CZ2006620A3 - Weighing device, weighing device calibration method and method of determining weight by making use of such device - Google Patents

Abstract

Weighing apparatus, in particular for weighing a patient on a hospital bed, comprising a loading surface (1) mounted on the frame (2), wherein between the loading surface (1) and the frame (2) are arranged on the sensor (3) connected to the electronic an evaluation unit (4) and a line (5) for capturing parasitic forces. The force transducers (3) are at least two with different characteristics and their outputs (6) are separately connected to the electronic evaluation unit (4). The following is a description of how to calibrate such a device and how to detect it by such a device.

Description

The invention relates to a weighing device, in particular for weighing a patient in a hospital bed, comprising a bed surface mounted on a frame, wherein force sensors connected to an electronic evaluation unit and a line for absorbing parasitic forces are arranged between the bed surface and the frame. The invention further relates to a method of calibrating such a device and a method of determining weight by such a device.

BACKGROUND OF THE INVENTION

Monitoring the patient's weight while staying in the hospital is very important as changes in the patient's weight provide the attending physician with information about the patient's food, fluid and excretion.

Conventional weighing is carried out on standard stationary balances, but to which the patient must be transported. However, such patient handling is not always appropriate or possible.

Another possibility is the use of ramp weights, when the patient is brought with the bed. However, this method is not suitable for patients permanently connected to support facilities.

Monitoring the patient's weight directly on the bed is an effective and modern solution. The advantage is the possibility to monitor weight gains or losses continuously without unwanted manipulation with the patient. The bedside weighing device also offers other options such as remote monitoring of whether the patient has left the bed, connection to a computer, blocking the scale when handling items that do not require weighing, etc. However, weighing the absolute weight of the patient and its changes is most important. Of which

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there is also a requirement for the accuracy of the weighing equipment. For absolute weight, the requirement is to weigh to an accuracy of about 1 kg and for weight gain to an accuracy of about 0.1 kg.

In principle, two types of bed configurations with weighing equipment are used on existing beds.

In the first type, the sensors are located in the chassis of the bed; the frame is the chassis frame and the weight is the patient including the bed area. The advantage of this solution is simpler construction. The main disadvantage is the increased weight that is also moving when the bed is lifted and the weighing of some accessories.

In the second type, the sensors are located in the loading area, ie. the frame is the undercarriage including the lifting mechanism and the loading platform frame, the weighted load is the patient pad. The advantage is less weight to be weighed and the ability to attach accessories to the bed so that it is not weighed.

In existing hospital beds, systems with four force sensors are used, theoretically only three sensors are possible. For best accuracy, the sensors are positioned as far as possible on the edge of the bed to obtain the largest measured base. Another factor influencing the accuracy of weighing is the principle of mounting individual sensors. They are used over ball, spikes, silent blocks, etc.

Known devices for weighing a patient in a hospital bed include a bed surface mounted on a frame, with force sensors connected to the electronic evaluation unit and a line for capturing the parasitic forces between the bed and the frame.

The signal from the most frequently four sensors is routed to the merge section, where all signals are combined into one signal. This is then processed in an electronic evaluation unit and presented on the display part of the system.

The disadvantage of this system is that high weighing accuracy can only be achieved by using a calibrated set of transducers that all have the same or very similar slope of the K characteristic and the same value of the displacement characteristic. In case of any inaccuracies on any sensor, the measured results are significantly distorted. Therefore, when using cheaper, less accurate sensors, the weighing accuracy is not sufficient.

It is therefore an object of the present invention to provide a weighing device that allows the use of cheaper sensors without affecting measurement accuracy. It is a further object of the invention to provide a method for calibrating such a device and a method for determining the weight of such a device.

SUMMARY OF THE INVENTION

This object is achieved by a weighing device, in particular for weighing a patient in a hospital bed, comprising a bed surface mounted on a frame, wherein force sensors connected to an electronic evaluation unit and a line for detecting parasitic forces are arranged between the bed surface and the frame. The invention is based on the fact that the force sensors are at least two with different characteristics and their outputs are separately connected to an electronic evaluation unit.

An advantage of the device according to the invention is the fact that thanks to the separate connection to the electronic evaluation unit, sensors with different characteristics can be used, which significantly reduces the construction of the device.

According to a preferred embodiment, the parasitic force receiving line comprises a pair of parallelograms arranged at opposite ends of the frame, each parallelogram comprising at least two arms connected on one side to the frame and on the opposite side to the sub-plate. The arms are elastically deformable at the point of connection to the frame and the auxiliary plate. The auxiliary plate is connected to the loading surface and a force sensor is arranged between the auxiliary plate and the frame.

