CA2188246A1

CA2188246A1 - Feedback system for monitoring position and orientation

Info

Publication number: CA2188246A1
Application number: CA002188246A
Authority: CA
Inventors: James V. Raso; Douglas Hill; Nelson G. Durdle; Edmond Lou
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-10-20
Filing date: 1996-10-18
Publication date: 1997-04-21
Also published as: US5955879A

Abstract

The invention is directed at a method and a device for monitoring the position of a second point relative to a first point. The device of the within invention is comprised of a transmitter for locating at the first point for transmitting atransmitter signal, means for producing the transmitter signal, a receiver for locating at the second point for receiving the transmitter signal and for producing an output signal therefrom, and means for collecting the output signal so that the position of the second point relative to the first point can be determined therefrom. The method of the within invention is comprised of producing a magnetic field from the first point, receiving the magnetic field at the second point and producing an output signal therefrom, and determining the position of the second point relative to the first point by using the output signal.

Description

FEEDBACK SYSTEM FOR MONITORING POSITION AND ORIENTATION

CROSS REFERENCE TO RELATED APPLICATION

This Application claims the benefit of United States of America Provisional Application Number 60/005,732 filed October 20, 1996.

FIELD OF INVENTION

The present invention relates to a method and a device for monitoring and measuring the position or orientation of one or more objects or subjects andproviding feedback with respect to the position or orientation, preferably in at least two dimensions. Further, the invention is related to a method and a device for monitoring and measuring the posture of a subject and providing feedback with respect to the subject's posture, such as by signaling when either a desirable or undesirable posture exists, so that a desirable posture can be established.

BACKGROUND OF INVENTION

Scoliosis, which is an abnormal curvature of the spine coupled with vertebral rotation, is most commonly found in adolescent f~males. This abnormal curvature and rotation causes deformity of the rib cage which results in asymmetries of the trunk. In a previous study (Mahood, J.K. et al. "Perceptions of Cosmetic Deformity in Scoliosis", Proceedings of the 2nd International Symposium on ThreeDimensional Scoliotic Deformities, Pescara, September, pp. 239-242, 1994), sevenfeatures of scoliosis were identified: shoulder height and shoulder angle differences, pelvis asymmetry, decompensation, waist crease, scapula height difference and waist asymmetry. These identified features account for 85% of the overall impression of trunk deformity. Further, studies have established the repeatability and rel;ability of measuring surface features. In other words, these seven features can be reliablymeasured to provide an objective score of cosmetic deformity.

Clinicians have few non-surgical treatment tools for children with potentially progressive spinal deformities such as scoliosis. Brace treatment is most commonly used despite poor compliance and much uncertainty as to effectiveness (Houghton, R. et al. "Monitoring True Brace Compliance", Proceedings of the 21st.
Meeting of the Scoliosis Research Society, Hamilton, Bermuda, September, p.101, 1986;

- 2 1-~8246 Ylikoski, M. et al. "Biological Factors and Predictability of Bracing in Adolescent Idiopathic Scoliosis", J Pediatric Orthopedics, Vol. 9, pp. 680-683, 1989). The Boston and Charleston braces are most frequently prescribed due to their low profile. To beeffective, the Boston brace is required to be worn for up to 23 hours/day. The night-5 time Charleston brace (Price, C.T. et al. "Nighttime Bracing for Adolescent IdiopathicScoliosis with the Charleston Bending Brace", Spine Vol. 15, No. 12, pp. 1294-1299, 1990) must be worn 8 hours/night. The degree of support and the extent of corrective action provided by a brace depends on the location, magnitude, and direction of the pressures exerted relative to the location of the spine (Emans, J. et al. "The Boston 10 Brace System for Idiopathic Scoliosis - Follow-up Results in 295 Patients", Spine, Vol.
11, ~o. 8, pp. 792-801, 1986).

However, it has been found that the constant pressure exerted by a brace may cause permanent deformation of the rib cage or the soft tissues directly under the 15 pressure points. Also, it is believed that the brace's action is not primarily passive via direct mechanical forces on the spine, but that its effectiveness requires the active cooperation of the patient or person, (Dworkin, B. et al. "Behavioral method for the treatment of Idiopathic Scoliosis, Proc. Natl. Acad. Sci. USA, Vol. 82, pp. 2493-2497, 1985) i.e., the patient or person uses their own muscies to reduce the spinal curvature 20 as she or he holds their body away from the pressure points.

Therefore, it is recognized that monitoring the posture of, and active correction of the posture by, the subject or patient is a useful aid to the treatment of various musculoskeletal conditions, such as scoliosis and spinal curvature, either on 25 its own or in conjunction with other treatment methods and devices. Specifically, treatment approaches that rely less on mechanical correction and more on providing appropriate feedback to the subject may have considerable potential.

