Patent Application
20190357811
The present invention relates to systems for ergonomic analysis of a subject, in particular a worker, and more in particular to systems applied to the analysis of movements, actions, and posture of a line operator responsible for vehicle assembly.
In the manufacturing and metal-engineering industry, workers are called upon to carry out sequenced and repetitive operations, for which it is necessary to guarantee a minimum level of ergonomic compatibility with humans in order to prevent risks to health and physical integrity of operators.
In this context, the metal-engineering industry, and in particular the automotive industry, are characterized by a plurality of tasks that are very different from one another and are carried out innumerable times during the day, with times dictated by the production needs. It thus becomes crucial to perform a careful ergonomic assessment of these actions in order to make—if and where required—postural corrections, and/or corrections of movement and/or of action.
The ergonomic analysis that can be carried out using the systems and methods based upon the prior art in general exploits the following techniques:
Finally, and in part as a consequence of the foregoing, with the systems and methods currently known any activity of ergonomic analysis performed on the worker's hand is substantially impracticable, and even less is it possible to implement this analysis in real time and with objective means not linked to the subjectivity of the operator responsible for ergonomic monitoring.
The object of the present invention is to solve the technical problem mentioned previously.
In particular, an object of the invention comprises providing a methodological supporting tool for ergonomic analysis in the stage of observation and design that will at the same time be objective and fast to implement. Particular reference will be made to the development of a methodology of analysis of the activities performed by a worker at a workstation, deriving, from this analysis, factors that are useful for improving in the design stage the product/process parameters on the assembly lines and/or optimising the characteristics of the workstation.
Moreover, an object of the present invention may be to provide a single interface for collection of ergonomic data from a plurality of devices forming part of the system, for example displays, devices for capturing the movement of the body, and/or devices for capturing the movement and force of the hands (for example, accelerometers, pressure sensors, etc.).
Further objects of the invention comprise:
The object of the invention is achieved by a sensorized glove and by a method having the characteristics that form the subject of the ensuing claims, which constitute an integral part of the technical teaching provided herein in relation to the invention.
The invention will now be described with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:
With reference to
The system 1 comprises:
With reference to
With reference to
A second plurality of pockets 16, which are substantially U-shaped, are, instead, sewn on the outer surface of the glove 10 and house corresponding linear extensometers, which, on account of the U shape of the pockets, are able to detect the relative movements of the various parts of the hand, for example in the palmar plane (for example, movements of divarication of the fingers).
The vector map of
With reference to
Sewn (or otherwise applied) in the (outer) layer 18 are a plurality of pockets 20 of a preferably quadrangular shape configured for housing a corresponding pressure sensor PS (see
Each pressure sensor forms part of a sensor network 22 having a layout such as to enable application of the individual sensors PS in predetermined areas of the hand. An example of such a sensor network is illustrated in
To ensure a more orderly and rational routing of the electrical connections that form part of the sensor network 22, applied on the outer glove 12, in particular on the back, in the area of the fingers, are one or more bands 26. The bands 26 are preferably made of self-adhesive material, such as Velcro® and withhold the electrical connections of the network 22, preferentially routing them along the fingers of the outer glove 12. According to an advantageous aspect of the present invention, the bands 26 may extend circumferentially as far as an opening of one of the pockets 20 in such a way as to obstruct it at the moment when they are positioned on the outer glove 12. This reduces or eliminates the possibility of accidental exit of the pressure sensors of the network 22.
Once again preferably, the outer glove 12 may be provided with inserts obtained with an elastic ribbon in positions corresponding to the fingers, oriented in a longitudinal direction of the fingers themselves. This enables a better adaptation to a range of different finger thicknesses.
The back (dorsal surface) of the outer glove 12 is moreover provided with a fixing portion made of self-adhesive material—for example Velcro—whereby it is possible to fix in a rapid way an inertial sensor 28, which makes it possible to provide the glove 2 with an absolute position reference in the case where the glove is used in the framework of a more complex system, such as the one that will be described with reference to the subsequent
The interface 24 is fixed with a band on the wrist of the worker, as illustrated in
With reference once again to
There now follows a description of a preferred mode of integration between the data of position/movement supplied by the sensors (extensometers EXT) on the inner glove 10 and the pressure data supplied by the sensors PS on the glove 12. It is possible to set in communication the sensors of the glove 10 and of the glove 12 using a data-transmission protocol, for example a data-transmission protocol of the UDP type.
The sensors on the glove 10 supply as output data the angles and co-ordinates for twenty-two (22) joints of the hand identified by the reference J in
For the purposes of this calculation the hypotheses listed below are adopted (see
i) Reference nomenclature for the segments of the fingers, starting from the metacarpals: proximal phalanx (segment at the root), intermediate phalanx (intermediate segment), and distal phalanx (top segment).
ii) It is assumed that there are five (5) distinct balls of known radius Rn. The value of the radius Rn is equal to a pre-set length for each distal phalanx (the lengths are estimated on the statistically most representative dimensions of distal phalanges), n being an index that ranges from 1 to 5. Each of the five balls is centred on the end of a corresponding intermediate phalanx, hence in the points TD, ID, MD, RD, and PD (the first letters standing for “Thumb”, “Index finger”, “Middle finger”, “Ring finger”, and “Pinky”, respectively), see
iii) The abduction of the distal phalanx with respect to the intermediate phalanx and the abduction of the intermediate phalanx with respect to the proximal phalanx are assumed as being zero.
