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Page 114 Yang et al. Intell Robot 2024;4(1):107-24 I http://dx.doi.org/10.20517/ir.2024.07

Human-Exoskeleton-Walker System

)
J(·
Supporting

+ cos( ) Force E,S
transformation
Walking Energy
Stepper Efficiency
Motor

∆ ( ) ξ(k) High-pass

−
Filter
− sin( ) cos( )
The modulation step The demodulation step

Figure 4. The block diagram of ESC. ESC: Extremum Seeking Control.

where Δ ( ) indicates the amount that the stepper motor should be moved to minimize the TCoT, which
realizes the supporting force adaptive tuning. From Equation (10), it can be seen that Δ ( ) consists of a DC
component, which is proportional to (·), and contains other higher frequency terms.
0
Following standard manipulations [26] , the equations of ESC can be updated as follows:

( ) = −ℎ ( − 1) + ( ( )) − ( ( − 1)), (11)
Δ ( ) = − [ ( ) cos( )], (12)

where is the adaptation gain, and ℎ ∈ (0, 1) is the HPF cut-off frequency.

Overall, with the proposed real-time optimization approach, the optimal supporting force can be found in
real time by walking several steps overground with the HEW system. As a result, the energy cost of the HEW
system will be reduced to the minimum value without slipping overground.

2.2 The coordinated motion planning of the robotic walker
The coordinated motion planning is to make the human-exoskeleton system and the robotic walker move
coordinately and avoid the “pull” or “push” between them. As shown in Figure 2, the coordinated motion
planning is based on the hip and knee joint angles of the exoskeleton robot. As shown in Figures 5 and 6, there
are four wheels of the robotic walker, and all wheels rotate around the axis.

As we mentioned in Figure 1, the exoskeleton robot is connected to the robotic walker with a solid cantilever;
therefore, the horizontal movement of the robotic walker is the same as the COM of the human-exoskeleton
system. Note that if the wheels are passive without any power, there is no active movement of the robotic
walker, and the human-exoskeleton system has to pull or push the robotic walker while walking overground.
If the wheels are actuated with the DC motors, they can drive the robotic walker to follow the movement
of the human-exoskeleton system and avoid the movement conflict between the human-exoskeleton system