Low-inertia thin film clutches

Abstract

The present disclosure describes use and construction of low-inertia thin film clutches and transmissions. The low-inertia thin film clutches include a soft inter-layer between the switchable adhesion layer and a backing to achieve a uniform force distribution. This design allows clutches to engage and disengage instantly with fixed or moving surfaces and prevents slipping and / or creeping. The adhesion layer uses a switching mechanism to switch between on and off states. The soft inter-layer, which is laminated between the switchable adhesion layer and an inextensible yet flexible backing, ensures uniform force distribution.

Description

LOW-INERTIA THIN FILM CLUTCHESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 622,403, filed January 18, 2024, which is incorporated by reference herein in its entirety.BACKGROUND

[0002] Robotic systems rely on clutching and transmission mechanisms to transmit a mechanical output to remote components such as wheels and / or end effectors to perform tasks. As we move towards an autonomous world, the efficiency and responsiveness of these mechanisms become essential elements for improving operating speed. These features are crucial for applications where energy conservation is a priority, such as in electric vehicles or other devices powered by batteries. Currently available clutches and transmissions, including friction clutches, electromagnetic clutches, and electrohydraulic clutches, have limitations primarily due to losses incurred when in converting electrical energy into mechanical outputs and / or transmitting that output to remote components. Further, the time needed to switch between on and off states and / or the weight of the clutch components themselves result in reduced efficiency and increased latency.SUMMARY

[0003] The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosure. The summary is not an extensive overview of the disclosure. It is neither intended to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure. The following summary merely presents some concepts of the disclosure in a simplified form as a prelude to the description below.

[0004] The present disclosure relates to methods and apparatus using thin films as switchable adhesives for low-inertia clutches and transmissions. Using thin film clutches for converting or transmitting mechanical forces offers the advantage of low-inertia elements with minimal mass. This characteristic provides several benefits, including enhanced dynamic performance, improved energy efficiency, and a more compact design. Low-inertia transmission, for instance, enables quicker response times thatallow for faster acceleration and deceleration. These faster acceleration and deceleration characteristics are especially advantageous in applications requiring rapid speed changes, such as high-performance vehicles or agile robotic systems. Reduced inertia also translates to lower energy requirements for altering a system's state and contributes to overall improved energy efficiency. Energy efficiency is a major factor in applications prioritizing energy conservation, such as electric vehicles and battery- powered devices. Further, rapid engagement and disengagement of low-inertia clutches allows motors or actuators to operate at an optimal speed and torque as designed, offering flexibility when adjusting the speed of an associated end-effector. Thin film clutches serve as a promising alternative to bulky clutch mechanisms, facilitating improved compact designs and reducing manufacturing costs, thereby promoting increased scalability and easy multiplexing.

[0005] Recent development of switchable adhesives using thin films has emerged as a promising strategy for creating low-inertia clutches. The adhesion properties of the switchable adhesives may be controlled using one or more thermal switching mechanisms, optical switching mechanisms, acoustic switching mechanisms, chemical switching mechanisms, gecko-inspired switching mechanisms, electromagnetic switching mechanisms, electrostatic switching mechanisms, and / or the like. Among the various switching mechanisms, electroadhesion (EA) stands out for the ability to achieve rapid engagement and disengagement. Present designs include a metalized flexible strip coated with an extremely thin dielectric material, facilitating a conformal overlap between the film-based clutch and its counterparts such as a rotating shaft and fixed surface. These single-layer thin-film clutches transmit the load by stretching and slipping, e.g., generating high stress in the front region when engaged with its counterpart and this section slips when fracture conditions are met. This stretching and slipping leads to a force concentration in the leading section of the clutch that rapidly (e.g., exponentially) decays toward the end of the clutch. Initially, only the front region bears most of the applied force. If the applied force is large, then it requires the front regions to creep forward- slip and stretch for other sections to contribute to the holding force. This sequential force transmission can result in partial slipping and a potential for a catastrophic slip.

