Dick H. Plettenburg

Efficiency of voluntary closing hand and hook prostheses

The Delft Institute of Prosthetics and Orthotics has started a research program to develop an improved voluntary closing, body-powered hand prosthesis. Five commercially available voluntary closing terminal devices were mechanically tested: three hands [Hosmer APRL VC hand, Hosmer Soft VC Male hand, Otto Bock 8K24] and two hooks [Hosmer APRL VC hook, TRS Grip 2S]. The test results serve as a design guideline for future prostheses. A test bench was used to measure activation cable forces and displacements, and the produced pinch forces. The measurements show that the hands require higher activation forces than the hooks and 1.5–8 times more mechanical work. The TRS hook requires the smallest activation force (33 N for a 15 N pinch force) and has the lowest energy dissipation (52 Nmm). The Hosmer Soft hand requires the largest activation force (131 N for a 15 N pinch force) and has the highest energy dissipation (1409 Nmm). The main recommendations for future prostheses are the following: (1) Required activation forces should be below the critical muscle force (∼ 18% of maximum), to enable continuous activation without muscle fatigue; and (2) hysteresis of mechanism and glove should be lowered, to increase efficiency and controllability.

Basic requirements for upper extremity prostheses: the WILMER approach

Many prostheses are not being used because of the discrepancy between the expectations of patients with an arm defect and the reality. A patient wants and expects a prosthesis that looks naturally beautiful, that is comfortable to wear and that is easy to use. None of the existing prostheses fulfils all these demands. Nevertheless by soundly informing and educating the patient and by a proper use of the state of the art in upper extremity prosthetics, a lot is gained in really helping the patient. Moreover, a lot still has to be done in developing new prosthetic devices that really fulfil the basic needs of a patient with an arm defect. Some examples of the efforts of the WILMER group in this field are discussed.

Efficiency of voluntary opening hand and hook prosthetic devices : 24 years of development?

Quantitative data on the mechanical performance of upper-limb prostheses are very important in prostheses development and selection. The primary goal of this study was to objectively evaluate the mechanical performance of adult-size voluntary opening (VO) prosthetic terminal devices and select the best tested device. A second goal was to see whether VO devices have improved in the last two decades. Nine devices (four hooks and five hands) were quantitatively tested (Hosmer model 5XA hook, Hosmer Sierra 2 Load VO hook, RSL Steeper Carbon Gripper, Otto Bock model 10A60 hook, Becker Imperial hand, Hosmer Sierra VO hand, Hosmer Soft VO hand, RSL Steeper VO hand, Otto Bock VO hand). We measured the pinch forces, activation forces, cable displacements, mass, and opening span and calculated the work and hysteresis. We compared the results with data from 1987. Hooks required lower activation forces and delivered higher pinch forces than hands. The activation forces of several devices were very high. The pinch forces of all tested hands were too low. The Hosmer model 5XA hook with three bands was the best tested hook. The Hosmer Sierra VO hand was the best tested hand. We found no improvements in VO devices compared with the data from 1987.

Endoscope Shaft-Rigidity Control Mechanism: “FORGUIDE”

Recent developments in flexible endoscopy and other fields of medical technology have raised the need for compact slender shafts that can be made rigid and compliant at will. A novel compact mechanism, named FORGUIDE, with this functionality was developed. The FORGUIDE shaft rigidifies due to friction between a ring of cables situated between a spring and an inflated tube. A mathematical model for the FORGUIDE mechanism working principle was made and used to obtain understanding of this mechanism, predict the maximum rigidity of a FORGUIDE shaft design, and tune its design variables. The mathematical model gave suggestions for significant performance improvement by fine-tuning the design. A prototype FORGUIDE shaft was built and put to a series of bench tests. These tests showed that the FORGUIDE mechanism provides a reliable and simple way to control the rigidity of a flexible shaft.

Assessment of body-powered upper limb prostheses by able-bodied subjects, using the Box and Blocks Test and the Nine-Hole Peg Test

Background: The functional performance of currently available body-powered prostheses is unknown. Objective: The goal of this study was to objectively assess and compare the functional performance of three commonly used body-powered upper limb terminal devices. Study design: Experimental trial. Methods: A total of 21 able-bodied subjects (n = 21, age = 22 ± 2) tested three different terminal devices: TRS voluntary closing Hook Grip 2S, Otto Bock voluntary opening hand and Hosmer Model 5XA hook, using a prosthesis simulator. All subjects used each terminal device nine times in two functional tests: the Nine-Hole Peg Test and the Box and Blocks Test. Results: Significant differences were found between the different terminal devices and their scores on the Nine-Hole Peg Test and the Box and Blocks Test. The Hosmer hook scored best in both tests. The TRS Hook Grip 2S scored second best. The Otto Bock hand showed the lowest scores. Conclusion: This study is a first step in the comparison of functional performances of body-powered prostheses. The data can be used as a reference value, to assess the performance of a terminal device or an amputee. Clinical relevance The measured scores enable the comparison of the performance of a prosthesis user and his or her terminal device relative to standard scores.

