Digging deeper...HERShovel™ for Women
(Click the puzzle pieces)
- Effects of various handles, blade (lift) angles, and use of auxillary D-grip
- Penetrometer testing of force necessary to insert blade
- Comparison of final (redesigned) prototype with earlier prototypes
The HERS™ design incorporates findings from research supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2009-33610-19668 of the Small Business Innovation Research Grants Program. This grant enabled Green Heron Tools to conduct interviews and focus groups with women farmers throughout the U.S. and to engage a team of engineers and ergonomists from Penn State University to support the design and testing of several pre- HERS™ prototypes. Thanks to engineering doctoral candidate Jesun Hwang and engineers Andy Freivalds and Aaron Yoder for their pivotal roles in conducting the USDA-funded research, highlights of which include:
Effects of various handles, blade (lift) angles, and use of auxiliary D-grip
Field and laboratory testing measured the effects of handle or grip type, blade (lift) angle, and use of an auxiliary D grip mounted partway down the shovel shaft on two physiological measures – volume of oxygen consumption (VO2) and heart rate (HR). VO2 and HR both relate to the amount of energy expended during shoveling, with a lower energy expenditure being desirable. Field testing was carried out by volunteer women farmers, and laboratory testing, by graduate students. Participants were also asked which handles and angles they preferred.
- An Analysis of Variance (ANOVA) with full factorial design found statistically significant* relationships in laboratory testing between lift angle and VO2, handle type and VO2, use of auxiliary
handle and VO2, and lift angle and HR. Specifically, a 36° angle (the largest tested), a wide D-handle and use of the auxiliary handle all reduced the physiological costs of digging and shoveling.
- Statistical significance is a measure of the likelihood that results are “real” as opposed to having occurred by chance. A relationship is statistically significant only when there is at least a 95% likelihood that the observed results are real.
- User preferences of women farmers who participated in the field tests, as well as participants in a Pennsylvania Women’s Agricultural Network field day who tested the prototypes more informally, also favored the larger angle, auxiliary handle and wide D handle.
Penetrometer testing of force necessary to insert blade
A soil penetrometer was adapted to measure the force necessary to insert various blades into various types of soil and into lab foundry sand. The blade eventually chosen for HERS™ was found to be superior to all other blades tested -- round, flat and serrated flat -- in both mediums in which it was tested (soil in a Penn State high tunnel and laboratory foundry sand). This meant that inserting the HERS™ blade required less force than inserting other blades.
Comparison of final (redesigned) prototype with earlier prototypes
The final prototype featured the HERS™ blade, a wooden shaft approximating the length of the medium-size HERS™, and an extended D grip approximating the width of the later HERS™ D grip.
The redesigned prototype was found to be superior to both the best earlier prototype (the 36° angle, wide D handle and auxiliary handle, with serrated flat blade) and a commercial garden shovel with square-point-flat-steel blade. More specifically, a two-sample t-test was used to determine differences in oxygen consumption, heart rate, perceived exertion, perceived discomfort and perceived fatigue.
- In comparing the combo prototype with the commercial shovel, statistically significant differences were found in all variables, all favoring the final prototype.
- In comparing the combo prototype with the best earlier prototype, statistically significant differences were found in all variables but normalized heart rate; again, all data favored the newest, redesigned prototype.
Figure 18: The effect of shovel type on physiological and subjective variables
*Significant differences between commercial or old best and redesigned (combo) shovel