With reference once again to
(x−x0)/(x1−x0)=(z−z0)/(z1−z0)
(x−x0)/(x1−x0)=(y−y0)/(y1−y0)
PA also belongs to the ball centred in P0 and having radius R, which is a known (imposed) quantity and corresponds to the length of the distal phalanx.
Physiologically the distal phalanx PA-P0 is shorter than the intermediate phalanx P1-P0; hence, we may assume R<L
R=dist (PA, P0)=[(xA−x0)2+(yA−y0)2+(zA−z0)2]1/2
L=dist (P1, P0)=[(x1−x0)2+(y1−y0)2+(z1−z0)2]1/2
Note: of the two solutions, the one with positive sign is to be chosen, given that we are dealing with lengths.
By intersecting the aforesaid straight line (passing through the two ends of the intermediate phalanx) with the ball of radius R centred in P0, two points are found, one of which is the point PA.
Expressing, using the straight-line equations provided above, y and z as a function of x
(x−x0)2[1+(y1−y0)2/(x1−x0)2+(z1−z0)2/(x1−x0)2]=R2
we obtain the solutions xA1 and xA2:
x
A1
=x
0
+R/L, and xA2=x0−R/L
The correct solution will be the one whereby the following condition is satisfied:
dist (PA,P1)>L
where
P
A1=P(xA1, yA1, zA1)=(x0+R/L, y0+(y1−y0) (xA1−x0)/(x1−x0), z0+(z1−z0) (xA1−x0)/(x1−x0))
P
A2
=P(xA2, yA2, zA2)=(x0−R/L, y0+(y1−y0) (xA2−x0)/(x1−x0), z0+(z1−z0) (xA2−x0)/(x1−x0))
Since PA is known, from trigonometry we obtain
dist(PA,PB)=2Rsin(β/2)=R1
where β is the angle of flexion supplied by the corresponding extensometer EXT.
To find the co-ordinates of PB, the ball centred in PA with radius equal to the distance between PA and PB, dist(PA,PB), is considered:
[(xB−xA)2+(yB−yA)2+(zB−zA)2]=dist2 (PA, PB)=R12
The above formula may also be re-written so as to obtain the co-ordinates of PB=(xB, yB, zB), as follows:
[(xB−x0)−(xA−x0)]2+[(yB−y0)−(yA−y0)]2+[(zB−z0)−(zA−z0)]2=R12
[(xB−x0)−(xA−x0)]2+[(yB−y0)−(yA−y0)]2+[(zB−z0)−(zA−z0)]2=R12
(xB−x0)2−2 (xB−x0) (xA−x0)+(xA−x0)2+(yB−y0)2−2 (yB−y0) (yA−y0)+(yA−y0)2+(zB−z0)2−2 (zB−z0) (zA−z0)+(zA−z0)2=R12
dist2 (PB, P0)+dist2 (PA, P0)−2[(xB−x0) (xA−x0)+(yB−y0) (yA−y0)+(zB−z0) (zA−z0)]=R12
R
2
+R
2−2xB (xAx0)+2x0(xA−x0) −2yB (yA−y0)+2y0(yA−y0)−2zB(zA−z0)+2z0(zA−z0)=R12=4R2sin2 (β/2)
Imposing that PB lies in the plane Π(ax+by+cz+d=0) passing through the points P0, P1, P2, we have
a=−2xB(xA−x0)=>xB=to/2 (x0−xA)
b=−2yB(yA−y0)=>yB=b/2 (y0−yA)
c=−2zB(zA−z0)=>zB=c/2 (z0−zA)
whence
P
B=(xB, yB, zB)=(a/2 (x0−xA), b/2 (y0−yA), c/2 (z0−zA))
This is an approximate solution, above all as regards definition of PA and PB for the thumb, but for the purposes of the calculation in question it is deemed acceptable.
It is necessary in the first place to define the reference direction and sense for the force vectors, which are each assumed as being applied in the middle point of each phalanx, or else—in the case of the palm—in the points associated to vectors represented by bordered arrows in
To define the direction, the intersection between the plane Π passing through the three points of the three phalanges (e.g., the point IM between the metacarpal and the proximal phalanx, the point IP between the proximal phalanx and the intermediate phalanx, and the point ID between the intermediate phalanx and the distal phalanx) and the plane Π′ passing through each phalanx in the middle point and orthogonal to Π is sought (this implies the condition of orthogonality to the phalanx: given that the phalanx is not flexible and is contiguous to the other phalanges, the plane orthogonal to the plane containing the phalanx is orthogonal to the phalanx).
