Table 1.
The ratio of maximum torque (output) to a given total normal force (input) for different handle surfaces, sizes, and shapes (mm) predicted by the model (a) and observed during the experiment (b). The model prediction was performed using Equation 5, assuming a uniform normal force distribution along the handle circumference (i.e., constant fn = total normal force/(2π) in Figure 2) and the coefficient of friction of 0.85 between the aluminum and the hand skin and of 1.43 between the rubber and the hand skin (Seo et al. 2009) to examine the combined effects of friction, handle shape (circular vs. elliptic), and handle size (medium size with the circumference of 160 mm vs. large size with the circumference of 239 mm) on torque generation.
| Estimated torque to total normal force ratio (mm) | ||||
|---|---|---|---|---|
| Handle surface | Handle size | Circular cylinder handle | Elliptic cylinder handle | |
| (a) Model Prediction | Aluminum μ = 0.85 |
Medium | 21.6 | 19.4 |
| Large | 32.4 | 28.3 | ||
| Rubber μ = 1.43 |
Medium | 36.3 | 32.7 | |
| Large | 54.5 | 47.6 | ||
| (b) Empirical Observation | Aluminum μ = 0.85 |
Medium | 17.6 | 12.9 |
| Large | 26.9 | 23.9 | ||
| Rubber μ = 1.43 |
Medium | 27.9 | 19.1 | |
| Large | 39.2 | 34.5 | ||