Soft shell grippers with highly tunable adhesion

Abstract

A soft shell gripper that relies upon suction (negative pressure) of an enclosed volume and wet and / or dry adhesion for purposes of robotic manipulation of objects for use in a myriad of fields and applications. The shell defines an enclosed volume to which negative pressure is applied following intimate contact with an object to be manipulated. The inclusion of spatially defined defects on the shell aids in tunability of the gripper.

Description

SU 2025-003BD 3215054W001SOFT SHELL GRIPPERS WITH HIGHLY TUNABLE ADHESIONCross Reference to Related Application

[0001] This application claims priority under relevant portions of 35 USC §119 and 35 USC §120 to US Patent Application Serial No. SN 63 / 700,636, filed: September 28, 2024, the foregoing application being incorporated by reference in its entirety.Statement Regarding Federally Sponsored Research or Development

[0002] This invention was made with government support under Grants CMMI 2239507 (WS) and CMMI 2141089 (WS), awarded by the National Science Foundation. The government has certain rights in the invention.Technical Field

[0003] This application is generally directed to the field of robotic manipulation, and more specifically directed to a soft shell gripper defined by an enclosed volume that enables tunable adhesion through the application of negative pressure / suction in relation to an object to be lifted and released.Background

[0004] Since the first industrial robot in the form of a multi-linkage arm was developed sometime during the 1950s, robotic manipulators have been developed and widely adopted for a number of industries. For example, robotic devices are now commonly found on automotive assembly lines, palletizing trays, and disaster sites, among others.

[0005] Over the last decade and along with the emergence of soft robotics, many soft grippers have been developed for compliant robotic manipulation of delicate objects. Examples have included pneumatically-powered multi -fingered soft grippers for food processing, universal robotic grippers based on jamming of granular materials, electroadhesion-based soft grippers for fabrics manufacturing, and gecko-inspired pillar arrays with dry adhesion for transfer printing and locomotion. As to the latter, the pursuit of highly tunable dry adhesion has very practical ramifications in the field of robotic32440119.1manipulation. More recently, several tunable dry adhesion technologies based on soft pillars have been developed for pick-and-place manufacturing applications. However, these more recently developed soft robotic grippers still suffer from critical performance metrics such as load capacity, energy consumption, activation time, and reliability. While grippers based on mechanical interlocking and suction effect have been adopted in various industries, soft grippers that can handle small and delicate objects reliably and robustly are yet to be invented. That is, as of today, it is still challenging to manipulate small, delicate, and curved objects safely and reliably, especially for those lightweight parts encountered in advanced electronics and precision devices. In this regard, it would be even more advantageous to develop a soft gripper apparatus that can equally utilize either or both dry or wet adhesion without significant modification.

[0006] As to various existing grippers, there are other difficulties and issues that have been encountered. For example, the high adhesion performance used by pillars in object picking relies upon an accurate alignment of the pillar body, as well as clean contact surfaces that are substantially free of contaminants, each of which are cumbersome to realize in practical applications. In addition, there are additional challenges for compliant manipulation of small objects in the releasing motion instead of the picking motion of these robotic devices. High tunability of adhesion is highly desirable such that easy release can be guaranteed. In addition, for certain industries, such as those in the advanced electronics and precision device fields, the presence of high electrical and magnetic fields can lead to malfunction of the manipulated small parts. Therefore, activation of gripper devices through electrical current and / or the presence of electrostatics should also be avoided.

[0007] Accordingly, there is a desired need to provide a gripper apparatus that is not encumbered by the above-noted issues, which is easy and versatile in terms of use and application and can be used to grip and lift and place objects using tunable wet or dry adhesion.Brief Description

[0008] Therefore and according to at least one aspect, there is provided a tunable adhesion soft gripper apparatus comprising a flexible shell made from a deformable fluid impermeable elastomeric material, the shell having an enclosed volume and an exteriorsurface, wherein a negative pressure applied to the enclosed volume while the shell is placed in compressive contact with an object creates an adhesion force enabling the object to be lifted and placed by the apparatus.

[0009] In at least one embodiment, the soft gripper apparatus has a hemispherical shape wherein the object of interest can be defined by a planar or curved configuration and wherein the adhesion between the object of interest and the shell gripper is one of dry adhesion or wet adhesion, or dry and wet adhesion.

[0010] According to at least one version, the apparatus comprises at least one defect provided at a tip of the flexible shell to enable tunability of the apparatus. In one embodiment, the object of interest is a plate having at least one defect.

[0011] In one or more versions, the object of interest and the flexible shell can be angularly misaligned with respect to one another, wherein the angular misalignment can be as great as 10 degrees.

[0012] According to another aspect, there is provided a method for tuning the adhesion of a gripper apparatus, the gripper apparatus comprising a retaining structure supporting a flexible shell having an enclosed volume, the method comprising: compressing the outer surface of the shell into contact with an object to be lifted in order to create deformation of the shell; and applying negative pressure to the enclosed volume to create a suction force in combination with dry adhesion of the shell with the object.

[0013] In at least one version, the flexible shell is defined by a hemispherical shape, wherein the object of interest can be defined by a planar or curved configuration.

[0014] The adhesion between the flexible shell and the object of interest can be that of dry adhesion, wet adhesion, or a combination of wet and dry adhesion.

