*2.1.3. Flexible fluidic "Bending" actuators*

Bending actuators are generating a bending motion when pressurized, which is used to manipulate objects in an adaptive and compliant way. Staines [120] presented vacuum operated and Baer [7, 8] pressure operated conceptual solutions for this problem (figure 5(a) and 5(b)).

**Figure 5.** Bending Actuators

The work by Orndorff and Ewing [27, 95] as well as Andorf et al. [5] introduce designs where bending occurs due to "anisotropic membrane stiffness". Craig et al. [18] point out that these types of actuators can be folded to reduce shipping volume specially for space applications. Figure 5(c)-5(e) show the different designs.

Bending actuators designed with multi-lumen hoses are represented by the work of Suzumori et al. [122–126] shown in figure 5(f). Radial reinforcements inhibit radial expansion so that the operating pressure is 1.4 − 4 *bar*.

There is a large variety of trunk-like bending actuators that create bending motion by adding structural constraints. A few examples are shown in figures 6(a)-6(c).

Monolithic bending actuators represent the last group in this section. Different research groups have been working on this topic during the last years [57, 71, 145, 146]. These actuators 572 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges Compliant Robotics and Automation with Flexible Fluidic Actuators and Inflatable Structures <sup>7</sup> Compliant Robotics and Automation with Flexible Fluidic Actuators and In atable Structures 573

**Figure 6.** Trunk-Like Bending Actuators and Monolithic Bending Actuators

are single material devices and mainly fabricated in on step. Operating pressures are mostly < 1 *bar*. Some prototypes are shown in figure 6(d)-6(e).

### *2.1.4. Flexible fluidic actuators - combined motion*

6 Will-be-set-by-IN-TECH

The work of Kukolj [73] shows an actuator with a net as the fiber reinforcement. This eliminates the friction between the fiber strands, but the friction between membrane and fiber reinforcement remains (figure 4(b)). Immega [58] enhanced this idea by implementing a stiff,

A newer design known as "Pleated Pneumatic Artificial Muscles (PPAM)" was introduced by Daerden and Lefeber [19, 21]. The design is similar to the Yarlott muscle. Figure 4(d) and 4(e)

Erickson [25] described a contraction actuator that can be considered an inverse rolling-lobe cylinder. This set-up has a large working range of 40-60% of the initial length (figure 4(f)).

Bending actuators are generating a bending motion when pressurized, which is used to manipulate objects in an adaptive and compliant way. Staines [120] presented vacuum operated and Baer [7, 8] pressure operated conceptual solutions for this problem (figure 5(a)

(a) [120] (b) [7, 8] (c) [95]

The work by Orndorff and Ewing [27, 95] as well as Andorf et al. [5] introduce designs where bending occurs due to "anisotropic membrane stiffness". Craig et al. [18] point out that these types of actuators can be folded to reduce shipping volume specially for space applications.

Bending actuators designed with multi-lumen hoses are represented by the work of Suzumori et al. [122–126] shown in figure 5(f). Radial reinforcements inhibit radial expansion so that the

There is a large variety of trunk-like bending actuators that create bending motion by adding

Monolithic bending actuators represent the last group in this section. Different research groups have been working on this topic during the last years [57, 71, 145, 146]. These actuators

structural constraints. A few examples are shown in figures 6(a)-6(c).

(d) [5] (e) [18] (f) [18]

show the design and the force-displacement characteristics of these artificial muscles.

folded membrane in between the fiber mesh (figure 4(c)).

*2.1.3. Flexible fluidic "Bending" actuators*

and 5(b)).

**Figure 5.** Bending Actuators

Figure 5(c)-5(e) show the different designs.

operating pressure is 1.4 − 4 *bar*.

This group of actuators produces multiple directions of motion. Griebel et al. [38] developed a placement actuator for EEG-electrodes that conducts a linear expansion in combination with a coaxial rotation (figure 7(a)). Paynter [99, 102] on the other hand supresses the linear motion on purpose in order to design an pure rotary drive. As shown in figure 7(b) a pre-twisted membrane is straightened when pressurized and thus generates a rotary motion.

**Figure 7.** Actuators with two directions of motion

Other concepts use several different cavities to create multi-motion actuators. Claus [16] presents a push-pull actuator while Wilson [139] combines expandable hoses to build a versatile robotic arm (figure 7(c) and 7(d)).

Alternative approaches are presented by Kimura and Brown. Kimura et al. [69] describe a principle that is called "whole skin locomotion". Here an elongated toroid turns itself inside out and hence can move over surfaces or through gaps (figure 8(a)). The concept by Brown et al. [14] is referred to as "jamming of granular material". The idea here is known from vacuum mattresses in ambulances. A flexible bag containing a granular material is shaped around an object and then evacuated. Friction, suction and mechanical interlocking connects gripper and object (figure 8(b)).

#### 8 Will-be-set-by-IN-TECH 574 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

**Figure 8.** Actuators based on Whole Skin Effects
