WO2005058159A1

WO2005058159A1 - Lifting position monitor using a solid state inclinometer

Info

Publication number: WO2005058159A1
Application number: PCT/GB2004/004335
Authority: WO
Inventors: John Philip Pelling
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-12-19
Filing date: 2004-10-12
Publication date: 2005-06-30
Anticipated expiration: 2006-06-19
Also published as: AU2004298885A1; EP1694209A1; NZ547726A; CA2547636A1

Abstract

A lifting position monitor is incorporated in a case (20) for attachment to the upper torso of a wearer. The case contains a micro-electromechanical motion sensor arrangement (52) capable of detecting movement in three mutually orthogonal axes, which is encapsulated with solid state integrated signal processing electronics (51) to provide respective outputs which represent complex movements in all three axes relative to a datum position. An electronic data processor (70) analyses the outputs to look for predetermined movement patterns with components in one or more of said axes and operates an alarm (76) to warn the wearer of a potentially dangerous lifting practice. The processor (70) can determine the three-dimensional direction, extent and speed of movements. Movement data may be recorded and downloaded (74) or sent wirelessly (75) to a remote location for remote monitoring and analysis of long-term movement patterns.

Description

LIFTING POSITION MONITOR USING A SOLID STATE INCLINOMETER

TECHNICAL FIELD OF THE INVENTION

This invention relates to lifting position monitors.

BACKGROUND

Numerous cases of back injury occur every year due to people performing potentially dangerous movements when handling, lifting or carrying heavy objects. Lifting position monitors are already known which are intended to provide a warning when a person adopts a poor lifting posture. However, such known devices, and in particular the tilt switches which they employ, are not very accurate and may be prone to spurious triggering during rapid movements for example. As a result, such monitors may become a nuisance to the user causing them to be ignored or discarded altogether.

The most common form of tilt switch employs a bead of liquid mercury which is contained within a sealed enclosure. In some orientations the bead completes a circuit between a pair of electrical contacts whereas in other orientations the circuit is incomplete. However, a bead of liquid suffers from inertia problems, and the angle of triggering is extremely variable. The kind of movements to which conventional tilt switches are capable of responding is very restricted, essentially being limited to the detection of large angular movements. Nurses and carers, for example, may carry out quite complex movements when lifting a patient. It has been shown that many injuries are caused by quite small movements, and the risk of injury increases significantly if an unsuitable lifting technique is repeated over a prolonged period.

Recently, micro-electromechanical sensors (MEMS) have become available which can be used to accurately determine tilt angle. Although it has already been proposed to use such devices in posture detectors these essentially do no more than conventional lifting position monitors which only detect angular movements in a single vertical plane on the front-rear axis of the body, and provide a warning when a predetermined safe tilt angle is exceeded.

The present invention seeks to provide a new and inventive form of lifting position monitor which is capable of accurate and reliable results.

SUMMARY OF THE INVENTION

The present invention provides a lifting position monitor which includes a case, attachment means for securing the case to the upper torso of a wearer, a micro-electromechanical motion sensor arrangement, mounted within the case, which responds to movements of the wearer and which is encapsulated with solid state integrated signal processing means to provide an output which represents movement relative to a datum position, and electronic data handling means which stores data derived from said output for use in the detection of potentially dangerous movement characteristics, characterised in that the micro-electromechanical motion sensor arrangement responds to movement in three substantially orthogonal axes and said signal processing means provides respective outputs for each of said axes.

The lifting position monitor is capable of detecting complex and potentially dangerous movements such as twisting. If such movements exceed predetermined parameters their occurrence can be recorded, and the detailed movement pattern can also be recorded for more detailed analysis.

The monitor may record movement patterns which are not potentially dangerous in themselves but which, whilst not presenting an immediate danger, could present a significant risk of long-term injury through prolonged repetition.

In addition to responding to the occurrence of predetermined complex movement patterns the monitor may also record movements which are not inherently dangerous but which are executed too quickly.

The device may include a warning alarm which is activated when a high risk lifting posture is being executed, before the wearer has applied an excessive strain to their back. The alarm may be audible and/or visual, and may operate remotely, e.g. by means of a radio link.