[0006] Despite the rapid switching capability of film-based clutches, such as electrical addressing, achieving full clutching may be delayed due to the initial forceconcentration and the creeping behavior needed to distribute this force uniformly across the clutch. Thus, a need has been recognized for an improved design approach for low- inertia thin film clutches and transmissions that enables an instant and uniform force distribution upon engagement.

[0007] The present disclosure provides ways of creating low-inertia thin film clutches and transmissions. The method and apparatus involve integrating a soft inter-layer between the switchable adhesion layer and a backing to achieve a uniform force distribution. This design allows clutches to engage and disengage instantly with fixed or moving surfaces, preventing slipping and / or creeping. The adhesion layer can employ one of a thermal switching mechanism, optical switching mechanism, acoustic switching mechanism, chemical switching mechanism, electromagnetic switching mechanism, electrostatic switching mechanism, or other switching mechanism for switching between on and off states. The soft inter-layer, which is laminated between a switchable adhesion layer and the inextensible yet flexible backing, ensures uniform force distribution.

[0008] In some cases, an improved clutch includes an adhesion layer that extends beyond a low-force end, referred to as a "tail" in this document. The tail lacks a soft layer above it, thus preventing joint stresses (e.g., peeling stresses and shear stresses) from passing to the tail region. This tail extension (e.g., a thin tail) may help mitigate stress concentration at the edges to reduce stress gradients and to inhibit crack initiation and propagation.

[0009] In some cases, an improved clutch system may include a thin-film clutch designed specifically for rotational applications. In such cases, the clutch system comprises a shaft, which can either rotate or remain stationary, and the shaft may be connected to a flexible thin-film clutch. Alternatively, the clutch can be affixed to a flexible rope wound around the shaft, with a specified number of turns. This flexible rope, when connected to the clutch, is further linked to a load or mass. In some cases, the improved clutch system may involve wrapping the shaft by interlacing two or more thin film clutch strips.

[0010] In some cases, an improved clutch system may include a transmission system comprising an inner shaft and an outer rim connected through bearings. The inclusion of a thin film clutch, which is permanently affixed to the outer rim and positioned torest on the inner shaft, allows for engagement between the thin film clutch and the inner shaft. This engagement results in the coupling of the inner shaft with the outer rim, thus providing a mechanism for transmitting rotational forces within the transmission system.[Oil] In some cases, an improved clutch system may include a set of thin film clutches wrapped around a rotary shaft, composing a torque multiplexer. One end of the thin film clutches may be attached to a linear or a torsional spring while the other ends of set of the thin film clutches are attached to loads or joints. Once an electrically addressed thin film clutch engages, the target load is pulled while each unaddressed thin film clutch of the set of thin film clutches remains stationary.

[0012] In some cases, an improved clutch system implementation may include a power regulation and distribution system composed of two or more mechanical power (e.g., velocity) sources, each paired with a clutch mounted on a shared bearing. The output force or speed may be regulated by rapidly engaging and disengaging the clutches with these velocity sources, and the output is further smoothed through a mechanical spring.

[0013] Aspects of the disclosure present a method that enhances the displacement of displacement- limited actuators, such as piezoelectric devices, through a process of accumulating small movements using two thin film clutches. In such cases, one of the thin film clutches remains stationary while the other thin film clutch undergoes oscillations with a minor displacement, creating a sinusoidal relative movement between the two thin film clutches. The oscillating thin film clutch grabs a counterpart, referred to as the slider, and the actuator then pulls the slider along with the load. As the slider is displaced, the stationary thin film clutch engages with it, and the first thin film clutch disengages. Subsequently, the disengaged clutch returns to its initial position and seizes the slider again. This cycle of grasping and releasing repeats at a high frequency, resulting in significant overall displacement.

[0014] The details of these and other aspects of the disclosure are set forth in the accompanying drawings and description below. Other features and advantages of the disclosure will be apparent from the drawings and description.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing and other objects, features, and advantages of the present disclosure set forth herein will be apparent from the following description of particular embodiments of those inventive concepts, as illustrated in the accompanying drawings. Also, in the drawings the like reference characters refer to the same parts throughout the different views. The drawings depict only typical embodiments of the present disclosure and, therefore, are not to be considered limiting in scope.