Imposing that Π passes through the points IM, IP, and ID, the equation of the plane (ax+by+cz+d=0) becomes
(x−xIM)·[(yIP−yIM)·(zIP−zIM)−(yID−yIM)·(zIP−zIM)]+(y−yIM)·[(xIP−xIM)·(zID−zIM)−(xID−xIM)·(zIP−zIM)]++(z−zIM)·[(xIP−xIM)·(yID−yIM)−(xID−xIM)·(yIP−yIM)]=0
whence
a=(yIP−yIM)·(zIP−zIM)−(yID−yIM)·(zIP−zIM)
b=(xIP−xIM)·(zID−zIM)−(xID−xIM)·(zIP−zIM)
c=(xIP−xIM)·(yID−yIM)−(xID−xIM)·(yIP−yIM)
d=−x
IM[(yIP−yIM)·(zIP−zIM)−(yID−yIM)·(zIP−zIM)]−yIM·[(xIP−xIM)·(zID−zIM)−(xID−xIM)·(zIP−zIM)]+−zIM·[(xIP−xIM)·(yID−yIM)−(xIDxIM)·(yIPyIM)]
To determine the second plane Π′ orthogonal to the plane Π, it is sufficient to impose the condition of orthogonality for the two vectors that identify each plane (normal vectors, i.e., their scalar product must be zero) and passage of the second plane Π′ a′x+b′y+c′z+d′=0 through the middle point of the phalanx in question (for example, the point IMM).
A vector that satisfies the condition of orthogonality to the vector (a, b, c) may also belong to the plane defined previously, and hence also the phalanx segment (for example, IP-IM) may constitute such a vector:
IP-IM=[(xIP−xIM), (yIP−yIM), (zIP−zIM)]
Imposing passage through the middle point of the phalanx (IMM=[(xIP+xIM)/2, (yIP+yIM)/2, (zIP+zIM)/2]) it is possible to write the equation of the second plane as
a′ (xIMM)+b′ (yIMM)+c′ (zIMM)+d′=0 (xIP−xIM)·(xIP+xIM)/2+(yIP−yIM)·(yIP+yIM)/2++(zIPzIM)·(zIP+zIM)/2+d′=0=>
a′=(xIP−xIM)
b′=(yIP−yIM)
c′=(zIP−zIM)
d′=(xIM2−xIP2)/2+(yIM2−yIP2/2+(zIM2−zIP2)/2
Gathering the equations of the two planes into a system, we obtain as solution the intersection straight line that identifies the direction of the vector and that passes through the middle point of the phalanx (IMM in the example).
Since it is necessary to identify also a sense to define the force vector, it is possible to consider the point of intersection between the straight line and the ball having a radius equal to the modulus of the force exerted in the point (there are two such points of intersection).
This point can be defined as the South pole of the ball centred in the middle point PIMM and having a radius R equal to the summation of the pressures detected by the sensors PS in points corresponding to the pockets 20, i.e., in the points associated to the finger-tips.
In cartesian co-ordinates, the ball of radius R centred in PIMM will have the following equation:
(x−xIMM)2+(y−yIMM)2+(z−zIMM)2=R2
The points of intersection with the intersection straight line of the two previous planes define the ends of the two vectors comprised between which is the vector sought (definition of sense of the force).
Gathering the equations of the two planes into a system, from the first equation we obtain x=(−by −cz−d)/a, and substituting in the equation of the second plane y=(−a′x−c′z−d′)/b′, it is possible to express both y and x as a function of z to obtain
y=z (a′c−c′a)/(b′a−ab′)+(a′d−d′a)/(a′c−c′a)=Az+B
x=z [(b(a′c−c′a)+c(b′a−a′b))/a(a′b−b′a)]+[(b(d′a−a′d)+d(c′a−a′c))/a(a′c−c′a)]=Cz+D
where
A=(a′c″c′a)/(b′a−ab′)
B=(a′d−d′a)/(a′c−c′a)
C=[(b(a′c−c′a)+c(b′a−a′b))/a(a′b−b′a)]
D=[(b(d′a−a′d)+d(c′a−a′c))/a(a′c−c′a)]
The above formulation is to be used only in the case where a≠0 and a′c≠c′a and a′b≠b′a.
Substituting x and y in the equation of the ball, we obtain the two co-ordinates z1 and z2 (belonging to the set of the real numbers; in any case, it is advisable to check that the discriminant of the equation is positive, i.e., (β2−4αγ)>0).
Assuming
α=(C2+A2+1)
β=2[C(D−xImm)+A(B−yImm)−zImm)]
γ=−R2+(D−xImm)2+(B−yImm)2+zImm2
we obtain
z
1=[−β−(β2−4αγ)1/2]/2α
z
2=[β−(β2−4αγ)1/2]/2α
whence
P
1
=P(x1, y1, z1)=(C[−β−(β2−4αγ)1/2]/2α+D, A[−β−−(β2−4αγ)1/2]/2α+B, [−β−(β2−4αγ)1/2]/2α)
P
2
=P (x2, y2, z2)=(C[+β−(β2−4αγ)1/2]/2α+D, A [+β−−(β2−4αγ)1/2]/2α+B, [+β−(β2−4αγ)1/2]/2α)
The correct triad will be the one that has the shorter distance from the co-ordinate corresponding to the tip of the thumb PTX, namely
P
IMMF (x, y, z)=min (dist (P1, PTX) dist (P2, PTX))
where:
dist (P1, PTX)=[(x1−xIMMF)2+(y1−yIMMF)2+(z1−zIMMF)2]1/2
and
dist (P2, PTX)=[(x2−xIMMF)2+(y2−yIMMF)2+(z2−zIMMF)2]1/2
For it to be a plane in cartesian form, all the coefficients that identify it (vector orthogonal to the plane) can never simultaneously be zero, and hence we can never simultaneously have a=b=c=0.
