Related Experiment Video
Updated: May 17, 2026
09:46
Training Persons with Spinal Cord Injury to Ambulate Using a Powered Exoskeleton
Published on: June 16, 2016
Quantifying anti-gravity torques for the design of a powered exoskeleton
Daniel Ragonesi1, Sunil K Agrawal, Whitney Sample
1Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA. ragonesi@udel.edu
Summary
This study measured upper limb joint torques in children with and without impairments, finding that gravity and stiffness torques exceed voluntary strength in disabled children. These findings are crucial for designing effective upper extremity exoskeletons.
Area of Science:
- Biomechanics
- Rehabilitation Engineering
- Pediatric Physical Therapy
Background:
- Designing upper extremity exoskeletons requires understanding joint torques (gravity, stiffness) and user strength.
- Children with upper limb impairments present unique biomechanical challenges for assistive device design.
Purpose of the Study:
- To characterize upper limb joint torques due to gravity and stiffness in children with and without upper limb impairments.
- To compare experimental torque data with a two-link lumped mass model.
- To assess the maximum voluntary torque capabilities of children with neuromuscular disabilities.
Main Methods:
- Experimental measurement of forearm force during arm movement in the sagittal plane for three subject groups: able-bodied adults, able-bodied children, and children with neuromuscular disabilities.
- Conversion of measured force to elbow and shoulder joint torques.
- Comparison of experimental torques to a two-link lumped mass model based on anthropometry.
- Measurement of maximal voluntary push and pull torques as a function of arm orientation for subjects with disabilities.
Main Results:
- Anthropometric models showed deviations from experimentally measured torques across the arm's range of motion.
- For children with disabilities, maximum voluntary applied shoulder and elbow torques were consistently lower than gravity torques throughout their range of motion.
- Gravity and joint stiffness torques significantly influence upper limb biomechanics in children, particularly those with impairments.
Conclusions:
- Experimental data on joint torques and strength capabilities are essential for designing effective upper limb orthoses and exoskeletons for children.
- Passive human joint torques due to gravity and stiffness are critical considerations for exoskeleton designers.
- Understanding the strength limitations of users with disabilities informs the development of assistive technologies that can effectively compensate for functional deficits.
Related Concept Videos
01:10Torque
Torque is an important quantity for describing the dynamics of a rotating rigid body. We see the application of torque in many ways in the world, such as when pressing the accelerator in a car, which causes the engine to apply additional torque on the drivetrain. Here, we define torque and provide a framework to create an equation to calculate torque for a rigid body with fixed-axis rotation.
Torque can be considered as the rotational counterpart to force. Since forces change the translational...
Torque can be considered as the rotational counterpart to force. Since forces change the translational...
01:19Net Torque Calculations
When a mechanic tries to remove a hex nut with a wrench, it is easier if the force is applied at the farthest end of the wrench handle. The lever arm is the distance from the pivot point (the hex nut in this case) to the person’s hand. If this distance is large, the torque is higher. Only the component of the force perpendicular to the lever arm contributes to the torque. Therefore, pushing the wrench perpendicular to the lever arm is more advantageous. If multiple people apply force to rotate...
00:57Power Expended by a Constant Force
The relationship between work done and the time taken to do it can be explained using the concept of power. For example, several sprinters in a race may have the same velocity when they reach the finish line, therefore doing the same amount of work, but the winner does it in the least amount of time. Thus, power is defined as the rate of doing work. Since work can vary as a function of time, the average power is defined as the work done during a time interval, divided by the time interval.
01:15Torque Free Motion
The torque-free motion refers to the movement of a rigid body in space when no external torques are acting upon it. This type of motion can be observed in environments where there are no external forces or frictions, like in outer space. For example, a rotation of Mars in space is a torque-free motion. Mars is an axisymmetric object, meaning it has an axis of symmetry along which it rotates, designated as the z-axis. The rotating frame of reference is defined such that the center of mass of...
01:10Work and Energy for Variable Forces
When an object is acted upon by a variable force, the amount of work done and the change in energy of the object can be more complex to calculate compared to when a constant force is applied. Work is the product of force and displacement, while energy is the capacity of a system to do work. When a constant force is applied to an object, the work done can be calculated as the product of the force and the distance moved in the direction of the force. However, when a variable force is applied, the...
01:30Machines: Problem Solving II
Machines are complex structures consisting of movable, pin-connected multi-force members that work together to transmit forces. Consider a lifting tong carrying a 100 kg load. It comprises movable sections DAF and CBG linked together with member AB.