WO2002015748A1

WO2002015748A1 - Method, device and pressure sensor cushions for detecting an incorrect sitting posture

Info

Publication number: WO2002015748A1
Application number: PCT/NL2001/000615
Authority: WO
Original assignee: Van Der Kamp, Henk, Willem
Priority date: 2000-08-21
Filing date: 2001-08-21
Publication date: 2002-02-28
Also published as: AU2001292442A1; NL1015970C2

Abstract

Method for detecting a person's incorrect posture when working at a workstation. The pressure between at least part of the person's arm and a support arranged at the workstation for supporting the part of the arm therefore is measured. A signal is emitted if the measured pressure is outside a predetermined pressure range. For calibration an upper value is added to and a lower value subtracted from the pressure measured when the correct posture has been assumed, in order to obtain and to store an upper pressure limit and, respectively, lower pressure limit for the pressure range.

Description

Meth , device and pressure sensor cushions for detecting an incorrect sitting posture

The invention relates to a method for detecting a person's incorrect posture when working at a workstation. WO 94/10877 discloses an ergonomic chair that is provided with pressure sensors __ which are connected to an analytical device which can control a warning buzzer when the measured pressure or pressure relationships from various sensors are outside predetermined limits. Incorrect posture when working gives rise to too high a strain in certain muscle groups, usually the muscles that have to counteract gravity. Examples of these are the neck muscles.

The best sitting posture when working is in general a personal posture in which the person is sitting relaxed and in which the forces on the structures are acceptable. In order to detect an incorrect sitting posture, according to WO 94/10877 the pressure between the back and the backrest and the pressure exerted by the person on the seat of the chair are measured, the ratio being a criterion for the incorrect sitting posture. In practice the pressure between a person's back and the backrest is found not to be an unambiguous criterion for a good or incorrect posture of the seated person.

The aim of the invention is to provide a method of the type mentioned in the preamble with which a reliable criterion for an incorrect sitting posture is obtained in a simple manner.

Said aim is achieved according to the invention in that the pressure between at least part of a person's arm and a support arranged at the workstation for supporting the part of the arm is measured and a signal is emitted if the measured pressure is outside a predetermined range. The inventor has found, surprisingly, that in order to achieve reliable detection of an incorrect sitting posture it suffices merely to measure the pressure between part of the seated person's arm, for example the lower arm or elbow and a worktop or armrest at the workstation.

The term incorrect posture is also used to refer to good posture that is maintained for a prolonged period or statically for too long. Furthermore, in addition to a workstation for a seated user, workstations for standing users (including for computers) are being used to an ever-increasing extent.

It is observed that it is known per se from the US Patent 5,993, 400 to determine the pressure between a part of a person's arm and a sheet wrapped around said arm of a cast, however, said cast has nothing to do with a support for a part of the arm at a workstation. Moreover, the pressure between the concerning part of the arm and the cast wrap is by no means responsive to the posture of a sitting or standing person. The invention also relates to a device for detecting an incorrect posture of a person when working at a workstation, which device is characterised by a pressure sensor pad or cushion that is equipped for placing between at least part of the person's arm and a support arranged at the workstation for supporting the part of the arm and a processing device connected thereto which emits a signal when the measured pressure is outside a predetermined pressure range .

The invention also relates to a pressure sensor pad or cushion to be used with the abovementioned method or device. Preferred illustrative embodiments of the method, device and pressure sensor cushion are described in dependent claims.

The invention will be explained in more detail below with reference to the drawings. In the drawings:

Figure 1 shows a side view of a person, drawn diagrammatically, in a seated position with a pressure sensor cushion according to the invention between the elbow and the worktop;

Figure 2 shows a plan view of said person; Figure 3 shows a side view of a person in a seated position with a pressure sensor cushion between lower arm (plus elbow) and an armrest;

Figure 4 shows a block diagram of a processing device according to the invention for processing the pressures measured by means of a pressure sensor cushion according to the invention; Figure 5 shows a section through a pressure sensor cushion according to one embodiment of the invention and;

Figure 6 shows another embodiment of the pressure sensor cushion according to the invention.

Despite the fact that RSI (repetitive strain injury) is one of the oldest clinical pictures - the torment of writer's cramp experienced by the monks in olden times - attempts are still being made, even to an increasing degree, to provide solutions to solve the RSI problem itself. Inflammation of the Achilles tendon or tennis elbow that has arisen as a result of incorrect striking technique is actually also an RSI. Computer and mouse-related RSI in any event results when people sit at the computer for too long in a posture that produces too much strain.

