Chapter 4 SRRP Elbow Exoskeleton
4.3 Prototype of SRRP elbow exoskeleton
As shown in Fig. 18(a), the CAD of the elbow exoskeleton for elbow with/without carrying angle and elbow flexion-extension motion and supination-pronation motion is presented. As shown in Fig. 18(b-e), the prototype of elbow exoskeleton is presented.
The support is a parallelogram using four short rotation bars connecting upper two revolute joints, and two long rotation bars connecting lower revolute joints, and making support having enough rigidity and maintaining link 1 of exoskeleton, and the spring in support can be adjusted by screw with different weight of upper arm and forearm. The exoskeleton consists of a spherical joint, two revolute joints, and a prismatic joint, and two springs, in which, spring 1 is for balancing gravity of link 5 i.e. sum of gravity of link 2 and link 3, and spring 2 is for balancing gravity of link 6 i.e. sum of gravity of link 4 and forearm, it also can be adjusted by screw with weight of forearm.
(a)
(b) (c)
(d) (e)
Fig. 18 Prototype (a) CAD of elbow exoskeleton (b) prototype of elbow exoskeleton (c) adjustment screw and spring in support (d) springs and exoskeleton (e)
adjustment screw in exoskeleton
Chapter 5
Results and Discussions of Simulations of Yaw and Roll Torques
5.1 Yaw and roll torques on exoskeleton joints for elbow flexion-extension motion in sagittal plane
Aims of verify test is assessing yaw and roll torques on every exoskeleton joint in elbow motion in sagittal and transverse planes with different elbow flexion angle and carrying angle.
Verify test for yaw and roll torque on exoskeleton joints by using adams, and there are some constraints for design models, first, using data of the relationship of elbow flexion angle and carrying angle in male and female [13], second, setting every joint is perfect joint, third, every spring is zero-free-length spring, forth, attachments of exoskeleton and arm are the same links, finally, models with gravity effects in simulations.
As shown in Table 5, yaw torque and roll torque effect on each exoskeleton joint for elbow flexion-extension motion in sagittal plane of male and female in different flexion angle and carrying angle. Maximum yaw torque of spherical joint, revolute joint 2, P joint happen when elbow flexion angle is 0 degree, magnitude are -38, -52
(10−2Nm), -8.2, -15, 14, 25 (10−4Nm), and maximum yaw torque of revolute joint 1
happen when elbow flexion angle is 30 degree, magnitude are 10, 14 (10−4Nm),
maximum yaw torque of spherical joint is the largest torque in all joints. Maximum roll
torque of spherical joint, revolute joint 1, revolute joint 2 happen when elbow flexion angle is 0 degree, magnitude are 31, 42 (10−2Nm), -24, -38, 39, 50 (10−4Nm), and
maximum roll torque of prismatic joint happen when elbow flexion angle is 30 magnitude are -16, -21 (10−4Nm), maximum roll torque of spherical joint is also the
largest torque in all joints.
Maximum yaw and roll torque of elbow in sagittal plane are 50, 12.3 (Nm) [27, 28], and torque which is below 20 presents of maximum torque of human joint does not
make human discomfort [29], the 20 presents of maximum yaw and roll torque of elbow are 50×20%=10, 12.3×20%=2.46 (Nm), the maximum yaw and roll torque of spherical joint i.e. -38, -52, 31, 42 (10−2Nm) are below 10, 2.46 (Nm)
Magnitude of yaw torque of spherical joint, revolute joint 2, prismatic joint decrease when flexion angle increases, carrying angle decreases, and when flexion
Table 14 Yaw and roll torque on exoskeleton joints in elbow extension-flexion motion in sagittal plane
(data given in degree, 1 is 10−2Nm, 2 is 10−4 Nm )
angle is 90 degree, carrying angle is the smallest, magnitude of yaw torque of spherical joint, revolute joint 2, prismatic joint is minimum, then increasing when flexion angle increases, carrying angle increases. Magnitude of roll torque of spherical joint, revolute joint 1, revolute joint 2 is the same trend to yaw torque of spherical joint, revolute joint 2, prismatic joint, and it realizes these yaw and roll torques effected by carrying angle i.e. when carrying angle increases, torque increases; carrying angle decreases, torque decreases. Magnitude of yaw torque of revolute joint 1 and magnitude of roll torque of prismatic joint are minimum when flexion angle is 0 degree, and increasing when flexion angle is 30 degree, than decreasing when flexion angle increasing, it realizes the trends of these two torque are effected by both flexion angle and carrying angle.
In most of flexion angle, yaw torque of spherical joint, revolute joint 2 are negative, revolute joint 1, prismatic joint are positive, meaning rotation direction of spherical joint, revolute joint 2 is outer rotation about carrying angle rotation axis, and revolute joint 1, prismatic joint is inner rotation. Roll torque of spherical joint, revolute joint 2 are positive, revolute joint 1, prismatic joint are negative, meaning rotation direction of spherical joint, revolute joint 2 is outer rotation about forearm axis, and revolute joint 1, prismatic joint is inner rotation.
Spherical joint has rotation DOF of carrying angle rotation axis and forearm axis forearm axis, and revolute joint 1 has rotation DOF of carrying angle rotation axis, other
joints do not have these two rotation DOF such that human arm and exoskeleton just effected by spherical joint and revolute joint 1, user would feel arm suffering torques which make arm outer rotating about carrying angle rotation axis and forearm axis.
