Vibration dummy apparatus

Vibration dummy apparatus adapted to sit on and be supported by a vehicle seat to accurately simulate human vibration response at an interface between the apparatus and seat cushions of the vehicle seat is disclosed. The apparatus includes a relatively hard and stiff skeletal frame structure having a pelvic girdle, a pair of femurs, and a pair of ball-and-socket joints for connecting their respective femurs to the pelvic girdle. Elastomeric plastic is formed over the skeletal frame structure. The elastomeric plastic has a substantially anatomically-correct, surface geometry. The elastomeric plastic formed over the pelvic girdle and the pair of femurs has mechanical properties including human-like, soft tissue spring and damping characteristics. A mass-spring system is connected to the pelvic girdle to at least partially simulate vibration response of an upper section of a human.

TECHNICAL FIELD
 This invention relates to vibration dummy apparatus and, in particular, to
 vibration dummy apparatus which are capable of simulating human vibration
 response.
 BACKGROUND ART
 Human vibration comfort has attracted more attention in recent development
 effort by OEM's and suppliers. This is due to the new phase of NVH
 improvement and competition in vehicle design. Improving human ride
 comfort has always been an issue for vehicle component designers and
 manufacturers. For seating and interior integrators, a great deal of
 effort has been focused on improving the ride comfort.
 Vibration transmissibility has been used as an indicator to measure the
 comfort of ride by researchers for many years. The ratio of acceleration
 of the seat cushion or seat back to that of the floorpan is used to
 measure the transmission of vibration from vehicle to the human occupant.
 A difficulty arises when a large number of human occupants are needed for
 a valid test or a component quality evaluation. Component suppliers
 usually cannot afford such expensive tests during prototype development
 stage. The number of tests involved to improve the quality of seating
 systems requires a quicker and more repeatable way to measure the seat
 vibration performance.
 A rigid mass dummy has been used to set a "benchmark" for the seat
 vibration performance measurement. The rigid mass dummy, however, cannot
 provide a similar transmissibility measurement to that of a human so its
 application is largely limited.
 In Gu, Y., "A Comparison Test Of Transmissibility Response From Human
 Occupant And Anthropodynamic Dummy", SAE paper 980655 dated Feb. 23-26,
 1998, a spring-mass dummy is described which was designed to match the
 human response in low frequency in a vertical direction. A six-axis
 hydraulic shaker table was employed as the excitation source to the
 occupied seat. Two seat samples, both measured with human occupants
 before, were used. For simplicity and comparison, a sweep sine signal in
 the vertical direction was used as the excitation signal. The
 transmissibility results measured for the dummy-loaded seat were compared
 to those of human occupants. The vibration response from a dummy-occupied
 seat was correlated to that from a human-occupied seat. A consistent
 relation was shown between the two measurements. However, there are
 problems of accuracy and stability of transmissibility measurement when
 utilizing such a spring-mass dummy.
 U.S. Pat. No. 3,501,777 discloses a urethane foam disposed over a simulated
 skeleton.
 U.S. Pat. No. 5,376,127 discloses polyethylene sheet material surrounding a
 endoskeleton.
 U.S. Pat. No. 5,166,381 discloses a lower leg cast of thermoplastic
 material.
 U.S. Pat. No. 5,526,707 discloses a simulated pregnant crash test dummy.
 U.S. Pat. No. 5,336,270 discloses a plastic material formed over inner
 components.
 U.S. Pat. No. 5,703,303 discloses a simulated torso for testing seats, with
 the torso being mounted on a boom.
 U.S. Pat. No. 5,465,605 discloses a carpet wear testing machine that rolls
 a simulated heel over the carpet.
 U.S. Pat. No. 3,592,041 discloses chair/seat testing by hydraulically
 controlled back and seat simulators.
 U.S. Pat. No. 5,379,646 discloses a test dummy with "back-specific"
 pressure units for testing vehicle seat backs.