[0015] According to at least one version, the method further comprises providing at least one defect on the exterior surface of the flexible shell. In at least one embodiment, the at least one defect is provided on a tip of the shell.

[0016] In addition, the object of interest and the flexible shell can be angularly misaligned with respect to one another prior to handling the object. According to at least one embodiment, the angular misalignment is as great as 10 degrees.

[0017] In terms of operation, the presence of an object such as but not limited to an adhesive substrate against a negatively pressurized soft hemispherical or other suitably shaped shell can significantly delay buckling of the shell, in which the adhesion strengths exhibited by this buckling-delayed shell is orders of magnitude higher (~ lOOx) than that of a non-pressurized shell. This strong adhesion under low negative pressure (~10 kPa) is not affected by misalignment (at least up to about 10 degrees). Furthermore, this adhesion does not significantly degrade even when the object to be handled by the gripper is dirty with the presence of surface contaminants. The unexpected and much increased adhesion strength of a pressurized soft shell can be attributed to the combined effect of adhesion and suction at the contact interface.

[0018] According to at least one version, an elastomeric shell gripper is herein provided for purposes of universal manipulation of small objects, enabled by adhesion of negatively pressurized soft hemispherical shells with adhesion tunability that can be further amplified by specific planting of artificial defects. It can be shown that almost infinite adhesion change can be achieved using standard quasi static mechanical testing (the fixed-displacement condition), and that dry adhesion change over two orders of magnitude (-800 times) can be achieved under negative pressure of -5 kPa within fractions of a second in manipulation demonstrations (the fixed-load condition). The activation mechanism is purely mechanical, involving low-pressure pneumatics, shell buckling, dry adhesion, and a suction effect, while not at all involving electrical and / or magnetic fields. Small lightweight objects, whether flat or curved, can be accurately and reliably picked and placed by the herein described shell gripper. Advantageously, these soft grippers exhibit unchanged adhesion in spite of misalignment (up to about 10 degrees) due to their unique geometry. These grippers are also robust against surface contaminants thanks to the suction effect that is produced at the contact surface. Universal manipulation of small objects (characteristic length -0.1-1 mm) can be achieved through the herein described gripper devices, and systems that include theherein described grippers have the potential to be scaled down for universal manipulation of smaller objects.

[0019] According to at least one version, pristine shells can be modified by introducing a judicially placed zone of artificial defects at the shell tip to increase the tunability of the dry adhesion of these soft-shell grippers to almost infinity (the fixed displacement condition). The shells with an artificial defect zone still provide strong adhesion despite the presence of surface contaminants, as would be encountered in real application scenarios. In accordance with at least one embodiment, a gripper apparatus in accordance with the herein described invention can be used to manipulate (i.e., pick and place) weights of the same surface smoothness as low as 31 mg and as high as 25.1 g, evidencing an adhesion tunability of ~800x in manipulation of objects (the fixed load condition). As such, the herein described soft-shell grippers provide a promising platform for accelerating the adoption of soft grippers in various industries.

[0020] An advantage realized by the present invention is that literally any object, regardless of geometry, can be handled and manipulated, including objects with flat or curved (convex, concave, etc.) surfaces, wherein each object can be easily picked and placed using the herein described gripper apparatus, and even in spite of significant misalignment between the shell gripper and the object. In addition, the herein described gripper apparatus can be used via dry or wet adhesion, further demonstrating versatility and applicability of the apparatus to literally any field that can utilize robotic manipulation.

[0021] These and further features and advantages will be readily apparent from the following Detailed Description, which should be read in conjunction with the accompanying drawings.Brief Description of the Drawings

[0022] FIG. 1(a) depicts a working principle of an examplary soft shell-based gripper made in accordance with aspects of the present invention, for purposes of object manipulation, depicting various sequential steps of a pick and place process using the shell-based gripper;

[0023] FIG. 1(b) depicts side elevational views of a shell-based gripper apparatus made in accordance with aspects of the present invention for purposes of picking and placing an object of interest using the gripper apparatus;

[0024] FIG. 1(c) depicts side elevational views of a shell-based gripper apparatus made in accordance with aspects of the invention, these views depicting various objects of interest that are gripped and lifted by the gripper apparatus;

[0025] FIG. 1(d) depicts side elevational views of a shell-based gripper apparatus made in accordance with aspects of the invention, illustrating objects of interest as lifted to demonstrate maxima and minima limits of the gripper apparatus;

[0026] FIG. 1(e) depicts side elevational views of dimensionally scaled versions of shell-based gripper apparatuses made in accordance with the invention and in operation for purposes of handling various sized objects of interest;

[0027] FIG. 2(a) depicts load displacement curves for an exemplary shell-based gripper made in accordance with aspects of the invention depicting displacement (preload) versus force F for various negative pressures being applied to the gripper;

[0028] FIG. 2(b) graphically depicts contact area evolution with force during pressurization and unloading steps of the shell-based gripper of FIG. 2(a) for various applied negative pressures;

[0029] FIG. 2(c) depicts graphically a relationship between maximum adhesion force Fmax and applied negative pressure for a shell-based gripper made in accordance with various aspects of the invention;

[0030] FIG. 2(d) graphically depicts the effects of thickness on the maximum adhesion force Fmax of a shell-based gripper made in accordance with aspects of the invention;

