Modelling and control of soft-rigid actuator for assistive technologies

Gaber, Mohamed

Modelling and control of soft-rigid actuator for assistive technologies

Publication Date

July 27, 2026

Creator

Gaber, Mohamed

Abstract

The soft robotics field has experienced notable growth over the past decade, especially in human interaction applications such as assistance and rehabilitation. The use of soft material to develop wearable robotic systems has demonstrated potential for safer, more comfortable, and lower-cost alternatives compared to rigid counterparts. Furthermore, 3D printing has become common for fabricating soft robots due to their accuracy, repeatability, affordability, and ability to create complex structures. A large-scale 3D-printed high-force actuator is developed for use in knee assistive applications. It is fabricated using Stereolithography (SLA) printing technology, which provides high accuracy and air-tight sealing. A washing technique using an ultrasonic cleaner is proposed to solve the washing problem of the complex internal cavities. The results show that full-cycle bending under low pressure, reaching 5 kPa. The blocking force output of the actuator reaches 65 N with an output torque of 6.8 Nm at a pressure of 50 kPa. A novel hybrid soft-rigid pneumatic actuator (SRA) design, model and fabrication technique is presented to be used for assistive applications. The SRA design is inspired by a compliant configuration of a four-bar mechanism that simplifies the actuator kinematic model. An innovative manufacturing method employing a desktop SLA 3D printer to create a multi-material actuator by printing the main soft part of the actuator from elastic material, and then a resin of rigid material is injected inside the chambers to create the rigid links. A 3D-printed pneumatic pinch valve is developed to control the large-scale actuators. The flow rate has been characterised and its effect on the pneumatic soft wearable robots’ dynamics. The valve affords different configurations with different flow rate limitations up to 50 SLPM/bar, with a 2 mm configuration. An artificial muscle is used to validate the valve with a pressure control experiment. The results show a fast response with 0.2 sec inflation time and 0.3 sec deflation time using the 2 mm valve configuration. The design of the 3D-printed pinch valve was then modified to decrease the opening delay time. That’s results in a single muscle operation frequency increased from 0.1 Hz to 3.5 Hz and a chain of five muscles was then controlled and reached 1.5 Hz, suitable for knee flexion assistance during walking. In this work, 3D printing is investigated to fabricate a large-scale pneumatic soft actuator and soft-rigid actuator to be used for knee assistance. Additionally, a 3Dprinted valve is developed for controlling pneumatic artificial muscles. The results show that SLA 3D printing can fabricate airtight, large-scale pneumatic actuators that work at low pressure and energy consumption. The SRA fabrication technique provides the ability to create multimaterial actuators by combining the 3D printing and moulding techniques. The modified pinch valve design is used to enhance the artificial muscle dynamics by increasing the input and output flow rate. These results prove the ability of the 3D printed actuators to be used for knee assistance and increase the opportunity toward portable assistive devices.

Item Type

ethesis

Thesis Type

PhD

Supervisors

Branson, David

University of Nottingham

Gilani, Negar

University of Nottingham

Keywords

Soft Robots

assistive devices