BRIEF DESCRIPTION OF THE DRAWINGS The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings:

Figure 1 is a top view of a lifting position monitor in accordance with the invention;

Figure 2 is a sectional view of the lifting position monitor on line ll-ll of Fig. 3;

Figure 3 is a sectional view of the lifting position monitor on line Ill-Ill of Fig. 2;

Figure 4 is a transparent view of a first form of integrated circuit inclinometer suitable for use in the monitor;

Figure 5 is an exploded view of the capacitive tilt sensor which is incorporated in the integrated circuit package;

Figure 6 is a diagrammatic vertical section through the tilt sensor, shown in a tilted condition;

Figure 7 is a general view of a second form of integrated circuit inclinometer which may be used in the monitor;

Figure 8 is a general view of the capacitive tilt sensor which is incorporated in the integrated circuit package of Fig. 7;

Figure 9 is a circuit diagram of the electronic circuitry which may be used in the lifting position monitor; Figure 10 is series of diagrammatic side views of a person wearing the lifting position monitor, using a low risk lifting posture;

Figure 11 is similar series of views showing a person assuming a poor lifting posture;

Figures 12a to 12c are a series of diagrammatic plan views showing a person wearing the lifting position monitor, executing a lift with and without twisting of the torso;

Figure 13 is a diagram showing the movement of a person using a staircase; and

Figure 14 is a series of diagrammatic side views showing a person moving between standing and seated positions.

DETAILED DESCRIPTION OF THE DRAWINGS

The lifting position monitor which is shown in Fig.s 1 to 3 has an elongate plastic case 20 which is moulded in two halves 21 and 22 with a longitudinal division. At the upper end of the case there is a small piezo sounder 23. A rear half of the case has a spring clip 25 enabling the monitor to be secured to a wearers clothing, e.g. clipped inside a shirt pocket.

Opposite sides of the case 20 are provided with a pair of push buttons 26 which can be depressed simultaneously to set a datum position, e.g. when the wearer is standing in a normal upright position.

The two halves of the case 20 are secured together by screws 27 and 28 which are inserted into aligned pillars. The case halves could also be snap-engaged. A rechargeable cell 30 is mounted on a printed circuit board 33 by means of a spring contact 34. The cell is rechargeable via a DIN type socket 49 mounted in the bottom of the case 20 when engaged with a docking station.

The circuit board 33 carries electrical circuitry, described below, which includes an integrated circuit package 50 incorporating a micro- electromechanical motion sensor (MEMS) which is encapsulated with solid state integrated signal processing electronics. Such devices have been developed for use in automotive applications, to trigger the release of an airbag in the event of a sudden impact, and are often referred to as solid state inclinometers or accelerometers. Fig. 4 shows one possible form of the integrated circuit 50, such as part No. SCA61T from VTI. Similar one and two axis devices are available from other manufacturers such as Analog Devices, Inc. The IC 50 is provided in a standard surface mount package containing the signal processing chip 51 and a micro- electromechanical sensor 52, which is shown in exploded detail in Fig. 5. An intermediate silicon wafer 53 is etched to provide a proof mass 54 which is connected to a surrounding frame 55 by a pair of elastically deformable limbs 56 formed of polysilicon material. The intermediate wafer 53 is sandwiched between outer silicon wafers 57 and 58, both insulated from the wafer 53 by respective glass layers 59 and 60. A metal film electrode 61 is deposited on each of the outer wafers 57 and 58 to form differential capacitive electrodes on opposite sides of the proof mass 54. The signal processing electronics 51 may typically apply a pair of square wave signals, 80° out of phase, to the electrodes 61. When the proof mass is at rest in its normal datum position it is held midway between the differential electrodes 61 , but when, as shown in Fig. 6, the integrated circuit accelerates in the direction of the arrow, or in the opposite direction, the spacing between the proof mass and the differential electrodes changes resulting in a change in capacitance between the intermediate wafer 53 and the two outer wafers 57 and 58. The on-chip electronics may use phase-sensitive demodulation techniques to detect the change in capacitance, and generate an output signal which is proportional to the acceleration of the sensor. The output may be in the form of an analogue or digital signal, or a pulse-width modulated signal. The output may be used to directly monitor acceleration along the respective axis. In addition however, the acceleration information can also be used to determine other parameters such as the distance moved relative to an initial datum position and the speed of movement. This information may be used in various ways, as described below, to actuate an alarm when predetermined potentially dangerous movement patterns are detected.