If a=0, only the following interesting and non-degenerate cases may be found:
With a=b=0 and c≠0, we have z=−d/c, and the two sub-cases with b′≠0 and b′=0 will be possible.
If a=b=0 and c≠0, substituting z in Π′ makes it possible to obtain y as a function of x (or x as a function of y) according to whether either a′ or b′ are possibly zero.
If a′=0 and b′≠0 we obtain y=(c′d−d′c)/cb′ and z=−d/c, which, once substituted in the equation of the ball, will yield the solutions x1 and x2
x
1
=x
IMM−[(R2−(−d/c−zIMM)2−((c′d−cd′)/cb′−yIMM)2]1/2
x
2
=z
IMM+[(R2−(−d/c−zIMM)2−((c′d−cd′)/cb′−yIMM)2]1/2
whence
P
1
=P (x1, y1, z1)=(xImm−[(R2−(−d/c−zImm)2−(c′d−cd′)/cb′−yIMM)2]1/2, (c′d−cd′)/cb′, −d/c)
P
2
=P (x2, y2, z2)=(xIMM+[(R2−(−d/c−zIMM)2−((c′d−cd′)/cb′−yIMM)2]1/2, (c′d−cd′)/cb′, −d/c)
The correct triad will be the one with the shorter distance from the co-ordinate corresponding to the tip of the thumb PTX, namely
P
IMMF (x, y, z)=min (dist (P1, PTX) dist (P2, PTX))
where:
dist (P1, PTX)=[(x1−xIMMF)2+(y1−yIMMF)2+(z1−zIMMF)2]1/2
and
dist (P2, PTX)=[(x2−xIMMF)2+(y2−yIMMF)2+(z2−zIMMF)2]1/2
If a′≠0 and b′=0, we obtain
x=(c′d−d′c)/a′c and z=−d/c
which, substituted in the equation of the ball, yields the solutions y1 and y2
y
1
=y
IMM−[(R2−(−d/c−zIMM)2−((d′c−cd′)/ca′−xIMM)2]1/2
y
2
=y
IMM+[(R2−(−d/c−zIMM)2−((d′c−cd′)/ca′−xIMM)2]1/2
and hence
P
1
=P(x1, y1, z1)=(yIMM−[(R2−(−d/c−zImm)2−((d′c−cd′)/ca′−xIMM)2]1/2, (c′d−d′c)/a′c,−d/c)
P
2
=P (x2, y2, z2)=(yIMM+[(R2−(−d/c−zIMM)2−((d′c−cd′)/ca′xImm)2]1/2, (c′d−d′c)/a′c, −d/c)
The correct triad will be the one that has the shorter distance from the co-ordinate corresponding to the tip of the thumb PTX, namely
P
IMMF (x, y, z)=min (dist (P1, PTX) dist (P2, PTX))
where:
dist (P1, PTX)=[(x1−xIMMF)2+(y1−yIMMF)2+(z1−zIMMF)2]1/2
and
dist (P2, PTX)=[(x2xIMMF)2+(y2−yIMMF)2+(z2−zIMMF)2]1/2
Following upon this calculation, there are hence known the middle points of application of the forces on the various areas of the hand that derive from the readings made by the sensors PS, with respect to the positions of the joints J, the postural data of which are collected by the extensometers EXT.
This enables definition of the direction of the force itself.
Operation of the glove 2 is described in what follows.
The glove 2 can be used for obtaining postural information on the hand (when the inertial sensor 28 is present on the glove), for obtaining the direction of the resultant of force when associated thereto is the reading of the pressure intensities with corresponding orientation of the surface on which pressure acts (direction of the force on the various sensors), and chiefly for recognising the type of grasp exerted by the worker when the postures of the fingers are associated to the pressure exerted by the fingers most involved in the posture being detected.
In particular, four different types of grasp may be detected:
a) GRIP: this is the type of grasp exerted, for example, at the moment of gripping an angle nutrunner set in a position corresponding to a joint; for the purposes of the test the results of which appear in
b) PALMAR: this is the type of grasp exerted, for example, at the moment of lifting of a standard weight; for the purposes of the test the results of which appear in
c) HOOK: this is the type of grasp exerted, for example, at the moment of lifting of a bucket with shaped handle having a known weight; for the purposes of the test the results of which appear in
d) PINCH: this is the type of grasp exerted, for example, at the moment when a screw is picked up from the working surface; for the purposes of the test the results of which appear in
To gather information for the purposes of recognition of the types of grasp, calibration tests are conducted on a plurality of operators.
In a case provided by way of example, calibration was carried out on twelve operators according to the following operating scheme:
1) evaluation of the maximum force of each operator in order to assess the ranges of forces; this envisaged the use of instruments such as a gripmeter and a pinchmeter up to the maximum force, with three repetitions;
2) evaluation of the accuracy and precision in acquisition of the force data (deviation from the expected value and the mean value) by gripping the gripmeter with a force of 5 kg kept constant for 3 s, with five repetitions; and
3) evaluation for recognition of the type of grasp (grip/pinch/palmar/hook); a cycle of the four types of grasp was carried out in succession (with neutral posture assumed between each type of grasp), with three repetitions.