[0031] FIG. 3(a) schematically depicts major events in adhesion characteristics of a soft shell gripper made in accordance with aspects of the invention under negative pressure against a substrate, the latter having a specified defect;

[0032] FIG. 3(b) are respective side and bottom views of a soft shell-based gripper made in accordance with aspects of the invention as against a substrate having the specified defect of FIG. 3(a);

[0033] FIG. 3(c) depicts experimental results of three (3) exemplary shell gripper samples, each sample having different thicknesses h that are disposed against substrates having specifically disposed and sized defects thereon;

[0034] FIG. 4(a) schematically depicts a defined angular misalignment between a shell-based gripper made in accordance with aspects of the invention and an object of interest to be picked up and placed by the shell -based gripper;

[0035] FIGS. 4(b) and 4(c) depict a graphical comparison between measured adhesion strengths of prior art gripping devices with varied soft shell-based grippers that are made in accordance with aspects of the invention;

[0036] FIG. 5(a) depicts a shell gripper sample made in accordance with aspects of the invention having a predefined defect zone and more specifically showing a side view, bottom view, and an enlarged meridional section view, respectively, thereof;

[0037] FIG. 5(b) depicts a force-displacement curve of the shell-based gripper sample of FIG. 5(a), under various applied negative pressures applied to the interior volume;

[0038] FIG. 5(c) depicts a graphical plot of a maximum adhesion force of shellbased gripper samples under different negative pressures, the samples having a no defect zone, as compared to those samples having predefined defect zones;

[0039] FIG. 5(d) depicts a force displacement curve for a shell gripper sample made in accordance with aspects of the invention, the sample having a predefined defectzone under negative pressure and further depicting imaged versions 1 - 4 taken at specific positions of the depicted force displacement curve;

[0040] FIG. 6(a) - 6(c)depict an exemplary soft shell-based gripper made in accordance with aspects of the invention comparatively illustrating adhesion to a dry plate, a plate having a water droplet disposed thereon, and the plate having a water layer disposed between the shell-based gripper and the plate;

[0041] FIG. 7(a) depicts a side elevational view of a shell -based gripper partially immersed in water;

[0042] FIG. 7(b) is a schematic depicting forces acting upon the shell of FIG. 7(a) when immersed in the water;

[0043] FIG. 7(c) graphically depicts maximum pull off force as a function of the activated negative force under the conditions shown in FIGS. 6(a)- 6(c); and

[0044] FIGS. 8(a)- 8(g) depict side elevational views of dimensionally scaled versions of shell-based gripper apparatuses made in accordance with the invention and in operation for purposes of handling various sized objects of interest.Detailed Description

[0045] The following description relates to various examplary embodiments of various soft shell-based gripper apparatus that relies upon suction (negative pressure) of an enclosed volume and adhesion (whether dry or wet) for purposes of robotic manipulation of objects for use in a myriad of fields and applications. Each of the various embodiments described herein are directed to a shell(s) commonly having a hemispherical or substantially hemispherical shell shape or configuration. It will be readily apparent, however, that there are numerous variations and modifications that can be made in accordance with the tenets of the herein described invention. For example, the shell gripper can assume other curved shapes for purposes of defining a suitable enclosed volume that can be acted upon (deflated) under negative pressure.

[0046] With reference to FIG. 1(a), an operation procedure for a shell-based gripper apparatus made in accordance with aspects of the present invention in terms of picking and releasing an object is now described. An essential feature is the application of negative pressure to an enclosed volume of the shell in order to increase the adhesion of a curved shell, which is otherwise much lower when non-pressurized. In this figure, the remainder of the gripper apparatus, including a retaining structure for the flexible shell, application of a preload to an object of interest, and a suitable means for creating and maintaining a negative pressure within the enclosed volume of the shell is not shown. Accordingly, the discussion of this operation procedure relates to the shell itself, which is referred to synonymously throughout as either “the shell” or “the shell gripper” or the “shell-based gripper.”

[0047] First, a nonpressurized shell gripper 20 is controlled to approach an object of interest 50, wherein the outer surface 22 of the shell 20 is acted upon through the use of an externally applied mechanical force so as to press against the object. This latter force creates a preload and a limited amount of deformation of the flexible shell. The shells described herein are fabricated from vinyl polysiloxane (VPS), which can be suitably molded or otherwise formed, each shell 20 being commonly defined by an internal volume 24, as well as a circular radius R, a thickness h and a height dimension formed in a hemispherical configuration. The VPS used in the described embodiments can include at least two (2) types, namely, VPS-8 which is pink in color and relatively soft, and VPS-32, which is green in color and relatively rigid. It will be understood that other suitable elastomeric materials can be utilized, such as polydimethylsiloxane (PDMS) and Ecoflex. When a sufficiently large contact area has been created between the shell 20 and the object 50, a negative pressure having a magnitude that is above pcris applied as shown in the second inset of FIG. 1(a). For purposes of discussion, pcrrepresents the critical buckling pressure of the flexible hemispherical shells 20 without contact to a substrate. Upon the application of negative pressure to the enclosed volume 24, the force between the shell 20 and the object of interest 50 changes from compression to tension (adhesion) with the resulting adhesion force becoming significantly much higher than that of a non-pressurized shell.

