while the present invention will be described more full hereinafter with reference to the accompanying drawings , in which aspects of the preferred manner of practicing the present invention are shown , it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention herein described while still achieving the favorable results of this invention . accordingly , the description which follows is to be understood as being a broad , teaching disclosure directed to persons of skill in the appropriate arts , and not as limiting upon the present invention . referring to the drawings , and particularly to fig1 there is shown a lifting capability assessment apparatus 20 constructed in accordance with the present invention . apparatus 20 includes a cylindrical robot 22 , a first adjustable shelf 24 , a second adjustable shelf 26 and a platform 28 . during lifting operations , platform 28 serves to provide a closed force system . a computer ( not shown in fig1 ) is provided for data acquisition and analysis in the manner described in detail below . cylindrical robot 22 is the preferred form of apparatus for providing the movable linkage necessary to create the three - dimensional freedom of movement required in lifting operations . the movable linkage includes multiple &# 34 ; links &# 34 ;. the term &# 34 ; link &# 34 ; is used in this description and in the claims in its kinematic sense , meaning a structure or body of arbitrary shape and construction which is sufficiently rigid to maintain its shape and which is a member of a movable linkage , or group of links . in a dynamic mode of operation this linkage interacts with the user by means of one of various load attachment means , discussed below , which is located on the outermost link of the linkage . the area of load attachment and user interaction will be referred to as the &# 34 ; endpoint &# 34 ;. there are several alternative ways to construct the linkage within the context of this invention . links may be joined together by hinge joints allowing one link to rotate relative to another . they may be joined together by a guideway allowing one link to move in a straight line relative to another . different pairs of links within a linkage may be joined in either of the above ways . cylindrical robot 22 comprises an upright column 40 which is fixedly secured at its base to platform 28 and extends upwardly to a height sufficient to accomodate a full range of lift task operations , for example , to a height of approximately eight feet . the outer link of the cylindrical robot is a horizontal arm 42 which is free to move vertically on column 40 , rotationally about the axis of column 40 and in linear extension and retraction . the outer end of arm 42 defines the &# 34 ; endpoint &# 34 ; of the movable linkage . the endpoint is movable in a three - dimensional region as described below . the complete movable linkage of cylindrical robot 22 will now be generally described with reference to fig3 - 5 , with a detailed discussion of the low friction bearings being presented immediately below in connection with fig6 . the first link of the movable linkage is a collar 44 that is mounted for low friction vertical movement along the outer surface of column 40 . a cylindrical carriage 48 that is concentric with collar 44 is rotatably mounted over the collar and has rotational freedom about the collar . a frame assembly 50 , substantially in the form of a sideways &# 34 ; a &# 34 ;, is fixedly secured to the rotatable carriage 48 . frame assembly 50 includes a pair of openings 54 , 56 that slideably receive the above mentioned arm 42 for linear extension and retraction . stops are provided at 60 and 62 ( fig3 ) to engage mating stop members 64 , 66 carried at the ends of arm 42 to limit the linear movement between a fully retracted position where stop 60 engages stop member 64 to a fully extended position where stop 62 engages stop member 66 , a linear travel of approximately 32 inches . the low friction bearing assemblies that facilitate the movement of the above linkage of the cylindrical robot will now be described with primary reference to fig6 . referring first to the vertical movement component , the cylindrical outer surface of column 40 includes a series of vertically extending ball races 70 that receive recirculating linear bearings 72 that are housed within the vertically movable collar 44 ( see broken away portion of fig6 ). fig6 also illustrates one of the two low friction ball bearing assemblies that permits concentric carriage 48 to rotate about collar 44 . one such bearing assembly is located at the top of carriage 48 and another at the bottom thereof . the ball bearing assembly includes ball bearings 80 and cooperative circumferential grooves ( not shown in detail ) in carriage 48 and collar 44 . fig6 also illustrates in a somewhat schematic fashion the relationship between arm 42 and two of the recirculating linear bearings 88 that are mounted within the openings 54 and 56 of frame assembly 50 and facilitate the low friction linear movement of arm 42 . the bearings of assemblies 88 travel in linear races 90 located on the outer surface of arm 42 . in a preferred embodiment , column 40 and arm 42 are formed as tubular members of aluminum . the surfaces for all rolling contacts with the mentioned recirculated linear bearings are teflon impregnated , hard anodized aluminum which provides a hardened , wear resistant surface ( harder than heat treated steel ) and a dry lubricating effect achieved by the teflon impregnation . the above - described bearing assemblies have been specifically chosen to provide low