A number of synonyms for RSI are, for example, work-related diseases and excessive strain injuries. Incorrect posture gives rise to excessive strain in certain muscle groups, usually the muscles that have to counteract gravity. The neck muscles and extensor muscles of the wrist are examples of these, but not the only ones. Working at the computer in a sitting or standing posture or other posture gives rise to there being too little movement, as a result of which various muscles have to perform a lot of static work. Because the blood requirement is high ut the circulation is poor - in particular there is no pumping action - circulation problems arise in the muscles after only two minutes.

In addition to this static overstraining of muscles, there are also muscle groups which are not used. The principle of "use them or lose them" then applies. On the one hand, the muscles placed under strain will become stronger and will shorten; on the other hand the unused muscle groups will become more flaccid. Nerves around or in the hardened muscles can be compressed, as a result of which this structure is also irritated. It is possible that capsule-ligament structures are overstressed or understressed as a result of continuously exerting the same strain at a certain angle on a joint. The joint as a whole becomes incorrectly stressed; as a result of which irritation processes can arise here as well. In addition, both understressing and overstressing give rise to an increased risk of cartilage degeneration.

In conclusion, it can be stated that all structures, such as a muscle, the joint, the capsule, etc. can give problems as a result of a static posture. The best solution in order to ensure that this does not occur is, of course, a change in posture in combination with the correct posture.

The best posture is a personal posture where the seated person is sitting relaxed and where the forces on structures such as ligaments, tendons, bones, joints, nerves, skin and muscles are acceptable.

In the case of a person who works at a screen there is clearly a difference between a touch typist and a non-touch typist. The touch typist can rest his/her elbows close to the body. The upper arm is, as it were, in direct contact with the trunk. In the case of the non- touch typist the desktop will have to be set higher, as a result of which the angle between the eyes and the keyboard becomes smaller. The keyboard is also pushed somewhat further away. As a result it is possible to look straight from the keyboard to the screen.

The angle that the upper arm makes with the trunk should not be more than 30° in the lateral direction and should not be more than 60° in the forward direction. The horizontal distance from navel to mid-hand should not be more than 45 cm. A relaxed posture for the neck, arm and back muscles and other muscles must be found within these angles and distances.

The head ought not to be bent and/or turned through more than 15 to 20°. The wrists should be supported on a wrist rest or on the desk at elbow height. The position of the wrist should consequently be in the extension of the lower arms. The angle of the elbows should be 90 to 120°. The thoracic spinal column does not have to be supported. The lower back must be held in a concave position by means of, preferably, a lumbar support. The hips and knees should be at an angle of 90°. The feet should be completely supported.

Although the optimum posture described above is known, it is found that people have a very poor feeling for posture and are even less capable of maintaining this posture while working, especially if the work demands concentration. It is also found that attention is given to posture only when pain results as a consequence of poor posture. People find it annoying if they are not in control of their work.

Work is often under high pressure, as a result of which little time is afforded to factors which have nothing to do with the work, such as posture and movement. In practice it has been found that one should not be under too many illusions that a posture is easy to change by means of instruction and a good ergonomic workstation.

As a result of many years of practical experience, the inventor has, by trial and error, conceived a method for detecting a person's incorrect sitting posture when working seated at a worktop in order thus to support the person in improving and "making his/her own" best personal posture/least stressful posture. With this method the pressure between at least part of the person's arm (lower arm and/or elbow) and a support (worktop or armrest) is measured. A signal is emitted if the measured pressure is outside a predetermined pressure range.

The inventor has found, surprisingly, that the pressure has to be measured only in one location, specifically between part of the person's arm and a support therefor. It appears from the figures 1-3 that the support is one at the workstation in the shown embodiment the desk top or armrest. Of course the pressure between part of the person's other arm and a support therefor can be measured in parallel. This was found to be adequate, despite the complex processes and diverse factors which, as indicated above, apply in respect of a good sitting posture.

Because, as has already been stated above, a good sitting posture is highly personal, it is advisable to offer the person the facility for carrying out a calibration before he or she starts to work. For this calibration the seated person assumes a correct sitting posture and the pressure between part of the person's lower arm and a support therefor is measured in this sitting posture. An upper value is added to this measured pressure and a lower value is deducted therefrom in order to obtain and to store, respectively, the upper pressure limit and lower pressure limit of the pressure range, within which pressure range the measured pressure will have to be in the case of a later correct working sitting posture. The upper- and lower values can be determined experimently, if desired dependant on the frequent or not frequent emission of signal as warning of an incorrect posture.

The emission of the signal responsive to a measured incorrect posture could be delayed with an adjustable time period. If desired the response to the measurement of an incorrect posture, can be adjusted both by the height of the upper- and/or lower value for defining the pressure range and the abovementioned time period.