The monitoring of a subject's or patient's posture typically requires the 30 actual taking of repeated measurements of the features of the trunk during waking hours, using these measurements to detect postural mal-alignment and signaling to the subject that a postural correction is required. In the specific area of monitoring subjects with spinal deformities, one or more features, such as the seven features noted above, must be measured and any differences from expected values determined.
35 In the case when more than one feature is being monitored, information from some or all the features may need to be combined to signal the need for postural improvement.

2l88246 Thus, the taking of actual measurements of these features on a constant basis is often a relatively impractical, inaccurate and cumbersome approach to monitoring and correcting posture. As a result, attempts have been made to develop 5 various devices for monitoring posture and providing feedback with respect to that posture so that the subject can actively correct any undesirable features of the posture.

For instance, a technique described by Schroth et al. (Lehnert, C.S.
"Introduction to the three-dimensional scoliosis treatment according to Schroth", Physiotherapy, Vol. 78 No. 11 pp. 810-815, 1992; Weiss, H.R. "The Progression ofIdiopathic Scoliosis under the Influence of a Physiotherapy rehabilitation Programme", Physiotherapy, Vol. 78 No. 11, pp. 815-821, 1992) called 'rotationalbreathing' attempts to actively correct the body shape. The continuous muscular training results in a re-education of the scoliotic posture into a corrected balanced 15 posture. An electronic device called the micro-straight orthosis uses behavioral principles and therapeutic theory to help correct spinal deformity as well as cosmetic appearances. This device uses chest and torso cables and a microcomputer to continuously measure the length of the spine. If the length of the spine is different from the expected value, an audible tone signals the subject every second until correct 20 posture is attained. Thus, one drawback of this device it that it provides feedback on the measured length of the spine only.

United States of America Patent No. 3,582,935 issued June 1, 1971 to Verhaeghe is directed at a device comprised of a belt connected to a triggering plate and 25 a spring switch arm which close an electrical circuit when they come into contact with each other. The belt is placed snugly about the waist of the subject. If the subject permits his abdominal muscles to relax and thus be distended, the trigger plate will engage the switch arm, resulting in the closing of the electrical circuit. Closure of the electrical circuit activates an audible signal cautioning the subject to tense the relaxed 30 abdominal muscles. This device is intended to signal the subject with respect to incorrect body posture, particularly in the abdomen. However, it would appear tohave limited application to other features of incorrect posture.

United States of America Patent No. 4,730,625 issued March 15, 1988 to 35 Fraser et. al. describes an article of apparel, that is worn by a subject, which includes a posture sensor. The posture sensor is comprised of an elongated strip which fits into a horizontal or vertical pocket on the back of the article of apparel. Semiconductor - strain gauges are mounted at the ends of these elongated strips. When the subject moves and a strain is applied to the gauges, the gauges produce an electrical signal which is proportional to the amount of strain applied. This patent specifically teaches a system for detecting changes in posture from the normal. However, many subjects 5 with spinal deformities or abnormalities do not have a normally symmetric trunk so it is not sufficient to monitor changes of posture in the midline of the back only. For example, the angle formed by the apices of the scapulae and the horizontal is animportant trunk feature to be monitored. Because the space between these bones is concave, the apparel of this invention will bridge this area of the back and mask the 10 true extent of this particular trunk feature.

As stated, each of these devices only monitors a single parameter, aspect or feature of posture. Further, these devices only monitor a parameter in a single dimension or plane. Therefore, these devices may not be suitable for subjects having 15 other postural abnormalities and they may not permit the subject to correct the deficient posture or abnormal features with any degree of accuracy. This is particularly so given the interplay of the features noted above, which may act together to produce the spinal deformity actually observed.

There is therefore a need in the industry for a relatively accurate method and a device, as compared to known methods and devices, for monitoring the position or orientation of one or more objects or subjects and providing feedback with respect to the position or orientation, in any dimension, and preferably in three dimensions.
Further, there is a need for a relatively accurate method and a device for monitoring the posture of a subject and providing feedback with respect to the subject's posture, such as by signaling when either a desirable or undesirable posture exists, so that a desirable posture can be established.

SUMMARY OF INVENTION
The present invention relates to a method and a device for monitoring the position or orientation of one or more objects or subjects and providing feedback with respect to the position or orientation, in any dimension, and preferably in three dimensions. Further, the invention is related to a method and a device for monitoring the posture of a subject and providing feedback with respect to the subject's posture, such as by signaling when either a desirable or undesirable posture exists, so that a desirable posture can be established.

In the apparatus form of the within invention, the invention is directed at a device for monitoring the position of a second point relative to a first point, the device comprising:

(a) a transmitter for locating at the first point for transmitting a transmitter signal;

(b) means for producing the transmitter signal;
(c) a receiver for locating at the second point for receiving the transmitter signal and for producing an output signal therefrom; and (d) means for collecting the output signal so that the position of the second point relative to the first point can be determined therefrom.

