Creating a Miniature Hydraulic System to Power the Delft Cylinder Hand

Creating a Miniature Hydraulic System to Power the Delft Cylinder Hand

van Dort, Mark (TU Delft Mechanical, Maritime and Materials Engineering)

Smit, G. (mentor)

Delft University of Technology

2019-10-09

To reduce the necessary input force of the user to exert a precision grip force above 30 N, the hydraulic circuit of the Delft Cylinder Hand can be expanded. This added hydraulic circuit has to be able to generate high enough pressures and volume flows to generate a pinch force of 30 N with all of the fingers, close the hand within 0.5 seconds and support both closing and opening movements. Furthermore, the combined weight of both the hand and the expanded hydraulic circuit had to stay underneath 350 grams. When creating this circuit, the addition of a hydraulic valve and pressure sensor at the hand was kept in mind. As a result, the hydraulic circuit only has to uphold the high pressure long enough for the hydraulic valve to close. This time was assumed to be 0.5 seconds. The expected weight for this addition is added when determining the combined weight of the hand and the expanded hydraulic circuit.

This study explores the possibilities for creating this expansion of the hydraulic circuit. First, the parts necessary to build a basic hydraulic circuit and the limitation for these parts were studied. Then, the required parameters for the hydraulic circuit were both calculated and measured. Based on those results, the hydraulic circuit was built with the chosen parts and the hydraulic circuit was tested. Based on the test measurements, possibilities for future optimisation of the hydraulic circuit were studied. The power source and the reservoir were left out of the scope of this research as those two parts can be placed more proximal on the forearm, and thus have a reduced impact on the weight experienced by the patient.

The built circuit enabled all the fingers of the Delft Cylinder Hand to exert a pinch force of 30 N and was able to uphold this pinch force for over 0.5 seconds and supported both closing and opening movements. The closing time was found to be between 0.9 and 1.2 seconds. However, applying a low pressure on the hydraulic circuit and removing the springs inside the fingers of the hand before turning on the motor reduced the closing time to 0.45 seconds. The combined weight of the hand and the expanded circuit, including the expected weight for the added hydraulic valve and pressure sensor, is 337 grams.

As the used external gear pump was found to have a relatively low efficiency, further improvements to the performance to the hydraulic circuit can be made by improving the pump efficiency. Furthermore, future research should focus on manufacturing a lightweight reservoir, finding a suitable power source and programming a lightweight control unit.

Delft Cylinder Hand
Upper limb prosthetics
Hydraulic

http://resolver.tudelft.nl/uuid:9b7b2803-7d84-44a9-b100-59882a77e547

2021-09-10

Student theses

master thesis

© 2019 Mark van Dort