friction movement between the movable links of the cylindrical robot to enhance the realistic &# 34 ; feel &# 34 ; of lifts performed with apparatus 20 . furthermore , the materials and structural design of these elements have been chosen to minimize the mass of the movable linkage while at the same time maintaining rigidity during both dynamic operations and the substantial bending moments and torsional effects caused by isometric operations . it will be appreciated that cylindrical robot 22 provides a linkage including three links . the outermost link , arm 42 , defines an endpoint that is movable within a three - dimensional arcuate region as best shown in fig2 . in the illustrated embodiment , the arcuate region defines an arc on the order of 140 degrees , a width measured from the inside arcuate boundary to the outside arcuate boundary of approximately 32 inches , and a height that is somewhat less than that of column 40 , e . g ., approximately 63 inches . with respect to the above definition of a linkage and its constituent links , cylindrical robot 22 provides a first guideway link defined by the vertical displacement of collar 44 along column 40 . robot 22 also defines a second rotational link defined by the rotation of carriage 48 and frame assembly 50 about the vertical axis of column 40 . the third link is defined by the guideway movement provided by the linear movement of arm 42 with respect to frame assembly 50 . other structures , for example an elbow arm structure or a gantry structure , may be utilized to provide the necessary linkage . a position sensor is provided for each link to sense the relative movement of that link with respect to another link during lifting operations . in this regard , position sensor 60 senses vertical movement of collar 44 with respect to column 40 by measuring cable movement in the drive assembly , as discussed in detail below in connection with fig7 a and 7b . a second position sensor 62 ( fig6 ) senses the rotational movement of carriage 48 and frame assembly 50 with respect to collar 44 . the third position sensor 64 ( fig6 ) measures the linear displacement of arm 42 with respect to frame assembly 50 . each position sensor 60 , 62 , 64 generates signals indicative of the position of one link with respect to another link in the linkage with the signals together being representative of the position of the endpoint . for use of apparatus 20 in two - dimensional dynamic testing , one - dimensional dynamic testing ( i . e . linear or curvilinear ) or static isometric testing , cylindrical robot 22 is provided with means for selectively locking a selected number of links against movement with respect to the other links . the locking function may be achieved by manually operative means such as locking pins or by computer controlled locking mechanisms . in a preferred embodiment , locking pins ( not shown ) are utilized to lock arm 42 with respect to frame assembly 50 and to lock carriage 48 against rotation with respect to column 44 . the locking of vertical movement of collar 44 with respect to column 40 is achieved through the drive system as described below . the description will now turn to a discussion of the drive assembly 100 which serves as a computer controlled drive system for driving collar 44 and the attached linkage vertically along column 40 when it is desired to move the actual load to the starting point of the test operation or , in other instances , were it is desired to position the &# 34 ; endpoint &# 34 ; near floor level for attachment of an actual load . as illustrated in fig2 the principal components of drive assembly 100 are located on platform 28 at a location that will not interfere with movement within the arcuate testing region . with further reference to fig7 a and 7b , drive assembly 100 includes a directional gear motor 104 which drives a chain 106 by means of a motor sprocket 108 . chain 106 in turn engages the clutch sprocket 110 of a spring actuated drive clutch 112 . sprocket 110 is fixedly secured to a clutch driver 114 which is engaged or disengaged with respect to a drive cone 116 according to the directional status of a drive solenoid 120 . when not energized , by computer command , solenoid 120 serves to engage driver 114 and drive cone 116 against the bias of a compression spring 122 to permit directional motor 104 to drive the paired cable spools 126 , 128 carried on spool shaft 130 . a cable 134 ( fig2 and 8 ) connected to collar 44 is reeled out and taken up on spools 126 , 128 to either raise or lower collar 44 and the associated linkage and load according to the direction of drive of motor 104 . cable 134 is shown in the top view of fig2 as it travels from spools 126 , 128 to the guide pulley arrangement leading to collar 44 . the schematic diagram of fig8 shows that the recirculating cable is directed by a series of guide pulleys 138 , 140 , 142 ( at the top of column 40 ), 144 and 146 . the end of cable 134 is affixed to collar 44 . the drive assembly also includes a brake clutch 150 that is similar in construction to the above mentioned drive clutch 112 . brake clutch 150 includes a brake solenoid 152 which operates through driver 154 and drive cone 156 to lock spool shaft 130 against rotation when it is desired to lock the vertical orientation of the linkage and attached load , for example , during isometric testing . brake clutch 150 also serves as a safety brake mechanism which , as explained below , operates to lock the linkage and load against falling when the system senses that the test subject has lost control of the load . the counterbalance assembly 220 