figure 13.

Figure 15 is a circuit diagram of the shift register, decoder drive and display of Figure 13.

Figure 16 is a circuit diagram of a zero and one decoder.

Figure 17 is a circuit diagram of a state counter.

Figure 18 shows the front elevation of the transmitter.

Figure 19 shows the front elevation of the receiver.

Referring to Figure 1, 1 represents generally a bed having a headboard 2 and a footboard 3. The patients location on the bed is determined by a series of weight sensing elements 4 mounted on the bedsprings under the mattress. The sensors 4 are located in an array around the perimeter of the mattress. Spacing of the sensors 4 is such that at least one sensor is activated when a patient's weight is shifted towards the edge of the bed 1. Sensors 4 are spaced a minimum distance in order to prevent a patient from getting between the sensors undetected. The operating principle is based upon the sensors functioning as a series of normally closed switches. Electrically, only one lead wire is required and also since the switches are normally in the "high" logic state, a malfunction such as a broken wire or accidental or intentional unplugging of the sensors is detected by the electronic monitoring system. Mechanically, the normally closed design allows the sensors to be internally preloaded, thus eliminating any method which may be otherwise required to fasten the assembly such that all parts remain as one integral unit.

Figure 2 shows the design principal of the sensors 4. The cap 5 and base 6 are fabricated of an insulating material such as, but not limited to, a plastics material. This design lends itself well to injection moulding. Edges on the cap 5 are rounded since the mattress is normally situated on top of the sensors. The rounded edges allow the mattress to flow freely over the sensors 4 during the movement of the mattress. The central post 7 is fabricated of a metallic conductive material. for example, brass, which also allows a lead wire 8 to be soldered or welded to it. The spring 9 may be coiled, leaf or flexure design and is not necessarily limited to a metallic design, as resilient material could also be used. A metallic lug 10 with a hole larger than the centre post diameter is cemented or otherwise fastened into the base as shown on Figure 2. The lug 10 has a lead wire 11 connected to it. The assembly of the sensor is accomplished by placing the spring 9 on the base 6 followed by the cap 5. An external force temporarily clamps the cap to the base thereby compressing the spring 9.

The centre post 7 is then inserted through the metallic lug 10 and base assembly 6 since the base is also provided with a clearance hole. The cap is designed with a blind hole 12 at its center with its diameter dimensioned such that the center post's mating diameter is held fast to the cap by an interference fit. The center post diameter may be serrated in order to provide a more positive fastening. A lead wire 8 can be fastened to the centre post. The assembly is designed such that when the temporary external clamping force is removed, the spring 9 is not completely extended back to its unloaded or unstressed state. This preload is experienced between the centre post 7 and the metallic lug 10 which forms the normally closed electrical junction. When the force exerted on the cap by the patient's weight exceeds the spring preload, the centre post and cap are deflected downward and thus breaking the electrical connection.

The base is designed such that electrical connections are formed in a cavity. A major consideration of this design is to isolate all metallic parts. This is accomplished by the blind hole in the cap and an insulating material mechanically fastened or bonded to the base. This may be, for example, an adhesive coated rubber sheet 13. The bonded rubber sheet also serves as a strain relief for the lead wires which are placed into open slots in the base. The slot may be dimensioned such that the wire is clamped to the base by the bonded insulating material. The insulating material serves a third purpose in that it may function as a bonding interface between the sensor and bedspring designs employing a flat plate; solid or perforated. Figure 2 also shows a mounting of the sensor on a conventional wire type innerspring 14.

Two holes are provided in the base to accommodate self-tapping screws 15. The screws are used to clamp the sensor onto adjacent wires using washers 16 or clamping dogs. Curved spring washers are particularly well suited for this purpose as they form a cavitv for the wire.

With reference to Figure 3. which is the logic flow design for the transmitter. the function of the transmitter is to interpret a signal pulse from the bed sensor 4, read the setting on the switches 17 and properly sequence a series of pulses of high and low tones and couple the informtion to the mains power line. Other features which have been added to improve reliability are a line sampler circuit 18 which will temporarily inhibit the transmitter 10 seconds if another transmitter is transmitting and the data pulses will be counted in order to assure proper data transmission. A tone director 19 tuned to the "High" frequency representing ones in the binary system (70 KHz) samples the line for transmissions of "ones" from other transmitters in order to avoid overlapping transmissions. The tone (LM 576) detector 19 output is used as the input to a 'oneshot' delay signal 18 (LM 555) which inhibits the transmitter 19 10 seconds prior to sending the serial data. This is accomplished by holding the state counters' 17 (CD 4017) reset input high for 10 seconds. If the transmitter 19 is not in a 10 second pause state and is otherwise set to receive a pulse (Manually reset), it will be described as being in state 1. If an input from the bed is detected in this state, the clock 20 will be activated and the system will advance to state 2.

STATE 2 State 2 is the first data state. In this state, the data flip flop 21 is set. This allows the zero or one oscillators 22 & 23 respectively to be controlled. Also in this state, the clock 20 advances the state counter 17 (CD 4017 Occade counter) from QOA to QIA which senses the first bit of informa tion on the digital switch 24. If the bit is OPCM, a zero is sent, if shorted to terminal C, a one is sent.

