TheHPM (H-Point Machine) is a physical device defined by the Society of Automotive Engineers (SAE). Its primary purpose is to establish and measure key reference points and dimensions of a vehicle, and it is widely used globally in automotive design. It accurately acquires the occupant's seating position within the vehicle and is a crucial device for converting this position into the seat's H-point. Among the many H-points, the SgRP point is paramount; as a design hard point (R-point), it forms the basis for overall vehicle space design, visibility design, and other related work.
The development of the first-generation HPM device has a fascinating history. In 1955. Professor Wilfred DePMster of the University of Michigan conducted in-depth research into skeletal kinematics, aiming to develop a three-dimensional physical device that could represent a seated operator, initially developed for military applications.
Meanwhile, Geoffrey of Ford Motor Company conducted a series of radiographic experiments, successfully creating a two-dimensional template describing a seated car occupant. In the late 1950s, Myal of General Motors completed the first prototype of a "comfort-sized human model" and proposed the reference point for the hip of the human model, namely the H-point. To ensure the model accurately reflected the actual human body in the United States, based on civilian and military data from that time, a median male weight of 77.3 kg was selected as the model's baseline weight. The reference height for the human model was set at 1803 mm, approximately 90% of the average male driver at the time. The outer contour of the seat contact area was designed based on the seat interface contours of eight men approximately 1803 mm tall and weighing 77.3 kg, while the contour of one subject considered the most representative was also selected as the basis for the human model's contour.
In 1962. SAE J826 first described this HPM device with a human body contour. This HPM device adopted the outer dimensions of a General Electric model, but the geometry was modified based on suggestions from Geoffrey et al. In 1968. SAE J826 was revised, specifying the use of longer legs and thighs, determined to be at the 95th percentile. A review of the relevant calculations revealed that Geoffrey's 90th percentile human model, adjusted by scaling the dimensions from hip to knee and knee to heel to match the 95th percentile male value, ultimately resulted in a leg length (thigh plus leg plus foot) exceeding the 95th percentile for male drivers at the time.
Over the decades, the uses of the HPM device have far exceeded its original design intent. SAE J1100 includes dozens of dimensions measured by the HPM device, covering measurements of hip space, leg space, and head space, among others. International organizations, including the International Organization for Standardization (ISO), have incorporated the HPM device into their standards. Furthermore, the HPM device is used as a platform for other measurement equipment, such as seatbelt and headrest testing. The US Federal Motor Vehicle Safety Standards use HPM devices with modified leg lengths to establish reference points for positioning crash test dummies.
Disadvantages:
While the widespread use of the HPM device demonstrates its importance, significant room for improvement remains. In the early 1990s, researchers at UMTRI conducted a study comparing the posture and position measurements of the HPM device with data from human subjects in three vehicle seats. They found that the SAE J826 H point was always located in the test seat relative to the human hip joint position, but the seat back angle measurement of the HPM device could not accurately represent the human torso posture.
In 1993. SAE convened a working group to consider improvements to the HPM device. Representatives from automakers, seat suppliers, and universities discussed and determined the need for a research and development program focused on developing a new HPM. Researchers from the Department of Biological Sciences at the University of Michigan Transportation Research Institute and the Biomechanical Design Laboratory at Michigan State University's College of Engineering collaborated to draft a plan, aiming to launch a completely new set of vehicle and seat design tools, including a revised HPM device, through four years of relentless effort. Eleven automotive companies actively participated in this project through annual donations.
This research program was named ASPECT (Automotive Seat and Package Evaluation and CoPMarison Tools), an acronym for Automotive Seat and Package Evaluation and Comparison Tools. Compared to the first generation, the HPM-II device had several significant advantages:
Firstly, it was easier to install, more flexible in disassembly, and convenient to transport; secondly, its design better conformed to the human back shape; and thirdly, it allowed for independent placement of the footrest and seat cushion. The device's biggest highlight lies in improving the undesirable correlation between the seat and layout in the current SAE J826 anthropomorphic model. Research revealed no strong correlation between the H-point, AHP (heel-to-toe point), and pedal point. However, when measuring using the HPM Generation 1 model, even slight changes in the H-point position altered the pedal reference point, thus affecting the driver's layout. The HPM-II, by allowing for separate foot placement and other parts of the device, effectively avoids this problem.