will now be described with reference to fig9 and 10 . assembly 220 includes a tension spring 222 that is secured at its lower end 224 to the base of column 40 . spring 222 extends upwardly to a point of securement to a member 226 that attaches the spring to a cam cable 228 . cable 228 then attaches to a grooved spiral cam 230 which converts the variable linear force exerted by spring 222 into a constant input torque to shaft 232 . shaft 232 conveys the contact torque rotary motion to counterbalance takeup spool 234 which converts the constant torque to a linear constant force via cable 236 . the constant force conveyed by cable 236 is applied to collar 44 via cable attachment . the selection of an appropriate spring constant for spring 222 in combination with the appropriate grooved spiral arrangement for cam 230 produces a constant force substantially equal to the weight of collar 44 and attached linkage assembly to counterbalance the effects of gravity , i . e ., the weight of collar 44 and attached linkage . fig1 depicts an alternative pulley arrangement for connecting spring 220 to cam 230 via cable 228 . this arrangement includes a pair of idler pulleys 240 , 242 that create a triple lead path for the cable for the purpose of permitting the use of a smaller takeup pulley at 234 . referring to fig1 - 13 , there is shown a universal load attachment means for securing an actual load to the endpoint of arm 42 . in the illustrated embodiment , the load attachment means takes the form of a depending arm structure that connects the end of arm 42 to a universal load securement plate 160 . plate 160 may be used with associated belts , bands , or the like , to secure an actual load . the depending arm structure includes a trunion 162 that is secured to the end of arm 42 by means of four bolts 164 , 165 , 166 , 167 that connect the trunion to an internal retaining collar 170 through a snap ring spacer 172 . trunion 162 includes a pluraility of ribs that are received in mating slots in the retaining collar to achieve a secure mating of the trunion to arm 42 and to spread the torsional loads and bending moments from both dynamic and isometric tests uniformally over the entire circumference of arm 42 . this type of load distribution is important in this area of the structure due to the substantial loads being transmitted versus the limited mass of arm 42 and related components , all of which , as explained above , are formed to be as light in weight as possible to reduce the inertial effects of the linkage during testing operations . trunion 162 connects to a depending structural member which carries a load cell 184 for sending signals to the computer representative of the weight of the load . by means of a connector 188 , the load cell is connected to a ball 194 that is received in a socket 196 secured to plate 160 . fig1 illustrates the attachment of an actual job load to arm 42 by means of an attachment means similar to that illustrated in fig1 and 12 . for isometric testing wherein the endpoint is locked against movement , a handle assembly 260 illustrated in fig1 and 15 is secured to the end of arm 42 by means of a trunion 162 similar to the one described above in connection with fig1 and 12 . a pair of handle assemblies 262 , 264 are detachably secured to trunion 162 . the grips 268 , 270 of the handle assemblies must be spaced apart at a distance appropriate to meet established test protocols . in this regard , handle assembly 262 is attached directly to trunion 162 by means a threaded retaining means 274 , creating a spacing between the centerline of arm 42 and grip 268 of approximately 31 / 2 inches . handle assembly 264 is attached to trunion 162 via a spacer member 276 , creating a spacing between the centerline of arm 42 and grip 270 of 9 inches . in actual operation , the handle assemblies would be connected in a manner that would equally space them from arm 42 , thus , fig1 is not representative of an actual handle configuration for testing , but serves the purpose of illustrating handle attachment both with and without spacers . in actual use , without spacers , the grips are spaced 7 inches apart . with the use of two spacers 276 , the grips are spaced 18 inches apart . as shown in detail in fig1 , handle assembly 262 includes a strain gauge assembly 280 , similar to the load cell shown in fig1 for measuring push / pull forces at that handle . handle assembly 264 includes a similar strain gauge 281 ( not shown in fig1 ). these two strain gauges also permit the measurement of handedness during isometric testing , i . e . a measurement of the proportionate amount of force applied by each hand . the data processing will now be described with reference to fig1 - 18 . fig1 is an overall diagram of apparatus 20 , including the related computer control as utilized for both dynamic and full isometric operations . as discussed above , in the dynamic mode the subject &# 39 ; s exertion on the load provides relative movement of links 44 , 48 / 50 and 42 within the linkage of the cylindrical robot 22 . position sensors 60 , 62 , 64 produce position signals x , y , z during dynamic testing . static load transducers 184 , 280 , 281 produce force signals mx , my , mz during isometric testing . all of the above mentioned signals are input to the device electronics 300 which , as shown in more detail in fig1 includes device power means , interface means and a signal conditioning system for producing information kx , ky , kz and kmx , kmy , kmz input to computer 310 . the device electronics 300 also includes means for detecting a falling load which occurs when