The Ergonomics Center Of North Carolina - Ergonomics Research


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PRODUCT EVALUATION

Research tools can be used to describe the physical requirements necessary to use a tool and the associated effort required by a person when using the tool. To assess the physical requirements necessary to use a tool, a variety of data types can be collected: level of vibration, torque requirements, activation forces, and pressure distributions. To assess the effort required by a person when using a tool, four types of data can be collected: muscle activity (timing, intensity, duration), joint positions (velocities and accelerations), force distributions (i.e. force over the palm), and physiological changes (O2 uptake). Quantifying and associating changes in the physical requirements associated with using a product with the effort required of individuals performing the task can document quantifiers of the improvements associated with product changes. The physical requirements can be compared to published safety standards or benchmarked against internal and/or competitors' requirements.

Case Study: Vibration Attenuation Methods Assessment of Carpentry Hammers

Background
Vibration induced white-finger or Raynaud's syndrome has been associated with the vibration delivered to the hand and upper extremity from hand tools. In an effort to minimize exposure to such vibration and improve the perceived comfort associated with tool use, hand tool designers collect vibration attenuation data during tool use to drive design changes and market their products. A client (a medium sized hand tool manufacturer) requested a vibration assessment of their hammers (wooden, steel, and fiberglass) be performed and compared with their competitors.

Approach
Two studies were conducted to report on the performance of commercially available carpentry hammers with respect to vibration. The first study (Study 1) investigated the differences between comparable steel carpentry hammers designed by different manufacturers. Each of the manufacturers utilized a different hammer design in combination with a different handle grip composition to affect the vibration attenuation characteristics of their hammer. The second study (Study 2) investigated the differences between multiple carpentry hammers of different handle and handle grip materials, all produced by the same manufacturer. The goal of Study 2 was to assess the vibration attenuation characteristics of four different hammer materials: wood, steel (2 designs), and fiberglass.

At the client's request, this set of investigations was performed in a specially constructed hammer testing apparatus. A second set of experiments was to be performed in which human subjects would strike/use the hammers.

Findings
In Study 1, the differences in the hammers were not physically significant (as agreed upon by the client), although statistically significant differences were identified for select vibration characteristics. In Study 2, the wooden handled hammers provided the lowest initial vibration and fastest attenuation of the vibration in each of the comparisons.

Case Study: Pressure Distribution Assessment of Seat Pans: Contours and Foam Types

Background
The pressure distribution characteristics of seven seat pans and foam types were evaluated. The seat pans under investigation included five client models (xxx1-5) and two competitor's models. The project involved human subject recruitment and scheduling, data collection, data and statistical analysis, and report development. The pressure distribution characteristics assessed included average peak pressure and average contact area. Discomfort ratings associated with each seat pan were assessed using a subjective survey.

Approach
Thirty human subjects participated in this laboratory study and performed four different office tasks while seated: sitting, typing, writing, and reading at a height adjustable workstation. Subject anthropometric dimensions were also recorded and analyzed. Analyses of these variables indicated that certain anthropometric dimensions had significant effects on measures of peak pressure, contact area, and discomfort. Task variability, however, did not significantly affect these measures.

Findings
The primary goal of the study was to determine the differences associated with seat pan contours, foam types, and competitor products. Key conclusions and recommendations resulting from this study include:

Seat pan contour. The contours of the client's xxx1 and xxx2 models are recommended over the xxx3 model due to greater levels of average contact area and lower discomfort ratings.
Foam type. Foam type did not significantly affect peak pressure, contact area, or discomfort.
Competitor comparison. Four of the five client seat pans were recommended over both competitors due to lower levels of peak pressure, greater average contact area, and lower discomfort ratings.

Data from the competitor comparison support the following conclusion:

The client's seat pans are recommended over both competitors due to lower levels of peak pressure, greater average contact area, and lower discomfort ratings.

Case Study: Pressure Distribution Assessment of Seat Pans: Competitor Comparison

Background
This project involves evaluating several seat pans (client and three competitors) utilizing established pressure mapping criteria and protocols. The seat pans will be evaluated using a Tekscan pressure mat to assess peak pressure (over the ischial¹ tuberosities and coccyx²) and contact area representing pressure distribution. The data will be processed by seat pan specifications (seat type, foam type, seat pan width, and material thickness) and subject anthropometry (height, weight, hip width, sex, and age).

Approach
Fifteen human subjects are expected to participate in this laboratory study. Since there were no task effects found in the previous seat pan assessment study, the participants will use the seat pans while performing a task representative of the types of tasks performed while seated in an office environment.

Subject anthropometric dimensions will be recorded and analyzed. Analyses of these variables assess the effect of certain anthropometric dimensions on measures of peak pressure, contact area, and discomfort.

The lowest of the three major bones that constitute each half of the pelvis.
A small triangular bone at the base of the spinal column in humans consisting of several fused rudimentary vertebrae.