Evaluation of the maximum force exerted by each operator both in the case of PINCH (using the pinchmeter) and in the case of GRIP (using the gripmeter)—cf. point 1 above—enables:
If in the sample the “weakest” operator is able to exceed the minimum threshold, then there is the reasonable certainty that it is possible to identify a given type of grasp for all the components of the sample; i.e., if the minimum threshold is reached by the weakest subject, certainly the strongest ones will be able to reach and exceed (even abundantly) the activation value. The minimum threshold activates recognition of the type of grasp, filtering any possible background noise or activations of the sensor that are not to be attributed to the type of grasp.
Then, the pressure maps, acquired by the sensors PS were analysed for the various postures of all twelve subjects in order to identify the areas of the hand involved in the various types of grasp.
The values of pressure/force exerted by the various subjects during the various types of grasp were evaluated for assessing the variability of the values due to the subjectivity of execution of the tests.
The results obtained from the pressure maps acquired by the sensors PS have highlighted for the various postures the part involved in the pressures enabling definition of the various types of grasp, meaning thereby that a given configuration of postures and pressures enables (instrumental) identification of a specific type of grasp and hence definition of the reference condition thereof (for the instrument) in order to recognise automatically which type of grasp is being exerted.
The pressure map of
The pressure map of
With reference to the diagram of
The pressure map of
With reference to the diagram of
The pressure map of
With reference to the diagram of
For each type of grasp, on the basis of the analysis of the previous pressure maps, a given area of the hand on which the majority of the pressure exerted by the hand itself must be concentrated was selected.
For recognition of the type of grasp, the pressures and positions of the areas of the hand involved in the grasp were analysed, and, by way of verification, the pressures and postures of the remaining area of the hand were also analysed. This is illustrated in
Instead, the areas of the pressure map where, for each type of grasp, the concentration of noise (where applicable) is to be expected are encompassed with jagged outlines. The pressure map visible in each figure of this group of figures is arranged as a set of matrices each associated to a sensor PS in a pocket 20, where each cell of each matrix (the so-called sensel, designated by SS) contains the value detected by a sensitive element of the sensor PS in the corresponding area of influence.
With reference to
For the PALMAR grasp, the pressure must be concentrated mainly on the intermediate and distal phalanges of all five fingers. There must not be any contact with the area of the palm. The sensels SS concerned for the PALMAR grasp in this specific example are 140 in number (38% of the total area). on this area the pressure must be at least 51% of the total pressure.
On the rest of the hand there may be a residual pressure (noise), which, however, must not exceed 49% of the total pressure. The angles of abduction between the four fingers must be more than 5° to differentiate them from those of the PINCH grasp, and the posture of the hand must correspond to the grasp.
For the HOOK grasp the pressure must be concentrated on the proximal and intermediate phalanges of four fingers and on the top part of the palm (pulley). The sensels SS concerned for the HOOK grasp in this specific example are 172 in number (48% of the total area). On this area, the pressure must be at least 51% of the total pressure. There must not be pressure on the thumb; i.e., any possible noise present on the thumb must not exceed the value acquired in the neutral posture. On the rest of the hand (and in particular on the distal phalanges) there may be residual pressure, which, however, must not exceed 49% of the total pressure. The posture of the hand must correspond to the grasp.
For the three-finger PINCH grasp, the pressure must be concentrated mainly on the intermediate and distal phalanges of the thumb, index finger, and middle finger. The sensels SS concerned for the three-finger PINCH grasp in this specific example are 84 in number (23% of the total area). On this area the pressure must be at least 51% of the total pressure. There must always be pressure on the thumb. On the rest of the hand there is frequently a residual pressure (noise), due to bending of the hand, which must not exceed 49% of the total pressure. The angle of abduction between the index finger and the middle finger must be less than 5°. The posture of the hand must correspond to the grasp.
The angles that describe the posture of the hand were evaluated during the tests thanks to the data collected via the extensometers EXT on the inner glove 10. A certain repeatability was detected in the angles of the joints of the hand in the various repetitions of the intra-subject test. By way of example,
In brief, by means of the sensorized glove 2, it is possible to provide a method for ergonomic analysis of a worker's hand that comprises the following steps:
In particular, the method forming part of the invention, which determines the type of grasp exerted by the hand includes:
Finally, it should be noted that it is possible to use the first and second sensor data for a cross check on the determination of the type of grasp. In particular, the information determined on the basis of the recording of the information coming from the mapping areas of the pressure map must be consistent with the information determined on the basis of the postural data reconstructed by means of the extensometer sensors EXT of the inner glove 10.