The form of sensor described above is only capable of responding to movement along one axis, but by using three orthogonally-mounted sensors (whether in the same i.e. package or separate packages) it is possible to obtain separate outputs for each of the three axes. More recent three-axis MEMS devices such as part No. LIS3L02AQ from ST Microelectronics are capable of providing separate outputs for all three axes of movement. As shown in Fig. 7, such devices include a single sensing element 52 within an integrated package 50, with on-chip CMOS signal processing electronics 51. The sensing element, which is shown in Fig. 8, incorporates suspended silicon structures which are attached to a substrate at a number of anchor points and are free to move on a plane parallel to the substrate. Movement of the structures is again detected capacitively.

Fig. 9 shows a block circuit diagram of the lifting position monitor, which is capable of monitoring and recording very complex movements. The monitor incorporates three mutually orthogonal electro-mechanical motions sensors 52x, 52y and 52z, which are connected to a microprocessor 70 via on-chip signal processing electronics 51. The first sensor 52x is arranged to monitor body movements in a front-rear direction, the second sensor 52y monitors vertical movements, and the third sensor 52z responds to side-to-side movements. The electronics 51 may provide the microprocessor with three raw data outputs representing the rate of acceleration along each of the three axes. The three sets of data are recorded in an electronic memory 72 and can later be downloaded via a data port 74, incorporated in the DIN connector 49, by which the monitor can be coupled to a docking station 77 which passes the data to a computer 78. The data can also be transmitted to a remote location, such as computer 78, using a wireless transmitting device 75, for real time monitoring and logging purposes. The microprocessor 70 may analyse the incoming signals so that any combination of movements which are known to pose a risk of injury can be used to operate an alarm 76 and provide an immediate warning to the wearer.

Information downloaded through the data port 74 can be subjected to detailed analysis and, if recorded and monitored for a prolonged period, the computer 78 can provide a detailed history of movement practices and enable cumulative risk assessments to be carried out. This may, for example, enable employers to monitor the incidence of poor working practices and initiate early remedial action. When the device 20 is secured to the upper torso of a wearer, as shown in Fig. 10, provided the wearer starts from a squatting position when lifting a heavy object β the monitor will not trigger an alarm. The device may, however, record each squat lift for subsequent download. On the other hand, if the wearer should attempt to lift the object from a poor lifting position, e.g. bending over as illustrated in Fig. 11, the monitor will detect the movement pattern and cause the sounder 23 to emit a penetrating warning signal. This action will also be recorded for later downloading.

The monitor is capable of responding to complex potentially dangerous movement patterns with components in more than one plane. The use of three orthogonal sensors allows the instantaneous direction of movement to be determined from the relative magnitudes of the three outputs. Thus, for example, if the wearer starts from a standing position shown in Fig. 12a and lifts without twisting of the torso as in Fig. 12b, large outputs will be produced in the x and y axes but the z-axis output will be relatively small. On the other hand, if the wearer makes a twisting movement during the course of the lift, as shown in Fig. 12c, this will produce output components from all three sensors. The detection of twist requires input from all three sensors since it is not desirable to detect people who are simply turning. Therefore, movement along the third axis (sensor 52z) is recorded only when movements in one of the other two axes exceed a given threshold. The datum position may be set manually by depressing the push buttons 26, or it may be established automatically by the on.- board microprocessor. In order to establish the original datum position the microprocessor 70 may store the outputs from all three sensors in a buffer (e.g. with a capacity of five seconds). Thus, if both the second and third axes movements exceed the threshold it is possible to look back to see what the original position of the third axis was at the beginning of the movement. If the respective thresholds are found to have been exceeded the microprocessor can generate a warning signal and save the detailed movement pattern for subsequent downloading.

Another potentially dangerous lifting condition which can be detected by the device is where the wearer executes a lift too rapidly. In this case, the magnitude of the acceleration output signal produced by the x-axis sensor will show that rapid movement has taken place over a dangerously short period, and a warning signal can again be produced to alert the wearer. Although it may be too late to prevent the lift in this instance the monitor will warn the wearer so that they may avoid such actions in the future.

The embedded software which controls the microprocessor 70 sets the parameters which trigger an activation which may result in the generation of a warning signal and/or the logging of an action. There are a number of qualifying conditions that need to be satisfied before a valid activation is signalled.

In a basic form of operation the x-axis and y-axis outputs may be used to determine the angle of stoop. When the monitor is tilted from the reference datum past a set threshold angle, the alarm warns the wearer and records key data for subsequent download.