the test subject has lost control of the load . this means may be rendered operative , for example , by detection of a downward acceleration value above a threshold value for a specified period of time or , in the alternative , may be rendered operative by detection circuitry sensing the test subject &# 39 ; s loss of grip with the load at either hand through contact switches ( not shown ) located where the subject manually engages the load . drive electronics 300 further includes the control circuitry for the drive system and associated power supply . computer 300 provides an analog and digital interface and also provides the software control and data acquisition and analysis as depicted in more detail in fig1 . in this regard , computer 310 preferably handles all force , velocity , acceleration and position information in a cartesian coordinate system . as illustrated , velocity values are computed as , for example , vx = dx / dt and acceleration values are computed as , for example , ax = dvx / dt , permitting the ultimate computation of the following vectors : the above system described in connection with fig1 - 18 permits the input of data from the position sensors and static force transducers and achieves the various processing functions necessary to operate the drive system and falling load safety brake mechanism , while also performing the numerical analysis necessary to control and provide test results in association with the test protocols described in more detail below . in the use of apparatus 20 , a preferred isometric protocol consists of seven different tests . each test positions the individual in a different posture , which is defined by the vertical position of the hands from the center of the two handles , the horizontal position of the feet from the center of the two handles , and the orientation of the arms , legs , and trunk . table 1 describes the seven standard isometric tests in terms of the anatomical position . the isometric handle attachment for apparatus 20 can vary in width . the width is set to 18 inches for all tests except the leg lift , where it is set to 7 inches . it is critical that the defined position is maintained during the entire isometric effort . for each test , the subject is asked to exert an effort in a particular direction while gripping the handles . all instructions to the subject are objective and given without any emotional appeals . the subject is asked to begin the exertion in a gradual , steady fashion , slowly building up to a maximal effort within the first two seconds . the subject will sustain the maximum exertion for three seconds . each test consists of three , five - second trials with a minimum rest period of 30 seconds between each trial . the average force generated during the last three seconds is reported and used to calculate the coefficient of variation ( cov ) over the three trials . any of the three trials can be repeated and a new cov is calculated . only tests with a cov less than or equal to 15 % is to be accepted for further analysis . from these tests , the percentile rankings , based on the above mentioned niosh industrial norms , are calculated and presented . also , the occasional , frequent and continuous lifting recommendations for each position are reported as previously described . two of the static tests involve pushing and pulling postures . niosh did not include these static positions in the guidelines , but blankenship gives percentile rankings , as well as occasional , frequent , and continuous percentages for static pushing and pulling tasks . blankenship &# 39 ; s values are used for these two tests . the seven tests are described below in terms of the anatomical position . ______________________________________ horizontal verticaltest posture distance______________________________________arm lift elbows flexed 90 forearm elbow degrees ; remaining and height posture is neutral . lengthtorso lift hips and shoulders 15 in . 15 in . flexed as required by the horizontal and vertical distances ; remaining posture is neutral . leg lift knees , hips , and 0 in . 15 in . shoulders flexed as required by the horizontal and vertical distances keeping the trunk as vertical as possible ; elbows are neutralhigh far shoulders and elbows 20 in . 60 in . lift flexed as required by the horizontal and vertical distances ; remaining posture is neutral . high near shoulders and elbows 10 in . 60 in . lift flexed as required by the horizontal and vertical distances ; remaining posture is neutral . push posture not determined elbow controlled ; amount by posture height of trunk inclination suitable to subject ; feet staggered . pull posture not determined elbow controlled amount height of trunk inclination suitable to subject ; feet staggered______________________________________ as discussed above , the isometric handle attached to apparatus 20 can vary in width . the width will be set to 18 inches for all tests except the leg lift where it will be 7 inches . the following percentages reported by blankenship are used to make the dynamic lifting recommendation . ______________________________________test occasional frequent continuous______________________________________arm lift 75 % 40 % 20 % torso lift 50 % 40 % 20 % leg lift 50 % 40 % 20 % high far 60 % 40 % 20 % high near 60 % 40 % 20 % push 80 % 40 % 20 % pull 70 % 40 % 20 % ______________________________________ these percentages use the specific extrapolations given for the occasional lift and the lower end of the range extrapolations given for the frequent and continuous lifts . the lower end of the ranges is more consistent