The transmitter may be comprised of one or more transmitters. Further, the transmitter may be any suitable transmitter capable of performing the necessary functions, as described herein. Further, the transmitter may be comprised of a first 20 transmitter loop and a second transmitter loop which is oriented in a different plant than the first transmitter loop, so that the transmitter transmits a first transmitter signal from the first transmitter loop and transmits a second transmitter signal from the second transmitter loop which are then received by the receiver to produce two output signals. The transmitter may also be comprised of a first transmitter loop, a 25 second transmitter loop and a third transmitter loop, all of which are oriented in different planes, so that the transmitter transmits a first transmitter signal from the first transmitter loop, a second transmitter signal from the second transmitter loop, and a third transmitter signal from the third transmitter loop which are then received by the receiver to produce three output signals.
The receiver may also be comprised of one or more receivers. Further, the receiver may be comprised of any suitable receiver able to perform the functions described herein. Further, the receiver may be comprised of a first receiver loop and a second receiver loop which is oriented in a different plane than the first receiver loop, 35 so that the transmitter signal is received by each of the first receiver loop and the second receiver loop to produce two output signals. The receiver may also be comprised of a first receiver loop, a second receiver loop and a third receiver loop, all of which are oriented in different planes, so that the transmitter signal is received by each of the first receiver loop, the second receiver loop and the third receiver loop to produce three output signals.

Where the transmitter is comprised of the first transmitter loop and the second transmitter loop and the receiver is comprised of the first receiver loop and the second receiver loop, the first transmitter signal and the second transmitter signal are each received by each of the first receiver loop and the second receiver loop to produce four output signals. Where the transmitter is comprised of the first transmitter loop and the second transmitter loop and the receiver is comprised of the first receiver loop, the second receiver loop and the third receiver loop, the first transmitter signal and the second transmitter signal are each received by each of the first receiver loop, the second receiver loop and the third receiver loop to produce six output signals.

Where the transmitter is comprised of a first transmitter loop, a second transmitter loop and a third transmitter loop, and the receiver is comprised of a first receiver loop and a second receiver loop, the first transmitter signal, the second transmitter signal and the third transmitter signal are each received by each of the first receiver loop and the second receiver loop to produce six output signals. Where the transmitter is comprised of the first transmitter loop, the second transmitter loop and the third transmitter loop, and the receiver is comprised of the first receiver loop, the second receiver loop and the third receiver loop, the first transmitter signal, the second transmitter signal and the third transmitter signal are each received by each of the first receiver loop, the second receiver loop and the third receiver loop to produce nine output signals.

Further, preferably, the first transmitter loop, the second transmitter loop and the third transmitter loop are all substantially mutually perpendicular to each other. Further, preferably, the first receiver loop, the second receiver loop and the third receiver loop are all substantially mutually perpendicular to each other.

As well, the transmitter signal producing means is preferably comprised of an oscillator which produces a variable transmitter signal. Any suitable oscillator for the purposes described herein may be used. Further, the transmitter signal producing means preferably produces the first transmitter signal, the third transmitter signal and the third transmitter signal alternately in succession.

2 t 88246 - Further, the output signal collecting means preferably produces a feedback signal for indicating the position and orientation of the second object relative to the first object. The feedback signal may be comprised of any suitable devices or ~y~lems for providing a signal to the user of the device, however, the feedback signal is 5 preferably comprised of sound, light, vibration or electrical stimulation. Alternatively, the feedback signal may be displayed on an oscilloscope.

In the preferred embodiment, the second point is comprised of a location on a human body.
Further, preferably, the receiver is comprised of at least a first receiver and a second receiver, each receiver comprising a first receiver loop, a second receiver loop and a third receiver loop, all of which are mutually perpendicular to each other, and wherein the first receiver is for locating at a first location on a human body and the 15 second receiver is for locating at a second location on a human body, so that the relative position and orientation of the first point relative to the first location and the relative position and orientation of the first point relative to the second location can be compared.

In the method form of the invention, the invention is directed at a method for monitoring the position of a second point relative to a first point, the method comprising:

(a) producing a magnetic field from the first point;
(b) receiving the magnetic field at the second point and producing an output slgnal therefrom;

(c) determining the position of the second point relative to the first point by using the output signal.

The magnetic field may be comprised of a first magnetic field and a second magnetic field which are produced alternately in different directions from the 35 first point. However, preferably, the magnetic field is comprised of a first magnetic field, a second magnetic field and a third magnetic field, each of which are produced alternately in different directions from the first point.

2l 88246 Further, the magnetic field may be received at the second point at two different positions. However, preferably, the magnetic field is received at the second point at three different positions.

As well, the method may be comprised of the following steps in the sequence set forth:

(a) producing a first magnetic field from the first point;
(b) receiving the first magnetic field at three different mutually perpendicular positions at the second point and producing three output signals therefrom;

(c) producing a second magnetic field from the second point in a different direction from the first magnetic field;

(d) receiving the second magnetic field at three different mutually perpendicular positions at the second point and producing three output signals therefrom;

(e) producing a third magnetic field at the second point in a different direction from each of the first magnetic field and the second magnetic field;
(f) receiving the third magnetic field at three different mutually perpendicular positions at the second point and producing three output ' signals therefrom; and (g) determining the position and orientation of the second point relative to the first point by using the output signals.