In a further embodiment a signal is emitted if the measured pressure is within the predetermined pressure range during a further adjustable time period. It is pointed out that the above of course also applies to other postures, such as, for example a standing posture or lying posture.

Preferably, the measured pressures are converted to digital form so that the pressure values can easily be processed in a personal computer.

The invention is not only suitable for a person working at a screen, but is also exceptionally suitable for a person working at a sewing machine, a telephonist, laboratory staff or people who assemble electronic equipment or who are reading a book, as soon as there is any risk of overstraining.

A seated person 1 is shown diagrammatically in Figures 1 and 2. This person is working at a screen 2. The person is sitting on a chair 3 at a worktop 4. The keyboard 5 is on the worktop 4. The arm 6 of the person 1 is resting on the worktop 4. A pressure sensor cushion 7 is arranged between the elbow and the worktop 4, which pressure sensor cushion 7 measures the pressure between elbow and/or part of the lower arm and the worktop 4. A round pressure sensor cushion is shown in Figure 2, but various shapes are possible. Figure 3 shows a similar seated person 1, the pressure sensor cushion 7 being arranged between elbow and part of the lower arm on the one hand and the armrest 8 of the chair 3. The other objects shown in Figure 3 have the same reference numerals as the corresponding objects in Figures 1 and 2. The invention also relates to a device for detecting a person's incorrect sitting posture when working seated at a worktop. This device comprises a pressure sensor cushion, as has been mentioned above and that is equipped for placing between at least part of the person's arm and a support therefor.

The device further comprises a processing device to which the pressure sensor cushion or cushions is or are connected. The processing device emits a signal when the pressure measured by means of the pressure sensor cushions is outside a predetermined pressure range. For this purpose the processing device, as is shown in Figure 4, can comprise a memory 9 in which an upper pressure limit and a lower pressure limit of a pressure range have been stored, within which range the measured pressure has to lie if it is not to generate a signal indicating incorrect sitting. According to one embodiment of the invention, the detection device also comprises an evaluation device 10, the inputs a, b thereof being fed the upper pressure limit and lower pressure limit from the memory 9. The pressure sensor cushion can be connected to the input c. A warning signal is emitted at the output d of the evaluation device if the pressure measured by means of the pressure sensor cushion is outside the abovementioned pressure range.

According to one embodiment of the invention, the detection device is provided with an adding device 11. The signal from the pressure sensor cushion is fed to the input c of the evaluation device 10 and is also fed to the input e of the adding device 11 and a corresponding input h of the subtraction device 12. A predetermined upper value is fed to the innut f of the addinsz device 1 1. whilst a nredetermined lower value is fed to the innut i

according to the invention can be implemented in a personal computer by means of software. It is then possible in a simple manner to choose, via the computer, between an acoustic and/or visual warning signal. This signal can be supplemented by exercises displayed on the screen or by information to be entered in accordance with the user's wishes.

If the person assumes an incorrect posture for too long a period and thus produces the wrong pressure on the pressure sensor cushion(s), a signal is automatically emitted, by means of which the person is warned to change his/her posture. Parameters which can be set are, for example, the working period at the screen, the good posture period, the incorrect posture period, etc. These time measurements are carried out by a timing device that is not shown.

The invention also relates to a pressure sensor cushion suitable for the methods and devices described above. In the case of disc-shaped pressure sensor cushions the diameter is preferably between 5 and 20 cm, whilst in the case of square or rectangular sensor cushions the length is preferably between 5 and 20 cm and the width is preferably between 5 and 20 cm. The thickness of the pressure sensor cushion is preferably less than 2 mm. If, however, a thickness greater than 2 mm is used, a recess is made in the top of the cushion to accommodate part of an arm, between which part of the arm and the support therefor the pressure has to be measured; see Figure 6. h order to prevent shifting of the pressure sensor cushion, the underside of the cushion is provided with an anti-slip layer or with a touch-and-close fastener, as is indicated diagrammatically in Figures 5 and 6 by the layer 14 of the pressure sensor cushion. Furthermore, the cushion can also be provided with fixing means for the part of the arm, which are not shown. The pressure sensor cushion(s) can be connected to the processing device via cables.

So as to experience as little nuisance as possible from the connection between the pressure sensor cushion and the processing device, the pressure sensor cushion is provided with a transmitter for wireless transmission of the measured pressure values, which pressure values are received by a receiver in the processing device, for example in or by the personal computer.

