Configuration Synthesis Method of Elbow & Wrist 4-DOF Redundant Rehabilitation Exoskeleton

doi:10.12068/j.issn.1005-3026.2025.20230232

Abstract

Abstract:

To address issues such as incompatibility caused by axis misalignment between rehabilitation robots’ exoskeletons and the human body， a configuration synthesis method for redundant rehabilitation exoskeletons was proposed. Firstly， the number of redundant motion pairs was determined through global static conditions， and geometric analysis was used to reduce the number of combinations of redundant motion pair types. Secondly， based on user comfort， possible redundant motion pair axis combinations were considered and appropriate combination modes were selected. Next， the possible position arrangement of redundant motion pairs was considered to determine the optimal position arrangement based on engineering constraints.Finally， the motion of redundant motion pairs was analyzed to determine the position and posture of the exoskeleton and human body. The results indicated that the optimal configuration can achieve the same position and posture between the exoskeleton and the human body under different axes misalignment conditions， effectively overcoming the problem of kinematic incompatibility.

Key words: human-robot compatibility, mechanism synthesis, human-machine closed loop, exoskeleton robot

CLC Number:

TP 242

Quan SHAN, Jian-cong HUANG, Shun ZHANG, Yan CHEN. Configuration Synthesis Method of Elbow & Wrist 4-DOF Redundant Rehabilitation Exoskeleton[J]. Journal of Northeastern University(Natural Science), 2025, 46(2): 64-75.

Figures/Tables 21

Fig. 1 Schematic of 1-DOF human limbs and exoskeleton

Fig. 2 Anatomical diagram of the elbow and wrist joints

Fig. 3 Schematic diagram of the closed loop of motion

Table 1 Synthesis of redundant motion pair types for elbows and wrists l1=4,l2=4

L₁

2R4P,2R3P1R,2R2P2R

2R1P3R,2R4R

L₂

2R4P,2R3P1R,2R2P2R

2R1P3R,2R4R

Table 2 Synthesis of redundant motion pair types for elbows and wrists l1=5,l2=3

L₁

2R5P,2R4P1R,2R3P2R

2R2P3R,2R1P4R,2R5R

L₂

2R3P,2R2P1R,2R1P2R

2R3R

Fig. 4 Schematic diagram of the motion process

Fig. 5 Variation of ∆H and ∆T when the exoskeleton axis meets the parallelism requirement with the body axis

Table 3 Synthesis of redundant motion pair types for elbows and wrists l1=4,l2=4

种类

合成

L₁

1P1R

2R3P1R

2R2P2R

2R1P3R

L₂

1P1R

2R3P1R

2R2P2R

2R1P3R

Table 4 Synthesis of redundant motion pair types for elbows and wrists l1=5,l2=3

L₁

2R4P1R

2R3P2R

2R2P3R

2R1P4R

L₂

1P1R

2R2P1R

2R1P2R

Fig. 6 Force and moment analysis at the elbow joint whenl1=4,l2=4

Fig. 7 Force and moment analysis at the wrist joint when l1=4,l2=4

Fig. 8 Force and moment analysis at the elbow joint when l1=5,l2=3

Fig. 9 Force and moment analysis of the wrist joint when l1=5,l2=3

Table 5 Force and torque conditions for elbows and wrists l1=4,l2=4

种类合成子链	轴线合成	传递力和力矩的方向
1P3R	$1 P x 1 R z - 2 R x y$	$F y ， F z$
2P2R	$1 P x 1 R z - 1 P y 1 R x$ $1 P x 1 R z - 1 P y 1 R y$ $1 P x 1 R z - 1 P z 1 R x$ $1 P x 1 R z - 1 P z 1 R y$	$F z ， M y$
		$F z ， M x$
		$F y ， M y$
		$F y ， M x$
3P1R	$1 P x 1 R z - 2 P y z$	$M x ， M y$