Further, the method may be further comprised of the following steps after the determining step:
(h) comparing the position and orientation of the second point relative to the first point with a reference position and orientation; and - 2~ 88246 (i) producing feedback to indicate a discrepancy between the position and orientation of the second point relative to the first point and the reference position and orientation.

SUMMARY OF DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
Figure 1- is a schematic diagram of the preferred embodiment of the device of the within invention;

Figure 2 - is a front view of a transmitter and a receiver of the device 15 shown in Figure 1;

Figure 3 - is a magnetic field at (0,r,0) from a square loop for the device shown in Figure 1;

Figure 4 - is a magnetic field generated by the square loop shown in Figure 3;

Figure 5(a) - is an RLC circuit in series for the transmitter of the device shown in Figure 1, wherein R is the resistor, L is the inductor and C is the capacitor;
Figure 5(b) - is a parallel RLC circuit for the receiver of the device shown in Figure 1, wherein R is the resistor, L is the inductor and C is the capacitor;

Figure 6 - shows the magnitude of the voltage at 4 channels (Tx-Rx, Tx-Ry, Ty-Rx and Ty-Ry wherein T is the transmitter and R is the receiver) with respect to the rotation of the angle in the x-y plane;

Figure 7 - shows the magnitude of the voltage at channel Tx-Rx at the distances of 30, 31, 32 and 35 cm with respect to the rotation of the angle in the x-y plane;

2 t 88246 Figure 8 - shows the results of the calculated distance r (with 1 standard deviation) as compared with the measured distance r;

Figure 9 - shows the mean value of the function Kxx; and Figure 10 - shows the results of the measured angle of rotation as compared to the calculated angle of rotation.

DETAILED DESCRIPTION
Referring to Figure 1, this invention is directed at a ~y~Lem or device (20), and a method, for monitoring at least one of the position and orientation of one or more objects or subjects and providing feedback with respect to the position or orientation, ~refelably in at least two dimensions. In the ~refe,led embodiment, the 15 device (20) is comprised of at least one transmitter (22)-(re~.~ed to in Figure 1 by the designation Rx), preferably an electromagnetic transmitter, at least one receiver (24) (referred to in Figure 1 by the designation Tx) and a microprocessor or microcontroller(26) which is attached to one or more objects or one or more subjects being monitored. The transmitter (22) and the receiver (24) may be attached directly or 20 indirectly to an object or subject. Most ~re~lably, The transmitter (22) is comprised of a fixed magnetic-dipole transmitting antenna and the receiver (24) is comprised of a freely moveable magnetic-dipole receiving antennae. The method of the within invention is preferably performed using the device (20).

It is believed that the theory of the operation of the device (20) is as set outbelow. Specifically, referring to Figure 3, in the preferred embodiment utilizing an electromagnetic transmitter (22), to calculate the magnetic field generated from a square loop abcd (Figure 3), the square loop abcd is divided into four finite lengths of wire. Each current-carrying wire produces a magnetic field at any point.
Superimposing the magnetic field of the four wires into a square results in the magnetic field generated from a square loop (Cheng, D.K. "Pield and Wave Electromagnetics", world student series 2nd Ed. Addison-Wesley, 1989). Assuming r >w and r < ~ (where r is the distance between the transmitter (22) and the receiver(24)), the magnetic fields generated from the wire ab and the wire cd cancel each other. The magnetic field generated from the square loop abcd shown in Figure 3 to the point (0,r,0) is described by Equation (1) as follows:

~~ ~oIW2 Equation (1) ~ 4n~ 3 ,~

Referring to Figure 4, the magnetic field generated from the square loop shown in Figure 3 at general point (r, ~, ~ ) in polar coordinates (where ~ is the angle of rotation) is given by Equation (2) as follows:

B # ~ 3 ~,2cos~+~sin~) Equation (2) 4~

Further, the following Equation (3) describes the magnetic flux generated from the transmitter(22), designated as 1 in the equation, to the receiver (24),designated as 2 in the equation, and wherein Nl and N2 are the number of turns in the transmitter (22) and the receiver (24) respectively and S2 is the cross sectional area 20 of the receiver (24):

~)12~o~ = N~N2 ~ ~~2 Equation (3) The following Equation (4) describes how the voltage (back emf) is related to the magnetic flux:

Ve.m.f. =~ dt Equation (4) The following Equation (5) describes the magnetic moment M0 where S
is the cross sectional area of the transmitter (22):

Mo = lsl Equation (5) Therefore, the relationship between the voltage and the distance between transmitter (22) and the receiver (24) is given by the following Equation (6):
~0 y = Kii *cos~-tNii Equation(6) 15 In Equation (6), K is a function of ~ and is channel related. Further, Vii is the voltage on the channel transmitted from i and received on i and Nii is the noisepicked up on the channel.