[0048] With this much increased adhesion and when the gripper retracts, the object 50 can be picked up and moved for deposition, as shown in the third inset of FIG. 1(a) with the negative pressure being maintained. To release the object, the negativepressure is removed from the internal volume 24 of the shell 20, thereby causing adhesion between the hemispherical shell 20 and the object 50 to revert to the much smaller value, which is a mere fraction of that of a hemispherical Johnson-Kendall- Roberts (JKR) solid. The shell gripper 20 thus cannot sustain the weight of the object 50, which is considerably greater than its non-pressurized adhesion force, and the object 50 is released, as depicted in the final inset of FIG. 1(a). As a result, the pick-and-place manipulation of the shell gripper 20 is completed. Note that during pick-and-place manipulation, the load applied to the gripper 20 (that is, the weight of the object 50) is constant, which is deemed as the fixed-load condition.

[0049] FIGS. 1(b) - 1(e) illustrate various demonstrations of another exemplary shell-based gripper 120 made in accordance with aspects of the present invention. A gripper apparatus 110 includes a retaining structure 114 that is sized and configured to support the shell-based gripper 120, as well as an arm 116 or other suitable structure coupled to the retaining structure 114 and including a means (not shown) for providing and maintaining negative pressure within the enclosed volume 24, FIG. 1(a) of the shell 120, which according to this version is made from VPS and is also defined by a hemispherical configuration that is further defined by a thickness h and a height dimension. In one version, a syringe can be utilized to create the required negative pressure or alternatively, an arm having a channel can be attached to any suitable pressure apparatus. The apparatus 110 further is capable of producing and applying a preload in the form of a compressive force acting downwardly relative to an object of interest. According to this embodiment, a load cell 119 is disposed above the retaining structure 114 and aligned vertically with the center axis of the shell gripper 120. It will be readily apparent that other devices can be employed for delivering the preload. As discussed herein, the preload creates a limited amount of elastic deformation in the flexible shell-based gripper 120.

[0050] First and as shown in FIG. 1(c), the working principle of the shell gripper 120 is again shown for the pick and place of a specific object of interest, which in this example is an acrylic plate 150 having an array of defects, which can include dimples or holes, by way of example. The outer or exterior surface 122 of the shell 120 of the herein described gripper apparatus 110 is initially brought in close proximity to the top surface of the acrylic plate 150, as shown in I. The shell gripper 120 is then compressed orpreloaded against the top surface of the object 150 using mechanical pressure applied to the gripper by the load cell 119. A suitable amount of pressure that produces shell deformation (e.g., about 3 mm) is applied, although this parameter can vary, for example, depending upon the object to be lifted, among other factors. Subsequently, negative pressure is applied to the enclosed volume 24, FIG. 1(a) of the shell gripper 120, as shown in II, thereby creating a suitable adhesive force. The gripper apparatus 110 is then, according to this demonstration, lifted with the plate 150 being adhered to the gripper 120 and held above a supporting surface or substrate 160 on which the plate 150 was initially disposed, as shown in III, for a predetermined period of time (e.g., 10 seconds). The gripping apparatus 110 and the object 150 are then lowered onto the substate 160, as shown in IV, and the pressure within the enclosed volume 24, FIG. 1(a) of the shell 120 is balanced with atmospheric or ambient pressure. Finally, and as shown in V, the gripper apparatus 110, including the shell-based gripper 120, is retracted upwardly from the substrate 160, in which the acrylic plate 150 is released back onto the substrate 160. For purposes of the foregoing embodiment, the exemplary shell-based gripper 120 is defined by a diameter of 20.0 mm, with the acrylic plate 150 being defined by 50 x 50 mm cross section of the top surface and a thickness of 1.65 mm, with a weight of 4.85g. The array of specifically disposed defects applied to the acrylic plate 150 according to this specific embodiment each have a diameter of about 1 mm with a depth of between 0.9 - 1.4 mm, and a spacing between the defects of 3 mm. It will be understood that each of the abovenoted parameters can be suitably varied.

[0051] FIG. 1(c) depicts other exemplary shell grippers 220 picking up a number of different and varied objects to demonstrate overall versatility. As shown, these objects of interest include, but clearly are not limited to a blueberry 170, a green grape 174, a cherry tomato 178, an acrylic hemispherical shell 182, a SD card 184, and an acrylic plate 188, the latter including an array of holes. In this described embodiment, the shell-based gripper handling each object of interest is fabricated from VPS-8 and has a diameter of 20 mm. As in the preceding, the gripper according to this embodiment is supported by a retaining structure that is sized and configured for retaining the gripper, as shown, and further includes an arm linking the enclosed volume of the shell gripper to a pressure source (not shown), as well as a load cell or other means capable of applying a compressive vertical force (preload) to the shell gripper. As to the particulars of each noted object, the blueberry 170 weighs 1.84 g and has a curvature of 30.1 m’1; the green grape 174 weighs 3.6 g and has a curvature along its major axis of 42.9 m'1; the cherrytomato 178 weighs 6.22 g and has a curvature of 44.48m-1; the acrylic shell 182 weighs 1.49 g and has a diameter of 20 mm; the SD card 184 weighs 1.77 g and has a cross section of 32 x 24 x2 mm; and the acrylic plate 188 having holes / defects has 3 holes each having a diameter of 1 mm and a spacing of 3 mm. The overall versatility of the herein described gripper is clearly demonstrated by the foregoing in which objects of varying size and geometry can easily be handled.