 DISCLOSURE OF INVENTION
 An object of the present invention is to provide a vibration dummy
 apparatus which closely matches human vibration response when random
 excitation signals are applied to a vehicle/seat occupied by the
 apparatus, thereby providing an improved tool in seat prototype
 development.
 In carrying out the above object and other objects of the present
 invention, a vibration dummy apparatus is provided. The vibration dummy
 apparatus is adapted to sit on and be supported by a vehicle seat to
 accurately simulate human vibration response at an interface between the
 apparatus and seat cushions of the vehicle seat. The apparatus includes a
 relatively hard and stiff skeletal frame structure. The skeletal frame
 structure, in turn, includes a pelvic girdle, a pair of femurs, and a pair
 of ball-and-socket joints for connecting their respective femurs to the
 pelvic girdle. The apparatus also includes elastomeric plastic formed over
 the skeletal frame structure. The elastomeric plastic has a substantially
 anatomically-correct, surface geometry. The elastomeric plastic formed
 over the pelvic girdle and the pair of femurs has mechanical properties
 including human-like, soft tissue spring and damping characteristics. The
 apparatus further includes a mass-spring system connected to the pelvic
 girdle for at least partially simulating vibration response of an upper
 section of a human.
 Preferably, the pelvic girdle and femurs are substantially geometrically
 correct.
 The mass-spring system includes a mass weight which is adjustable and a
 spring having an adjustable spring rate.
 The pelvic girdle includes a pair of coxae wherein the first pair of
 ball-and-socket joints connect their respective femurs to their respective
 coxae.
 The plastic formed over the pelvic girdle and the pair of femurs has an
 effective stiffness in a range of 6 to 140 kPa.
 The elastomeric plastic may be a castable urethane elastomer molded over
 the skeletal frame structure.
 Preferably, the mechanical properties are substantially the same as
 mechanical properties of bulk muscular tissue in a state of moderate
 contraction.
 The new vibration dummy apparatus utilizes a compressive lower torso and
 combines it with a metal spring-mass upper torso to reproduce human
 vibration response at the interface between the dummy apparatus and seat
 cushions. This combination differs from a pure metal spring-mass system of
 the prior art in the following areas: (1) it utilizes the spring and
 damping in both the rubber lower torso and the metal mechanical part to
 reproduce a human vibration response so it is structurally unique; (2) it
 produces a system response without damper friction problems so as to
 greatly improve vibration coherence; (3) it produces a body pressure
 distribution similar to a human on the seat cushions because of its lower
 torso structural compliance and greatly improves the posture stability
 during vibration; and (4) the weight of the moving mass can be adjusted to
 match different percentiles of humans.
 Differences between this new vibration dummy apparatus and other mechanical
 dummies is that (1) it uses a soft human tissue-like lower torso so it
 matches compliance better than the previous ones; and (2) it utilizes the
 spring and damping characteristics of the compliant lower torso. The lower
 torso is integrated with the spring-mass load simulating the top body of
 human so that the integrated dummy consists of two parts. This unique
 design greatly improves the accuracy and stability of transmissibility
 measurement and provides a direct application tool in seat prototype
 development.
 The above objects and other objects, features, and advantages of the
 present invention are readily apparent from the following detailed
 description of the best mode for carrying out the invention when taken in
 connection with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION
 Referring now to FIG. 1, there is illustrated a vibration dummy apparatus
 constructed in accordance with the present invention, generally indicated
 at 10. As illustrated in FIG. 1, the vibration dummy apparatus 10 sits on
 and is supported by a vehicle seat, indicated by phantom lines 12, to
 accurately simulate human vibration response at an interface between the
 apparatus 10 and seat cushions 14 and 16 of the vehicle seat 12. In turn,
 the seat 12 is positioned on a shaker table, indicated by phantom lines
 17. The apparatus 10 includes a relatively hard and stiff metal skeletal
 frame structure, generally indicated at 18, a pelvic girdle 20, a pair of
 femurs 22 (only one of which is shown), and a pair of ball-and-socket
 joints 24 (only one of which is shown) for connecting their respective
 femurs 22 to the pelvic girdle 20. The pelvic girdle 20 and femurs 22 are
 substantially geometrically accurate and includes a pair of coxae 25 (only
 one shown). (The pelvic girdle 20 and the femurs 22 of FIG. 1 are not
 illustrated as being geometrically accurate. However, in the above-noted
 co-pending applications, which are hereby incorporated by reference, the
 pelvic girdle 20 and the femurs 22 are so illustrated). The pair of
 ball-and-socket joints 24 connect their respective femurs 22 to their
 respective coxae 25.
