Development of a tractor operator-operation environment coupled biomechanical model and analysis of lower limb muscle fatigue

For the quantitative analysis and evaluation of tractor pedal operation comfort, this study developed a tractor operator-operation environment coupled biomechanical model in AnyBody Modeling System. First, operator model and operation environment model were generated according to Chinese adult male anthropometric dimensions and Dongfanghong LX804 tractor design parameters. To couple these two models, the connections between operator model's palms, feet, pelvis and operation environment model's steering wheel, joystick, pedals, seat were created. The release scheme of limb joint angle constraints was designed, which allowed limbs to fulfill the kinematic requirement of operating devices. Then, to drive the model, a driver device with a rotation angle range of 0°-42°and a spring with a stiffness of 37.85Nm/rad were added to pedal hinge based on the driving data of pedal force and pedal travel collected by sensors. Subsequently, to validate the model, the surface electromyography signals of lower limb muscles were acquired using the test system of Cometa MiniWave. The average relative error between the lower limb muscle activity calculated from electromyography signals and that computed from the model was 9.2%. Finally, the model was employed to simulate the dynamic process of pedal operation and analyze lower limb fatigue. The results demonstrated that the fatigue exhibited a tendency of first decreasing and then increasing as pedal rotation angle increased, and reached a lower level within the pedal rotation angle range of 8°-17°.     

Motion Control of a 6WD/6WS wheeled platform with in-wheel motors to improve its maneuverability

Multi-axle driving mobile platform that are favored in special environments require high driving performance, steering performance, and stability. Among these, six wheel drive and six wheel steering vehicles hereinafter called 6WD/6WS, gain structural safety by distributing the load and reducing the pitching motion during rapid acceleration and braking. 6WD/6WS mobile platforms are favorable for military use, particularly in off-road operations because of their high maneuverability and mobility on extreme terrains and obstacles. 6WD vehicles that use in-wheel motors can generate independent wheel torque without a need for additional hardware. Conventional vehicles, however, cannot generate an opposite driving force on wheels on both sides. In an independent steering and driving system six-wheel vehicles show better performance than conventional vehicles. This paper discusses the improvement of the cornering performance and maneuverability of 6WD/6WS mobile platform using independent wheel torque and independent steering on each wheel. 6WD/6WS vehicles fundamentally have satisfactory maneuverability under low speed, and sufficient stability at high speed. Consequently, there should be a control strategy for improving their cornering performance using the optimum tire forces that satisfy the driver’s command and minimize energy consumption. From the driver’s commands (i.e., the steering angle and accelerator/brake pedal stroke), the desired yaw moment with virtual steering, desired lateral force, and desired longitudinal force are obtained. These three values are distributed to each wheel as torque and steering angle, based on the optimum tire force distribution method. The optimum tire force distribution method finds the longitudinal/lateral tire forces of each wheel that minimize cost function, which is the sum of the normalized tire forces. This paper describes a 6WS/6WD vehicle with improved cornering performance and the results are validated through TruckSim simulations.

     

The ergonomic value of a bidirectional haptic interface when driving a highly automated vehicle

Advances in technology have fueled the development of driver assistance systems. Even today, these systems can take over parts of the driving task. However, the interface becomes more and more complex with an increasing number of functions. One way to reduce such complexity is to venture the haptic channel. While haptic feedback in lateral direction is comparatively easy to realize via the steering wheel, the longitudinal direction forms a challenge. With conventional control elements, that is, pedals, haptic interaction can only be partially realized (this is due to the division of accelerator and brake pedals). Haptic signals, like forces added to the accelerator pedal, can only transmit information regarding the amount of acceleration, not the desired deceleration. In this context, two-dimensional control elements show great potential regarding future highly automated vehicle driving. Therefore, an experiment conducted at the Institute of Ergonomics of the Technische Universität München investigated the influence of haptic feedback of assistance systems on driving performance when using an active side stick as control element. Additionally, the impact of vehicle vibrations and accelerations were explored. Besides objective performance data, subjective assessment was also reported. The results show that adding assistance significantly improves driving performance. Moreover, subjective ratings indicate a reduction in workload. Accelerations and vibrations, however, had no verifiable effect on the driving performance. This fact was confirmed by the subjects’ subjective assessment. This paper shows that two-dimensional control elements can be a reasonable alternative to steering wheel and pedals when driving a highly automated vehicle.     

