A new method for extending the range of conductive polymer sensors for contact force

Abstract This paper describes a technique for extending the force range of thin conductive polymer force sensors used for measuring contact force. These sensors are conventionally used for measuring force by changing electrical resistance when they are compressed. The new method involves measuring change in electrical resistance when the flexible sensor, which is sensitive to both compression and bending, is sandwiched between two layers of spring steel, and the structure is supported on a thin metal ring. When external force is applied, the stiffened sensor inside the spring steel is deformed within the annular center of the ring, causing the sensor to bend in proportion to the applied force. This method effectively increases the usable force range, while adding little in the way of thickness and weight. Average error for loads between 10 N and 100 N was 2.2 N (SD = 1.7) for a conventional conductive polymer sensor, and 0.9 N (SD = 0.4) using the new approach. Although this method permits measurement of greater loads with an error less than 1 N, it is limited since the modified sensor is insensitive to loads less than 5 N. These modified sensors are nevertheless useful for directly measuring normal force applied against handles and tools and other situations involving forceful manual work activities, such as grasp, push, pull, or press that could not otherwise be measured in actual work situations. Relevance to industry Force measurement instruments are important for providing ergonomics practitioners with a quantitative means for assessing the magnitude of physical stress associated with a particular operation, and for measuring the reduction in force associated with an ergonomic intervention

Use of computer aided drafting for analysis and control of posture in manual work

Computer aided design (CAD) in conjunction with digitised anthropometric manikins can be used for analysis and control of stressful work postures, one of the most frequently cited occupational risk factors of upper extremity cumulative trauma disorders. This paper describes the use of macros for manipulating manikins and workstation components and for designing the workplace. AutoCAD, a popular computer aided design software package, was used to demonstrate the feasibility of these concepts. Specifically, macros are used for drawing work equipment using parametric designs, manipulating manikins and analysing jobs. In comparing the macros to the use of primitive CAD commands, the macros not only decrease the amount of time needed to create workstation components, but they also make the task easier for the user and decrease the risk of errors. Despite the limitation of anthropometric data and manikins, CAD is an effective method for identifying postural stresses and redesigning the workstation to control the identified stresses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28529/1/0000326.pd

A video-based system for acquiring biomechanical data synchronized with arbitrary events and activities

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Maximal dynamic range electrotactile stimulation waveforms

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Inlernattov, a]]ournatua[ The effects of power hand tool dynamics and workstation design on handle kinematics and muscle activity

Abstract Reaction force and workstation design aspects of right angle nutrunner operation were studied in order to better understand their effects on handle kinematics and muscle activity. Tool reaction force factors included spindle target torque (25 Nrn and 50 Nm) and joint hardness (35 ms and 900 ms build-up time). Workstation factors included orientation (horizontal and vertical) and operator distance (10 cm and 35 cm) from the tool. Dependent variables included handle displacement and velocity, work done on the tool-hand system, power involved in doing work, and EMG activity in the forearm and upper arm muscles. Isometric and eccentric strength corresponding to exertions against the tool for velocities of 0 m/s, 0.084 m/s, 0.251 m/s, 0.503 m/s and 0.754 m/s were measured and the relationship between strength and handle kinematics during tool operation was studied. Six inexperienced volunteers (four males and two females) participated. Subjects operated a 58.5 cm long, 3.6 kg right angle nutrunner on a fastener 120 cm off the floor using the fight hand while standing. The handle was most stable (defined as minimum average peak velocity and displacement) when torque was 25 Nm, when vertical workstations were closest (10 cm) to the operator, or when horizontal workstations were farthest (35 cm) from the operator. Greater handle stability was observed for the horizontal workstation than for the vertical workstation. The hard joint (35 ms build-up) resulted in 307% greater peak handle velocity and 195% greater average power acting against the operator compared to the soft joint, however total work against the operator was 134% less for the hard joint. Little correlation was observed between static or dynamic strength and handle kinematics. EMG latency was measured from the onset of torque build-up. The average latency was 38 ms for the hard joint and 171 ms for the soft joint. Relevance to industry Ergonomic aspects of right angle nutrunner parameters are important for designing workstations and selecting power hand tools in assembly operations that maximize performance and quality, while minimizing physical stress. These parameters include process factors (torque and joint hardness) and workstation design factors (orientation and distance from the operator)

Upper limb mechanical changes following short duration repetitive eccentric exertions

Background. Power hand tool use is considered a risk factor for upper extremity musculoskeletal disorders. It is unclear if submaximal eccentric activity inherent to power tool use adversely affects the mechanical properties of muscle. Methods. This study investigated in vivo changes in human upper limb dynamic mechanical properties following exposure to short-term repetitive submaximal eccentric exertions that are similar to operating an industrial power hand tool. Eighteen subjects (12 males and 6 females) were assigned to one of three exercise groups (isometric, eccentric or control) and exercised 10 min for 60 repetitions at 50% of isometric forearm supination maximum voluntary contraction. Supination strength and dynamic mechanical properties (stiffness, effective mass, and damping) of forearm rotation, modeled as a single-degree-of-freedom system during maximal exertion, were ascertained prior to exercise, immediately following exercise and 24 h later. Findings. Strength decreased for the isometric (17%) ( P < 0.05) and eccentric (34%) ( P < 0.01) groups following exercise. Only the eccentric exercise group had a reduction in mechanical stiffness (53%) ( P < 0.01) and effective mass (58%) ( P < 0.05). The other groups had no changes in mechanical properties. Interpretation. The change in mechanical properties following repetitive submaximal eccentric activity could negatively impact the ability of the arm to react to rapid forceful loading during repetitive industrial work activities and may indicate mechanical strain on the upper limb

A silicon-based tactile sensor for finger-mounted applications

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A 16-channel 8-parameter waveform electrotactile stimulation system

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder