Pneumatic and Hydraulic Microactuators: Research and Development.

The technological tendency to close the physical gap between robots and humans requires the development of new, large stroke, miniature actuators that are inherently safe in contact with biological tissue. Flexible fluidic actuators that deform due to an internal pressure loading are envisioned to fulfil these needs. This research provides an in-depth analysis of flexible fluidic actuators with a bending and twisting deformation, with topics ranging from theoretical deformation analysis and stroke optimisation to production, augmentation and application.

A theoretical model is developed that predicts the deformation of bending actuators in good agreement with measurements on prototypes. Further, this model is used to optimise the bending deformation while limiting internal stresses, resulting in more robust actuators. Two new processes for producing bending actuators are introduced: a single step micromoulding method that enlarges the pressure range; and a full lithography production process that makes further miniaturisation possible. With the introduction of a full lithography process, other lithographical techniques can be applied to augment the functionality of these actuators. As such, two different embeddable conductive paths are analysed: for strain sensing applications and for signal and power transfer between actuator base and tip.

By introducing layered inflatable voids in a cross pattern, a twisting deformation is induced, resulting in a new type of twisting actuator that consists of a single material. The actuator performance, expressed in twisting angle per actuator length, is optimised in function of its geometrical parameters. Four of these optimal twisting actuators are combined in a 2DOF tilting mirror platform, experiencing a tilting deformation of ±25 and ±29.

In another application, six bending actuators are combined in line to form a mimicking cilia array. For the first time, known to the author, an independently controllable cilia test setup is developed, that is used to validate existing ciliary propulsion theory. The flow inducing performance of this cilia array is tested with a resulting maximal net fluid flow of 19mm/s. Also flow direction can be reversed by only changing actuation frequency or duty cycle. Further, a small camera is mounted on the tip of a bending actuator resulting in a 1.66mm diameter chip-on-tip flexible endoscope, where actuation resulted in an increased field of view of 45. Lastly, a general tool is presented that iteratively designs actuators until the end effector follows a predescribed path upon pressurization. Based on a set of inflatable structures that are cross-breeded and mutated from generation to generation, better performing structures are rewarded in this evolutionary selection mechanism, where suitability is assessed by means of finite element modelling.