一种用于AFS的半实物仿真平台

为了给自适应前照灯系统（Adaptive Front-Lighting System,AFS）提供一个控制算法验证平台,开发了一套基于汽车驾驶模拟器的AFS半实物硬件仿真平台。在该仿真平台中,PC机采集驾驶模拟器的档位、油门、离合、刹车、方向盘等驾驶信息,由车辆动力学模型模拟实际车辆行为,采用AFS控制模型计算车灯转角控制量,并发送至电机驱动模块进而控制车灯转动,同时将车灯转角信息反馈至PC机。实验表明,该系统能实时记录和显示AFS工作过程中的多种参数,便于进行实验观察和数据分析,从而为AFS系统的控制算法提供一个检验和修正的平台。     

Human Factors Considerations for a Combined Brake-Accelerator Pedal

Abstract

The results of a series of nine experiments over a three-year period arc reported, Experiments One through Six. previously published, indicated that a pedal which actuated an accelerator upon depression of the toe and actuated the brake upon depression of the heel saved 0·2 sec (one car length at 60 mph) over the conventional separate controls.

Experiment Seven investigated the effect on reaction time of: the angle the pedal made with the floor; the force required to actuate the brake control; the force required to actuate the accelerator control; and the seat reference distance. The minimum time was 0·241 see. Little penalty resulted when the pedal angle was between 30 and 40°, brake actuation force was between 13 and 21 lb, accelerator actuation force was between 4 and 8 lb, and seat reference distance was between 4n and 55% of the person's height.

Experiment Eight investigated the effect on reaction time of; the angle the pedal made with the floor; seat height from the floor; the angle of twist of the pedal; and seat reference distance. The minimum time was 0·284 see. Little penalty resulted when the pedal angle was between 30 and 45^°, seat height was between 8 and 10 in. from the floor, the angle of twist was between 90 and 104^°, and the seat reference distance was between 40 and 50% of the person's height. Experiment Nine investigated, for older subjects, the effect on reaction time of; pedal angle; seat reference distance: and the angle of twist of the pedal. The reaction time of the optimum combination was 0270 sec. The savings of 0-18 sec (versus conventional) for student subjects increases to 0·23 sec for subjects aged 60. Instruction time averaged 30 sec.     

Directional control–response compatibility of joystick steered shuttle cars

Shuttle cars are an unusual class of vehicle operated in underground coal mines, sometimes in close proximity to pedestrians and steering errors may have very serious consequences. A directional control–response incompatibility has previously been described in shuttle cars which are controlled using a steering wheel oriented perpendicular to the direction of travel. Some other shuttle car operators are seated perpendicular to the direction of travel and steer the car via a seat mounted joystick. A virtual simulation was utilised to determine whether the steering arrangement in these vehicles maintains directional control–response compatibility. Twenty-four participants were randomly assigned to either a condition corresponding to this design (consistent direction), or a condition in which the directional steering response was reversed while driving in-bye (visual field compatible). Significantly less accurate steering performance was exhibited by the consistent direction group during the in-bye trials only. Shuttle cars which provide the joystick steering mechanism described here require operators to accommodate alternating compatible and incompatible directional control–response relationships with each change of car direction.

Practitioner Summary: A virtual simulation of an underground coal shuttle car demonstrates that the design incorporates a directional control–response incompatibility when driving the vehicle in one direction. This design increases the probability of operator error, with potential adverse safety and productivity consequences.     

Anthropometry of the Hong Kong male and the design of bus driver cabs

This study investigated the proposition that the crabs of buses imported into Hong Kong were not suited to the anthropometric characteristics of the local Chinese bus drivers. A ‘recommended’ cab design was derived from static anthropometric data; relationships between pedals, steering wheel and seat, and the range of seat adjustments were specified. Overall static anthropometric data were available but additional data had to be estimated by constructing manikins based on the available Hong Kong static data with joint positions derived from data for the US male population. Seven bus cab designs in current use were compared with the ‘ recommended’ design. None of them satisfied all the ‘recommended’ design specifications, the most serious deviations being the excessive height of the seat above the floor and pedals, and insufficient lateral separation between the pedals.     