[0016] FIG. 1A shows a cross-sectional view of a thin film composite clutch that comprises a switchable adhesion layer, a soft interlayer, and a flexible but inextensible backing, illustrating attachment to a fixed surface, in accordance with aspects of the present disclosure;

[0017] FIG. IB shows a cross-sectional view of two thin film clutches, demonstrating attachment to each other, in accordance with aspects of the present disclosure;

[0018] FIG. 2 shows a graph of force distribution graph against clutch length plotted for Young’s modulus ratios of backing to soft layer, in accordance with aspects of the present disclosure;

[0019] FIG. 3A shows a cross-sectional views of a composite thin film clutch which has an adhesive layer extension at the back, referred to as tail, illustrating attachment to a fixed surface, in accordance with aspects of the present disclosure;

[0020] FIG. 3B shows a cross-sectional view of two thin film clutches with tails, attaching / detaching to each other, in accordance with aspects of the present disclosure;

[0021] FIG. 4 shows a graph of joints (shear and peel) stresses evolving in the adhesion layer when a force is applied to one edge of the clutch, depicting peaks when the soft layer and backing ends, in accordance with aspects of the present disclosure;

[0022] FIG. 5A shows a cross-sectional view of a thin film clutch wherein soft and adhesion layers are patterned to accommodate pockets that allow interstitial fluids such as air to escape quickly by reducing the escape distance, in accordance with aspects of the present disclosure;

[0023] FIG. 5B shows a cross-sectional view of a thin film clutch with an array of thru-holes that allow interstitial fluids to escape through the clutch, in accordance with aspects of the present disclosure;

[0024] FIG. 5C shows a cross-sectional view of a thin film clutch with soft and thin layers designed as protuberances, in accordance with aspects of the present disclosure;

[0025] FIG. 6A shows an oblique view of a circular thin film comprising an adhesion layer, a soft interlayer, and a stiff backing, which can transmit in-plane forces and torques, in accordance with aspects of the present disclosure;

[0026] FIG. 6B shows an oblique view of a circular composite thin film clutch with an adhesion layer extended out as brim, suppressing the peeling mode of failure, in accordance with aspects of the present disclosure;

[0027] FIG. 7 shows a cross-sectional view of a circular clutch where a stiff core wrapped with a soft layer and coated with adhesion layer, attaching to the inner side of a grounded tube when adhesion is turned on, in accordance with aspects of the present disclosure;

[0028] FIG. 8A shows a cross-sectional view of a thin film clutch design where the switchable adhesive flaps are attached to both sides of a stiff carrier and inserted in a fixed dual guide rail, in accordance with aspects of the present disclosure;

[0029] FIG. 8B shows a cross-sectional view of a thin film clutch design where the switchable adhesive flaps are attached to both sides of a stiff carrier and inserted in a preloaded flexible dual guide rail, in accordance with aspects of the present disclosure;

[0030] FIG. 9 shows a cross-sectional view of two thin film clutches attached to the sides of a deformable but inextensible round object, providing additional compliance for high force capacity, in accordance with aspects of the present disclosure;

[0031] FIG. 10 shows an oblique view of a thin film clutch wrapped around a circular shaft, amplifying the adhesion force through a curved design, in accordance with aspects of the present disclosure;

[0032] FIG. 11 shows an oblique and a close-up view of a patch of thin film clutch attached to a flexible but inextensible string, which increases the wrapping angle and thus increases the adhesion force, in accordance with aspects of the present disclosure;

[0033] FIG. 12 shows an oblique view of multiple strands of thin film clutches that are wound on a shaft, in accordance with aspects of the present disclosure;

[0034] FIG. 13 shows an oblique and a close-up view of multiple strands of thin film clutches that are wound on two shafts which are connected to each other using a spring, in accordance with aspects of the present disclosure;

[0035] FIG. 14 shows an oblique view of two counter rotating cylinders that are wrapped with a single thin film clutch, allowing clutch to engage and disengage with the target cylinder, in accordance with aspects of the present disclosure;