The following Equation (7) describes the relation between the angle of 20 rotation and the voltage output:

~N~V * K~CC = ~U16~ Equation (7) V~-Nxx~

The quality factor Q on the transmitter (22) can be calculated by the following Equation (8):

Q = _ Equation (8) The transmitting voltages on the capacitor C and the inductor L are described in the following Equation (9):

2 1 8824b IVL( ~)I=IVC(1~)I= ~VC~)¦ Equation (9) The following Equations (10) and (11) describe the Q factor, and the current through the receiver (24):

Q = ~RC Equation (10) IIL( j~)l=lIc(1c~)l= QII( jc~)l Equation (11) Referring to Figure 1, in the pre~lled embodiment, the components of 20 the device (20) may be separated into two ~y~ s or functional ~ sifications: i) the programmable digital data acquisition ~yslelll; and ii) the transmitter (22) - receiver (24) system with the associated circuitry. The data acquisition ~y~lem is preferably comprised of any microcontroller or microprocessor (26) suitable for the specific purposes, and able to perform the necessary functions, as described herein. The 25 microcontroller (26) provides for the programmability of the data acquisition ~y~Le Preferably, the microcontroller (26) is relatively small in size, such that it is readily portable, and has a relatively low power consumption. In the prere~led embodiment, a microcontroller integrated circuit was chosen which has low power consumption and a built-in analog-to-digital (A/D) converter (28). Specifically, a Motorola MC68HC16 30 16-bit modular microcontroller integrated circuit is used.

Small size and low power consumption are achieved by minimizing the number of integrated circuits (IC), and turning off the power for any IC not in use.
Further, to reduce power requirements the read-only memory (ROM) (30) is a low-35 power CMOS integrated circuit which holds the control program. The static randomaccess memory (RAM) (32), used to store the acquired data, is fabricated using an advanced low-powered CMOS device, designed for high-speed and low power applications. It is particularly well suited for battery backup of nonvolatile memory applications. Further, the device (20) is preferably further comprised of a programmable real-time-clock (RTCj (34) which controls the sample duration and interval, and provides an interrupt to the microcontroller (26). Also, it can beprogrammed to be in a low-power STOP mode, except at the specific times when it is acquiring data. The block diagram of the device (20) is shown in Figure 1.

Referring to Figure 1, the MC68HC16 microcontroller (26) is comprised of a true 16-bit CPU, a system integration module, an 8/10-bit A/D converter (28), a queued serial module, a general-purpose timer, and a 1024-byte standby RAM (32). In this prefelled embodiment, the device (20) is further comprised of a driver (36).
Preferably, the driver (36) is comprised of a Wein Bridge Oscillator combined with a voltage follower (38). The oscillator produces a sine wave signal to the transmitter (22), and the voltage follower (38) is used to avoid undue loading. Preferably, a fourth order Butterworth bandpass filter is used and is designed to have a high quality factor (Q). The fixed gain of the system is set so that a full range (0 to 5V) can be obtained.
The multiplexer (MUX.) (40) is controlled by the microcontroller (26) to select the required channel. The A/D converter (28) is prefelably set to 10 bit resolution and its resolution error is preferably + 12.5 mV in the full range scale.
Any transmitter (22) and receiver (24) may be used that are suitable for the purposes, and able to perform the functions, described herein. However, preferably both the transmitter (22) and the receiver (24) are comprised of ferrous materials.
More particularly, the transmitter (22) and the receiver (24) are comprised of ferrite cubes with three mutually orthogonal loops as shown in Figure 2. Any suitable dimensions and weights of the cubes may be used. However, the dimensions of the cube in the preferred embodiment are 2.0 cm for the transmitter (22) and 1.3 cm for the receiver (24) and their weights are 30 g and 10 g respectively. Preferably, these components are as small as possible and therefore, these components are preferably miniaturized where such miniaturization is possible or available.

In the preferred embodiment, the loop diameters are small relative to the distance (r) between the transmitter (22) and the receiver (24) so that each loop may be regarded as an infinitesimal dipole. Eight hundred turns of 36 AWG wire are preferably wound around the transmitter (22) in each direction, and 500 turns of 38 AWG wire are preferably wound around the receiver (24). Using larger diameter wire in the transmitter (22) results in a smaller resistance.- Therefore, higher Q of the transmitting signal can be obtained. Using smaller wire in the receiver (24) results in a better pick up. The number of turns are dependent upon the size of the transmitter (22) and the receiver (24). The ~refelled number of turns was specifically chosen because of the preferred size of the transmitter (22) and the receiver (24). The operating 5 range (distance) of the device (20) can be changed by altering the specification of the components (i.e., changing the number of turns, the size of the wire and/or the size of the core).

The transmitter (22) acts as a fixed magnetic-dipole transmitting antenna 10 which produces a far-field component and a near-field component. The near-field intensity is dominant when the distance between the transmitter (22) and the receiver (24) is less than one wavelength ( ~ ) (25 km) of the transmitting signal. Only the near-field component is considered. The near-field component is frequency independent and decreases by the inverse cube of the distance (Vr3). Each loop of the 15 transmitter (22) antenna is in turn excited with a driving signal identical in frequency and phase. A twelve kilohertz driving frequency was chosen in the preferred embodiment because that particular frequency is least affected by other EM
(electromagnetic) signals. Each excitation produces a single axis transmitter dipole with three independent outputs at the receiver (24). Therefore, nine measurements (3 20 orthogonal loops x 3 outputs) are available to solve for the six unknowns: x, y, z for position and yaw, pitch, and roll for orientation.