According to a further preferred embodiment, the parasitic force absorbing line comprises a pair of pivot mechanisms arranged at opposite ends of the frame. Each pivot mechanism comprises at least one longitudinal member attached on one side pivotable to the frame and on the other side attached or supported on the loading surface. A force sensor is arranged between the longitudinal and the frame.

The above object is also achieved by a method of calibrating a device according to which a weight of known mass mo is placed at any point on the loading surface and the output signals of 3m _2m are detected by force sensors under load of a known weight mo.

Thereafter, weights of known mass m-ι are placed at any other place in the mattress platform, where m-ι may be equal to m ₀ and the output signals Si _m ia and S _2m i of the load cell are determined under load of known mass ητη.

Subsequently, weights of known mass m _{3 are} placed in any other place of the mattress platform, where m ₃ may be equal to m _2, and output signals S _1m2 and S _2m2 of the load cells are detected under load of the known mass of known mass m ₂ .

Then, weights of known mass m _{3 are} placed at any other other place of the mattress platform, where m ₃ can be equal to m _2, and output signals Si _m 3 3 S _{2 m} 3 of load cells are detected under load of known mass m ₃ .

Subsequently, the displacement values Oi and O ₂ of the sensor characteristics and the slope Ki and K ₂ of the sensor characteristics from the set of equations are determined.

Simo ⁼ Ki * moi + Oi

S ₂ mo ⁼ K ₂ * (rrio-moi) + O ₂

Simi ^{: =} Ki * mii + Oi

S _2m i ⁼ K ₂ * (mi - mu) + O ₂

Sim2 ⁼ Ki * rn ₂₁ + O 1

S ₂ m2 = K ₂ * (m ₂ - m ₂ i) + O ₂

Slm3 ⁼ Ki * m ₃ i + O ₁

S ₂ m 3 ⁼ K ₂ * (lTl3 - ΠΙ31) + O2 where

Simx is the output signal of the first load cell under load m _x S _2m x is the output of the second load cell under load m _x , mx is the weight of x, m _x i is the part of the weight of x acting on the first load cell,

O1 is the displacement value of the characteristic of the first sensor,

O2 is the displacement value of the first sensor characteristic,

K1 is the slope of the first sensor, and

K ₂ is the slope of the first sensor characteristic.

and set the value of K |, K2, O1, _O2 stores the electronic unit.

The newly designed calibration method allows the use of sensors with different characteristics.

According to a preferred embodiment of the calibration method, the weight load of the MO selects zero and the detected output signals Sl OA _{m 2 m} with two force transducers at loading the laying surface zero.

Thereafter, weights of known mass πη are placed at any point on the loading surface and the output signals Si _m ia and S2mi of the force transducers are detected when the load is loaded with a weight of known mass mi.

Subsequently, in any other place of the laying surface a weight with the known weight value _m2, where _m2 may be equal to mi and the output signals Si _{m 2} and _{2 m} 2 force transducers at loading the laying surface with a weight with the known weight value _m2.

The system of equations is adjusted so that the displacement values O1 and O ₂ of the sensor characteristics are determined from the relations Oi = Si _m o and 0 ₂ = S _2m o, and the slope of the sensor characteristics K1 and K ₂ is determined from the relations

Oi * (S2m2 ”S2ml) ⁺ 02 * (Sim1 Sim2) ⁺ Slm2 * S2m1“ θ1ηη1 θ2ω2

Κι =

ΓΠι * (θ2-S2m2) ~ ΓΠ2 * (θ2-S2ml)

Kfiszmi-Oz)

Κ ₂ = m / K! -Si _m i + Οι

The above object is also achieved by a method for the mass determination device according to the invention in which the weighed object placed on the loading surface, and subtracting the output signals Si and S2 _{P P} force transducers.

Then the weight of the weighed object acting on the first force transducer is determined from the relation mi _p = (S _1p -Oi) / Ki and at the same time the weight of the weighed object acting on the second force transducer is determined from the relation m2 _P = (S2 _P -O2) / K _second

Subsequently, the total mass m _{p of the} weighed object is determined as the sum of the values mi _p and rri2 _P , where

Si _p is the output signal of the first sensor when the load is loaded by the object to be weighed,

S2 _P is the output signal of the first load cell under load, mi _p is the weight of the weighed object acting on the second load cell, m _2p is the weight of the weighed object acting on the second load cell,

O1 is the displacement value of the characteristic of the first sensor,

O ₂ is the displacement value of the characteristic of the first sensor,

K1 is the slope of the first sensor, and

K2 is the slope of the first sensor characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

The weighing device according to the invention will be described in more detail by way of examples

1 is an example of the characteristics of the sensors used. Giant. 2 to 5 are schematic examples of various embodiments of the device according to the invention and FIG. 6 is an example of a specific construction of the device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The weighing device, in particular for weighing a patient in a hospital bed, according to FIG. 2, comprises a loading surface 1 mounted on the frame 2 by means of sliding guides 5 for absorbing parasitic forces.