[0036] FIGS. 15A and 15B show two cross-sectional views of a transmission design where the thin film clutch permanently attaches to the outer rim and engages / disengages to the inner shaft, where the shaft and rim are assembled using two bearings, in accordance with aspects of the present disclosure;

[0037] FIGS. 16A-C show a front view and two cross-sectional views of a transmission design where a belt connects two counter rotating rims to an output shaft, two flexible clutches are used to couple the outer rims to the inner counterrotating shafts, and a bevel gear mechanism is used to drive both shafts using a single motor, creating an antagonistic clutch pair to rotate the output shaft in both directions, in accordance with aspects of the present disclosure;

[0038] FIG. 17 illustrates a method for creating pre-curved thin film clutches by pre-stretching the adhesion layer and laminating with the soft layer and backing, in accordance with aspects of the present disclosure;

[0039] FIG. 18 shows an oblique view of a set of thin film clutches resting on a rotating cylinder wherein one side is attached to the loads and the other sides to the springs where, by addressing the desired set of clutches, a single force output can be multiplexed to manipulate a higher number of loads, in accordance with aspects of the present disclosure;

[0040] FIGS. 19A and 19B show an oblique and cross-section view of a clutch mechanism used to amplify the output of a displacement-limited actuator using an oscillating and a fixed clutch, in accordance with aspects of the present disclosure; and

[0041] FIG. 20 shows an oblique view of two independent counter rotating cylinders that share a single thin film clutch, allowing clutch to engage and disengage with the target one to change the direction, in accordance with aspects of the present disclosure;

[0042] FIGS. 21A and 21B illustrate the analogy between electrical H-bridge switches used to control current flow in a DC motor, and electromechanical switches based on low- inertia thin-film clutches (Switched Clutch Actuation, SCA) for controlling robotics joints or end-effectors;

[0043] FIGS. 22A and 22B depicts the construction of an SCA unit comprising two velocity sources, one from a constantly rotating shaft and the other from mechanical ground, and two concentric thin-film clutches mounted back-to-back via a low-friction bearing, enabling power regulation between the mechanical power source and the end-effector; and

[0044] FIGS. 23A and 23B show an SCA system with two opposing velocity sources, concentric thin-film clutches, and a load-bearing tendon coupled to springs, allowing antagonistic force and speed control of a robotic joint or end-effector.DETAILED DESCRIPTION

[0045] The detailed description below refers to the accompanying figures, which are an integral part of this document. Similar symbols in the figures typically denote similar components unless the context dictates otherwise. The illustrative embodiments discussed in the detailed description, figures, and claims are not intended to impose limitations. Alternate arrangements can be employed, and modifications can be made without deviating from the scope of the subject matter presented in this document. It is evident that the aspects of the present disclosure, as broadly outlined herein and depicted in the figures, can be organized, substituted, amalgamated, isolated, and configured in numerous diverse arrangements — all of which are explicitly considered in this context.

[0046] As discussed above, existing solutions provide electroadhesive clutches composed of metalized flexible strips covered with an extremely thin dielectric layer. These clutches consist of an un-pattemed single layer that necessitates stretching and slipping to transfer the load. Due to their design, force distribution is not immediate. Instead, the force distribution results in stress concentration at the pulling end, transmitting force to other sections only when this high-stress region slips. The stress concentration also initiates the slipping at lower forces, overall rendering these clutches less efficient, with lower force-density and slower response. As such, a need has been recognized for highly responsive clutches with uniform stress distribution. Aspects of the present disclosure describes clutch designs that create uniform stress distribution in the clutches using a soft interlayer that enables all sections to contribute to the clutching force. Such clutches diminish the peak joint stresses that cause the peeling and relocate major joint stresses away from the edges, which are the regions where any fracture would be initiated. These clutch designs also may shorten the air escape distance and allow fast engagement and disengagement time, amplify the braking force through curved designs, amplify displacement of small actuators, and / or may multiplex a mechanical force output.