STATE 3 The following clock cycle adv ances the state counter to Q2A and the second bit of data is sent in a similar manner as was in state 2. These are tone bursts whose frequencies are those set in zero and one oscillators and with a pulse width equal to one clock pulse. Each digit requires four bits and obviously this system is designed for a maximum of 4 digits.

STATES 4-17 Similar to states 2 and 3, a flip flop 21 is located between the two state counters and functions to enable one coun ter while disabling the other.

STATE 18 State 18 resets the data flip flop 21, sets the inhibit 1 second controller 14A, and checks to see if the limit on the number of data sends has been reached by sensing Q8B- If the limit has been attained, the system is inhibited. If the limit has not been reached (This is detected by the transmitter and sends a signal back to the transmitter and enters the transmitter logic at B). the transmitter continues through another cycle and completes to state 19 where it shuts off the transmitter via the limit counter. A momentary closing of the manual reset switch restores the transmitter to state 1.

Figure 4 shows the power supply circuit.

The 12V of the secondary filament transformer 25 is coupled to a diode bridge 26 which supplies unregulated DC voltage to the LM 340-8 voltage regulator 27. The output is 8VDC to the CMOS circuits.

Figure 5 shows the power amp circuit based on a LM 380 2W. audio amplifier* available in integrated circuit form in 8 or 14 pin configuration (Audio amplifier 28) Figure 6 illustrates the controlled osclllators for generating the zero and one tone bursts. Frequencies are determined by the resonance of the RC circuit. fn = 1/ (2zRC) This is accomplished by precision RC components. This system will utilize 50 and 70 KHz for zero tones respectively. It may be necessary to filter the oscillator in order to purify the sine wave output. This may be accomplished by adding a tank circuit, represented generally by 29 which is essentially a tank circuit (LT and CT) where the frequency = 1/(2z) V 1/(LC) Figure 7 shows the tone decoder 19 and reset 18 circuitry The tone decoder 19 detects "ones" from other receivers and inhibits the transmitter for 10 seconds by using the LM 555 - I.C in a "one shot" configuration. The "STATE 1" and "Counter control bar" inputs at the N and gate to assure that the transmitter will not listen to itself while transmitting.

Figure 8A shows the oscillator portion of the clock 20 which oscillates as long as the input circuitry is high from the bed. The RC circuit is set at about 1 Hz but in practice, will be increased by decreasing the value of R or C or both.

Figure 8B shows the control portion of the clock 20 which is designed to inhibit the clock which is a basic technique utilized in the logic control of the transmitter. The X input is the 1 second inhibit, while awaiting a transmission complete "one" tone from the oscillator. (X will change state if a tone "one" is decoded.) A maintains the full one second bulge in the event that a one is decoded (to prevent overlapping signals) and Y disables the system in State 19 which is the top state.

Figure 9 shows the X circuitry. This circuit holds the system in state 18 for 1 second, while awaiting a transmission complete "one" signal from the transmitter at B terminal as previously explained.

Figure 10 shows the switching logic 24 used to switch the zero and one pulses into their appropriate oscillators 22 and 23 respectively at each clock pulse. A "high" pulse from the switch common indicates a one and will give an output at the one terminal when the clock is high. No output from the common will produce a high signal from the zero terminal when the clock is high. The input sequence is obtained from the state counter 17 strobing the switch setting as described in the following paragraph.

Figure 11 shows the state circuitries 17.

This circuitry reads the setting on the digital thumbwheel switch 49. The basic components are two decade counters 30 and 31 respectively (CD 4017) which advance one data state per clock pulse and produces serial data through the switching circuit described on Figure 10. The switching from one counter to the other is accomplished through the JK flip flop while state 19 (the last data point) stops the data transmission.

Figure 12 shows the input circuitry 32 and 33. The two beds, are wired in series with two sensors 4 per bed shown, although in practice more are used. The diodes 34 and 35 allow the beds on the panel to be lit only when the bed switch is on the ON position.

The SPDT switches 38 are located on the transmitter front panel and more beds can be cascaded in a similar manner. The capacitor 36 and resistor 37 function as a filter to prevent the system from responding to spikes while switching.

Figure 13 represents the receiver logic.

The receiver is designed to communicate with the transmitter as well as receive the serial input data and display it. The logic is designed to monitor its data and send back a complete transmission one tone to the transmitter if good data is received. An audible tone is also generated if the receiver detects a transmission from the transmitter. The logic block diagram for the receiver shows two detector circuits tuned to the zero and one frequency respectively. The output pulse train is used to generate the clock 40.

Due to the nature of the circuitry, the first data pulse is not transfered into the shift register 41 but is stored in the flip flop 42 and subsequent data pulses lag the clock 40 by one pulse. In order to feed the 16th bit of information into the shift register, the logic is designed to utilize a local oscillator 43 to generate clock pulses from the 4017 counter 44 once the 16 input bits have been sent from the transmitter. This allows the 16th bit of information into the shift register.