Between the loading surface 1 and the frame 2 there are arranged two force sensors 3 connected to the electronic evaluation unit 4. Unlike the sensors in known constructions of this type, the sensors used have different characteristics. That is, the first encoder 3 has a slope Ki value Oi characteristics and displacement characteristics, while the second transducer 3 has a slope K ₂ O characteristics and the value of the characteristic shift ₂ (see FIG. 2). Both force sensors 3 have outputs 6 connected separately to a two-input electronic evaluation unit 4.

The evaluation unit 4 has a non-drawn display for displaying the resulting data.

Before the first use, the device must be calibrated so that sensors 3 with different characteristics can be used. The calibration is carried out by first placing a weight of known mass m ₀ at any point on the mattress platform 1 and determining the output signals Si _m o and S _2m o of the load cells under load of the mattress platform 1 with a known mass m ₀ .

Thereafter, weights of known mass m _{b are} placed in any other place of the mattress platform 7 where πη can be equal to m ₀ and the output signals Sinu and S _2m as well as the load cells 3 are detected when the mattress platform 1 is loaded with a known mass ηη.

Subsequently, a weight of known mass m _{3 is} placed at any other place of the loading surface 1, where m ₃ may be equal to m ₂ and the output signals Sim2 and S _2m 2 of the load cells 3 are detected ₂ .

Then at any yet other place of the laying surface 1 a weight with the known weight value _m3, where _m3 may be equal to _m2 and the output signals Si _m3 and S _{2 m3} force transducers 3 at loading the laying surface 1_ weight with the known weight m ₃ .

Subsequently, the displacement values Oi and O ₂ of the sensor characteristics and the slope Κί and K ₂ of the sensor characteristics are determined by solving the system of equations:

Si _m o = Ki * moi + Oi

S ₂ mo ⁼ K ₂ * (mo - moi) + O ₂

S _1m i = K ₁ * m ₁ i + Oi

S ₂ mi ⁼ K ₂ * (mi - mu) + O ₂

Sim2 = Ki * m ₂₁ + O 1

S ₂ m2 = K ₂ * (m ₂ - m ₂ i) + O ₂

Si _{m 3} = Ki * m ₃ i + Oi

S _2m3 = K ₂ * (m ₃ - m ₃ i) + O ₂ where

Simx the output signal of the first transducer at loading the laying surface with the weight m _x S _{2 m} x is the output signal of the second transducer at loading the laying surface with the weight m _x, m _* is the mass of the weight x, m _x i is the part of the weight of the weight x loading the first force transducer ,

Oi is the displacement value of the characteristic of the first sensor,

O ₂ is the displacement value of the characteristic of the first sensor,

Ημ is the slope of the first sensor, and

K ₂ is the slope of the first sensor characteristic.

The general procedure for solving a system of equations is well known and will not be described in detail.

The calibration is terminated by storing the determined values Κι, K2, Οι, O2 in the memory of the electronic evaluation unit 4.

The above calibration procedure can be significantly simplified by selecting a load weight of m _{0 of} zero.

In a first step therefore detects the output signals S _{1 m} OA S2mo two force transducers 3 at loading the laying surface zero one ..

Thereafter, weights of known mass πη are placed at any point in the loading surface 1, and the output signals Smu and S2mi of the load cells 3 are detected under load of a known weight mi and then a known weight is placed at any other location. mass m ₂ , where m ₂ may be equal and the output signals S _1m2 and S2m2 of the load cells 3 shall be determined under load of the loading area 1 by a weight of known mass m ₂ :

The above set of equations is adjusted so that the displacement values of O1 and O2 of the sensor 3 characteristics are determined from the relations Oi = Si _m o and 02 = S2mo, and the slope values K1 and K2 of the sensor characteristics 3 are determined from simplified relations obtained :

θ1 (S2m2 ^- S2ml) ⁺ θ2 (S- | m1 ~ Slm2) ⁺ S- | m2 * S2m1 ~ Sim1 S2m2

Ki = ΤΙΤΙ * (02 - S2m2) - 2Π2 * (Ο2 - S2ml)

KfíSzmrOz)

K ₂ = m- | * Ki - Siml + Ol

During weighing, the patient to be weighed must of course lie on the bed surface of the bed provided with the device according to the invention.