The transmitter (22) uses the series resonant approach to transmit the signal, as shown in Figure 5a, and the receiver (24) uses the parallel resonant approach 25 to detect the signal, as shown in Figure 5b.

The transmitter (22)-receiver (24) system is preferably first calibrated by fixing the distance (r) between the transmitter (22) and the receiver (24). The distance for the calibration will depend on the range of distances required for the par,ic~ilar 30 application of this device (20). At that distance, the receiver (24) is rotated in the x-y plane only from 0 to 360 degrees with 10 degree increments. The magnitude of theoutput signal is then read with an oscilloscope. Nine measurements (3 loops x 3 outputs) are obtained each time. Figure 6 shows the magnitude of the voltage at channels Tx-Rx (Transmit from x channel - Receive from x channel), Tx-Ry (Transmit 35 from x channel - Receive from y channel)" Ty-Rx (Transmit from y channel - Receive from x channel), and Ty-Ry (Transmit from y channel - Receive from y channel), with respect to the rotation of the angle in the x-y plane in the preferred embodiment. The magnitude from Tx-Rz, Ty-Rz, Tz-Rx and Tz-Ry will vary for each application. Thefirst calibration was at the minimum distance, which provides the largest signal. The next test increases the distance betweèn the transmitter (22) and the receiver (24). At each of the distances, the calibration steps were repeated.

Relating the above device (20) to use on subjects having scoliosis or other postural abnormalities or undesired features of posture, the device (20) is preferably a portable, low-power training device, as described above, to provide active feedback on the position and orientation of the subject, preferably in at least two dimensions, and 10 more preferably, in three dimensions. This device (20) has applications for postural training and control. Experimental results have been compared to theory to determine the accuracy of the device (20). It has been found that the sm~llest distance and rotation angle that can be detected by the device (20) is 5 mm (range 30 to 45 cm) and 0.5 degrees respectively. This device (20) can provide feedback to scoliotic and other 15 subjects to assist the subject in learning how to position himself properly with the ultimate aim to reduce their spinal deformity or undesirable posture.

Specifically, the device (20) and method of the within invention relate to monitoring locations of anatomical features that permit the calculation of the 20 asymmetry of these and other anatomical structures. More specifically, the invention relates to a device (20) comprised of at leastone transmitter (22), ~re~lably anelectromagnetic transmitter, at least one receiver (24) and a microprocessor (26) which is attached to the trunk of the subject whose posture is to be monitored. The transmitters (22) and the receivers (24) may be attached to the subject in any suitable 25 manner permitting the functioning of the device (20) in the manner described herein.
Specifically, the transmitters (22) and the receivers (24) may be attached directly to the skin using adhesive pads well described in the prior art or, in the case of the transmitter (22), may be secured in an elastic apparel worn around the trunk of the subject.
The receivers (24) are attached to one or more objects or one or more subjects being monitored. The transmitter or transmitters (22), microprocessor (26) and receiver or receivers (24) may be attached directly or indirectly to an object, objects, subject or subjects.
Signals to the subject or the user of the device (20) may be continuous or activated only when certain definable orientations fall within or outside of a given - range or ranges depending upon the specific application of the device (20). Signals concerning the position and orientation may be in the form of sound, light, vibration, electrical, output to a computer or any other available signaling ~yslem or device.

The device (20) may be powered by any suitable power source, compatible with the device (20), including battery or AC power.

As states above, monitoring posture has been used as an aid to the treatment of various musculoskeletal conditions such as spinal curvature. This requires repeatedly measuring features of the trunk during waking hours, using these measures to detect postural mal-alignment or undesirable features and signaling to the subject that a postural correction is required. In the specific area of monitoring subjects with spinal deformities, one or more features must be measured and any differences from expected values determined. In the case when more than one feature is being monitored, information from some or all the features may be combined tosignal the need for postural improvement.

The within invention provides an electromagnetic device (20) comprised of a microcomputer that will monitor and measure one or more topographical features of the trunk related to the presence of abnormal spine curvature or other undesirable postural features. This includes but is not limited to monitoring and measurement of shoulder heights, shoulder angles, scapular heights, trunk shift,longitudinal waist contours and pelvic obliquity.

Further, the device (20) preferably analyzes these measurements in order to provide relative differences in the measurements or differences from preset conditions or measurements. Based on this analysis by the device (20), feedback is preferably provided to the subject. For example, if the intention is to return the angle of the shoulder to a more symmetric condition, then receivers (24) are placed on each shoulder to monitor the inclination of the shoulders relative to the transmitter (22) and return this information to the microprocessor (26). The microprocessor (26) then compares the shoulder angle measurements. In the normally aligned subject, this difference between the measurements will typically be zero. If the difference is greater than a preset difference then a signal or other form of feedback is transmitted to the subject.