[0047] The techniques listed above allow thin-film clutches to outperform existing ones in terms of a high-force density as all sections of the clutch contribute to the braking force, an improved engagement / disengagement time with short air-escape distance designs, a high-force density due to reduced joint stresses, a high-force density as the peak joint stresses relocated to less critical regions, and improved energy efficiency as there is no slipping or creeping (e.g., no energy is lost to friction).

[0048] A clutch is a general mechanical component that finds widespread application in machinery, automobiles, robotics, and other fields. Due to the size and / or mechanics of currently available clutches, the low-inertia thin film clutches designed using aspects of the present disclosure have advantages over previously available clutches including, for example, being low-inertia, fast (e.g., fast to turn on or off) and efficient (e.g., low energy consumption). As such, these novel clutches may expand the application of clutches into areas previously untapped, such as haptic interfaces, robotic hands, and the like, where space is at a premium, low weight is needed, and switching must occur rapidly and with very little energy. These clutches can, for instance, be used to connecta single electric motor to multiple robot joints, producing large savings in weight and expense.

[0049] FIG. 1 A shows a first illustrative thin film clutch 100a having a first configuration. This clutch configuration includes a thin adhesion layer 103, a soft interlayer 102, and a flexible but largely inextensible backing 101. The soft interlayer 102 is sandwiched between the adhesion layer 103 and the backing 101. This composite architecture may comprise of low-modulus silicones as the soft interlayer 102, metal coated dielectric materials as adhesion layer 103, and stiff polymers or metals as the backing 101. The operating principle of the adhesion layer 103 can be based on various principles including but not limited to electrostatic, thermal, chemical, light, electromagnetic, and / or ultrasonic stimuli. The friction between the adhesion layer 103 and a fixed surface 104 (e.g. a counter surface) can be controlled (i.e., turn off and on) by these stimuli. In cases with electrostatic based clutching, the adhesion layer 103 may be composed of a metal deposited thin dielectric layer. The thickness of metal deposition is less than 100 nm whereas the thickness of the dielectric layer is typically less than 10 m. The effective thickness of the dielectric layer (thickness divided by the relative permittivity) may range from 10 nm to 10 pm. For operating voltages of 100 V to 300 V, the strength of clutch may vary from 10 kPa to over 1 MPa with typical strength of 100 kPa. The countersurface of the clutch 100a can either be a fixed surface 104 or another clutch 100b facing upwards as shown in FIG. IB.

[0050] The incorporation of the soft layer 102 in the design is instrumental in achieving a uniform distribution of the applied load across the clutch surface. The force distribution is determined by the ratio of Young’s moduli of the backing to the soft interlayer 102. A higher ratio results in a more uniform force distribution. The equation below describes how the applied load distributes itself along a thin flat clutch, assuming the clutch is sufficiently thin to prevent bending moments caused by the applied load and that the soft interlayer 102 has a significantly lower Young’s modulus compared to the backing (i.e., Esoft « Ebacking). The thickness of the backing 101 and soft interlayer 102 may be lower than 50 pm, composing a total clutch thickness less than 100 pm. The Young’s modulus of the backing may vary from 1 GPa to tens of GPa whereas the soft interlayer may have elastic modulus ranging from tens of kPa up to 1 MPa. Additionally, the assumption may be made for modeling purposes that the softinterlayer 102 undergoes pure shear deformation while the backing 101 experiences pure tensile deformation. Based on these assumptions, the force can be expressed as:CD

[0051] Here Gsoft is the shear modulus of the soft interlayer 102, Eback is the Young’s modulus of the backing 101, hsojt is the thickness of the soft interlayer 102, hback is the thickness of the backing 101.

[0052] In FIG. 2, the graph illustrates the distribution in applied load along the length of the clutch (e.g., clutch 100a, clutch 100b) for different ratios of Young’s moduli between the backing 101 and soft interlayer 102. The higher the moduli ratio, the more linear the decrease in force. A perfectly linear graph indicates that each segment of the clutch 100a possesses an identical holding force. Conversely, a decaying force graph implies that most of the clutching force originates from the front edge where the slope is steeper. This signifies a force concentration in this region, with significantly lower holding force in other sections. Introducing an extremely soft interlayer 102 in the clutch design facilitates the transfer of a greater portion of the applied load to the distant sections of the clutch 100a. This, in turn, enhances the efficiency of clutching force per unit area.