5.2 Yaw and roll torques on exoskeleton joints for elbow flexion-extension motion in transverse plane
As shown in Table 6, yaw torque and roll torque effect on each exoskeleton joint for elbow flexion-extension motion in transverse plane of male and female in different flexion angle and carrying angle. Maximum yaw torque of spherical joint spherical
joint, revolute joint 2, prismatic joint happen when elbow flexion angle is 90 degree, magnitude are -148, -148 (10−2Nm), -250, -260, -260, -260 (10−4Nm), and maximum
yaw torque of revolute joint 1 happen when elbow flexion angle is 60 degree,
magnitude are -12, -20 (10−4Nm), maximum yaw torque of spherical joint is the largest
torque in all joints. Maximum roll torque of spherical joint, revolute joint 1, revolute
joint 2, prismatic joint happen when elbow flexion angle is 90, 120, 60, 30 degree, magnitude are -145, -146 (10−2Nm), 340, 340, -110, -110, -56, -53 (10−4Nm),
maximum roll torque of spherical joint is also the largest torque in all joints.
Table 6 Yaw and roll torque on exoskeleton joints in elbow extension-flexion motion in transverse plane
Maximum yaw and roll torque of elbow in transverse plane are 78, 12.3 (Nm) [28], and 20 presents of maximum yaw and roll torque of elbow are 78 ×20%=15.6,
12.3×20%=2.46 (Nm), the maximum yaw and roll torque of spherical joint i.e. 148, -148, -145, -146 (10−2Nm) are below 10, 2.46 (Nm).
Magnitude of yaw torque of spherical joint, revolute joint 2, prismatic joint
increase when flexion angle increases, carrying angle decreases, and when flexion angle is 90 degree, carrying angle is the smallest, magnitude of yaw torque of spherical joint, revolute joint 2, prismatic joint is maximum, then decreasing when flexion angle increases, carrying angle increases.
Magnitude of yaw torque of revolute joint 1 has similar trend to yaw torque of other joints, difference is maximum yaw torque of revolute joint 1 in flexion angle is 60 degree, it realizes magnitude of yaw torque effected by flexion angle i.e. flexion angle increasing from 0 degree, magnitude of yaw torque increasing, and then decreasing.
Magnitude of roll torque of spherical joint, revolute joint 2, prismatic joint also has similar trend to yaw torque of joints, difference is maximum magnitude happen in
(data given in degree, 1 is 10−2Nm, 2 is 10−4 Nm )
different flexion angle, and magnitude of roll torque of revolute joint 1 increasing when flexion angle increasing from 0 degree, it realizes roll torques also effected by flexion angle.
In most of flexion angle, yaw torque of spherical joint is positive, revolute joint 1, revolute joint 2, prismatic joint are negative, meaning rotation direction of spherical joint is inner rotation about elbow rotation axis, and revolute joint 1, revolute joint 2, and prismatic joint is outer rotation. Roll torque of spherical joint, prismatic joint are negative, revolute joint 1, revolute joint 2 are positive, meaning rotation direction of spherical joint, revolute joint 2 is inner rotation about forearm axis, and revolute joint 1, prismatic joint is outer rotation.
Human arm and exoskeleton just effected by spherical joint and revolute joint 1 for the same reason in elbow flexion-extension motion in sagittal plane, user would feel arm suffering torques which make arm inner rotating about elbow rotation axis and forearm axis.
Chapter 6
Conclusions and Future Works
6.1 Conclusions
In this thesis, a design methodology of kinematic compatible and gravity balanced exoskeleton is presented. Kinematic compatibility, operating degree-of-freedom of human arm are defined. Types of exoskeleton for elbow with/without carrying angle, shoulder, and arm are presented. A prototype of SRRP kinematic compatible and gravity balanced elbow exoskeleton is assembled to demonstrate kinematic compatibility of exoskeleton. Simulations by adams verify yaw and roll torques on exoskeleton joints.
For elbow with carrying angle in flexion-extension motion, yaw and roll torques on exoskeleton joints are below to 20% maximum yaw and roll torque of elbow verifying feasibility of the SRRP exoskeleton. Yaw and roll torques of female is larger than which of male in most of elbow flexion angle in elbow flexion-extension motion in sagittal plane realizing carrying angle effects. Yaw and roll torques of female nearly equal to which of male in most of elbow flexion angle in elbow flexion-extension motion in transverse plane i.e. carrying angle affects slightly realizing that designing of a gravity balanced exoskeleton for elbow flexion-extension motion in transverse plane is easier than motion in sagittal plane.
6.2 Future works
This thesis design elbow exoskeleton for elbow with/without carrying angle and flexion-extension and supination-pronation motion, shoulder exoskeleton, and arm exoskeleton. However, there are still progress and improvement to be done
1. Verify test only simulates elbow flexion-extension motion in sagittal and transverse plane, for other types of elbow exoskeleton, and other motions for different types of shoulder exoskeleton and arm exoskeleton, the yaw and roll torque might be
difference, which should be realized.
2. Although the series of the joints in the exoskeleton does not affect the compatibility of the exoskeleton, it should still be optimized for different types of exoskeleton and the range of motion of the corresponding joint.
3. The length of the exoskeleton links should also be optimized for smaller workspace and avoiding singularities to occur and having collision with upper arm and forearm.
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