Evaluation of the Reliability of the Shoulder and Knee Joint of the KPSIT C50 Dummy Adapted to Crash tests carried out at low speeds.

▪ The durability and reliability of the joints of the KPSIT C50 dummy were assessed. ▪ The joints of the KPSIT dummy were compared with the joints of the Hybrid III 50th centil male dummy. ▪ The repeatability of the characteristics of the resistance moment in the joints depending on the cycles of measurements was demonstrated. ▪ The result shows the reliability and durability of the joints of the KPSIT C50 dummy. The article presents the results of experimental studies on the reliability and monitoring of the condition of the knee and shoulder joints of an anthropometric dummy designed for low-speed crash tests. Next, the characteristics of the resistance moments in the joints of the KPSIT C50 dummy are compared with the characteristics of the drag torque of the HYBRID III C50 dummy. The patented and manufactured knee and shoulder joints of the KPSIT C50 dummy characterized by a simple structure. The article presents a comparison of the resistance moments in the knee and shoulder joints of the KPSIT C50 dummy before crash tests and after a series of 200 crash tests. It has been shown that the patented solutions that have been used for low-speed crash tests do not need to be calibrated after a series of 5 crash tests, as is the case with the Hybrid III dummy. In addition, the results of experimental research presented in the article confirm the durability of the KPSIT C50 dummies joints and the possibility of using the joints for other centiles of anthropometric dummies.


Introduction
Anthropometric dummies, which reproduce individual parts of the human body, are used for crash tests.Tests performed with the use of dummies supply information what happens to each part of the human body when an accident occurs.Gerenal Motors' research on safety includes the search for new solutions and information on the safety of the driver, passengers, and especially children [1,2,3,4].Anthropometric dummies are expected to be highly accurate and reliable when performing crash tests.The purpose of the dummies is to reproduce human behavior during a collision as best as possible.The biggest threat to the implementation of crash tests is the lack of repeatability of results and possible damage, especially to the joints of the dummy.The lack of reproducibility of results is related to the structure of anthropometric dummies [5,6,7].
While the lack of repeatability and inconsistency of motion characteristics can be eliminated through calibration, the strength of the joints is not.According to the manufacturer's data, the Hybrid III dummies must be checked before the crash test, while the joints must be calibrated to maintain repeatability of results and avoid possible measurement errors [8,9,10].
In the first years, human corpses and animals such as pigs were used for crash tests [11].Volunteers also took part in the Eksploatacja i Niezawodność -Maintenance and Reliability Vol. 26, No. 1, 2024 crash tests.Unfortunately, experiments on pigs and human carcasses were not satisfactory, as the data supplied to scientists turned out to be not very reproducible.The solution was "anthropomorphic test devices (ATDs)", now better known as crash test dummies [12,13,14].
Before anthropometric dummies became the standard for crash testing, they had to go a long way in improving their design and data collection.The origins of anthropometric dummies used for crash tests date back to the 1920s, when vehicles began to gain more and more popularity, and the number of road accidents and casualties began to increase steadily [15,16,17].The first dummywas patented in 1949 by Samuel W. Alderson [18].At that time, crash tests were a novelty, there was a lack of reliable data on the impact of forces on the human body.At that time, there were no tools to measure such impacts [19,20,21].Research on the behavior of dummies during crash tests, taking into account their similarity to the human body, has led to the development of procedures for assessing injuries to the head, face, chest, abdomen, lower and upper limbs, which are used by all manufacturers around the world [25,26].The joints used in the crash test anthropometric dummy (Hybrid III) must be removed, calibrated, and reinstalled after several crash cycles.
For dummies representing men or women at the 50th percentile, the differences in joint structure are less visible, but for dummies representing children, the joint structure is different [27,28,29].The dummies, representing children aged 12 and 6, have simple joint structures.In the case of a dummy depicting a 3-month-old baby, the shoulder joints resemble the structure of a child's doll.However, the elbow or knee joint does not occur at all.The upper and lower limbs constitute one element.
It should be noted that the ideal design solution for dummy would be a solution that would ensure the lack of frequent calibration and the durability and reliability of the joints.[30,31,32].
The purpose of using dummies in crash experiments is to reduce the number of deaths caused by traffic accidents [33,34,35].The topic of traffic accidents is discussed in articles [36,37,38,39].It should be noted that thanks to dummies, it is possible to predict the likelihood of people being injured in a road accident [40,41,42,43].
The next part of the article presents the design assumptions of the KPSIT C50 shoulder and knee joints, the characteristics of the drag torque in the KPSIT C50 joints, which were compared with the Hybrid III dummies, and the torque resistance characteristics of the KPSIT C50 dummies after a cycles of crash tests.