[0052] FIG. 1(d) illustrates another exemplary gripper apparatus that includes a shell-based gripper 220, the latter being made from VPS-32 with a diameter of 20mm and a thickness of -1.1mm, and the maximum and minimum limits (weight) of 452.81 g and 0.71 g that can be picked up and released, respectively. FIG. 1(e) illustrates respective shell-based gripper apparatus 320, 330, each having a shell-based gripper made from VPS-8 and having smaller dimensions than the preceding versions that are suitably configured for picking up other smaller and arguably more delicate objects of interest, in this instance, a salmon egg 340 and black tobiko roe 344, respectively. According to this embodiment, the diameter of the shell gripper 320 picking up the salmon egg 340 is 10 mm and the diameter of the shell gripper 330 picking up the roe 344 is 3 mm, depicting the scalability and versatility for the robotic handling and manipulation of various objects. The salmon egg 340 has a diameter of 6.6 mm and weighs 232 g, while the roe 344 has a diameter of 2.1 mm, with each roe weighing 5.3 mg.

[0053] The following describes adhesion characterization experiments that were conducted for various shell-based grippers made in accordance with aspects of the invention. In each of these experiments, the various shell grippers were placed under negative pressure against a fixed glass substrate on a suitable testing apparatus (not shown), such as an Instron Microtester. More specifically and for use in these tests, a plurality of hemispherical shells was fabricated, each of the shells being fabricated / molded from VPS-8 and having a diameter of 20mm, a thickness h of 1 ,32mm, and a critical buckling pressure pcr= 5.88 kPa. As shown by the results of FIGS. 2(a) - 2(c), each of the fabricated shells were tested under various applied negative pressures ranging from 0 kPa to 1.8 pcr. The loading by the testing apparatus was in displacement control and quasistatic, which is approximately the fixed displacement condition for adhesion characterization. Negative pressures were applied after each shell had been elastically compressed or preloaded into contact with the glass substrate by adisplacement 5 =2 mm, 2.5mm, or 3mm, as shown in FIG. 2(a). It can be observed that upon application of the negative pressure, the contact area between the glass substrate and the shell decreased by a small amount (FIG. 2b). In the meantime, the force between the shell and the substrate dropped sharply (FIG. 2a). For certain negative pressures 1.2- 1.8 pcr, the force changed from compression (positive) to adhesion (negative), as shown in FIG. 2(a), while for applied pressures ranging from 0 to 1.0 pcr, such change was not observed (FIG. 2(a)). The load-displacement curves of FIG. 2(a) clearly evidence adhesion tunability as high as ~60x before and after the application of negative pressure ~1.5 pcr, from 3 mN to 180 mN. In addition, the high adhesion state was sustained over a large displacement range during retraction of the shell gripper (FIG. 2(a)), which permits stable manipulation under the fixed load condition. It is believed that the much-enhanced adhesion at 1.2-1.8 pcrwas the result of delayed buckling of the hemispherical shells under negative pressure in the presence of the adhesive substrate.

[0054] FIG. 2(b) depicts the contact area evolution concurrently occurring during the various loading sequences of FIG. 2(a). It is noted that the instable catastrophic failure beyond a certain displacement threshold is always induced by shell buckling. FIG. 2(c) plots the maximum adhesion force, Fmax as defined in FIG. 2(a), against varied applied pressure for a VPS-8 shell gripper having a diameter of 20mm and a thickness of 1.32mm. It can clearly be seen from this latter plot that only negative pressure with a sufficient magnitude that is larger than pcrcan bring about enhanced adhesion of the thin shell.

[0055] The effect of wall thickness on the flexible shell under negative pressure has also been investigated. FIG. 2(d) shows that when the wall thickness of the shell h is relatively small, the maximum adhesion force is also quite small. This might be attributed to the fact that when the thickness dimension h is very small, the whole region in contact is too compliant for buckling to play a significant role. As the thickness h increases, however, the maximum adhesion force increases quickly. According to this embodiment, the maximum adhesion force can be as high as 300 mN for a VPS-8 shell having a 20mm diameter. However, it has been determined that further increases in the thickness h of the shell gripper beyond a certain range ( / R> 0.2) does not result in further increase in the maximum adhesion force Fmax. The reasons for these observations have been further examined using experimentation and modeling as follows.

[0056] The following qualitatively explains the experimentally observed much- enhanced adhesion of the pressurized hemispherical shells made in accordance with aspects of the present invention. In various adhesion characterization experiments that were performed, it was observed that the catastrophic failure of pressurized shells occurred during retraction when the unattached portion of the shell buckled suddenly and the interfacial edge crack propagated unstably across the interface. When the applied pressure was slightly above pcr, (e g., 1 .1 >c;), the adhesion was not enhanced during the unloading cycles. At higher pressures, for example 1.5 pcr, enhanced adhesion occurs before simultaneous buckling and catastrophic failure across the interface upon retraction of the shell. In addition, and significantly, the catastrophic interfacial failure always initiated from the edge of the shell. This observation greatly simplified modeling efforts as other complicated interfacial phenomena such as suction, while important, was not deemed as relevant in determining the advancement of an interfacial edge crack under applied negative pressure and retraction.