The second count of the 4017 counter 44 generates the transmission complete 'one" tone and sends it back to the transmitter. It also latches the display 45. The third cycle is used to reset the system. The event timer is used to automatically reset the system after a reasonable time in the event a partial transmission is received. The component circuits will be discussed individually as was in the transmitter text. The power supply, power amplifier and controlled local circuit oscillator circuits are identical to that of the transmitter shown in Figures 4, 5 and 6 respectively. The controlled local oscillator is tuned to the 'one' frequency (70 KHz).

This is used to generate the transmission complete tone.

Figure 14 shows the reset and alarm logic.

The Z input is from the automatic reset one shot 46 while the reset is from the last data pulse of the counter. The manual reset 50 also resets the system. An input from either Z or reset also activates the alarm which is inhibited by the manual reset.

Figure 15 shows the shift register 41, decoders 47 and LED display modules 45.

The shift registers 41 (CD 4015) Transfer the serial data input to parallel as required by the decoder/display driver IC's 47 (14511) The 14511 circuitry also converts the 4 digit binary into the seven segment code required for the LED display 45. For a system requiring less than 4 digits, some of the drivers may be ommitted Figure 16 shows the zero and one decoder circuitry 38 and 39. Its function is to decode the incoming serial data from the transmitter and generate clock pulses for the shift register 41 and counter 48. The Z output is from the automatic reset circuit 46 which is a one shot at a 5 second setting activated by the first data pulse. This resets the system after enough time for one data transmission routine. This is introduced to reset the system in the event of an incomplete transmission or a stray data pulse A stray data pulse from other than a transmitter is unlikely due to the design of the LM 567 tone detector as it requires at least 30 cycles at the tuned frequency prior to producing an output signal. The data output of the data flip flop 42 is from the Q output which is either high or low depending on a one or zero input and is synchronised with the shift register 41 by the clock input.

Figure 17 shows the circuitry of the state counter 48. The purpose of this circuit. is to check the data transmission. provide an oscillator for the counter and utilize the counter (4017) to properly control the receivers logic sequence. When 16 data pulses are received by the . 16 counter 48 (746161) the output will enable the LM 555 one shot to function as a clock for the 4017 decode counter. The first output of the counter (Terminal 2) provides an additional clock pulse to shift the 16th data bit into the shift register 41. The two count activates the transmission complete one tone to the transmitter as well as latching the display 45 and the three count resets the system.

Figure 18 shows the transmitter including switches 38 and 38A for channel 1 and channel 2 respectively: the thumwheels 49 for manually setting the switches of state counter 17 to the room number.

Figure 19 shows the receiver with manual reset switch 50 and digital display 45.

In a preferred embodiment of Figures 1-19, the intergrated circuits LM567. LM555 and LM380n are of the type manufactured by National Semiconductor Corp. of Santa Clara. U.S.A.

WHAT I CLAIM IS 1. An electronic apparatus for monitoring the condition of a patient including at least one sensor for sensing the movement of a patient out of bed, a transmitter electrically connected to said sensor and responsive to a signal from said sensor and capable of emitting impulses corresponding to the location of said sensor, the impulses being fed to a mains power line and received by a receiver located remote from the transmitter.

2. An apparatus in accordance with claim 1 in which the receiver includes a digital display which displays the location of the out of bed condition.

3. An apparatus according to claims 1 or 2 in which a visual or audible alarm is activated when the receiver receives impulses from the transmitter.

4. An apparatus according to claims 1, 2 or 3 in which the transmitter circuitry includes means for sending impulses to the receiver to give warning of a sensor that is defective or unplugged from the transmitter.

5. An apparatus according to claims 1, 2, 3, or 4 in which the receiver circuitry includes means for checking incoming transmissions so that if incomplete transmissions are received, instructions to resend will be made.

6. An apparatus according to claims 1,2,3,4 or 5 in which the transmitter includes means for interrogating the mains power line for other transmitter impulses and if present delays the sending of impulses until the line is clear.

7. An apparatus substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. by National Semiconductor Corp. of Santa Clara. U.S.A. WHAT I CLAIM IS

1. An electronic apparatus for monitoring the condition of a patient including at least one sensor for sensing the movement of a patient out of bed, a transmitter electrically connected to said sensor and responsive to a signal from said sensor and capable of emitting impulses corresponding to the location of said sensor, the impulses being fed to a mains power line and received by a receiver located remote from the transmitter.

2. An apparatus in accordance with claim 1 in which the receiver includes a digital display which displays the location of the out of bed condition.

3. An apparatus according to claims 1 or 2 in which a visual or audible alarm is activated when the receiver receives impulses from the transmitter.

4. An apparatus according to claims 1, 2 or 3 in which the transmitter circuitry includes means for sending impulses to the receiver to give warning of a sensor that is defective or unplugged from the transmitter.

5. An apparatus according to claims 1, 2, 3, or 4 in which the receiver circuitry includes means for checking incoming transmissions so that if incomplete transmissions are received, instructions to resend will be made.

6. An apparatus according to claims 1,2,3,4 or 5 in which the transmitter includes means for interrogating the mains power line for other transmitter impulses and if present delays the sending of impulses until the line is clear.

7. An apparatus substantially as described with reference to the accompanying drawings.