The evaluation unit 4 subtracts the output signals Si _p and S2 _{P of} both force sensors 3 and determines a portion of the patient's weight on the bed bed 1 acting on the first force sensor 3 with the relation mi _p = (Si _p -Oi) / K- | . At the same time, the part of the patient's mass acting on the second force sensor 3 is determined from the relation m2 _P = (S2 _P -O2) / K2.

Subsequently, the total mass m _p of the patient as a weighted sum of the values _P I am _2p.

The individual symbols used indicate:

Si _p is the output signal of the first sensor when the load is loaded by the object to be weighed,

S _2p is the output signal of the first load cell under load, mi _p is the weight of the weighed object acting on the second load cell, rr »2 _P is the weight of the weighed object acting on the second load cell,

Oi is the displacement value of the characteristic of the first sensor,

O2 is the displacement value of the first sensor characteristic,

K1 is the slope of the first sensor, and

K ₂ is the slope of the first sensor characteristic.

FIG. 3 shows another embodiment of the weighing device according to the invention. The embodiment of Fig. 3 differs from the embodiment of Fig. 2 in the construction of the parasitic forces receiving line 5, consisting of a pair of pivot mechanisms arranged at opposite ends of the frame 2. Each pivot mechanism comprises one longitudinal member 9 attached to one side pivotable to the frame 2. On the opposite side, one longitudinal 9 attached to the bed surface and the other longitudinal 9 is only supported by the bed surface. A force sensor 3 is arranged between each longitudinal member 9 and the frame 2. The calibration of the device and the weighing method are the same as in the above-described embodiment.

FIG. 4 shows another embodiment of the weighing device according to the invention. The line 5 for absorbing the parasitic forces comprises two parallelograms with a spring,

Two force transducers 3 are again arranged between the bed surface of the bed and the frame 2. The device calibration and weighing method are the same as those described above.

Fig. 5 shows yet another embodiment of the weighing device according to the invention. The parasitic force guide 5 comprises a pair of parallelograms arranged at opposite ends of the frame 2. Each parallelogram comprises two arms 7, connected on one side to the frame 2 and on the other side to the telescopic column 10 for positioning the bed 1. A force sensor 3 is arranged between each telescopic mast TO and the frame 2. The arms 7 are rigid, only at the point of attachment to the frame 2 and to the telescopic pole 10 are elastically deformable. This can be achieved, for example, by making the legs 7 of sheet metal of appropriate thickness and by bending the sheet at the sides.

A specific embodiment with such arms 7 is shown in Fig. 6. The parasitic force receiving line 5 comprises a pair of parallelograms arranged at opposite ends of the frame 2. For simplicity, only the parallelogram at the left end of the frame 2 is shown in FIG. the arms 7, connected on one side to the frame 2 and on the opposite side to the sub-plate 8. The metal arms 7 are elastically deformable at the point of connection to the frame 2 and the sub-plate 8, otherwise they are reinforced at the edges by bending the sheet. The auxiliary plate 8 is connected to the loading surface 7 by means of a telescopic column 10. A force sensor 3 (not shown) is arranged between the auxiliary plate 8 and the frame 2. The calibration of the device and the weighing method are again the same as in the above-described embodiments.

Claims (6)