Vehicle and driver attributes affecting distance from the steering wheel in motor vehicles

The current study was designed to confirm that female drivers sit closer to the steering wheel than do male drivers and to investigate whether this expected difference in sitting position is attributable to differences in the physical dimensions of men and women. Driver body dimensions and multiple measures of sitting distance from the steering wheel were collected from a sample of 150 men and 150 women. The results confirmed that on average, women sit closer to the steering wheel than men do and that this difference is accounted for by variations in body dimensions, especially height. This result suggests that driver height may provide a good surrogate for sitting distance from the steering wheel when investigating the role of driver position in real-world crash outcomes. The potential applications of this research include change to vehicle design that allows independent adjustment of the relative distance among the driver's seat, the steering wheel, and the floor pedals.     

Biomechanical model to predict loads on lumbar vertebra of a tractor operator

A biomechanical model is important for prediction of loads likely to arise in specific body parts under various conditions. The biomechanical model was developed to predict compressive and shear loads at L4/L5 (lumbar vertebra) of a tractor operator seating on seats with selected seat pan and backrest cushion materials. A computer program was written to solve the model for various inputs viz. stature and weight of the tractor operators, choice of operating conditions, and reaction forces from seat pan and backrest cushions. It was observed that maximum compressive and shear forces ranged 943–1367 N and 422–991 N, respectively at L4/L5 of tractor operators steering the tractor with leg and hand control actions and occasionally viewing the implement at back. The compressive forces were maximum (1202–1367 N) with coir based composite seat backrest cushion materials (thickness of 80 mm, density of 47.19 kg/m³) and were minimum (943–1108 N) with high density polyurethane foam (thickness of 44 mm, density of 19.09 kg/m³) for the seats.Relevance to industryThe biomechanical model of a tractor operator is important for theoretical understanding the problem of sitting and is also valuable in prediction of compressive and shear loads at L4/L5 of operator under various operating conditions. It will help in design of tractor seat for operator's comfort.     

On supervisory control of mobile platform on four swivel wheels

A mobile robotic platform with four driving swivel wheels, whose centers are situated at the vertices of a rectangle, is considered. Each of the wheels can rotate about its horizontal axis in a common way, and the plane of the wheel situated in a fork can turn with respect to the platform about the perpendicular axis. These turns and rotations of four wheels are performed using eight drives. The platform can move, perform translational and rotational motion without wheel slip if and only if the fork orientation and wheel angular velocities satisfy certain relations. This study presents the relations to which program values of fork turning angles and wheel angular velocities calculated for automatic control of the platform motion or operator control should satisfy. The scheme of supervisory (with an operator) control of the platform motion and its virtual analogue are described.     

The real issues in fuzzy logic applications

The transition from Boolean Logic to Fuzzy Logic is shown by modifying a ladder diagram consisting of discrete variables with values of 0 and 1 to include intermediate values. Properties of membership functions are discussed as they influence the control output. The concept of compromise and output blending is shown. Important observations regarding the presence of rules are presented. The notions of “gain” and “time” are introduced, and a PID controller using Fuzzy Mechanisms is shown. In one example, the level and temperature of a tank are controlled; in another example the engine power and the turning of the wheels of an automobile are controlled as a function of the gas pedal and the steering wheel excitation.     

线控转向系统的转向盘力反馈控制策略研究

线控转向系统取消了转向盘和转向轮之间的机械连接,因而可以根据车况主动提供路感,提高车辆的操纵稳定性.首先研究了转向刚度力矩、由侧向加速度确定的转向盘回正力矩、由轮胎回正力矩确定的转向盘回正力矩、转向阻尼力矩等进行转向盘力反馈的四种力矩.然后,研究了四种组合的转向盘力反馈控制策略及其进行双纽线试验、蛇行试验的性能.结果表明,调整各种力反馈方案的相应参数可以获得低速时的转向轻便性和高速时的良好路感.     