- When using the device (20) for a subject having a postural abnormality, such as scoliosis, the transmitter (22)-receiver (24) ~y~L~ are first calibrated, as previously described, by fixing the distance between the transmitter (22) and the receiver (24) at 30 cm. At that distance, the receiver (24) is rotated in the x-y plane only 5 from 0 to 360 degrees with 10 degree increments. The magnitude of the output signal is read with an oscilloscope. Nine measurements (3 loops x 3 outputs) are obtained each time. As described above, Figure 6 shows the magnitude of the voltage at channels Tx-Rx,Tx-Ry,Ty-Rx and Ty-Ry with respect to the rotation of the angle in the x-y plane. The magnitude from Tx-Rz, Ty-Rz, Tz-Rx and Tz-Ry were less than 200 10mV. The magnitude of the voltage on the Tz-Rz channel at distance 30 cm was 2688 mV. The next test increases the distance to 30 cm, 31 cm, 32 cm and 35 cm between the transmitter (22) and the receiver (24). At each of the distances, the calibration steps are repeated. Figure 7 shows the results obtained from the channel Tx-Rx at the distance 30 cm, 31 cm, 32 cm and 35 cm with respect to the angle of rotation in x-y plane in the 15 preferred embodiment. Figure 8 shows the accuracy on calculating the distance r from the received data upon testing and calibrating the prerelled embodiment of the device (20). The mean values and the standard deviation of the calculated distance r, are 29.94 + 0.18, 30.92 +0.18, 32.06 + 0.37 and 35.11 + 0.38 cm. The smallest distance that can be detected is 5 mm in the distance range of 30 to 45 cm. Figure 9 shows the variation of 20 the function K with respect to the angle of the rotation. Figure 10 shows the accuracy on calculating the angle from the received data. The average error in calculating the angle is 0.149~ + 0.36~. The resolution on measuring the angle is 0.5~.

Although the device (20) and the method of the within invention are 25 prere~ably used for scoliosis correction, the device (20) and method have broader applications. For instance, a subject may use information from this device (20) to learn to utilize certain'muscles to improve posture and reduce low back pain. Information from this device (20) may also be used to monitor how a person lifts and turns. Thus, the device (20) has applications in back care programs associated with safety in industry 30 and rehabilitation for back injuries. Based on feedback from this device (20), a subject could train himself and his muscles to find and maintain correct positioning andposture. This has applications in back care programs associated with safety (prevention and occupational health and safety monitoring) in industry and rehabilitation for back mlurles.
This invention also has application in a broader range of areas where monitoring parameters related to position, orientatibn or a subset of these parameters - and relaying information about the parameters to a controller are desired.
Information from the receivers (24) may be used to provide signals that indicate the alignment and relative position of points or objects in one or more dimensions, preferably three dimensions. The feedback response in this device (20) may be from a 5 computer, machinery or an individual. This information can be used to initiate a signal and/or a response.

Further, this invention may have applications for robotics and virtual reality. This device (20) can be used to monitor or track positioning, and in particular 10 three dimensional positioning, of one or more parts of a mechanism or of a body including but not limited to head, trunk, leg, foot, finger and/or hand. These applications may have many potential uses in entertainment, military and industry.
This invention may also be used for applications related to but not limited to biomechanical analysis, graphic and cursor control, stereotaxic localization, anatomical 15 measurements, simulations, kinematics, and biomechanics.

As well, this device (20) and method may have applications in guidance for 3-dimensional positioning and orientation. This device (20) and method may be used to assist in the assembling of equipment in unsafe environments, remote locations or assist in guidance in situations where alignment can not be monitored directly. This invention may also be used to guide equipment in surgery, for stereotaxic surgery or for providing information of the precise location of a probe or equipment for surgery. For instance, using computer graphics as feedback if one receiver (24) is on a movable object and one receiver (24) is on a fixed or movable 25 object, one can monitor the alignment.

Claims

1. A device for monitoring the position of a second point relative to a first point, the device comprising:

(a) a transmitter for locating at the first point for transmitting a transmitter signal;

(b) means for producing the transmitter signal;

(c) a receiver for locating at the second point for receiving the transmitter signal and for producing an output signal therefrom; and (d) means for collecting the output signal so that the position of the second point relative to the first point can be determined therefrom.

2. The device as claimed in claim 1, wherein the transmitter comprises afirst transmitter loop and a second transmitter loop which is oriented in a different plane than the first transmitter loop, so that the transmitter transmits a firsttransmitter signal from the first transmitter loop and transmits a second transmitter signal from the second transmitter loop which is then received by the receiver to produce two output signals.

3. The device as claimed in claim 1, wherein the transmitter comprises afirst transmitter loop, a second transmitter loop and a third transmitter loop, all of which are oriented in different planes, so that the transmitter transmits a first transmitter signal from the first transmitter loop, a second transmitter signal from the second transmitter loop, and a third transmitter signal from the third transmitter loop which are then received by the receiver to produce three outputsignals.

