WO1992015247A1

WO1992015247A1 - Exoskeletal measurement system

Info

Publication number: WO1992015247A1
Application number: PCT/US1992/001712
Authority: WO
Inventors: Beth Marcus; Philip Churchill
Original assignee: Exos, Incorporated
Priority date: 1991-03-07
Filing date: 1992-03-06
Publication date: 1992-09-17

Abstract

An exoskeletal measurement system (10) for simultaneously monitoring load and motion on the human body includes: means for sensing the motion of a joint (16); means for detecting the load (32) on a human link segment remote from that joint; and means for correlating (36) simultaneously the motion of the joint and the load on the human link segment for representing the stress on the human body.

Description

EXOSKELETAL MEASUREMENT SYSTEM

FIELD OF INVENTION This invention relates to an exoskeletal measurement system for simultaneously monitoring load and motion on the human body.

BACKGROUND OF INVENTION Industrial designers, health and safety officers, and ergono ists estimate the motion of human joints and the load on human link segments to design safe and comfortable equipment and environments. One attempt to quantify such motion and load action includes videotaping the human action and then analyzing the activity subsequently or in real time. Such techniques lack precision; the video views are sometimes obscured and it is intrusive to workers. In addition, the analysis is typically complex, requires large, powerful computers or requires substantial time to complete. Another attempt uses electromyography (EMG) to measure muscle activity of the intrinsic muscles from which the muscle force exerted is inferred. For example, the intrinsic muscles of the hand are monitored to infer total grip force. Laboratory studies have shown that the total grip force can be inferred from the EMG. However, there is no proof that the EMG is correlated with the actual load or force applied in the field. There is also a time difference between muscle action and electrical activity measured by EMG. In addition, only the total grip force is monitored; there is no separate evaluation of each finger and thumb, for example.

SUMMARY OF INVENTION It is therefore an object of this invention to provide an exoskeletal measurement system which measures the motion of a human joint and the load on a remote human linkage segment simultaneously to correlate the true stress on the human body part.

It is a further object of this invention to provide such an exoskeletal measurement system which measures directly and precisely the load and motion on human body parts.

It is a further object of this invention to provide such an exoskeletal measurement system which measures motion and load directly, with minimum inference, in the actual environment.

It is a further object of this invention to provide such an exoskeletal measurement system which is comfortable for the subject, lightweight, unintrusive, and is rugged and reliable for field use.

It is a further object of this invention to provide such an exoskeletal measurement system which can be calibrated to provide absolute measurement of motion and load or can develop relative measurement of the subject's activity against the subject's own capabilities.

The invention results from the realization that a truly effective device for measuring the stress on a human body can be achieved by simultaneously measuring the motion of a human joint and the load on a remote human link segment to temporally correlate the motion and load to represent the true stress on the human body.

This invention features an exoskeletal measurement system for simultaneously monitoring load and motion on the human body. There are means for sensing the motion of a joint and means for detecting the load on a human link segment remote from that joint. There are also means for simultaneously correlating the motion of the joint and the load on the human link segment to represent the stress on the human body. In a preferred embodiment the means for sensing may include a first mounting plate on one side of the joint and a second mounting plate on the other side of the joint. The means for sensing may also include a mechanical linkage interconnecting the mounting plates. The mechanical linkage may include at least one pivot and sensor means for detecting the motion of the joint in at least one degree of freedom. The mechanical linkage may also include a second pivot. One of the pivots may be associated with each mounting plate and the sensor means may be associated with one of the pivots. The means for sensing may also include at least one load sensor for sensing the load on the human link segment. The load sensor may be a force sensor or a pressure sensor. The pressure or force sensor may include an array of pressure sensing elements. The means for correlating may include calibration means for calibrating the load and the motion to an external reference. The calibration means may include an external load cell for determining the load on the human link segment and an external motion cell for determining the motion of the joint.

DISCLOSURE OF PREFERRED EMBODIMENT Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in whic :

Fig. 1 is a pseudo-three-dimensional diagrammatic view of an exoskeletal measurement system according to this invention showing an exoskeletal unit mounted on the human hand and external load and motion cells interconnected with a computer;

Fig. 2 is an enlarged, detailed view of the exoskeletal measurement device of Fig. 1; Fig. 3 is a block diagram of the system of Fig. 1; Fig. 4A shows the force sensed by the exoskeletal measurement system when the hand is using two different tools;

Fig. 4B illustrates the motion of the wrist joint in two degrees of freedom which occurs simultaneously with one of the two tools shown in the force sensing of Fig. 4A;

Fig. 5 is an illustration of the wrist motion during cutting using a standard grip knife for both radial and ulnar deviation and flexion and extension, where the motion is shown as a percentage of maximum motion;

Fig. 6 is a view similar to Fig. 5 for a pistol grip knife;

Fig. 7 is an illustration of the force on the fingers and thumb during cutting using a standard grip knife; and

Fig. 8 is an illustration of the force on the fingers and thumb during cutting using a pistol grip knife.