一种基于轻量级矢量地图的无人车导航方法

现有的差分全球定位系统通常需要高精度地图数据的支持,然而高精地图制作成本高昂,且 庞大的地图数据对车载电脑性能及网络通讯带宽有较高要求。该文提出一种基于低数据量矢量地图的智能车导航方法,通过引入道路标签机制,从高层次抽象组织道路点,以便快速建立矢量导航地图,并大幅度降低道路点的重复存储。基于该地图的导航方法自动规划最优全局路径,通过基于预瞄点与历史点的几何学算法进行路径跟踪与避障,从而将上位机计算出的方向盘转角、油门和制动踏板深度信息传递到车辆底层控制器,以控制车辆按规划路径行驶。该方法的有效性和准确性在自主开发的无人驾驶平台上得到了验证。     

Simulated effect of driver and vehicle interaction on vehicle interior layout

Digital human modeling is an essential tool to reduce cost and to save time in a design process where humans take the part of users of the design. Considering this phenomenon for a vehicle interior, the importance of the seat track location and adjustment ranges become important. This paper presents the effect of driver and vehicle interaction on vehicle interior layout based on simulation approach. This simulation method includes two optimizations. The first optimization problem is the physics-based seated posture prediction. In order to represent physical drivers, 4,500 virtual drivers are generated based on an anthropometric database-ANSUR. Interaction forces between the digital human and pedal, seat, ground, and steering wheel are incorporated in the physics-based posture prediction. Three different pedal reaction moments (0, 20, and 40 N m) are implemented into the formulation to examine the effect of pedal reaction moment on driver seat location and adjustment ranges. To study the effect of shear forces, the physics-based posture prediction is compared to kinematics-based posture prediction. After posture predictions are completed, individuals' preferred seat locations are used in a second optimization problem to predict the seat track location and adjustment ranges. For a specific vehicle with 20 N m pedal reaction moment, adjustment ranges are predicted as 223 mm and 82 mm in horizontal and vertical directions, respectively. Also, it was shown that shear force due to the interaction between the driver and the seat pan and the pedal reaction moment are both influential to the seat track location and adjustment ranges.Relevance to industryThe simulation model presented in this paper is useful in vehicle and seat design and can be easily used for virtual design assessment in vehicle design.     

Optimization of vehicle accelerator-brake pedal foot travel time

This study was directed towards reducing the lag time between stimulus and incidence of braking. The effect of the relative vertical heights of the brake and accelerator pedals on foot travel time was the subject of the first part of the investigation. In the second part, two new pedal designs in which the accelerator was mounted directly on the brake pedal were evaluated. A significant reduction in foot travel time of approximately 12·5% was realised by locating the accelerator pedal 25–50 mm (1–2 in) higher than the brake pedal. Mounting of the accelerator pedal adjacent to or directly on the brake pedal allowed reductions in braking lag time of 46% to 74%.     

Evaluation of five steering input devices in terms of muscle activity,upper body kinematics and steering performance during heavy machine simulator driving

Work related upper body musculoskeletal symptoms and disorders constitute a major problem for operators of heavy machinery. Steering input devices mediate risk factors of upper body musculoskeletal disorders. Little research has been conducted to compare the multiple commercially available steering input devices in a multi-faceted approach. The present study evaluated five commonly used steering input devices (conventional steering wheel, fast steering wheel, miniature steering wheel, first-order joystick and second-order joystick) in terms of muscle activity, upper body kinematics and steering performance during heavy machine simulator driving. Fifteen healthy males novice to operation of heavy machinery completed five laps on a simulated track with each steering input device. Results showed a generally lower muscle activity when using the joysticks. The conventional and fast steering wheel increased mean wrist and shoulder flexion/extension angles and participants spent more time in wrist flexion/extension angles corresponding to moderate and poor comfort levels. An increased elbow protonation angle was found for the three steering wheels compared to the joysticks. The conventional steering wheel showed slowest track completion time and was subjectively ranked worst. The first-order joystick was ranked highest but also showed the highest amount of steering reversal rates, posing a risk of increased repetitiveness. Overall, the second-order joystick is considered superior ergonomically compared to the other steering input devices evaluated. However, all evaluated steering input devices exceeded muscle activity and/or joint angle recommendations.Relevance to the industry: Compared to steering wheels, joystick steering showed reduced muscular activity and less awkward joint postures, suggesting a reduced risk of developing musculoskeletal disorders in the long term. However, the results warrant efforts to further develop joystick steering resulting in a reduction of exposure level beyond the existing solutions.     

