Design of a Fully Actuated 4-DOF Robotic Finger With Joint-Specific Hybrid Remote Actuation
Authors: Hyojae Kang, Hyun-mok Jung, Joonho Lee, Dongil Park, Hyunmin Do, Jongwoo Park, Jeongdo Ahn
Organizations: Advanced Robotics Research Center, Korea Institute of Machinery & Materials (KIMM) · Mechanical Engineering, University of Science & Technology (UST)
This paper presents a fully actuated 4-DOF robotic finger using a joint-specific hybrid remote-actuation architecture. The metacarpophalangeal (MCP) joint is driven by two coordinated rigid-link transmission sets, whereas the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints are independently actuated by closed-loop wire transmissions incorporating circular rolling-contact joints (RCJs). A larger transmission radius is used at the PIP joint than at the DIP joint. The RCJ wire geometry maintains the total wire-loop length during joint rotation, and the DIP wire routing is designed so that PIP motion does not affect its differential actuation for a fixed MCP configuration. The distal wire transmission, MCP linkage, and fingertip kinematics are analytically modeled. In experiments, the transmission behavior was quantitatively evaluated from the ball-screw displacements measured using ArUco-marker tracking. MCP actuation produced measurable displacements of the PIP and DIP transmission units, whereas isolated PIP and DIP actuation with the MCP fixed supported the intended mechanical decoupling between the distal transmissions. The mean peak fingertip forces under isolated MCP, PIP, and DIP actuation were 21.28 N, 9.22 N, and 5.75 N, respectively. The resulting finger postures were also examined using objects of different geometries and sizes.
Figures & tables
Figure 1: Design of the proposed finger: (a) Dimensions, (b) Overall configuration and joint arrangement, (c) Detailed transmission components.
Figure 2: Wire-routing configuration of the finger.
Figure 3: Equivalent RCJ actuation-wire geometry for closed-loop wire-length.
Figure 4: DIP wire routing through the PIP RCJ during PIP rotation.
Figure 5: Coordinate frames of the finger and kinematic diagram of the MCP joint actuation.
i
ai−1 [mm]
αi−1 [deg]
di [mm]
θi
1
0
0
da
0
2
0
−90
0
q1−90
3
0
−90
0
q2−θf3
4
lf3
0
0
q3+θf3
5
lr1
0
0
q3−θf4
6
lf4
0
0
q4+θf4
Table 1: MDH parameters of the proposed finger
Variable
Associated motion
Range [deg]
q1
MCP A/A
−30 to 30
q2
MCP F/E
−78.40 to 0
q3
PIP RCJ rolling motion
−45 to 0
q4
DIP RCJ rolling motion
−45 to 0
Table 2: Operating ranges of motion of the finger
Figure 6: Reachable fingertip workspace of the proposed finger.
Symbol
Description
Value
da
D 1 from RC 2 to the MCP joint
98.62 mm
lu1
L 3 of the MCP transmission link
28.01 mm
lu2
D 1 from the MCP joint to S 4
19.27 mm
p1,0
RC 2 of the ball-screw-side U 5
6.39, 12.10, 85.98 mm
p2,0
RC 2 of the ball-screw-side U 5
-6.39, 12.10, 85.98 mm
α
IA 6 of the MCP-side S 4 offset
51.25 ∘
Table 3: Kinematic Parameters of the Finger
Specification
Proposed finger
Degrees of freedom
4
Degrees of actuation
4
Motion
MCP A/A & F/E, PIP F/E, DIP F/E
Fingertip force
21.28 N (MCP Only)
9.22 N (PIP Only)
5.75 N (DIP Only)
Table 4: Technical specifications of the finger.
Figure 7: ArUco marker setup and measured displacement changes of the PIP and DIP ball-screw units induced by MCP motion.
Figure 8: Representative motions of the fabricated finger: (a) F/E motion, (b) MCP A/A motion, and (c) motion beyond the nominal operating range.
Figure 9: Experimental setup and fingertip force under independent actuation of each joint.
Figure 10: Finger postures during interaction with various objects.