[0057] The role of suction effect within the contact area was effectively demonstrated using substrates with individual defects in the adhesion characterization testing. With reference to FIGS. 3(a) - 3(c), characterization experiments were conducted of a number of pressurized hemispherical shells 320 made in accordance with aspects of the invention against fixed polycarbonate (PC) substrates, the latter objects 350 each having a small through hole 354 (defects) of varying sizes formed therein. More specifically and according to these examples, the holes of the various substrates tested had diameters of 1 mm, 2 mm, and 3 mm, respectively.

[0058] Similar to prior adhesion characterization tests that were performed on smooth substrates, the and referring to the schematic view of FIG. 3(a), each of the shells 320 were compressed or preloaded against a PC substrate 350 with a hole 354 by a displacement of 3mm first, with the center of the hole 354 and the center of the shell hemisphere being vertically aligned with one another. An internal negative pressure was then applied and the corresponding interfacial crack growth emanating from the through hole 354 of each substrate 350 was monitored. The detached area can be imaged and the largest radius of the debonded area a can be determined as the center crack size. As shown, when the applied negative pressure was higher than a critical value pcr, the centercrack propagated unstably, and the interface failed catastrophically while buckling of the shell 320 happened at the same time or ensues immediately, as shown in the last inset of FIG. 3(a). The critical center crack size at the last moment before catastrophic failure is denoted as ac. It is reasoned that the tip of the shell 320 that covers the small hole 354 in the substrate 350 is mostly flat given its small size. With this assumption, well- established membrane blister test results were used in order to interpret the hole test results, as shown in FIG. 3(c). Here, the critical pressure pB can be related to the critical crack size acand the surface energy y between the VPS shell gripper and the PC substrate using the following equation:in which E and v are Young’s modulus and Poisson’s ratio, respectively, for the fabricated shell material VPS-8, and h being the thickness of the shell. These results demonstrated that when the hole is sufficiently small (a < ac), or for any given applied pressure within a threshold (p < PB), the crack emanating from the hole either does not grow or grow stably, due to the presence of adhesion between the substrate and the shell. The foregoing indicates that, for interfaces contaminated with small enough defects, even without suction effect within the contact region, strong enhanced shell adhesion under negative pressure still occurs. It should be noted that there may be instances in which the shell buckles first with an edge crack propagating catastrophically towards the center instead of failing by a center crack propagation. In these latter cases, as expected, the pcr- acrelationship no longer follows the member blister test as governed in Eqn. 1. Yet still, in all cases, the shell gripper exhibits enhanced adhesion when compared with a nonpressurized shell against a smooth substrate.

[0059] Due to their unique hemispherical or semi-hemispherical geometry, the herein described shell-based grippers are much more tolerant for misalignment with an object or interest to be handled than previously reported pillar designs, the latter designs being previously described. With reference to FIGS. 4(a) - 4(c), a comparison was made to generally and comparatively quantify the misalignment tolerance of adhesion of soft solid pillars, soft hollow pillars, and soft shells, the latter being made in accordance with aspects of the invention, in order to demonstrate the advantage of the shell-based grippers in this critical performance metric. FIG. 4(a) schematically illustrates an angularmisalignment between a shell-based gripper 420 and an object of interest 450, the misalignment creating an angle (0) relative to the horizontal, as shown. FIGS. 4(b) and (c) present the adhesion characterization results of these three (3) types of shell-based grippers made from the same elastomer VPS-8, with the same radius of 3 mm for the soft hollow pillars and soft solid pillars, and a radius R of 10 mm for each of the flexible soft shells. As can be seen in this example, the adhesion strengths of the shell-based grippers made in accordance with the present invention were substantially constant for misalignments ( ) up to 10 degrees, regardless of being non-pressurized or pressurized, while the adhesion strengths for soft solid pillars and soft hollow pillars degraded significantly after a misalignment (0) of merely 2 degrees. It was observed that the soft hollow pillars were only slightly better than the soft solid pillars in this regard. Accordingly, these results clearly demonstrate the advantage of misalignment tolerance of shell grippers, when compared with conventionally known soft solid pillars and soft hollow pillar designs. This specific advantage enables shell grippers as described herein to be practical to adopt.

[0060] According to a further embodiment, the reliability and robustness of the herein described shell grippers can be further enhanced in terms in object manipulation by demonstrating tunability of their adhesion characteristics. Such tunability can be realized according to one version by increasing the upper bound of the adhesion strength, and when the shell is pressurized for object pick-up. The tunability can also be realized by decreasing the lower bound of the adhesion strength when the shell is non-pressurized for object release. It is imperative that these two efforts stay independent and do not cancel the effect of one another. First, the approach of defects planting for decreased lower bound of tunable dry adhesion of these hemispherical shells is analyzed. It is known that at the object releasing step, the hemispherical shell is non-pressurized and the critical contact area at pull-off is small (~1.6 mm for a thin VPS-8 shell having a 20 mm diameter). By planting defects upon the shell tip in a small area (e.g., a substantially circular area with a diameter of 3 mm) containing the critical contact area, the adhesion at the releasing step will be even smaller. It would be ideal if the presence of this small defect zone did not significantly affect the upper bound of tunable adhesion under negative pressure, such that tunability is increased.