The use of pressure mapping to assess the comfort of agricultural machinery seats

Interface pressure measurement gives an objective value to human comfort. Prolonged sitting is known to contribute to musculoskeletal disorders. Driving a tractor involves several actions such as steering, operating levers, buttons, brake and clutch pedals, and looking behind to observe and maneuver the machine. These operations affect sitting posture and create a pattern of loading on the structures of the operator's body.The aim of this study was to study barometric mapping at the operator's buttocks-seat interface for comfort evaluation of the agricultural and forestry machine seats. Three different tractor seats (A “low cost”; B “medium cost”; C “high cost”) were tested during ploughing, harrowing and haying operations, by 8 different operators. Two standardized conditions were used, one on a track with ridges and one on an asphalted surface, with driving tests conducted on both. From each test, the following values were obtained: maximum pressure peak (P_max); average pressure value (P_avg); and the average percentage of cells activated by pressures ranging between 50 and 130 g/cm² (NC_50-130), 131–400 g/cm² (NC_131-400) and higher than 400 g/cm² (NC_401-1000). Mean values of P_avg, P_max, NC_131-400, recorded after the two lab tests (on the road and the ridged track) carried out with seat-A tractors were greater (p < 0.05) than those obtained in tests with more comfortable seats (seats B and C). P_avg and P_max mean values recorded after three field tests carried out with A-seat tractors were greater than those obtained in tests with more comfortable seats (B and C). Similarly, the cell activation in the pressure interval 131–400 g/cm² (NC_131-400) in A-seat tests was significantly greater than that of both B and C seats. Based on our findings, it is possible to conclude that the analyzed pressure indexes in this study are useful instruments to describe the characteristics of seat mapping and compare agricultural machine seats as a function of operator's buttocks-seat interface, thus highlighting the comfort rate obtainable in dynamic situations by the operator.SummaryThe sitting posture is one of the main factors that contribute to musculoskeletal disorders. The methodology is based on barometric mapping for comfort evaluation. Tractors seats were tested in three agriculture operations and on two standardized tracks. The study showed indicators to evaluate barometric maps in dynamics conditions.     

Autonomous car driving by a humanoid robot

Enabling a humanoid robot to drive a car requires the development of a set of basic primitive actions. These include walking to the vehicle, manually controlling its commands (e.g., ignition, gas pedal, and steering) and moving with the whole body to ingress/egress the car. We present a sensor‐based reactive framework for realizing the central part of the complete task, consisting of driving the car along unknown roads. The proposed framework provides three driving strategies by which a human supervisor can teleoperate the car or give the robot full or partial control of the car. A visual servoing scheme uses features of the road image to provide the reference angle for the steering wheel to drive the car at the center of the road. Simultaneously, a Kalman filter merges optical flow and accelerometer measurements to estimate the car linear velocity and correspondingly compute the gas pedal command for driving at a desired speed. The steering wheel and gas pedal reference are sent to the robot control to achieve the driving task with the humanoid. We present results from a driving experience with a real car and the humanoid robot HRP‐2Kai. Part of the framework has been used to perform the driving task at the DARPA Robotics Challenge.     

A Review of:“Fundamentals of Psychology”. By FRANK A. GELDARD. ( New York,John Wiley and Sons. ) [Pp.437.] 57s.

Abstract

Industrial Design is a discipline which, despite an early pre-occupation with styling and making technology saleable, is now centrally concerned with user needs. This is reflected in Coventry's unique degree course in the Industrial Design/Transport Department at Lanchester Polytechnic. The course contains a significant commitment to Human Factors and this is evident in the range of design projects which are undertaken either by students or as sponsored research. The emphasis in these projects is on practical designs which meet user requirements.

This paper describes the following typical course projects:

1. The competition winning design for a dinghy which can be used as an emergency life-raft.

2. An adaptation of a standard front-wheel-drive car with a transverse slide seat to allow easy access for a wheel chair user.

3. The design for a bus seat which can be used either as a conventional seat or as a standee ‘lean’ seat.

4. Design of a vehicle for use by spina bifida children.

5. Design for a pedal driven power unit for transport and machine uses in Developing Countries.

6. The design of adult tricycles for the transport of mothers plus children under 5 yr.

It is concluded that greater collaboration between industrial designers and ergonomists would be possible if the latter published their data in a more accessible form, and that designers must place greater emphasis on the product evaluation aspect of their work.