The Lightweight Delft Cylinder Hand: First Multi-Articulating Hand That Meets the Basic User Requirements

Rejection rates of upper limb prostheses are high (23%-45%). Amputees indicate that the highest design priority should be reduction of the mass of the prosthetic device. Despite all efforts, the mass of the new prosthetic hands is 35%-73% higher than that of older hands. Furthermore, current hands are thicker than a human hand, they operate slower and do not provide proprioceptive force and position feedback. This study presents the Delft Cylinder Hand, a body powered prosthetic hand which mass is 55%-68% lower than that of the lightest current prosthetic hands, operates faster, has an anthropomorphic shape, and provides proprioceptive force and position feedback. The hand has articulating fingers, actuated by miniature hydraulic cylinders. The articulating fingers adapt to the shape of the grasped object. Its functional scores are similar to that of current prosthetic devices. The hand has a higher mechanical performance than current body-powered hands. It requires 49%-162% less energy from the user and it can deliver a higher maximum pinch force (30-60 N).

A structured overview of trends and technologies used in dynamic hand orthoses

The development of dynamic hand orthoses is a fast-growing field of research and has resulted in many different devices. A large and diverse solution space is formed by the various mechatronic components which are used in these devices. They are the result of making complex design choices within the constraints imposed by the application, the environment and the patient’s individual needs. Several review studies exist that cover the details of specific disciplines which play a part in the developmental cycle. However, a general collection of all endeavors around the world and a structured overview of the solution space which integrates these disciplines is missing. In this study, a total of 165 individual dynamic hand orthoses were collected and their mechatronic components were categorized into a framework with a signal, energy and mechanical domain. Its hierarchical structure allows it to reach out towards the different disciplines while connecting them with common properties. Additionally, available arguments behind design choices were collected and related to the trends in the solution space. As a result, a comprehensive overview of the used mechatronic components in dynamic hand orthoses is presented.

Grasp force optimization in the design of an underactuated robotic hand

For people without the ability to use their hands, gripper-equipped robotic aids may provide partial rehabilitation. This article discusses the optimization of an underactuated mechanism for a new prototype gripper on robotic aid ARM. When the underactuated mechanism of the tentacle-like Soft Gripper is translated to a three-phalange equivalent for the prototype, increasing forces on the proximal phalanges tend to drive objects out of the grasp when the finger flexes. To obtain equal grasp forces on all phalanges, the pulley radii in the mechanism were optimized. This could however only decrease the ratio between highest and lowest force from 4.0 to 2.9. An extra bi-articular tendon was added to the mechanism, which further improved this ratio to 1.5. The prototype gripper that was fitted with the bi-articular mechanism stably grasps and holds objects. Preliminary test with disturbance forces and torques on the grasped objects show a performance increase with respect to a parallel gripper mounted on ARM. However, some improvements on the bi-articular mechanism are necessary to make the force in the bi-articular tendon linearly dependent from the actuation force of the gripper.

Steerable Catheters in Cardiology: Classifying Steerability and Assessing Future Challenges

Objective: This review aims to provide a structured classification of the underlying steering mechanisms in steerable catheters and to assess their future challenges. Methods: Existing, patented, and experimental designs of steerable catheters are classified with respect to their steerability. Subsequently, the classification is used as a tool for defining future requirements and challenges for steerable cardiac catheters. Results: The results of the classification provide two categories of steering at a fundamental level: 1) Force generation in the tip and 2) force transmission to the tip. The former group consists of force generating steering mechanisms as a result of 1) electric, 2) thermal, and 3) magnetic actuation. The latter group comprises force transmitting steering mechanisms as the result of 4) hydraulic chamber actuation or 5) mechanic cable actuation. Each category can be further subdivided into multiple subcategories. Future requirements and challenges are found for steering and positioning capabilities, cardiac applications and safety, and miniaturization potential. Conclusion: A structured classification is presented which identifies the different steering mechanisms in steerable catheters. The classification proves to be a useful tool in determining future requirements and challenges, being invaluable for future application-driven design. Significance: Using the applied classification as a tool for future design will not only provide insight into previously applied steering technology, it will identify new and unexplored options too. Additionally, insight into the requirements and challenges for catheter steering toward and inside the heart, will allow more dedicated systems, allowing intervention- and patient-specific instrument manipulation.

Comparison of Mechanical Properties of Silicone and PVC (Polyvinylchloride) Cosmetic Gloves for Articulating Hand Prostheses

Current articulating electric and body-powered hands have a lower pinch force (15-34 N) than electric hands with stiff fingers (55-100 N). The cosmetic glove, which covers a hand prosthesis, negatively affects the mechanical efficiency of a prosthesis. The goal of this study is to mechanically compare polyvinylchloride (PVC) and silicone cosmetic gloves and quantify the stiffness of the finger joints, the required actuation energy, and the energy dissipation during joint articulation. Six cosmetic gloves, identical in size but made from different materials, were mechanically tested: three PVC and three silicone. The silicone gloves required less work and dissipated less energy during flexing. They also had a lower joint stiffness and required a lower maximum joint torque. Based on energy requirements, joint stiffness, and required joint torque, the tested silicone glove is most suitable for application on an articulating hand prosthesis.