Innovative joints KPSIT C50 Dummy
The main assumption for the construction of the KPSIT dummy was that all parts of the dummy should correspond to the shape and weight of the human body.Figure 1 shows the KPSIT C50 dummy, representing the 50th percentile male.Each joint is equipped with a set of ball bearings and a joint housing that protects it from damage.The compression spring is responsible for the shape of the corresponding stiffness characteristics.The advantage of this design solution over physical dummy joints is that the joints are not permanently connected to any part of the dummy's body, making it easy to replace damaged components with new ones.In contrast to the male Dummy Hybrid III 50th Centil, its joints are permanently attached to parts of its body.3 shows the shoulder joint of a KPSIT dummy, which consists of three elements connected together.
Figure 4 shows the left part of the designed elbow joint of the manikin.Figure 5 shows the right part of the designed elbow joint of the manikin.The elbow, knee and thigh joints of the physical manikin have one degree of freedom.The joints enable movement towards the X axis. Figure 6 shows the knee joint of the KPSIT C50 dummy.

Data and research methods
A strain gauge force sensor was used to characterize the moment of resistance in the joints.The characteristics of the resistance moment were made on the basis of point measurements occurring in particular ranges of motion.To measure the range of motion, a protractor was used, which was placed in the central point of the joint mounting screw.On the basis of the test results, the moment of resistance in the individual joints was determined.The moment of resistance is represented in the form of equation 1 [30,31,36].An example of the course of the components of the moment of resistance is shown in Figure 7. Fig. 7.An example of the course of the components of the moment of resistance [30].

Results and discussion
Satisfactory results of the similarity of the moments of resistance in the shoulder and knee joints of the KPSIT C50 physical dummy allowed for the implementation of a cycles of crash tests at low speed.The dummy was used for front, rear, and side tests at low speeds from 15 km/h to 20 km/h. Figure 12 shows the KPSIT C50 dummy taking part in a rear crash test using a sports seat.Figure 13 shows the KPSIT C50 dummy taking part in a frontal crash test using a passenger vehicle seat.
Figure 14 shows the KPSIT C50 dummy taking part in a frontal crash test using a bus seat.

Conclusions
The article presents one of the elements of the comparison of the KPSIT C50 dummy with the Hybrid III 50th centil male dummy and presents changes in the characteristics of the torque of resistance in the joints after a cycles of crash tests.The main objective of the study has been confirmed, it has been shown that the joints used in the shoulder and knee joints of the KPSIT C50 dummy remain functional after a cycles of 200 crash tests and do not require calibration of the joint or its replacement with a new one.In addition, it should be noted that the constructed knuckle joint KPSIT C50 can be used in other KPSIT dummy representing the remaining percentile of both male and female populations.
What is also very important: the current Hybrid III dummies are designed for tests at higher crash speeds, starting from 25 km/h in frontal and side crash tests, and at a speed of 16 km/h in the rear test using the BioRid II dummy.Preliminary studies performed on a group of volunteers showed a very good agreement in displacement of the KPSIT C50 dummy with studies on volunteers.
Further research will expand the studies on a larger sample and extend the work to include comparative studies of the KPSIT cervical joint with volunteers and the Hybrid III 50th centil male dummy during crash tests carried out at low speeds.
The breakthrough came in 1977 with the launch of the Hybrid III.It has become a standard dummy in the automotive industry.The dummy Hybrid III is continuously improved by Humanetics and remains the primary crash test dummy.It differs from the previous generation model mainly in the more advanced design of the neck and individual parts of the human body.Additionally, Hybrid III is available in a wider range of sizes than previous crash test dummies.Hybrid III family dummy have high biofidelity with the human body [22,23,24].

