Climbing robots using adhesion force - Microspine

  5. Climbing robot using microspine

  There are climbing robots using microspines which are mimicking spiders, insects, cats' feet. This mechanism consumes low-energy when not moving and has strong forces on soft material, such as wood. These robots can't climb glass, metal or smooth surfaces. But these kinds of materials rarely exist in natural environment, so robots with mirospines are widely used.

  Spinybot II is a climbing robot on hard walls [1]. It climbs reliably on a wide variety of hard, outdoor surfaces including concrete, stucco and brick. It employs two rows of spines on each foot. Each spine having a tip diameter of approximately 25㎛ with maximum force per spine/asperity contact of 1-2 N.

Fig. 1 View of upper section of SpinybotII on concrete wall and detailed view of several spines independently engaging asperities on the concrete surface.

  Its climbing speed is about 2.3cm/s and uses 7 servo motors with 10 toes in each leg. The sequence of motions is accomplished using an under-actuated mechanism consisting of a single rotary RC servo motor and an elastic band that is initially loose and becomes taut as the leg moves upward. At the end of stroke, a hard stop causes the leg to remain pressed against the wall.

Fig. 2 Side and plan view of one foot containing 10 toes The toes can deflect independently of each other. In addition, the entire foot can displace in the distal (y) direction due to an unactuated prismatic joint. The attachment trajectory of the foot consists of an upward (+y) motion, followed by lift-off motion (-x), touchdown (+x), and a downward pull (-y).

Climbing robots using adhesion force - Spider robot

 4. Spider robot

   Spiders also use dry adhesive, which rely primarily on Van der Waals forces. Climbing robots are researching using dry adhesive. There are climbing robots using dry adhesion force: 1) wheeled locomotion system and 2) inspired by the locomotion of geckos. I will introduce a climbing robot, Abigaille II, inspired by the locomotion of spider.

   The feet of Abigaille II consist of a two-layer adhesive, which was manufactured in two steps. First, a 1×3㎠ layer with microposts was manufactured by casting Polydimethylsiloxane (PDMS) in a microstructured mold. There are scanning electron microscope (SEM) images of microposts placed in adhesive used by spider robot in following figure (Fig. 1). The second layer is consisted of 1×1㎠ macroposts array. Each post has about 1㎟ cross-section area with approximately 3 mm tall.

Fig. 1 SEM images of the microposts in the adhesive used in the climbing robot: (a) magnification at 2500X and (b) magnification at 5000X

   
   Abigaille-II has 36 DOF of which 18 are actively controlled. In order to reduce the robot’s mass, its mechanical structure consists of mosaic composition of Printed Circuit Boards(PCB) (Fig. 2). 

Fig. 2 (a) Leg’s geometry and (b) CAD model of the robot.

  It has sensors in each foot to analyze forces during climbing. Fig. 3 shows the force characterization and scheme of different phases in one step cycle. (Fig. 3) It moves as single leg moves while other legs fix their position on wall and repeating this movement to all legs. It can move 4.5cm/s on ground, 0.1cm/s on vertical wall.

Fig. 3 Force characterization on legs 1, 6, and 5 during climbing: (a)–(c) force graph of legs 1, 6, and 5; and (d) Scheme of different phases in one step cycle.

Fig. 4 Snap shots of robot transitioning from ground to wall.

Climbing robots using adhesion force - Gecko robot

  3. Gecko robot

   As the gecko become on issue, a lot of climbing robots mimicking gecko were developed. These robots use dry adhesion force generated by pad which consists lots of microfibers. I will post the representative gecko robot, whose name is sticky bot [1].

   This robot is describing Gecko very well. This robot's system is comprised of 12 servo motor and 38 DOF (Fig. 1(a)). Four servo motors actuate segmented toes using a double-rocker linkage and steel cables in metal sleeves (Fig. 1(b)). It rolls-in to attach and rolls-out for detachment. As each force of setae is about dozens micro newton, it can be detached easily by rolling-out.

Fig. 1 (a) Stickybot and (b) Schematic of cross section view of Stickybot toe fabricated via Shape Deposition Manufacturing.

   It uses anisotropic adhesive for more useful to climb vertical surfaces (Fig. 6)

Fig. 6 Directional stalks comprised of 20 Shore-A polyurethane. Hairs measure 380 μm in diameter at the base. The base angle is 20◦ and the tip angle is 45◦.

   This robot can climb efficiently on smooth plane. But it is hard to climb wet or rough surface as micofibers can be damaged.
 To overcome these problems, it should be used in combination with other things.

Climbing robots using adhesion force - Biomimetic forces

  2. Biomimetic forces

  There are many animals which climbs wall, trees or something. It's obvious that they should overcome gravity force, them downward, to climb walls. They have been evolved various mechanism: 1) mechanical interlocking, such as hook and snap, 2) sucker, 3) frictional systems and 4) Adhesion force [1]. In this post, I will talk about mechanical interlocking, friction and adhesion forces.