4. The device as claimed in claim 1, wherein the receiver comprises a first receiver loop and a second receiver loop which is oriented in a different plane than the first receiver loop, so that the transmitter signal is received by each of the first receiver loop and the second receiver loop to produce two output signals.

5. The device as claimed in claim 1, wherein the receiver comprises a first receiver loop, a second receiver loop and a third receiver loop, all of which are oriented in different planes, so that the transmitter signal is received by each of the first receiver loop, the second receiver loop and the third receiver loop to produce three output signals.

6. The device as claimed in claim 2, wherein the receiver comprises a first receiver loop and a second receiver loop which is oriented in a different plane than the first receiver loop, so that the first transmitter signal and the second transmitter signal are each received by each of the first receiver loop and the second receiver loop to produce four output signals.

7. The device as claimed in claim 2, wherein the receiver comprises a first receiver loop, a second receiver loop and a third receiver loop, all of which are oriented in different planes, so that the first transmitter signal and the second transmitter signal are each received by each of the first receiver loop, the second receiver loop and the third receiver loop to produce six output signals.

8. The device as claimed in claim 3, wherein the receiver comprises a first receiver loop and a second receiver loop which is oriented in a different plane than the first receiver loop, so that the first transmitter signal, the second transmitter signal and the third transmitter signal are each received by each of the first receiver loop and the second receiver loop to produce six output signals.

9. The device as claimed in claim 3, wherein the receiver comprises a first receiver loop, a second receiver loop and a third receiver loop, all of which are oreinted in different planes so that the first transmitter signal, the second transmitter signal and the third transmitter signal are each received by each of the first receiver loop, the second receiver loop and the third receiver loop to produce nine output signals.

10. The device as claimed in claim9, wherein the first transmitter loop, the second transmitter loop and the third transmitter loop are all substantially mutually perpendicular to each other, and wherein the first receiver loop, the second receiver loop and the third receiver loop are all substantially mutually perpendicular to each other.

11. The device as claimed in claim 10, wherein the transmitter signal producing means comprises an oscillator which produces a variable transmitter signal.

12. The device as claimed in claim 11, wherein the transmitter signal producing means produces the first transmitter signal, the second transmitter signal and the third transmitter signal alternately.

13. The device as claimed in claim 10, wherein the output signal collecting means produces a feedback signal for indicating the position and orientation of the second object relative to the first object.

14. The device as claimed in claim 13, wherein the feedback signal is comprised of sound, light, vibration or electrical stimulation.

15. The device as claimed in claim 13, wherein the feedback signal is displayed on an oscilloscope.

16. The device as claimed in claim 10, wherein the second point comprisesa location on a human body.

17. The device as claimed in claim 9, wherein the receiver comprises a first receiver and a second receiver, each receiver comprising a first receiver loop, a second receiver loop and a third receiver loop, all of which are mutually perpendicular to each other, and wherein the first receiver is for locating at a first location on a human body and the second receiver is for locating at a second location on a human body so that the relative position and orientation of the first point relative to the first location and the relative position and orientation of the first point relative to the second location can be compared.

18. A method for monitoring the position of a second point relative to a first point, the method comprising:

(a) producing a magnetic field from the first point;

(b) receiving the magnetic field at the second point and producing an output signal therefrom;

(c) determining the position of the second point relative to the first point by using the output signal.

19. The method as claimed in claim 18, wherein the magnetic field comprises a first magnetic field and a second magnetic field which are produced altnerately in different directions from the first point.

20. The method as claimed in claim 18, wherein the magnetic field comprises a first magnetic field, a second magnetic field and a third magnetic field, each of which are produced alternately in different directions from the first point.

21. The method as claimed in claim 18, wherein the magnetic field is received at the second point at two different positions.

22. The method as claimed in claim 18, wherein the magnetic field is received atthe second point at three different positions.

23. A method for monitoring the position and orientation of a second point relative to a first point, the method comprising the following steps in the sequence set forth:

(a) producing a first magnetic field from the first point;

(b) receiving the first magnetic field at three different mutually perpendicular positions at the second point and producing three output signals therefrom;

(c) producing a second magnetic field from the second point in a different direction from the first magnetic field;

(d) receiving the second magnetic field at three different mutually perpendicular positions at the second point and producing three output signals therefrom;

(e) producing a third magnetic field at the second point in a different direction from each of the first magnetic field and the second magnetic field;

(f) receiving the third magnetic field at three different mutually perpendicular positions at the second point and producing three output signals therefrom; and (g) determining the position and orientation of the second point relative to the first point by using the output signals.

24. The method as claimed in claim 23, further comprising the following steps after the determining step:

(h) comparing the position and orientation of the second point relative to the first point with a reference position and orientation; and (i) producing feedback to indicate a discrepancy between the position and orientation of the second point relative to the first point and the reference position and orientation.