Fig. 1 .
Fig. 1.KPSIT C50 dummy.The main assumption of the construction of the KPSIT physical dummy is to reproduce the dynamics described by the characteristics of the moments of resistance of individual joints of the human body (Hybrid III 50th centil male dummy).One of the main assumptions of the dummy design was a simple Repair of individual joints in the KPSIT dummy involves the replacement of the ball bearing or the entire bearing with its housing.To disassemble them, it is enough to unscrew the two screws attaching the joint to individual parts of the mannequin's body.Correct operation of the designed mannequin joint does not require disassembly and calibration after a specified number of test cycles.The only check that needs to be done is to check the alignment of the bolt that presses the spring against the joint.Remember that the shoulder joint is a ball and socket joint that connects the upper limb to the human torso.The advantage of the shoulder joint design solution is that damaged elements can be easily replaced with new ones.The ball bearing is part of the first part of the joint.It is the main element in it.The bearing is placed in a steel housing, which protects the bearing against damage.The joint allows simple assembly to the dummy structure using two screws.The second part of the joint consists of a steel pipe with a locking cam.A security hole is made in the back of the steel pipe.A steel bolt is placed in the security hole to protect the joint from slipping out and damaging the ball bearing.At the beginning of the steel pipe, holes were made for mounting the tension springs and the main hole for mounting the third element of the joint.The third element of the designed joint is the dummy arm.The upper part of the arm has holes for mounting tension springs and a main hole for connecting the arm to the steel pipe of the designed joint.The KPSIT C50 shoulder joint is shown in

Fig. 2 .
Fig. 2. KPSIT C50 Dummy Shoulder Joint.The shoulder joint allows flexion and extension movement consistent with the movement of the human body.A locking cam located in the shoulder edge prevents damage to the joint and prevents further movement beyond the range of motion of the human shoulder joint.

Fig. 3 .
Fig. 3. Shoulder Joint KPSIT C50 Physical Dummy.Abduction movement in the shoulder joint is possible thanks to the use of tension springs.Tension springs connect the second element of the shoulder joint to the third.The joint design prevents damage to the tension springs.The maximum range of motion of the shoulder joint during the abduction movement Figure

Fig. 4 .
Fig. 4. The left part of the designed elbow joint.

Fig. 5 .
Fig. 5.The right part of the designed elbow joint.
that is a function of the joint angle,   (̇) -component that is a function of the angular velocity at the joint,  =   −   (  ) -constant selected on the basis of initial conditions,  0 ,   -torques and initial joint angles.

Fig. 8 .
Fig. 8. Strain gauge mounted on the example of the elbow joint of a 50th percentile male physical dummy.

Fig. 9 .
Fig. 9. Strain gauge used in research.The characteristics of the moment of resistance were compared with the characteristics of the moment of resistance of the Hybrid III 50th centil male dummy.The research and determination of the characteristics for the Hybrid III 50th percentile dummy were carried out at PIMOT and presented in the papers [31,32] The characteristics of the torque of resistance of the shoulder joint of the KPSIT C50 physical dummy coincide with the stiffness values of the Hybrid III 50th centil

Figure 10 showsFig. 10 .Fig. 11 .
Figure10shows the characteristics of the moment of resistance of the shoulder joint of the KPSIT C50 dummy.

Fig. 12 .
Fig. 12. KPSIT C50 dummy taking part in a frontal crash test using a passenger vehicle seat.

Fig. 14 .Figure 24 .Fig. 15 .Fig. 16 .Fig. 17 .Fig. 18 .
Fig. 14.KPSIT C50 dummy taking part in a frontal crash test using a bus seat.Over the course of 24 months, the KPSIT C50 physical dummy has undergone a cycles of 200 crash tests.The drag torque characteristics of the patented joints were checked each time after a cycles of 25 crash tests.The characteristics of the drag torque in the shoulder joint of the KPSIT C50 dummy are shown in Figures 15 to 23.The characteristics of the drag torque in the shoulder joint of the KPSIT C50 dummy, taking into account all cycles of crash test measurements, are shown in Figure 24.
The paper presents an analysis of the characteristics of the resistance moment in joints during a cycles of crash tests.The results of the analysis show that the vapor characteristics remain virtually unchanged after a cycle of 200 tests.It has been shown that the use of an innovative solution allows for fast, efficient and trouble-free performance of crash tests at low crash speeds.-Maintenance and Reliability Vol. 26, No. 1, 2024