 An elastomeric plastic 26 is formed over the skeletal frame structure 18.
 The elastomeric plastic 26 has a substantially anatomically-correct,
 surface geometry. The elastomeric plastic 26 formed over the pelvic girdle
 20 and the pair of femurs 22 has mechanical properties including
 human-like, soft tissue spring and damping characteristics. The plastic 26
 formed over the pelvic girdle 20, and the pair of femurs 22 has an
 effective stiffness in a range of 6 to 140 kPa. The elastomeric plastic 26
 may be a castable urethane elastomer molded over the skeletal frame
 structure 18.
 The castable urethane elastomer is known as "Skinflex III". The plastic 26
 is made from Skinflex III components by mixing 300 grams of Skinflex III
 Part "A" into 600 grams of Skinflex Part "B" and then mixing in
 approximately 1200 grams of Skinflex III Part "C" which is a plasticizer.
 These components are available from Chembar, Inc. of Groveport, Ohio.
 The apparatus 10 also includes a mass-spring system, generally indicated at
 30, fixedly connected to the pelvic girdle 20 for simulating vibration
 response of an upper section of a human including all parts of a human
 located above the pelvic girdle 20. The mass-spring system 30 includes a
 mass weight 32 which is adjustable and is mounted on a post 34 fixedly
 secured to the pelvic girdle 20. The system 30 also includes a spring 36
 having an adjustable spring rate.
 Alternatively, the system 30 can be made smaller if additional bones and/or
 bone assemblies of the skeletal frame structure 18 are provided such as a
 thoracic cage and lumbar vertebrae as disclosed in the above-noted
 applications.
 Test Setup
 One 5th percentile female, one 50th percentile male, one 95th percentile
 male and the apparatus 10 took part in a test wherein different levels and
 orientations of vibration were applied to a vehicle seat. All sensors
 signals generated by B&K accelerator pads 40 on the seat were recorded and
 stored for reference.
 Human/Dummy Validation Test
 The test results from three subjects compared to the dummy apparatus are
 shown in FIG. 2 through FIG. 4 and their corresponding values are noted in
 Table 1.
 TABLE 1
 SEAT COMISON RESULT
 ROAD 0.04 g 0.08 g 0.12 g
 F5 113.6 99.63 90.82
 M50 102.3 93.61 81.11
 M95 100.3 106.0 94.6
 Avg 91.9 91.0 85.6
 Dummy 147.9 110.3 96.1
 In the three levels of random signal, it appears that the lowest level
 shows the largest deviation from dummy to humans. This is most likely due
 to the rigid motion caused by friction in the mass-spring system 30 when
 low vibration input was applied. For the other two levels, the results
 from the dummy match much better with those from the humans. It appears
 that the dummy matches the 95th percentile male quite well.
 In summary, the results measured with the dummy apparatus 10 was compared
 with those measured with three human subjects in different percentiles and
 a good match was found in the first transmissibility resonance and overall
 vibration response.
 While embodiments of the invention have been illustrated and described, it
 is not intended that these embodiments illustrate and describe all
 possible forms of the invention. Rather, the words used in the
 specification are words of description rather than limitation, and it is
 understood that various changes may be made without departing from the
 spirit and scope of the invention.