This invention may be accomplished with an exoskeletal measurement system which simultaneously monitors load and motion on the human body. There are some means for sensing the motion of a joint, such as a wrist for example, and there are means for detecting the load on the human link segments remote from the joint, for example the forearm or the fingers on either side of the wrist. The motion output and the load output are received by a computer which simultaneously correlates them to present corresponding temporal joint and load activity for representing the true stress on the human body. The motion sensing means utilizes an exoskeletal device which includes a first mounting plate on one side of the joint and a second mounting plate on the other side of the joint: for example, one mounting plate on the hand in front of the wrist and another on the forearm behind the wrist. There is a mechanical linkage interconnecting the mounting fore and aft of the wrist. This mechanical linkage includes at least one pivot and a sensor for detecting the motion of the joint in at least one degree of freedom. In one construction there is a pivot on the forearm mount and another pivot on the hand mount. A linkage extends from each of these pivots and is joined at an intermediate pivot. A sensor such as a Hall effect sensor is associated with at least one of the pivots in order to sense the angular motion of the hand. Preferably two Hall effect sensors are used, one to measure wrist flexion/extension and another to measure radial/ulnar deviation. That is, one measures the up-and-down motion and the other measures the side-to-side motion of the wrist. Typically one or more passive pivots, that is, a pivot without an associated sensor, is used to accommodate for ancillary motions which occur that are neither true flexion/extension nor radial/ulnar deviations. The link segments, which in the case of a wrist joint may be the fingers and thumb, include one or more load sensors for sensing the load on those link segments simultaneously with the sensing of the wrist angle motion. This load sensor or sensors may be a force sensor or a pressure sensor. The pressure sensor may include an array of pressure sensing elements so that the distribution of the pressure at the particular segment can be discretely determined.

The system can be used to correlate the human body part motion relatively or in an absolute sense. That is, with the exoskeletal device in place on the wrist and hand, a subject can grip an external reference load cell and then an external reference motion cell in order to establish the actual forces and angles experienced by the hand and wrist. These values can be calibrated with the signals from the exoskeletal device and the load sensors so that in subsequent activities the actual loads and motions imposed on the hand and wrist can be directly determined. Alternatively, the subject can be made to exercise his hand through a full range of motion and loads in order to determine the maximum load an motion levels obtainable for that subject and to place the hand in a neutral position. Subsequently, when the subject performs any specific activity the load and motion required by that activity can be compared to the subject's own maximum load and motion ranges to determine the relative stress being imposed upon that subject's human body part.

There is shown in Fig. 1 an exoskeletal measurement system 10 for simultaneously monitoring load and motion on wrist 12 and hand 14. An exoskeletal measurement device 16 includes a first mount 18 which includes platform 20 secured to forearm 21 by strap 22. A second mount 24 includes a platform 25 mounted to hand 14 by means of elastic straps 26 and 28. A mechanical linkage 30 interconnects platforms 20 and 25 across the wrist joint 12. Hand 14 includes one or more load sensors 32 which may be sensors such as piezoelectric sensors manufactured by IC Sensors, or pressure sensors such as FSR's (force sensing resistors) manufactured by Interlink or Tekscan, or pressure sensor arrays such as FSR's manufactured by Interlink or Tekscan. The output from motion sensors, shown on screen 33, Fig. 1, and load sensors 32 are provided over cable 34 to computer 36 which may be an IBM PC AT compatible. Cable 34 simultaneously supplies both the force signals 34a and the motion signals 34b. Computer 36 also receives an input from load cell 38 and motion cell 40. Load cell 38 may be a Model 41 load cell manufactured by Sensotec; motion cell 40 may be a flexible linkage incorporating a high-precision encoder manufactured by Hewlett Packard.

In Fig. 1, the joint whose motion is monitored is wrist 12, and the human link segments on which the load is being sensed are the fingers 42 and 44 and thumb 46 of hand 14. Mechanical linkage 30 includes a pair of links 50, 52, Fig. 2, pivotably interconnected at pivot 54. Link 52 is connected at its other end to pivot 56. Pivots 54 and 56 rotate about axes 58 and 60 perpendicular to the plane of the drawing. Pivot 60 is in turn interconnected with pivot 62 which rotates about axis 64. Pivots 54 and 56 include Hall effect sensors 66 and 68, respectively, which sense the angular motion about axes 58 and 60 representative of the flexion/extension of wrist 12. Another Hall effect sensor 70 is employed in pivot 62 to sense the radial/ulnar deviation of wrist 12. Additional passive pivots 72, 74 are provided to accommodate for motions of the hand not in the flexion/ extension dimension and not in the radial/ulnar dimension. Pivot 72 rotates around axis 76; pivot 74 rotates around axis 78.