With reference to
The sensors that can be installed on the wearable network 4 include, in combination or as alternatives to one another:
The wearable sensor network 4 envisages that the sensors 30 are located on corresponding parts of the operator's body, where these parts of the operator's body have a correspondence with a reference scheme of the human skeleton illustrated in
The reference scheme 4RIF includes segment elements for defining bones of the human skeleton connected by joint elements for definition of joints of the human skeleton. The joint elements are preferably point-like elements and are identified by the references jC1Head, jT1C7, jT9T8, jL1T12, jL4L3, jL5S1, Root, jRightC7Shoulder, jRightShoulder, jRightElbow, jRightWrist, jLeftC7Shoulder, jLeftShoulder, jLeftElbow, jLeftWrist, jRightHip, jLeftHip, jRightKnee, jRightAnkle, jRightBallFoot, jLeftKnee, jLeftAnkle, jLeftBallFoot. The same references are reproduced also in
The inertial sensors 30 are arranged in points representative of a respective segment element; in particular, they may be fixed (by means of the aforementioned bands or other type of wearable accessories in general) on respective parts of the body in positions corresponding to points representative of the segment element identified (at a software level) by the joint elements of
The network 4 enables acquisition of the kinematics of the body of a person (in the case in point, a worker). In other words, it enables acquisition of the trajectories, postures, angles of rotation that each segment element and joint element of the body assumes during any activity and specifically a working activity. The network 4 is configured for supplying at output values representing a rotation in space (i.e., rotations about the axes x, y, and z) and the spatial co-ordinates for each point monitored.
The above values can be acquired by the processing unit 8, which can automatically evaluate the postures assumed by the worker throughout the working cycle. For instance, it is possible to process the co-ordinates of the joints to obtain angles of rotation of the body joints, in accordance with the indications specified in the ergonomics standards.
The analysis that can be performed by means of the network 4 may be integrated with the analysis conducted on the worker's hands via the glove 2. In general, it is possible to set the network 4 in communication with one or more gloves 2.
The standard distribution of the joints where the postural angles used for the purposes of the ergonomic assessments are detected is represented schematically in
angle of the torso;
angle of the shoulder; and
angle of the elbow and the knee.
For these angles some definitions and some hypotheses are introduced, namely:
Conditions:
shoulders=(jRightShoulder+jLeftShoulder)/2 (1)
hips=(jRightHip+jLeftHip)/2 (2)
{right arrow over (V)}
torso
=
shoulders
−
hips (3)
{right arrow over (V)}
hips=jLeftHip−jRightHip (4)
Initially, the hip vector {right arrow over (V)}hips is projected in the horizontal plane, namely, {right arrow over (V)}hipsXY={right arrow over (V)}hips with the component {right arrow over (V)}hips(z)=0.
Then, the sagittal plane Ω is calculated as
with:
(a, b, c)={right arrow over (V)}hipsXY
and
d={right arrow over (V)}
hips
XY(0)·
Given the following:
the direction coefficients of the plane
that contains the straight line passing through {right arrow over (V)}torso are calculated as follows:
a
pi=1; bpi=k; cpi=−(l+k·m)/n
Hence, the projection of the torso vector sought corresponds to the intersection of the two planes Π and Ω:
{right arrow over (V)}
1=(api, bpi, cpi)×(a, b, c)
{right arrow over (V)}
2
={right arrow over (V)}
hips×(0,0,1)
The method proposed is independent of the position of the subject with respect to the reference triad of the acquisition system. Moreover, a check on the arccosine enables distinction of the correct sign of the value in the case of flexure (positive sign) and extension (negative sign) of the torso.
A. Calculation of reference geometries
B. Application of method of solution
Conditions:
Conditions:
Since the position of the terminal points of the skeleton (top part of the head, end of the hand, end of the foot) is not available, the lateral movements, the flexo-extensions, and the prono-supinations (twisting) of the hands and of the head are calculated on the basis of the information coming from the sensors on the wearable network 4.
The prono-supinations of the hand are instead calculated starting from the rotations of the elbow. Biomechanically, the wrist does not turn: in other words, the hand does not turn with respect to the forearm (using the wrist as hinge). Prono-supination of the hand takes place because, starting from the elbow, there is a rotation of the ulna with respect to the radius; the two long bones are constrained always in the same point both in the wrist and in the elbow but can be cross one another, thus generating prono-supination of the hand. Hence, the prono-supinations of the hand are caused by “rotation” of the long bones starting from the elbow.
The aim of the system 1 according to the invention is the creation of a methodological supporting instrument for ergonomic analysis in the observation and design stage that will at the same time be objective and fast to use.
The development of the methodology of assisted analysis is aimed at a detailed and objective assessment of the activity performed at a workstation, by drawing, from the verification stage, the main factors useful for improving, in the design stage, the product/process parameters on assembly lines.
The general aim is implementation and development of methods for ergonomic assessment of the process in order to apply the data and the information obtained also in the stage of design of new workstations or in the stage of redesign/modification of existing workstations.
For this purpose, the system 1 supplies a simple interface for gathering ergonomic data at input from a working activity, namely, coming from:
The ergonomic methods currently available for the assessments include:
In addition to the above, the system enables pre-arrangement of the data for transfer to a specific software for time and ergonomic analysis known as TiCon (automatic).
The features of the system 1 include:
The system 1 enables two different methods of data analysis, namely:
Manual analysis enables execution of an assisted ergonomic analysis starting from one or two synchronised video clips, through:
Automatic analysis enables reading of the data at output from the wearable sensor network 4 and the glove (which records the movements of the user) for automatic recognition of the majority of the critical postures.
The above analysis has been implemented prevalently for some ergonomic methods (OCRA Checklist and MURI); moreover, in this way, some input data are also available for the TiCon© software.