  A. Hook

  Interlocking mechanism using hook is classified into long-term attachment and short term-attachment. Common long-term attaching mechanisms can be found in parasitic animals. A lot of hook-like attachment devices has been developed by parasitic mites. An example of hook for short-term attachment is tarsal claw used to interlock with surface texture (Fig. 1). Bees, wasps, butterflies and other insects can be locked with each other with different systems of hooks.

Fig.1 Tarsal claws of Tarantula [2]

  Animals use other interlocking mechanisms like snap, clamp and spacer. But, these are complicated or unsuitable for climbing robots.

  B. Friction

  The mechanism using friction force is based on surface profile and mechanical properties of materials, the combination of which results in an increase of the contact forces in the contact area. Benefits of systems are fast, precise and reversible. Dry adhesion force as well as friction force is used by Geckos. The main principle of this mechanism is that, with an increasing load, single outgrowths of both surfaces slide into gaps in the corresponding part. This results in an increase of lateral load acting on adjacent elements. High lateral forces lead to an increase of friction between single sliding elements.

  C. Adhesion

  The principle of adhesion force is increasing Van Der Waals force as enlarging contact surface using microfibers. Dry adhesion and wet adhesion are common in insects, spiders, lizards and frogs (Fig. 2(a)).  As the mass of the creature increases, the radius of the terminal attachment elements decreases. This allows larger number of setae to be packed into same area, hence increasing the linear dimension of contact and adhesion strength. Spiders and geckos can generate high dry adhesion, whereas beetles and flies increase adhesion by secreting liquids at the contacting interface (Fig. 2(b)).

Fig. 2 (a) Terminal elements of the microfiber attachment pads of a (i) beetle, (ii) fly, (iii) spider, and (iv) gecko, (b) The dependence of terminal element density on body mass. [3]

  1) Dry adhesion

  Dry adhesion is typically shown from the gecko. Early stage of this technology, engineers didn’t know that the force between feet of gecko and wall. A research showed that Van Der Waals force is key force in interaction between gecko feet and wall, replacing capillary adhesion based theory. It analyzed prediction and actual interacting forces in gecko setae (Fig. 3). Prediction based on Van der Waals force predicts actual result very precisely compared to capillary based prediction. This proves functionality of Van der Waals in biological adhesion between geckos feet and wall.

Fig. 3 Force of gecko setae on highly polarizable surfaces versus for surface hydrophobicity. (A) Wet adhesion prediction (B) van der Waals prediction. (C) Results from toe on highly polarizable semiconductor wafer surfaces differing in hydrophobicity. (D) Results from single seta attaching to highly polarizable MEMS cantilevers differing in hydrophobicity. [4]

  The following figure shows the schematic structure of Tokay gecko (Fig. 4). A lot of setae are typically 30–130 mm in length and 5–10 mm in diameter. The attachment pads on two feet of the Tokay gecko have an area of approximately 220 mm2. About 3 millon setae on their toes can produce a adhesive strength of approximately 20 N.

Fig. 4 Schematic structure of a Tokay gecko, including the overall body, one foot,  a cross-sectional view of the lamellae and an individual seta. ρ represents the number of spatula [5]

  2) Wet adhesion

  Frogs and arboreal salamander can attach to wet or flooded environments. Tree frog toe attachment pads consist of a hexagonal array of flat-topped epidermal cells of approximately 10 mm in size separated by approximately 1 mm wide mucus-filled channels; the flattened surface of each cell consists of a submicrometre array of nanopillars or pegs of approximately 100–400 nm diameter (Fig. 5). The pads are permanently wet by mucus secreted from glands that open into the channels between epidermal cells. They attach to mating surfaces by wet adhesion

Fig. 5 Morphology of tree frog toe pads. (a) White tree flog. SEM images of (b) toe pad, (c) epidermis with hexagonal epithelial cells, (d) high-magnification image of the surface of a single hexagonal cell showing peg-like projections, and (e) trans mission electron microscope image of cross section through cell surface [6]

Climbing robots using adhesion force - Introduction

1. Introduction

  Climbing robots are developed to help people. A lot of climbing robots are researched for various purpose, such as window cleaning [1], wall painting [2], exploration [3] and rescue operation. Climbing robots use forces, such as chemical or vaccum cups. Chemical adhesion, like hot melt adhesive, consumes low-energy when not moving, but costs high-energy when moving. Method using vacuum cups can generate high adhesion forces on smooth surface, but it's noisy, weaker, and energy inefficient on rough surfaces [4].

 In order to overcome these shortcomings, scientists are researching the Biomimetic adhesion mechanism. They found that eight fundamental attachment mechanisms have been used for climbing: 1) hooks, 2) lock or snap, 3) clamp, 4) spacer or expansion anchor, 5) suction, 6) dry adhesion, 7) wet adhesion, and 8) friction [5]. Especially, dry adhesion and friction are used for climbing robot. 

Functional principles of Biological attachment systems and physical effects involved

 Following posts, I will write about Biological attachment forces in detail, introduce robots using Biomimetic mechanism and their pros and cons.