By means of the method, the device and the pressure sensor cushion according to the invention, a person can be corrected in an easy and friendly manner, whilst the pressure sensor cushions are not felt to be an inconvenience. The person at work will therefore also soon have the tendency continually to correct his/her posture. Because the most important reason for the occurrence of the current RSI clinical picture, specifically when seated at the computer for too long in a posture under strain, can be prevented by this means, this simple "posture reminder" is highly effective in reducing complaints and costs.

Claims

1. Method for detecting a person's incorrect posture when working at a workstation, characterised in that the pressure between at least part of a person's arm and a support arranged at the workstation for supporting the part of the arm is measured and a signal is emitted if the measured pressure is outside a predetermined range.

2. Method according to Claim 1, characterised in that for calibration an upper value is added to and a lower value subtracted from the pressure measured when the correct posture has been assumed, in order to obtain and to store an upper pressure limit and, respectively, lower pressure limit for the pressure range.

3. Method according to Claim 1 or 2, characterised in that the signal is only emitted after the measured pressure is outside the predetermined range during a first adjustable time period.

4. Method according to Claim 1, 2 or 3, characterised in that a signal is emitted if the measured pressure is within the predetermined range during a second adjustable time period.

5. Method according to one of Claims 1 - 4, characterised in that the measured pressures are converted to digital form.

6. Device for detecting an incorrect posture of a person when working at a workstation according to the method of one of Claims 1 - 5, characterised by a pressure sensor cushion that is equipped for placing between at least part of the person's arm and a support arranged at the workstation for supporting the part of the arm and a processing device connected thereto which emits a signal when the measured pressure is outside a predetermined pressure range.

7. Device according to Claim 6, characterised in that the processing device is provided with a memory for storing the upper pressure limit and lower pressure limit of the pressure range, an evaluation device, to which the stored upper pressure limit and lower pressure limit and the measured pressure while the person is working are fed and at the output of which a signal is emitted when the pressure measured during working is higher than the upper limit or lower than the lower limit.

8. Device according to Claim 6 or 7, characterised in that a calibration device is present.

9. Device according to Claim 8, characterised in that the calibration device is provided with an adding device, wherein an upper value is fed to the one input and a pressure measured when the person has the correct posture is fed to the other input and wherein the upper pressure limit can be obtained at the output for feeding to the memory, and a subtraction device, wherein a lower value is fed to the one input and a pressure measured when the person has the correct posture is fed to the other input and wherein the lower pressure limit can be obtained at the output for feeding to the memory.

10. Device according to one of Claims 6 - 9, characterised in that the signal is only emitted after the measured pressure outside the predetermined range during a first adjustable time period.

11. Device according to one of Claims 6-10, characterised in that a signal is emitted if the measured pressure is within the predetermined range during a second adjustable time period.

12. Device according to one of Claims 6 - 11, characterised in that the pressure sensor cushion is com ected to an analogue/digital converter.

13. Device according to one of Claims 6 - 12, characterised in that a timing device is present for determining time parameters during the pressure measurement, the signal being emitted when a time threshold is exceeded.

14. Method according to one of Claims 1 - 5, characterised in that said method is implemented in a personal computer by means of software.

15. Device according to one of Claims 6 -13, characterised in that said device is implemented in a personal computer by means of software.

16. Pressure sensor cushion for detecting a person's incorrect sitting posture when working seated at a worktop according to the method according to one of Claims 1 - 5 or

14 or suitable for the device according to one of Claims 6 - 13 or 15.

17. Pressure sensor cushion according to Claim 16, characterised in that the length is 5 - 20 cm.

18 Pressure sensor cushion according to Claim 16 or 17, characterised in that the width is 5 - 20 cm.

19. Pressure sensor cushion according to Claim 16, characterised in that it is disc- shaped with a diameter of between 5 and 20 cm.

20. Pressure sensor cushion according to Claim 16, 17, 18 or 19, characterised in that the thickness is less than 2 mm.

21. Pressure sensor cushion according to Claim 16, 17, 18 or 19, characterised in that the top of the cushion has a recess for partially accommodating the part of an arm.

22. Pressure sensor cushion according to one of Claims 16 - 21, characterised in that the underside of the cushion is provided with an anti-slip layer.

23. Pressure sensor cushion according to one of Claims 16 - 21, characterised in that the underside of the cushion is provided with touch-and-close fastening.

24. Pressure sensor cushion according to one of Claims 16 -21, characterised in that the cushion is provided with fixing means for the part of an arm.

25. Pressure sensor cushion according to one of Claims 16 - 24, characterised in that the cushion is provided with cables for communication of the measured pressure values.

26. Pressure sensor cushion according to one of Claims 16 - 24, characterised in that the cushion is provided with a transmitter for wireless transmission of the measured pressure values.