Design and characterisation of a dual-branched chain turning assist device

doi:10.11996/JG.j.2095-302X.2025051094

Abstract

Abstract:

Regular turning is a critical nursing measure for preventing pressure ulcers in long-term bedridden patients. Existing mechanical turning-assist devices exhibit excessive structural rigidity without considering human turning biomechanics, while inflatable types demonstrate misalignment between the human joint rotation center and the mechanism rotation centers, potentially causing injuries during turning procedures. Therefore, researching supine turning-assist devices with human-mechanical movement synergy holds significant importance. Based on the research foundation of human turning kinematics, a dual-branch chain turning-assist device driven by a planar linkage mechanism is designed, and the main stress positions are the shoulder and hip regions. The mathematical model is established and the design parameters are deduced. The linkage transmission angle is analyzed using graphical methods, and at the same time, the kinematic simulation of the device, the workspace analysis and the experiments on extraction of the human turning center of gravity trajectory are performed, so as to carry out a kinematics graphic. This comprehensive approach enabled kinematic characterization of the entire device. The results show that the angle of assisting the human body to turning angles of 30°~45°, maintaining uniform contact stress distribution between human body and dual-branch chains, effectively preventing pressure ulcers.. The transmission angles range from 42.19° to 90.00°, and the mechanism has good force transmission efficiency in this angle range. This study verified the rationality of the device design. The dual- branch chain structure can fit the motion process of the shoulder and hip, provide multi-segment support chain contact, prevent localized pressure concentration, and meet the human-machine coordination principles and ergonomic requirements for rehabilitation aids. These findings establish a foundation for turning rehabilitation research and clinical application of assistive devices.

Key words: roll-over assist, human center of gravity trajectory analysis, dual-branched chain structure, kinematic graphical representations analysis, organizational configuration

CLC Number:

TH789

LIU Zheng, PAN Guoxin, YAO Pengzhen, LIU Tian, SU Peng. Design and characterisation of a dual-branched chain turning assist device[J]. Journal of Graphics, 2025, 46(5): 1094-1104.

Figures/Tables 20

Fig. 1 Integral model of double branched chain type rollover assist device

Fig. 2 Oscillating guide bar mechanism sketch

Fig. 3 Sketch of the initial position of the shear mechanism

Fig. 4 Branched chain kinematics model

Table 1 Data sheet of auxiliary side-rotation support chain D-H

坐标系变换	a_i_-1/mm	θ_j
M₀~M₁	0	0
M₁~M₂	a₁	θ₂
M₂~M₃	a₂	θ₃
M₃~M₄	a₃	θ₄
M₄~M₅	a₄	0

Fig. 5 Transmission angle variation sketch

Fig. 6 Transmission angle angle change chart

Fig. 7 Trajectory diagram of shoulder rollover assisted pivot chain

Fig. 8 Trajectory diagram of the hip lateral rotation assisted pivot chain

Fig. 9 Error analysis diagram for shoulder lateral rotation assisted strut chain

Fig. 10 Hip-assisted branched chain error analysis plot

Fig. 11 Angular velocity simulation graph

Fig. 12 Angular acceleration simulation graph

Table 2 Parameters for the range of motion between individual strands

支链名称	关节变量	变量范围/(°)
肩部	γ₁	0~40
肩部	γ₂	0~40
臀部	γ₃	0~36
	γ₄	0~12
	γ₅	0~36

Fig. 13 Side-turning support chain workspace ((a) Shoulder 3D workspace; (b) Hip 3D workspace)

Fig. 14 Workspace projection map ((a) Workspace on shoulder x-z plane; (b) Workspace on the x-z plane of the hip)

Fig. 15 Double branched chain type rollover assist device test bench

Fig. 16 Experimental diagram of double branched chain assisted rollover

Fig. 17 Human center of gravity trajectory curve

Fig. 18 Error of human center of gravity trajectory change

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