1. College of Transportation, Jilin University, Changchun 130022, China 2. Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun 130022, China 3. School of Engineering, University of Manchester, Manchester M13 9PL, UK
Blue sheep was selected as the object to test the variation of its limbs vertical ground reaction force by variable slope channel with built-in pressure plate, in order to supply bionic prototype for quadruped robots with excellent climbing performance. Results showed that the peak vertical force and the vertical impulse on the left and right sides of the front and hind limbs were completely symmetrical when the sheep walking on the flat ground. The symmetry index of the front limbs was 99.16% and 99.62% respectively, and the symmetry index of the rear limbs was 98.65% and 99.42% respectively. Along with the increasing of slope angle, the blue sheep adjusted the vertical force distribution to prevent lameness, which caused fluctuations in the symmetry index of the left and right hoof. When walking on flat ground, the forelimbs of blue sheep showed higher vertical force than the rear limbs. With the increasing of slope, the vertical force borne by the rear limbs gradually increased. The difference index on the left and right sides of the blue sheep limb has a similar change pattern on different slopes. The mean difference indexes on the left and right limbs of the blue sheep from 0 to 35 degrees were 1.298, 1.305 7, 1.174 4, 1.223 75, 1.017 5, 0.890 5, 0.777 8 and 0.753 5 respectively.
Xiang-yu LIU,Hai-lin KUI,Zhi-hui QIAN,Lei REN. Vertical ground reaction force characteristics of blue sheep based on different slopes walking. Journal of ZheJiang University (Engineering Science), 2021, 55(9): 1668-1675.
Fig.2Scene photograph of vertical force acquisition experiment
Fig.3Multiple hoof prints generated by pressure plate
Fig.4Vertical force - time curve of blue sheep's hooves
α/(°)
Fpyq/(N·kg?1)
Fpyh/(N·kg?1)
Fpzq/(N·kg?1)
Fpzh/(N·kg?1)
0
4.75±0.59
3.65±0.14
4.79±0.48
3.70±0.31
5
3.15±0.21
2.39±0.19
2.69±0.14
2.08±0.34
10
2.66±0.33
2.39±0.29
3.04±0.73
2.46±0.63
15
3.72±0.15
3.26±0.26
3.24±0.49
2.48±0.31
20
2.25±0.15
2.62±0.27
3.27±0.29
2.78±0.20
25
2.34±0.25
3.01±0.30
2.34±0.37
2.33±0.26
30
1.81±0.47
2.80±0.50
2.40±0.32
2.64±0.65
35
2.23±0.21
2.83±0.34
2.61±0.13
3.63±0.37
Tab.1Peak vertical force of blue sheep's hooves
α/(°)
Iyq/(N·s·kg?1)
Iyh/(N·s·kg?1)
Izq/(N·s·kg?1)
Izh/(N·s·kg?1)
0°
2.65±0.47
1.71±0.22
2.66±0.33
1.72±0.21
5°
1.53±0.39
1.03±0.14
1.37±0.38
0.86±0.23
10°
1.04±0.30
0.92±0.22
1.13±0.13
0.99±0.12
15°
1.11±0.10
0.96±0.19
1.13±0.15
0.88±0.19
20°
0.81±0.11
1.08±0.18
1.11±0.14
0.97±0.14
25°
0.77±0.17
1.23±0.23
0.79±0.15I
0.87±0.12
30°
0.57±0.19
1.15±0.18
0.73±0.09
1.00±0.14
35°
0.32±0.06
0.73±0.17
0.30±0.05
0.50±0.09
Tab.2Vertical impulse of blue sheep's hooves
Fig.5Statistics graph of normalized peak vertical force for sheep's hooves
Fig.6Statistics graph of normalized vertical impulse for sheep's hooves
α/(°)
SFQ/%
SFH/%
α/(°)
SFQ/%
SFH/%
0
99.16
98.65
20
68.81
94.24
5
85.39
87.03
25
100
77.41
10
67.76
97.15
30
75.42
94.29
15
87.10
76.07
35
85.44
77.95
Tab.3Symmetric index of peak vertical force
α/(°)
SIQ/%
SIH/%
α/(°)
SIQ/%
SIH/%
0
99.62
99.42
20
72.97
89.81
5
89.54
83.50
25
97.47
70.73
10
92.04
92.93
30
78.08
86.96
15
98.23
91.67
35
93.75
68.49
Tab.4Symmetric index of vertical impulse
Fig.7Comparison of peak vertical force between left hoof and right hoof
Fig.8Comparison of vertical impulse between left hoof and right hoof
α/(°)
DFY
DFZ
α/(°)
DFY
DFZ
0
1.301 4
1.294 6
20
0.858 8
1.176 2
5
1.318 0
1.293 3
25
0.777 4
1.004 2
10
1.113 0
1.235 8
30
0.646 4
0.909 1
15
1.141 1
1.306 4
35
0.788
0.719
Tab.5Difference index of peak vertical force
α/(°)
DIY
DIZ
α/(°)
DIY
DIZ
0
1.549 7
1.546 5
20
0.745 2
1.144 3
5
1.485 4
1.743 0
25
0.626 0
0.908 0
10
1.130 4
1.141 4
30
0.495 7
0.73
15
1.156 3
1.284 1
35
0.438 4
0.6
Tab.6Difference index of vertical impulse
Fig.9Comparison of peak vertical force between front hoof and rear hoof with different slopes
Fig.10Comparison of vertical impulse between front hoof and rear hoof with different slopes
Fig.11Variation rule of difference index with slope
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