Table 5 Force and torque conditions for elbows and wrists l1=4,l2=4

种类合成子链	轴线合成	传递力和力矩的方向
1P3R	$1 P x 1 R z - 2 R x y$	$F y ， F z$
2P2R	$1 P x 1 R z - 1 P y 1 R x$ $1 P x 1 R z - 1 P y 1 R y$ $1 P x 1 R z - 1 P z 1 R x$ $1 P x 1 R z - 1 P z 1 R y$	$F z ， M y$
		$F z ， M x$
		$F y ， M y$
		$F y ， M x$
3P1R	$1 P x 1 R z - 2 P y z$	$M x ， M y$

Table 6 Force and torque conditions for elbows

种类合成子链	轴线合成	传递力和力矩的方向
4P1R	$1 P x 1 R z - 3 P x y z$	$M x ， M y$
	$1 P x 1 R z - 3 P y y z$	$M x ， M y$
	$1 P x 1 R z - 3 P y z z$	$M x ， M y$
3P2R	$1 P x 1 R z - 2 P y z 1 R x$	$M y$
3P2R	$1 P x 1 R z - 2 P y z 1 R y$	$M x$
2P3R	$1 P x 1 R z - 1 P y 2 R x y$	$F z$
	$1 P x 1 R z - 1 P z 2 R x y$	$F y$
1P4R	$1 P x 1 R z - 3 R x x y$	$F y ， F z$
	$1 P x 1 R z - 3 R y x y$	$F y ， F z$
	$1 P x 1 R z - 3 R z x y$	$F y ， F z$

Table 6 Force and torque conditions for elbows

种类合成子链	轴线合成	传递力和力矩的方向
4P1R	$1 P x 1 R z - 3 P x y z$	$M x ， M y$
	$1 P x 1 R z - 3 P y y z$	$M x ， M y$
	$1 P x 1 R z - 3 P y z z$	$M x ， M y$
3P2R	$1 P x 1 R z - 2 P y z 1 R x$	$M y$
3P2R	$1 P x 1 R z - 2 P y z 1 R y$	$M x$
2P3R	$1 P x 1 R z - 1 P y 2 R x y$	$F z$
	$1 P x 1 R z - 1 P z 2 R x y$	$F y$
1P4R	$1 P x 1 R z - 3 R x x y$	$F y ， F z$
	$1 P x 1 R z - 3 R y x y$	$F y ， F z$
	$1 P x 1 R z - 3 R z x y$	$F y ， F z$

Table 7 Force and torque conditions for wrists

种类合成子链	轴线合成	传递力和力矩的方向
2P1R	$1 P x 1 R z - 1 P y$	$F z ， M x ， M y$
2P1R	$1 P x 1 R z - 1 P z$	$F y ， M x ， M y$
1P2R	$1 P x 1 R z - 1 R x$	$F y ， F z ， M y$
1P2R	$1 P x 1 R z - 1 R y$	$F y ， F z ， M x$

Table 7 Force and torque conditions for wrists

种类合成子链	轴线合成	传递力和力矩的方向
2P1R	$1 P x 1 R z - 1 P y$	$F z ， M x ， M y$
2P1R	$1 P x 1 R z - 1 P z$	$F y ， M x ， M y$
1P2R	$1 P x 1 R z - 1 R x$	$F y ， F z ， M y$
1P2R	$1 P x 1 R z - 1 R y$	$F y ， F z ， M x$

Fig. 10 Mechanism sketch

Fig. 11 Enlarged human-machine interface

Fig. 12 Motion process of the exoskeleton and the human body when the coordinates of the starting point of the connecting rod b are （40,50,0）

Fig. 13 Motion process of the exoskeleton and the human body when the coordinates of the starting point of the connecting rod b are （0,0,50）

Fig. 14 Motion process of the exoskeleton and the human body when the coordinates of the starting point of the connecting rod b are （40,50,50）

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