Detailed Comparison with HPM Generation 1: Device Size The anthropomorphic definition of the HPM Generation 1 device was based on a combination of 50th, 90th, and 95th percentile male values derived from various civilian anthropomorphic surveys in the early 1960s. However, further research revealed that the HPM device does not actually need to represent a specific percentile of any particular population. Percentiles correspond to population demographics, which are dynamic; choosing specific percentiles only applies to specific populations, and these values quickly lose accuracy as demographic data changes. Several considerations indicate that extreme anthropomorphic model sizes are not ideal. Oversized mannequins may not fit vehicles or seats designed for smaller populations, while undersized mannequins may lack sufficient seat indentation to represent larger populations. Therefore, measuring the dimensions of a medium-sized male occupant is currently the most ideal choice, and these dimensions have been used in the development of crash models, ensuring continuity between HPM-II and future crash dummies.
A significant improvement of HPM-II compared to the single-piece backplate of the first-generation HPM device is its ability to simulate human back support. Computer simulations, based on previous research by Haas and Reed et al., have shown that one or two relatively simple kinematic connections at the lumbar vertebrae are sufficient to represent human spinal kinematics. Ideally, two lumbar vertebrae are used, positioned anatomically at the T12/L1 and L5/S1 joints.
The contour dimensions of the backplate and seat plate also use the dimensions of a medium-sized American male. Researchers analyzed and merged hip and thigh contour data from seven subjects who were approximately of medium size to obtain preliminary contours, and then used computers to develop a full-size model of the contours.
The HPM-II reference mannequin's height was set at 1753 mm, and its mass at 77.3 kg. However, the HPM-II mannequin does not represent a complete human body, so more comprehensive measurements were required. Researchers measured thirty men (height ranging from 1582 to 1923 mm, with an average height of 1778 mm; weight ranging from 57 to 141 kg, with an average weight of 85 kg) sitting in a typical vehicle seat with a seat height (H30) of 270 mm. After selecting a comfortable seat back angle, the subjects placed their heels on the force-measuring platform and adjusted their foot position to ensure no significant horizontal force was applied to the platform. The vertical support force of each subject was recorded in three trials. Linear regression analysis was performed on body weight to estimate the average heel support force of a person matched to the reference anthropometry. Subtracting 5.8 kg from the reference weight yielded a target mannequin weight of 71.5 kg.
The mass distribution of a mannequin is not directly equivalent to the actual mass distribution of a human body because it does not include the head, arms, and legs, which constitute a significant percentage of body weight. Similar to the HPM-1 mannequin, the HPM-II does not attempt to reposition the head and arm mass within the chest cavity; instead, its mass distribution is determined based on performance considerations. The mannequin components without detachable weights weigh 16.3 kg, representing 23% of the total mannequin mass. Related charts illustrate the distribution of mass weights.
The HPM-II model is primarily designed as a seat measurement tool, applicable independently of the vehicle's overall layout. For typical seat measurements, legs or shoes are not required. However, since legs and shoes are integral parts of the HPM-1 mannequin, leg and shoe components are provided to the HPM-II model to maintain continuity. The length of the legs and thighs is adjustable and they are constructed from lightweight components. After installing the HPM-II onto the seat, the leg and thigh sections are then attached to the HPM-II device. This process does not alter any anthropomorphic model measurement data, including the H-point position. The shoe section is the same length as the SAE H-point anthropomorphic model shoe but features a symmetrical planar profile and a flat-soled design. During measurement, only one shoe and leg section are used.
In summary, the HPM device has played a crucial role in automotive design since its inception. The HPM-II (second generation) device, while inheriting the advantages of the first generation, has undergone comprehensive and in-depth improvements addressing many shortcomings. From device size, joint motion linkages, contours, mass and mass distribution to auxiliary parts, HPM-II exhibits more scientific, rational, and practical characteristics. It not only solves the problems of the first-generation device but also better adapts to the ever-evolving needs of modern automotive design. It provides the automotive industry with a more accurate and reliable measurement tool for seat design, vehicle space planning, and other areas, powerfully driving automotive design towards a more human-centered, safer, and more efficient direction.
