# Patent

## Title
Method for robotic handling using thermo-reversible dry adhesives

## Abstract

One embodiment includes an application of multilayer thermo-reversible dry adhesives in robotic handling of objects.

## Background
This application claims the benefit of U.S. Provisional Application No. 60/925,418, filed Apr. 20, 2007.


FIELD OF THE INVENTION
The field to which the disclosure generally relates includes dry adhesives used in the robotic handling of objects.
BACKGROUND
Gecko feet pads, with nanohair structures on them, are examples of smart dry adhesives. The working principle of the Gecko adhesion is that the nanohair structure allows the foot pad to make maximum contact with a counter surface regardless of its roughness and chemical composition. This is accomplished by nanohairs that are relatively long and protruding from the foot pad at an angle so that adjacent nanohairs can contact the counter surface regardless of its topography. The maximum contact further allows for accumulation of millions of small van der Waals (in the range of microNewtons) interactions between the Gecko foot pad and the counter surface, leading to an overall adhesion force (pull-off force) of about 10 N/cm2. When the detaching force is employed in a peel-off mode, however, the complete detachment is achieved gradually by overcoming small adhesion forces corresponding to very small areas. Thus, the adhesion is easily reversed. Overall, the attractiveness of the Gecko adhesion lies in the combination of adhesive strength (10 N/cm2), reversibility, and the ability to adapt to a variety of surfaces in terms of both the surface roughness and composition. The above unique features of the Gecko adhesion has stimulated scientific research efforts to produce synthetic smart dry adhesives that work using the same principle as the Gecko feet. Up to now, the two best synthetic Gecko adhesives show maximum pull-off force of 3 and 10 N/cm2, respectively. Both adhesives suffer from severe adhesion loss after only one or two attaching/detaching cycles, as a result of breakdown of the nano structures. Often this occurs when adjacent elongated structures simulating the nano hairs of the Gecko foot pad bond to each other. In addition, synthetic Gecko adhesives are expensive to produce and large-scale manufacturing is practically too difficult.
SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION
One embodiment includes an application of multilayer thermo-reversible dry adhesives in robotic handling of objects.
Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1A illustrates a method according to one embodiment.
FIG. 1B illustrates a method according to one embodiment.
FIG. 1C illustrates a method according to one embodiment.
FIG. 1D illustrates a method according to one embodiment.



DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following description of the embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring to FIGS. 1A-1D, one embodiment of the invention includes a robot 10 having a thermo-reversible dry adhesive 12 on a portion of the robot, for example but not limited to on the tip of a robot arm 14. In one embodiment, at least one of a heating or cooling wire may be provided and embedded in the robot arm. In another embodiment, at least one of a heating or cooling wire may be attached to the thermo-reversible dry adhesive. In various embodiments, the thermo-reversible dry adhesive may comprise a dry adhesive layer 16 and a shape memory polymer layer 18.
Still referring to FIGS. 1A-1D, one embodiment includes a method of picking up an object 20 using the robot 10 having the thermo-reversible dry adhesive 12 on a portion of the robot, for example the robot arm 14. Referring to FIG. 1A, the dry adhesive layer 16 may first be heated by a brief electrical current through the heating wire to a temperature above the glass transition temperature of the shape memory polymer. Then the dry adhesive layer on the robot may be pressed against the intended object 20 to make contact, as shown in FIG. 1B. The dry adhesive layer may then be cooled down either by natural cooling or using a cooling wire. This causes a strong adhesive bond to be formed between the dry adhesive layer and the object. In one embodiment, the pull-off force may be approximately 40 N/cm2 relative to glass, but the pull-off force may vary depending upon the object. The strong adhesion between the object and the dry adhesive layer allows the object to be moved by the robotic arm.
As shown in FIG. 1C, in one embodiment, the robot arm 14 may be controlled to carry the object 20 to a target location 22. Then the object 20 may be released at the target location by heating the dry adhesive layer again using electrical current through the heating wire to a temperature above the glass transition temperature of the shape memory polymer, as illustrated in FIG. 1D. In one embodiment, the detachment of the object from the dry adhesive layer requires only a relatively small force, for example about 0.5 N/cm2. In another embodiment, the detachment requires only a small force of about 0.3 N/cm2. In another embodiment, the detachment requires a force not greater than 2 N/cm2.
In another embodiment, a Peltier thermal electric device, which is capable of both heating and cooling, may be utilized to heat and cool the thermo-reversible dry adhesive. The Peltier device may include a PN junction and may be constructed and arranged so that current flowing through the PN junction in one direction causes the device to heat one side thereof and current flowing through the PN junction in the opposite direction causes one side thereof to cool the device.
In one embodiment, the robot having a thermo-reversible dry adhesive on the tip of the robot arm may be used to handle a wide variety of large objects. For example, the robot may be used to handle windshield glass in an automotive assembly plant. In one embodiment, the dry adhesive is heated and pressed against the surface of the windshield glass. Upon cooling, a strong adhesive bond is formed and the windshield glass may be moved with the robot arm. Once the windshield glass is in place, the dry adhesive and robot arm may be detached from the glass by heating the dry adhesive.
In various embodiments, the dry adhesive layer 16 may be an epoxy elastomeric dry adhesive. In various embodiments, the shape memory polymer layer 18 may be an epoxy shape memory polymer. In various embodiments, the components of the dry adhesive or the components of the shape memory polymer may include a rigid epoxy and a flexible epoxy. The range of possible crosslinking chemistries which may be used to achieve a dry adhesive or shape memory polymer may include alpha, omega-diaminoalkanes, organic multi-carboxylic acid, anhydride, or catalytic (as in imidazole type) crosslinking reactions. There are many different ways to achieve the appropriate relationships between the molecular properties. For example, the dry adhesives or shape memory polymers may include a rigid epoxy, an epoxy extender, and a crosslinking agent; or a rigid epoxy, a flexible crosslinking agent, and a flexible epoxy; or a rigid epoxy, a rigid crosslinking agent, and a flexible epoxy; or a rigid epoxy, a flexible epoxy, and a catalytic curing agent; or a rigid epoxy, a crosslinking agent, and a diluent; or a flexible epoxy, a crosslinking agent, and a diluent; or a rigid epoxy and a flexible crosslinking agent; or a flexible epoxy and a catalytic curing agent; or a flexible epoxy and a crosslinking agent; and wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, the epoxy extender has one epoxide group, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride, and the diluent is a monoamine or a mono-carboxylic acid. In various embodiments, the catalytic curing agent (or catalytic cure) promotes epoxy-to-epoxy or epoxy-to-hydroxyl reactions. The catalytic curing agent may include, but is not limited to, tertiary amines, amine salts, boron trifluoride complexes, or amine borates. In one embodiment, the components of the dry adhesive may be present in an amount sufficient to provide, upon curing of the composition, a dry adhesive having a glass transition temperature (Tg) of −90° C. to 200° C. and having a pull-off strength of 1-200 N/cm2 from a substrate. In another embodiment, the dry adhesive may have a glass transition temperature of −90° C. to 25° C. In one embodiment, the components of the shape memory polymer composition may be present in an amount sufficient to provide, upon curing of the composition, an epoxy shape memory polymer having a change in storage modulus of 2 to 3 orders of magnitude before and after its glass transition.
One embodiment of the invention includes a multilayer thermo-reversible dry adhesive having a first layer made from an aromatic diepoxide (rigid epoxy), an aliphatic diepoxy (flexible epoxy), and a diamine curing agent, and a second layer made from an aliphatic diepoxy and an amine. In one embodiment the multilayer thermo-reversible dry adhesive has a curved structure.
Numerous shape memory polymers may be utilized in various embodiments of the invention. For example, starting with a typical aromatic diepoxy/diamine system with a Tg of about 90° C., the aromatic epoxy component is replaced systematically with an aliphatic diepoxy to yield a series of epoxy shape memory polymers with Tg's ranging from 3° C. to 90° C. As such, a shape memory polymer may be tailored for use with a dry adhesive as desired for a particular application operated within certain temperature ranges.
Some embodiments refer to a multilayer epoxy dry adhesive. It should be understood that more than two layers may be utilized. For example, there may be two or more layers of the shape memory polymer layer, which may be in a side by side relationship or an overlying relationship. Likewise, there may be two or more dry adhesive layers in a side by side relationship or an overlying relationship. As such, a device with custom or tailored properties may be manufactured.
One embodiment of the invention includes a method of making a multilayer thermo-reversible dry adhesive comprising heating 3.6 g of EPON 826 (the diglycidyl ether of bisphenol A epoxy monomer) to about 75° C. and mixing the same with 2.16 g of neopentyl glycol diglycidyl ether (NGDE) and 2.3 g of Jeffamine D-230, which is the curing agent poly(propylene glycol)bis(2-aminopropyl)ether. Jeffamine D-230 is a polyetheramine that is difunctional, primary amine with an average molecular weight of about 230. The primary amine groups are located on secondary carbons at the end of the aliphatic polyether chain. Jeffamine is available from Huntsman.
The mixture was then poured into an aluminum pan and cured in an oven at about 100° C. for 1.5 hours. Then a mixture of 2.6 g of NGDE and 1.15 g of an amine such as Jeffamine D-230 was poured into the aluminum pan on top of the first cured epoxy layer and cured for 1.5 hours at 100° C. In a third step, the oven temperature was raised to 130° C. for post-curing for about one hour. At the end of the post-curing, the cured two-layer epoxy was demolded. A double layer epoxy was obtained with the first layer which had a thickness of about 2 mm and functioned as a shape memory polymer with a glass transition of about 45° C. and a second layer as a dry adhesive having a thickness of about 1 mm. The yielded double layer epoxy structure had a slightly curved structure due to the thermal mismatch between the first and second layers. This curvature can also be created by specifically designed molds to achieve the curved structure.
The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.

## Claims

1. A method of moving an object comprising:
providing a robot having a robot arm and a thermo-reversible dry adhesive attached to the robot arm;
heating the dry adhesive and pressing the adhesive against an object to make contact;
cooling down the adhesive so that a strong adhesive bond is formed;
controlling the robot arm to carry the object to a target location; and
releasing the object comprising heating the dry adhesive again and using a force not greater than 2 N/cm2 to detach the robot arm and adhesive from the object.

2. A method as set forth in claim 1 wherein the adhesive bond has a pull-off force greater than 10 N/cm2.

3. A method as set forth in claim 1 comprising using a force not greater than 0.3 N/cm2 to detach the robot arm and adhesive from the object.

4. A method as set forth in claim 1 wherein the thermo-reversible dry adhesive comprises a shape memory polymer layer and a dry adhesive layer underlying the shape memory polymer layer.

5. A method as set forth in claim 4 wherein the dry adhesive layer comprises:
at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride.

6. A method as set forth in claim 4 wherein the shape memory polymer layer comprises:
at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride.

7. A method as set forth in claim 1 wherein the object comprises a sheet of glass.

8. A method as set forth in claim 1 wherein the robot further comprises a thermal electric device comprising a PN junction constructed and arranged so that current flowing through the PN junction in one direction causes the device to heat one side thereof and current flowing through the PN junction in the opposite direction causes one side thereof to cool the device, the thermal electric device being positioned to heat and cool the thermo-reversible dry adhesive.

9. A method as set forth in claim 1 wherein the object comprises an automotive windshield glass.