The sensor signals 80, Fig. 3, received over cable 34 from the exoskeletal device 16 on human hand 14 are amplified and converted to digital form by the amplifiers and A to D circuits 82 in computer 36. These signals are then compared to previous similar signals from the same subject or from the external calibration units 38, 40 in the calibration/user interface 84 to provide the relative or absolute calibrated values of motion and load detected. This information is then accumulated in the data collection unit 86 for display or storing in data files 88. Data files 88 can be further analyzed by feature extraction software 89 to yield descriptive parameters which summarize the important features of the data such as shown in Table I. TABLE I Individual Force Sensor Maximums Area Under Individual Force Curves Maximum Flexion/Ext. Angle change Positive slope of Flex/Ext.Angle Negative Slope of Flex/Ext. Angle Maximum Radial/Ulnar Angle change Positive slope of Radial/Ulnar Angle Negative Slope of Radial/Ulnar Angle In operation, after the system has been calibrated using load cell 38 and motion cell 40, the force characteristic for a new tool 90 and an old tool 92, Fig. 4A, can be obtained from data collection unit 86 using the system according to this invention. This gives an immediate representation of the relative merits of using two different tools with respect to the force applied. The motion characteristics for the flexion/extension motion 94 and the radial/ulnar deviation 96, Fig. 4B, can be simultaneously obtained on the same time scale in terms of the degrees or angle of motion. Characteristics 94 and 96 are those for the new tool 90 in Fig. 4A. Those for the old tool 96 have been deleted for clarity.

Alternatively, it may be desirable to ascertain the force and angle characteristics obtainable from the data collection unit 86 using the feature extraction software 89, Fig. 3, for a subject relative to the subject's own capabilities, not in absolute terms. This is shown in Fig. 5, where the motion is expressed along the vertical axis not in terms of degrees, but rather in a percent of maximum motion achievable by this particular subject. The radial deviation and ulnar deviation depicted by curve 100 shows a substantial motion in the region 102, where its percentage exceeds 50% of the subject's capability. This corresponds to getting the wrist into the cutting posture for this knife.

Once the posture is achieved the wrist assumes a static ulnar deviated posture for the remainder of the cut.

The flexion/extension curve 104 also shows use of a large percentage of the range, as indicated in region 106, during the initial getting into position phase, in contrast to relatively little flexion/extension, approximately 30-40% maximum and again a relatively static posture.

In contrast, as shown by the radial/ulnar curve 101,

Fig. 6, and flexion/extension curve 103, the motion is high in the positioning phase, region 105, for the pistol grip knife, significantly less during the cutting phase than for the standard knife region 107, and high again in the final region 108.

The force applied with the standard grip knife is illustrated for each finger and the thumb, 110, 112, 114, 116 and 118, respectively, Fig. 7, where it can be seen that the force required is uniformly high. In contrast, the force applied with the pistol grip knife, Fig. 8, is considerably less as indicated by the corresponding curves 110a, 112a, 114a, 116a and 118a.

From these comparisons of force and angle we can infer that by optimizing the positioning phase or "set-up" phase of the task to minimize the wrist excursions, the overall stress on the body can be less with the pistol grip than with the straight knife. This optimization would most likely be achieved through altering the height or orientation of the workpiece (in this case the object to be cut) . Without measuring force and angle together we could not determine that the large excursions for the pistol grip knife were not in the active use phase of the task.

Although specific features of the invention are shown in some drawings and not others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention.

Other embodiments will occur to those skilled in the art and are within the following claims:

What is claimed is:

Claims

1. An exoskeletal measurement system for simultaneously monitoring load and motion on the human body, comprising: means for sensing the motion of a joint; means for detecting the load in a human link segment remote from that joint; and means for correlating simultaneously the motion of said joint and the load on said human link segment for representing the stress on the human body.

2. The exoskeletal measurement system of claim 1 in which said means for sensing includes a first mounting plate on one side of said joint and a second mounting plate on the other side of said joint.

3. The exoskeletal measurement system of claim 2 in which said means for sensing includes a mechanical linkage interconnecting said mounting plates.

4. The exoskeletal measurement system of claim 3 in which said mechanical linkage includes at least one pivot and sensor means for detecting the motion of the joint in at least one degree of freedom.

5. The exoskeletal measurement system of claim 4 in which said mechanical linkage includes a second pivot.

6. The exoskeletal measurement system of claim 5 in which one of said pivots is associated with each mounting plate and said sensor means is associated with one of said pivots.

7. The exoskeletal measurement system of claim 1 in which said means for sensing includes at least one load sensor for sensing the load on the human link segment.

8. The exoskeletal measurement system of claim 7 in which said load sensor is a force sensor.

9. The exoskeletal measurement system of claim 7 in which said load sensor is a pressure sensor.

10. The exoskeletal measurement system of claim 9 in which said pressure sensor includes an array of pressure sensing elements.

11. The exoskeletal measurement system of claim 8 in which said force sensor includes an array of force sensing elements.

12. The exoskeletal measurement system of claim 1 in which said means for correlating includes calibration means for calibrating the load and motion to an external reference.

13. The exoskeletal measurement system of claim 12 in which said calibration means includes an external load cell for determining the load on said human link segment and an external motion cell for determining the motion of the joint.

14. The exoskeletal measurement system of claim 1 in which said correlation means includes means for representing said motion and said force as a percentage of the maximum capacity of an individual.