PATENT CLAIMS A weighing device, in particular for weighing a patient in a hospital bed, comprising a bed surface (1) mounted on a frame (2), wherein between the bed surface (1) and the frame (2) there are arranged force sensors (3) connected to the electronic evaluation unit (4) and secondly to the line (5) for capturing the parasitic forces, characterized in that the force sensors (3) are at least two with different characteristics and their outputs (6) are separately connected to the electronic evaluation unit (4) . Device according to claim 1, characterized in that the guide (5) for absorbing the parasitic forces comprises a pair of parallelograms arranged at opposite ends of the frame (2), each parallelogram comprising at least two arms (7) connected on one side to the frame (2) and on the opposite side to the auxiliary plate (8), the arms (7) being elastically deformable at the point of attachment to the frame (2) and the auxiliary plate (8), the auxiliary plate (8) being connected to the bed ( 1) and a force sensor (3) is arranged between the auxiliary plate (8) and the frame (2). Device according to claim 1, characterized in that the guide (5) for absorbing the parasitic forces comprises a pair of pivot mechanisms arranged at opposite ends of the frame (2), each pivot mechanism comprising at least one longitudinal member (9) connected on one side pivotal to the frame (2) and attached or supported on the supporting surface (1) on the opposite side, a force sensor (3) being arranged between the longitudinal (9) and the frame (2). Method for calibrating a device according to any one of claims 1 to 3, characterized in that a weight of known mass mo is placed at any point of the loading surface and the output signals S _1m0 and S2mo of the load cells are detected under load of a known weight , then weights of known mass mi are placed at any other place on the mattress platform where I can be equal to and the output signals of Simi and S2mi of the load cell are detected when the mattress platform is loaded with a known mass πη, • · · * * 9 «• 9 · · 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 999 99 99 99 thereafter, a load of known mass 1TI3 is placed on any other place of the mattress platform, where 1TI3 may be equal to nri2 and the output signals of Sim2 and S2m2 of the load cell are detected under load of the mass of known mass m2, and place any weights of known mass ITI3 at any other place of the loading surface, where nri3 may be equal to rri2 and the output signals Si _m 3 and S2m3 of the load cells shall be detected under load of known mass 013, then the displacement values O1 shall be determined and O2 sensor characteristics and slope K1 and K ₂ sensor characteristics from the set of equations S _1m o = Ki * m _O i + O1 S2mo ⁼ K2 * (mo-moi) + O2 Simi ⁼ Ki * mn + O1 S2mi ⁼ K2 * (mi - mu) + O2 Slm2 = K1 * m ₂ 1+ O1 S2m2 ⁼ K2 * (m2 - ΓΠ2) + O2 Slm3 = Ki * m ₃ 1+ Ol S2m3 ⁼ K2 * (m 3 - m ₃₁ ) + O2 where Simx is the output signal of the first sensor when the load is loaded by the mass m _x S2mx is the output signal of the second sensor when the load is loaded by the mass m _x , m _x is the weight of the weight x, m _x1 O1 is the displacement value of the characteristic of the first sensor, O2 is the displacement value of the first sensor characteristic, K1 is the slope of the first sensor characteristic a K ₂ is the slope of the first sensor characteristic and the determined values Ki, K ₂ , O-1, O _{2 are} stored in the memory of the electronic evaluation unit. Method according to claim 4, characterized in that the load mass mo is selected at zero and detects the output signals Si _m o and S2mo of the two load cells at zero load, then a weight of known mass mi is placed at any point of the load surface. with output signals Si _m ia S _2m i of load cells under load of known weight mi, then weights of known mass m _{2 are} placed on any other place of the loading area, where m ₂ can be equal to πη and output signals are detected Si _m2 and S _2m2 of the load cell under load of a known mass of m ₂ , and the system of equations is adjusted so that the displacement values Oi and O ₂ of the sensor characteristics are determined from the relations Oi = Si _m o and 0 ₂ = S _2m o , and the slope of the sensor characteristics Ki and K ₂ is determined from the relationships Ol * (S ₂ m2 “S _2m - |) + 0 ₂ * (Sim1” Si _m 2) + Si _m 2 * S _2m i 'SimrS _2m2 Ki = mi * (O ₂ - S _2m 2) - m ₂ * (O ₂ - S _2m i) Ki * (with _2m iO ₂ ) K ₂ = A method for determining the weight of a device according to any one of claims 1 to 3, wherein the weighing object is placed on the loading surface and the output signals Si _p and S _2p of the force sensors are read, then determining the weight of the weighing object acting on the weighing object. the first force transducer from the relation mi _p = (Si _p -O ₁ ) / K ₁ and at the same time the mass of the object to be weighed on the second force transducer is determined from the relation m _2p = (S _2p -O ₂ ) / K ₂ and then the total mass m _{p of the} weighed object is determined as the sum of the values m _1p and m _2p , where Si _p is the output signal of the first sensor when the load is loaded by the object to be weighed, S _2p is the output signal of the first load cell under load, m _1p is the weight of the load on the second load cell, • 4 4 »4 4 4 4 4 · 4 4 4 4 4 4 4 44 4444 • 44 44 4 4 4 4 4 4 4 4 4 4 4 444 44 4 44 • 4 4 4 444 4 4 · 4 4 4 4 4 44 44 ιτΐ2ρ is the weight of the weighed item acting on the second force sensor, Oi is the displacement value of the characteristic of the first sensor, O2 is the displacement value of the first sensor characteristic, K1 is the slope of the first sensor, and K ₂ is the slope of the first sensor.