Product Evaluation

Research tools can be used to describe the physical requirements necessary to use a product and the associated effort required by a person when using the product. To assess the physical requirements, a variety of data types can be collected: postural deviation, level of vibration, torque requirements, activation forces, and pressure distributions. To assess the effort required by a person when using a product, 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 of using a product 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.

Biomechanical Assessment of Arborist Pruning Saws

Surprisingly, little research has been conducted on the ergonomics of handsaws.  Therefore, the objectives of this research were to evaluate the effects of saw design and work height on the biomechanical responses of the user.  More specifically, this study evaluated the effects of six different arborist pruning saws on muscle activation levels, wrist angle, productivity, and subjective assessment of the user.

Eighteen participants performed a simple sawing task at three different heights using six different arborist handsaws.  As they performed this task, the electromyographic activity of several muscle groups of the forearm (flexor and extensor digitorum), arm (biceps brachii long and short heads) and shoulder girdle (posterior deltoid, infraspinatus and latissimus dorsi) were sampled.  Also gathered were the wrist postures in the radial/ulnar plane at the beginning and ending of the sawing stroke, the time to complete the sawing task and a subjective ranking of the six different saws.

The results showed the benefits of a bent handle design (37% reduction in ulnar deviation).  Also, as work height increased the biceps muscles increased their activation levels (~19%) while the posterior deltoid activity decreased (~17%) with the higher location.  The subjective responses of the participants generally supported the objective data, but also emphasized the benefit of having the hand close to the saw blade for control and force-producing capability.

Vibration Attenuation Assessment of Carpentry Hammers 

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.

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.

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. recommended over both competitors due to lower levels of peak pressure, greater average contact area, and lower discomfort ratings.

Pressure Distribution Assessment of Seat Pans: Competitor Comparison

The pressure distribution characteristics of seven office chair 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.

Thirty human subjects participated in this laboratory study and performed four different office tasks while seated: sitting, typing, writing, and reading. The seat pans were evaluated using a Tekscan pressure mat to assess peak pressure (over the ischial1 tuberosities and coccyx2) and contact area representing pressure distribution. The data was 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).

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.
  • Certain anthropometric dimensions had significant effects on measures of peak pressure, contact area, and discomfort. Task variability, however, did not significantly affect these measures.

Data from the competitor comparison support the following conclusion:

  • The client’s seat pans were recommended over both competitors due to lower levels of peak pressure, greater average contact area, and lower discomfort ratings.
  1. The lowest of the three major bones that constitute each half of the pelvis.
  2. A small triangular bone at the base of the spinal column in humans consisting of several fused rudimentary vertebrae.