For operation of the system 1 in manual mode, it is indispensable to acquire at least one video clip of the workstation that is to be analysed. If the video clip is the only kind of data that is acquired, then only a manual analysis is possible. If, instead, acquisition of the video clip is combined with acquisition of the data from the wearable network 4 and/or from the sensorized glove 2, then it is possible to carry out an automatic analysis.
The software has two interfacing modes:
a) “input mode”, where the software autonomously activates the manual mode or automatic mode according to the files loaded; in the case of activation in manual mode it is possible to select the ergonomic items that are to be implemented manually; and
b) “output mode”, where visible (on a screen) is the distribution in time of the characteristics entered manually or calculated starting from the data-acquisition files of the network 4 and the glove 2.
The system 1 according to the invention is preferably entirely implemented and managed via software. The premises for ergonomic analysis are the availability of at least one video clip of the working activity that is to be analysed, or else (either in combination or as an alternative) an IVR (Immersive Virtual Reality) system.
The second option is implemented in particular in the design stage when the physical workstation for the operator does not yet exist, and envisages integration of the glove 2 and of the wearable network 4 with the IVR system in combination with the use of real tools and objects, such as wrenches, screwdrivers, and line structures in a context commonly identified as “mixed reality”. To be able to pursue this option, it is necessary to have available a CAD model of the workstation that is to be analysed, and it is likewise necessary to know the working cycle of the task to be performed.
The software whereby operation of the system 1 is implemented is configured for reading the majority of the commercially available types of video files. In the case of manual analysis, it is possible to proceed with post-processing analysis of the various ergonomic items that are to be assessed.
In the case of operation in IVR mode, instead of the availability of the video clip of the operator working at the workstation, a video file is provided, obtained following upon implementation of the following operating logic:
importation into the virtual environment of the CAD model of the workstation to be analysed;
definition of the logic of movement of the tools (wrench, screwdriver, etc.) to be used in the virtual environment;
assignment of the real object to the corresponding virtual object;
preparation of the user who will be wearing both the network 4 and the glove 2; and
reproduction of the work task and recording of the data.
In this way, it is possible to generate a video file (for example, in .mpg format) to be used instead of the video clip captured on-line at the real workstation, integrating it with the data recorded by the network 4 and the glove 2.
In this regard, reference may be made to
It should be noted that the use of physical elements such as the structure F or the screwdriver T in the IVR system is preferable in order to prevent erroneous interpretations of the postural data and, above all, of the grasp data.
At the start, the software is set in INPUT mode. In this mode, the processing unit 8 automatically acquires the data coming from the wearable sensor network 4 and/or from the sensorized glove 2, or else receives the input data via manual data entry. In this mode, it is possible to select the ergonomic method that is to be used for the assessment.
Represented in
Once the video and animation files of the software dummy have been opened (the software dummy being represented in the central image of
The OCRA (Occupational Repetitive Actions) Checklist method consists, as is known, of a synthetic index for assessment of the work risk factors affecting musculo-skeletal disorders of the upper limbs that is able to identify the risk of overload of the upper limbs due to repetitive work.
If the data of the network 4 are available (i.e., in the case where the data files acquired by means of the device are available), the following characteristics already calculated are automatically available:
i) arm almost at shoulder height;
ii) hand above the head;
iii) extreme prono-supinations of the elbow;
iv) extreme flexo-extensions and deviations of the wrist;
If data acquired by the sensorized glove 2 are also available, also the following further characteristics are automatically available (according to the methodologies already described previously):
v) recognition of the various types of grasp, with notification of the presence of an incongruous grasp (pinch grasp, palmar grasp, or hook grasp: in this connection, these types of grasp can cause biomechanical overloads if they are repeated frequently or even damage due to squeezing of the sinovial capsules of the tendons of the hand; hence they must be detected and, if they are carried out frequently, they contribute to raising the ergonomic-risk index); and
vi) recognition of the static actions.
The ergonomic items that are not analysed automatically may be analysed manually by the user. An example of graphic interface that can be used for this purpose is illustrated in
The ergonomic items may be selected in a menu “ITEM” that appears on the right of the screen. In this embodiment, it is possible to analyse up to a maximum of four ergonomic items at a time, but it is possible to carry out the analysis also by selecting just one item at a time.
In the case where a data file generated by acquisition by the network 4 has been selected, after entry of an enable command by the user (for example, by pressing a button “play” or “start”, see reference PL in
If, instead, no motion-capture files coming from the network 4 and/or from the glove 2 are available, it is possible to proceed with manual analysis as follows (
1. pressing the key PL to run the video clip or continue display thereof; by pressing the key PL again the video clip is paused;
2. pressing, on a keypad KYP, the character or characters corresponding to the ergonomic item that is being analysed in the instants of the video in which the item is present; in the example in the figure, the representative characters are “A”, “S”, “K”, and “L”;
3. once acquisition of all the necessary ergonomic items is through, displaying and checking again, if so required, the acquisition just concluded, and then passing to the output step.
Using a mode-selection menu, it is then possible to pass to the OUTPUT mode, thus displaying the results for the data entered.
An example of screen containing results is illustrated in
i) arm almost at shoulder height;
ii) hand above the head;
iii) extreme prono-supinations of the elbow;
iv) extreme flexo-extensions and deviations of the wrist;
vi) static technical actions: holding an object in static grasp for at least 4 s.