The monitor may also respond to more complex movements. For example, the alarm activation thresholds for various lifting movements may be: stoop: = stoop > 70° with lateral < 15 ° lateral: = lateral >20 ° with stoop < 35 ° twist: = stoop > 60 ° with lateral > 25 ° An activation may also be triggered by movements within the angle thresholds but which exceed critical distance parameters. Such activations may need to be recorded but do not necessarily trigger an alarm. For example, it may be desired to keep a record of the number of times a wearer executes a lift from a squatting posture (Fig. 10), but the conditions which signal this event cannot be identified by stoop angle. However, the condition may be signalled when the device travels along the z-axis by say > 300 mm.

The embedded software must also take account of events which may cause a false activation. For example, a false squat lift may be signalled when going downstairs, as indicated in Fig. 13. The difference with descending stairs is that there is an associated x-axis movement of say > 250 mm. Therefore if this x-axis displacement occurs simultaneously (in the time it takes to travel along the z-axis by 300 mm), the activation is dismissed.

Similarly, by sitting down, as shown in Fig. 14, the monitor may also travel through a z-axis displacement greater than 300 mm. However, if the person does not move along the z-axis again by more than 150 mm within 20 seconds, it can be assumed that the person has sat down.

Another possible false activation might occur when a wearer descends in an elevator, which will also exceed the 300 mm z-axis activation threshold. However, if the z-axis movement is greater than 2,000 mm it can be assumed that the wearer is not lifting and the activation can again be discounted.

It can thus be seen that in the simple example discussed above the logic for identifying a valid squat lift is as follows: 2,000 mm > Zmax - Zmin > 300 mm and

X & Y < 250 mm and

(Zmin + 150)mm < 20 sees from Zmax

When the displacement reaches 300 mm in the z-axis, Zmax may be taken as the higher z-axis reading. The 20 second period can start from this point, or alternatively, from the point 300 mm below Zmax.

When the monitored conditions do not exceed the activation parameters, the speed of movement is important and needs to be recorded. Sudden movements generate considerable pressure on the spine. Therefore if this sudden movement exceeds the set threshold the device also records this and alerts the wearer by means of the alarm (although it may be too late to prevent the movement in this instance).

The microprocessor may put the monitor into a low power mode to preserve battery life when no movements have been detected for, say three minutes. Normal functions are resumed when movements are detected.

It will be appreciated that the features disclosed herein may be present in any feasible combination. Whilst the above description lays emphasis on those areas which, in combination, are believed to be new, protection is claimed for any inventive combination of the features disclosed herein.

Claims

1. A lifting position monitor which includes a case (20), attachment means (25) for securing the case to the upper torso of a wearer, a micro- electromechanical motion sensor arrangement (52), mounted within the case, which responds to movements of the wearer and which is encapsulated with solid state integrated signal processing means (51 ) to provide an output which represents movement relative to a datum position, and electronic data handling means (70) which stores data derived from said output for use in the detection of potentially dangerous movement characteristics, characterised in that the micro-electromechanical motion sensor arrangement (52) responds to movement in three substantially orthogonal axes and said signal processing means provides respective outputs for each of said axes.

2. A lifting position monitor according to Claim 1 in which the output of said signal processing means (51) provides respective acceleration signals for the three axes.

3. A lifting position monitor according to Claim 1 which includes an audible and/or visual alarm (76) and said data handling means (7O) is arranged to analyse the outputs and trigger the alarm when potentially dangerous movement characteristics are detected.

4. A lifting position monitor according to Claim 3 in which said data handling means (70) is arranged to analyse the direction of movement in all three axes to look for potentially dangerous movement characteristics.

5. A lifting position monitor according to Claim 3 in which said data handling means (70) is arranged to analyse the extent of movement in all three axes to look for potentially dangerous movement characteristics.

6. A lifting position monitor according to Claim 3 in which said data handling means (70) is arranged to analyse the speed of movement in all three axes to look for potentially dangerous movement characteristics.

7. A lifting position monitor according to Claim 3 in which said data handling means (70) is arranged to maintain a record of the detection of movement characteristics which fall within predetermined parameters.

8. A lifting position monitor according to Claim 7 in which said data handling means (70) is arranged maintain a record of the detection of movement characteristics which fall within predetermined parameters but which do not trigger the alarm.

9. A lifting position monitor according to Claim 7 in which said data handling means (70) is arranged maintain a record of the detection of movement characteristics which fall within predetermined parameters and result in triggering of the alarm.

10. A lifting position monitor according to Claim 1 which includes means for transmitting stored data via a wireless link for external recording and analysis.