Fig 1.
A CAD model (left) and a physical prototype (right) of the proposed soft linear actuator, called reverse pneumatic artificial muscle (rPAM), which offers convenient physical and fluidic connectors to operate rigid kinematic linkages.
Fig 2.
The fabrication process of the proposed rPAM.
Table 1.
Parameters of the soft actuator model.
Fig 3.
Geometric parameters of the rPAM before (left) and after deformation (right).
Fig 4.
Static stress-strain response of Dragonskin 10 silicone rubber.
Blue dots are experimental data points from multiple compressive and tensile material loading tests, while the red dashed line is the Ogden model curve fit. The mean error for this Ogden fit is 1.1 ± 15 kPa.
Table 2.
Parameter values of the Ogden model.
Table 3.
Experimental parameters of the rPAM model.
Fig 5.
Experimental (mean and standard deviation), analytical, and numerical results for 4 different external loads of 0, 100, 200 and 300 g under input pressures of 0 to 190 kPa.
Fig 6.
A CAD model (left) and a physical prototype (right) of the 1-DoF revolute joint operated by the proposed rPAMs in antagonism.
Fig 7.
The geometric model of the 1-DoF joint setup.
The black and brown lines represent the rigid joint links, while the red lines represent the rPAMs. The green lines are the calculated moment arms for each soft actuator. It should be noted that the actuator is vertically symmetric.
Fig 8.
Comparison of model predictions and experimental results for a range of input pressures ranging from 41 to 96 kPa for both rPAMs.
Contour plots of the resulting steady-state joint angle in degrees are displayed for simulation (a) and experimental (b) results. Joint angle values are stepped at 3 degrees, annotated on the curves, and indicated as color coding from blue to red. The mean error between the model and the experimental results is 0.27 ± 1.1 degrees.
Fig 9.
Mean and standard deviation of the error between the model and experimental results of the 1-DoF soft actuated joint (shown in their entirety in Fig 8).
Fig 10.
A box plot representation of the dynamic coefficients for joint response to duty cycles of 35% to 65% under 138 kPa (20 psi).
The red line is the median, the blue box is the 25th and 75th percentile, the black lines are the bounds of the non-outlying data, and the red circles are the outliers. The 25th and 75th percentiles of are (0.4123,0.3240) rad/s2, (0.9859,1.7316) rad/s and (1.2577,1.637) rad/PWM. and the median of the
is 0.2006 rad/s2, 1.2319 rad/s and 1.6022 rad/PWM.
Fig 11.
(a) The relation between the duty cycle of the solenoid valve and the resulting pressure, with an input pressure of 137 kPa (20 psi) and a pulse-width-modulation frequency of 30 Hz. (b) Steady state angle response at various duty cycles and the corresponding mapping mapping function from the experiment (Blue dotted line) and the model prediction (Red solid line).
Fig 12.
(a) A comparison of the two control algorithms on a step response. Small variations in the starting point of each trial are a result of frictional effects. (b) A comparison of the two control algorithms tracking 0.2 Hz (top) and 1 Hz (bottom) sinusoidal waves.
Fig 13.
The feedforward assisted sliding mode controller offers precise position control under step reference signals in both directions.
Fig 14.
A series of snapshots taken from a 0.5 Hz sinusoidal wave tracking experiment using the SM+FF controller.
Fig 15.
Amplitude (top) and the corresponding phase shift values (bottom) of tracking sinusoidal waveforms of 10-degree amplitude over a range of frequencies.
The standard deviations for these experiments were small enough (around 0.04 degrees) not to warrant plotting, highlighting the repeatability of our joint behavior.
Fig 16.
(a) A comparison of the two control algorithms following a sine wave with an external torque of 0.1 N-m acting in the positive direction. (b) Experimental comparison of the two control algorithms when a 200 g weight is added as a sudden disturbance after the step function has been reached.