[0061] A CO2 laser (Epilog Laser Cutter, 40 Watts) or other suitable apparatus can be used to pattern the VPS-8 shell tip 520 according to this specific embodiment. Substantially circular areas of different diameters, 3 mm, 5 mm, and 8 mm, were tested. FIG. 5(a) shows a laser-processed VPS-8 shell 520 with an enlarged view of the laser- processed circular region 526 with side bottom and meridional section views being shown. Arrays of tapered columns 530 were formed after laser processing, each column 530 having a depth of ~60 um and a width of -90 um. Adhesion characterization experiments demonstrated that the non-pressurized adhesion of these laser-processed shells 520 is almost zero, while their adhesion under 1.5 pcris still much enhanced compared with the non-pressurized case. The load displacement behavior of shells with a defect zone 526 is similar to the pristine shell (FIG. 5(b)). For shells having a 3 mm defect zone, their adhesion is comparable to those pristine shells, -120 mN, which represents a tunability close to infinity. For shells with an 8 mm defect zone, their adhesion under 1.5 pcris -150 mN. While these are lower than the upper bound of dry adhesion of pressurized pristine shells of the same size and thickness (-180 mN), this level of adhesion was still much higher than the lower bound that is virtually zero. Thus, a defect zone 526 that is large can significantly decrease the lower bound of adhesion. The fact that the shell having the 8mm defect zone has very high adhesion when pressurized guarantees misalignment tolerance for defected shells (referring back to FIGS. 4(b) and 4(c)).

[0062] With continued reference to FIGS. 5(a) - 5(d), the contact area evolution during pressurization and unloading steps were monitored in order to gain additional insights into the underlying physics behind observed increased adhesion tunability. The load displacement curve has been plotted in correspondence with the contact delamination process for the shell with 8 mm defect zone when the applied negative pressure is 1.0 pcr. When retraction starts, the defect zone is still partially in contact due to the roughness generated by laser processing, and the adhesive force slowly increases and plateaus to -25 mN as retraction increases and 5 decreases from 3mm to ~2mm (Steps 2-3 in FIG. 5(d)). At around 6 = 1.8mm, the adhesion force increased quickly to the maximum value of -60 mN while the contact area shrinks in the defect zone, and a center crack grew radially (FIG. 5(d)). During this center crack growing process, the edge crack front stayed more or less the same and the true contact area approached almost zero (Steps 3-4 in FIG. 5d), before the edge crack and the center crack merged andcatastrophic failure happened across the interface (Step 4 in FIG. 5(d)). It is then clear that the more than doubling of dry adhesion during retraction comes from contribution from suction effect. Similarly, those shells with smaller defect zones exhibit similar adhesion level to that of pristine shells under pressure because of suction effect. These experimental results clearly proved the contribution of suction effect to the enhanced dry adhesion of pressurized soft shells.

[0063] It is found that in pick-and-place demonstrations, the adhesion tunability is lower than that in adhesion characterization tests on an Instron machine, which mostly is caused by the increase of lower bound adhesion. For instance, for the 20 mm diameter shell grippers that are tested in this study, the lowest dead weight glass substrate that can be released is ~3 mN, whereas under testing apparatus (e.g., Instron), the adhesion force is measured to be roughly zero. The reason for this latter discrepancy is attributed to electrostatic effect that is more dramatic under the fixed load condition. Accordingly, it is therefore inferred that if the shell gripper is made of highly conductive elastomeric materials in lieu of or in combination with an elastomeric material, such as VPS, that is used in the embodiments described, this electrostatic effect will be significantly reduced to a negligible level, and the tunability will increase.

[0064] Each of the hemispherical elastomeric shells previously described herein were fabricated using commercially available elastomer vinylpolysiloxane (VPS), following a commonly used mold-and-replica method. Another ultrathin layer of VPS can be deposited onto the mold-cast shells to smoothen out the roughness.

[0065] Each of the foregoing examples has been generally directed to aspects of dry adhesion between the gripper and the object of interest. However, the herein described shell gripper is equally capable of picking and placing objects via wet adhesion. With reference to FIGS. 6(a)-6(c), there is shown a hemispherical shell 620 having an enclosed volume 624, wall thickness h, and height dimension. The shell 620 is fabricated from VPS and has a radius of 10 mm, a diameter of 20 mm and a wall thickness of 1.5 mm. The shell 620 is shown schematically as retained in a gripper apparatus including a load cell 619 and means for creating a negative pressure within the enclosed volume 624 for three (3) specific situations. More specifically, the shell gripper 620 is shown relative to a dry glass substrate 634, FIG. 6(a), a water droplet 640 disposedon the glass substrate 634, and a water layer 650 between the substrate 634 and the shell gripper 620.

[0066] FIGS. 7(a) - 7(c) depict a side elevational image of a hemispherical shell 720 partially immersed in a water layer 750. As shown in FIGS. 7(a) and the schematic FIG. 7(b). a meniscus 745 forms between the exterior surface of the shell 720 and the water layer 750. As in the preceding, the flexible shell 720 is part of a gripper apparatus that includes a retaining structure 714 and a load cell 719, the latter capable of providing a compressive preload. FIG. 7(c) depicts comparative graphical plots of negative pressure applied to each of the shells 620 720 for the conditions shown in FIGS. 6(a) - 6(c). As clearly indicated, the herein described shells exhibit similar characteristics in terms of adhesion irrespective of whether the adhesion is dry or wet.