with the d . o . t . physical demand levels . the comprehensive protocol has three phases : an isometric , a standard dynamic , and a job task phase . the isometric phase consists of two of the seven tests from the isometric protocol : the arm lift and the leg lift . the testing procedure for the isometric phase of the comprehensive protocol is identical to the isometric protocol procedure . instead of making lifting recommendations directly from the results of the isometric tests , the average forces measured statically helps determine the maximum amount of weight a person can lift dynamically . the standard dynamic phase consists of two sagittal plane lifts and one 3d lift . the sagittal lifts are based on the isometric positions , permitting extrapolations of the isometric results to the dynamic tests . the first dynamic test is a floor ( 15 in .) to standard bench height ( 30 in .) lift . the beginning weight is 40 % of the isometric leg lift results . the second 2d lift , a waist to shoulder height lift , uses heights normalized to the individual &# 39 ; s height rather than standard heights . for this lift , the box is placed on a table adjusted to waist height and positioned under the shelf , which is adjusted to the subject &# 39 ; s shoulder the initial weight for this lift is equal to 80 % of the average force produced during the isometric arm lift . using both fixed heights and normalized heights allows for more flexibility in the database . also , using both heights is necessary in order to extrapolate the beginning loads from the isometric tests , since extrapolations can only be made from the same posture . to find the maximum weight the person can lift , the protocol uses a modified version of the psychophysical lifting method similar to the one used by jiang et al . ( 1986 ). for each test , a series of five repetition trials are performed . after each trial , the weight is increased by either 2 . 5 , 5 , or 10 pound increments , depending on the perceived difficulty of the lifts . this process continues until either the subject wishes to stop or the tester feels it is unsafe for the test to continue , based on observations of the subject . the last weight successfully lifted for all five repetitions is recorded as the maximum weight achieved . the 3d dynamic test is administered in the same manner as the 2d lifts . the test begins with the box on the floor . the subject picks up the box , turns to the right 90 degrees , takes two to three steps , turns to the left 90 degrees , and places the box on the shelf at bench height . this activity reflects the most frequently occurring lifts observed in industry ( drury et al ., 1982 , u . s . department of labor , 1982 ). the initial weight used for this lift is 75 % of the maximum floor to bench weight measured in the 2d standard dynamic lift . seventy - five percent was chosen as a safety precaution to compensate for the twisting motions involved during this activity . for these three dynamic lifts , the lifting recommendations are reported on a frequency basis . the occasional recommendation is the actual maximum lift performed . the frequent recommendation is 40 % of the maximum weight recorded , and the continuous recommendation is 20 % of the maximum weight recorded . these percentages are in agreement with the d . o . t . physical demand levels . the last part of the comprehensive protocol is the job task phase . this phase allows apparatus 20 to be fully utilized in recreating job tasks because the tests are customized , they are not compared in the standard database . to define a task , the tester enters the following : beginning and ending position of the box ( this can be recorded prior to testing by moving the box through one repetition of the task ); starting weight in box or weight of object if an attachable object is used ( weight in box can be expressed as a percentage of an isometric or dynamic result from the first two parts of the protocol , or a specific weight ); the maximum weight for each test is found in the same manner as in dynamic testing . once the maximum weight is found , the mpl and al can be calculated to determine if the job is acceptable according to the niosh guidelines . in summary , the lifting capability testing apparatus 20 has the capability to measure both isometric and three - dimensional dynamic activities . the related software implements both testing modes with the isometric and the comprehensive protocols . the results provide recommendations concerning an individual &# 39 ; s lifting capabilities that are based on existing research and databases . in the drawings and specification there have been disclosed typical preferred embodiments and although specific terms are employed , they are used in a generic and descriptive sense only and not for purposes of limitation , the scope of the invention being set forth in the following claims .
the lifting capacity of a human subject is assessed through dynamic testing protocols utilizing a cylindrical robot that tracks the path of the lift and provides load position information to a data analysis system . the movable linkage of the cylindrical robot moves in a very low friction manner and is designed to be extremely lightweight , while having remarkable strength and rigidity to withstand bending moments and torsional effects . thus , the apparatus permits three - dimensional lift testing of actual loads , including actual job loads , with the test subject experiencing the true feel and inertial effects of the load . static force transducers and related means are provided to permit isometric testing .