In the case where also the data of the glove 2 were collected, to the items in question there would be added the item of point v) above, i.e., recognition of the various types of grasp and of incongruous grasps.
By querying on the graph a point where an ergonomic item is present (for example, by clicking the point with the mouse), it is possible to display the corresponding instant of the video clip where said item occurs. In the case of acquisition of the motion-capture data by the network 4, the corresponding posture of the equivalent dummy is reproduced (
Once acquisition is through, it is moreover possible to check again the times calculated on the basis of the OCRA Checklist method, i.e., the times associated to occurrence and protraction of the various items.
The data may moreover be exported in a high-compatibility format for external analyses, for example in a Microsoft® Excel® spreadsheet.
A second ergonomic method is the OCRA Index method, based upon the ISO 11228-3 standards, which may enable further movements of the body to be evaluated, for example: rotation of some joints through an angle that exceeds predetermined thresholds. Via this analysis, it is possible to obtain an evaluation of an index of risk for the worker.
The operating modes of data acquisition and assessment of the ergonomic items are the same as those already described.
A further ergonomic method is the MURI method, whereby it is possible to divide the time interval observed into a number of study periods so as to obtain a division of the actions performed by a worker, for example analysed automatically and simultaneously. At the end of the assessment, it is possible to obtain a number of evaluations of the actions performed by a worker, instead of a single evaluation of the ergonomic analysis (i.e., based upon a single ergonomic-risk index).
In combination with other ergonomic methods, also the EM-MURI ergonomic method may be used, which consists in an extended version of the MURI analysis (i.e., with more parameters evaluated). The purpose of this method is to enable a rapid assessment of the ergonomic risks and to overestimate certain ergonomic risks in such a way as to highlight the actions on which it may be interesting to conduct a subsequent analysis.
After reading the video file corresponding to the video acquired by means of the device 6 and, if available, also the motion-capture file acquired with the network 4, the various periods into which the task to be analysed is to be divided are defined.
As the video clip is run, the key PL (play/pause) can be used to pause the video clip at the final instant of the study period forming part of the set of periods into which the task is to be divided, and the study period is identified by pressing a dedicated key; this operation is repeated until all the study periods have been considered.
The time of start and end of the period selected are recorded automatically by the software that calculates duration thereof, starting from the (start/end) data entered manually.
In the case where data of the network 4 are available, the ergonomic items that do not refer to loads to be moved will be analysed automatically by the software. The reason for this is that in the MURI method one datum that cannot be collected using the sensors described is the load (weight) to be moved or carried so that this datum must be entered manually. The remaining data necessary for assessment can arrive automatically from the sensors.
In the case where only the video clip is available, after all the periods that identify the task to be analysed have been entered, it is necessary to select the ergonomic item that is to be analysed. The video clip is then restarted, and the period corresponding to that item is automatically highlighted and selected.
While a period is highlighted, the operator who carries out the analysis must type in a vote that he intends to attribute to the corresponding ergonomic item in the period in question. The voting system envisages the following scale: 1 acceptable; 2 investigate; 3 unacceptable; these votes may possibly be associated to colours (e.g., green=acceptable; yellow=investigate; red=unacceptable).
In the output mode, a graph is displayed summarising the MURI data divided into periods/operations that have been analysed. An example of this graph is displayed in
Yet a further ergonomic method corresponds to the EAWS method and corresponding TiCon software for ergo-characterization, i.e., for the activity of definition of the ergonomic parameters that distinguish from the ergonomic standpoint an activity (described in the acquisition of times or operation) on the basis of the workstation to which said activity has been assigned (balancing).
The analysis via the EAWS method is performed with the TiCon software, which may advantageously be fed with the data drawn from the system 1 since it enables, for example, assessment of:
RULA (Rapid Upper-Limb Assessment) ergonomic method: this method is used for assessing musculo-skeletal risks due to incongruous postures maintained in a continuous or repetitive way during working activity.
NIOSH (National Institute for Occupational Safety and Health) ergonomic method: this method may be used for assessing the risk involved in lifting loads.
Snook & Ciriello ergonomic method: this method is used for assessing a risk correlated to transporting on the flat, pulling, or pushing a load.
Sue Rodgers ergonomic method: this method is used for analysis of muscle fatigue, in particular in the Brazilian industry.
Irrespective of the ergonomic method that is chosen for the ergonomic analysis via the system 1, the general steps listed below of the method for ergonomic analysis of a worker using the system 1 can thus be identified.
These steps comprise:
Acquiring a second set of postural data from the wearable sensor network 4 comprises acquiring the trajectories, postures, and angles of rotation of each segment element and joint element of said reference scheme during performance of the task.
By means of the above method and using the system 1 it is hence in general possible to identify aspects that are critical from an ergonomic standpoint, and/or to provide an ergonomic assessment in compliance with company and international standards, and/or to re-plan a workstation or a sequence of operations to reduce the ergonomic risk to which the operator is exposed.
Of course, the details of implementation and the embodiments may vary widely with respect to what has been described and illustrated herein, without thereby departing from the sphere of protection of the present invention, as defined by the annexed claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18153288.8 | Jan 2018 | EP | regional |