[0067] FIGS. 8(a)- 8(g) illustrate yet another gripper apparatus defined by a hemispherical shell 820, a retaining structure 814 and load cell 819, as well as an extending arm 812 and means (not shown) for creating a negative pressure within the enclosed volume of the shell 820. The apparatus shown demonstrates the ability to handle (pick and place) various objects having curved or other geometries that include chocolate covered almonds 860, hard boiled egg 864, soft wet tofu 868, a half-peeled quail egg 872, a concave egg white piece 876, a grape 880 and edible tablets 884.

[0068] While the invention has been described in terms of particular variations and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the variations or figures described. In addition, where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with one or more variations of the present invention. Additionally, certain of the steps may be performed concurrently in a parallel process, when possible, as well as performed sequentially as described above. Therefore, to the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the inventions found in the claims, it is the intent that this patent will cover those variations as well.

[0069] To the extent that the claims recite the phrase “at least one of’ in reference to a plurality of elements, this is intended to mean at least one or more of the listed elements, and is not limited to at least one of each element. For example, “at least one of an element A, element B, and element C,” is intended to indicate element A alone, or element B alone, or element C alone, or any combination thereof. “At least one of element A, element B, and element C” is not intended to be limited to at least one of an element A, at least one of an element B, and at least one of an element C.

[0070] This Detailed Description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

[0071] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes,” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes,” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0072] Parts List for FIGS. 1(a) - 8(g) shell or shell gripper outer surface, shell enclosed volume, shell object of interest gripper apparatus retaining structure arm load cell shell or shell-based gripper outer or exterior surface, shell acrylic plate substrate blueberry green apple cherry tomato acrylic shell SD card acrylic plate with holes shell or shell gripper hemispherical shell substrate hole (defect) shell or shell gripper object of interest shell or shell-based gripper circular region columns shell gripper enclosed volume substrate water droplet water layer714 retaining structure719 load cell720 shell gripper740 substrate745 meniscus750 water layer 812 extending arm 814 retaining structure819 load cell820 flexible shell / shell gripper 860 chocolate covered almonds 864 hard boiled egg868 soft wet tofu 872 half peeled quail egg 876 concave egg white piece 880 grape 884 edible tablets

[0073] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description set forth herein has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of one or more aspects set forth herein and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects as described herein for various embodiments with various modifications as are suited to the particular use contemplated and in accordance with the following appended claims. Additional embodiments include any one of the embodiments described above and described in any and all exhibits and other materials submitted herewith, where one or more of its components, functionalities or structures is interchanged with, replaced by or augmented by one or more of thecomponents, functionalities or structures of a different embodiment described above and as set forth in the following appended claims.

Claims

Claims1. A tunable adhesion soft gripper apparatus comprising: a flexible shell made from a deformable fluid impermeable elastomeric material, the shell having an enclosed volume and an exterior surface, wherein a negative pressure applied to the enclosed volume while the shell is placed in compressive contact with an object creates an adhesion force enabling the object to be lifted and placed by the apparatus.

2. The soft gripper apparatus according to claim 1, wherein the flexible shell has a hemispherical shape.

3. The soft gripper apparatus according to claim 1, wherein the object of interest can be defined by a planar or curved configuration.

4. The soft gripper apparatus according to claim 1, wherein the adhesion is dry adhesion.

5. The soft gripper apparatus according to claim 1, wherein the adhesion is wet adhesion.

6. The soft gripper apparatus according to claim 1, further comprising at least one defect provided at a tip of the flexible shell to enable tunability of the apparatus.

7. The soft gripper apparatus according to claim 6, wherein the object of interest comprises a substrate, the substrate having at least one defect.

8. The soft gripper apparatus according to claim 7, wherein the at least one defect in the substrate comprises at least one hole aligned with the center axis of the shellbased gripper.

9. The soft gripper apparatus according to claim 1, wherein the object of interest and the flexible shell can be angularly misaligned with respect to one another without significantly disturbing the adhesion force therebetween.

10. The soft gripper apparatus according to claim 9, wherein the angular misalignment can be as great as 10 degrees.

11. A method for tuning the dry adhesion of a gripper apparatus, the gripper apparatus comprising a substrate and a shell having an enclosed volume, the method comprising: a. compressing the outer surface of the shell into contact with an object to be lifted in order to create deformation of the shell’ b. applying negative pressure to the enclosed volume to create a suction force in combination with dry adhesion of the shell with the object.

12. The method according to claim 11, the flexible shell has a hemispherical shape.

13. The method according to claim 11, wherein the object of interest can be defined by a planar or curved configuration.

14. The method according to claim 11, wherein the adhesion is dry adhesion.

15. The method according to claim 11, wherein the adhesion is wet adhesion.

16. The method according to claim 11, further comprising providing at least one defect on the exterior surface of the flexible shell.

17. The method according to claim 16, wherein the at least one defect is provided on a tip of the shell.

18. The method according to claim 16, wherein the object of interest includes at least one defect.

19. The method according to claim 18, in which the object of interest is a substrate and the at least one defect is at least one hole.

20. The method according to claim 11, wherein the object and the flexible shell can be angularly misaligned with respect to one another prior to picking the object up.

21. The method according to claim 20, wherein the angular misalignment is as great as 10 degrees.

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