[0053] Because the soft interlayer 102 facilitates the transmission of applied load to the far rear section of the clutchlOOa, characteristics of the soft interlayer 102 is pivotal in determining the load capacity. Given that the cross-section of the clutch 100a transitions from a finite thickness to zero at the rear end, joint stresses (including peeling and shear stresses) reach their peak at the rear end. The peeling stress may therefore lift off this edge, causing detachment. In addressing this failure mode, FIG. 3A introduces a design approach for a clutch 200 to extend only the thin adhesion layer 103, an extension known as the "tail" 105 in this document. By prolonging the tail 105 of the adhesion layer 103 beyond the soft and backing layers, the discontinuity of these layers is confined within the clutch area, well away from the edge, the primary location of crack initiation. The tail 105 serves a dual purpose in this design: 1) diminishing the peaks of joint stresses and 2) relocating the joint stresses away from the edge. Similar to the clutch design depicted in FIG. 1, a clutch 200 featuring a tail design can be employedeither to secure onto a fixed surface 104 as in FIG. 3A or engage with another clutchFIG. 3B.

[0054] FIG. 4 shows a graph of the shear and peel stresses (referred to as joint stresses) within the adhesion layer 103 as a function of clutch length. These stresses reach their peak at the point where the backing 101 and soft interlayer 102 conclude, potentially leading to peeling under higher forces. However, in the extended region (e.g., the tail 105), these stresses gradually approach zero, which effectively shifts the critical stressconcentrated areas away from the edge. This is needed because clutches are prone to peeling if these stresses accumulate near the clutch's perimeter. Peeling manifests when an edge of the clutch 200a becomes separated from the adherent surface, and this separation progresses across the entire surface of the clutch 200a.

[0055] The critical function of moving the joint stresses away from the edge of the clutch 200a may be achieved in other ways as well. For instance, the soft interlayer 102 may be tapered at the edge so that the backing layer attaches directly to the adhesion layer.

[0056] Some other configurations of thin film clutches are shown in FIGS. 5A-C. These configurations take advantage of patterned layers to reduce the engagement time by shortening the air escape distance. FIG 5A depicts a clutch 300 having a clutch design where the soft interlayer 102 and the adhesion layer 103 are patterned to accommodate pockets 106 (e.g., wells). These pockets 106 allow clutches to engage and disengage quickly, as they shorten the escape distance when the clutch 300 is turned on, and similarly shorten rush-in distance when the clutch 300 is turned off. FIG 5B illustrates another clutch 400 having a design to reduce this distance by incorporating thru-holes 107. The holes can have either regular or irregular pattern, with minimum distance as small as 10 nm and maximum distance as large as 10 mm. FIG 5C shows clutch 500 designed to use a technique of switching thin film clutches fast by reducing the mean escape distance. In this configuration the soft interlayer 102 and the adhesion layer 103 are designed as protuberances 550.

[0057] A circular clutch configuration, similar to the linear clutch design of the clutch 200 of FIG. 3 A is shown in FIGS. 6A and B. Here the clutch layers are designed in a circular pattern with an extended adhesion layer (e.g., a tail extension 105 of the adhesion layer), as shown in FIG. 6B, or without the extension of the adhesion layer as shown in FIG.6A. A force in any in-plane direction can be applied to the clutch 600 or clutch 650. When forces are applied at the center of the clutch composite, they are resisted by adhesion force between the clutch plates and brim. This design of the clutch 600 and 650 can resist complex loading composed of normal forces, shear forces, in-plane torsion, and out-of-plane moments.

[0058] FIG. 7 shows a configuration of a clutch 700 having a cylindrical clutch design where a rigid core 701 is enveloped by a soft layer 702 that is coated with a thin adhesion layer 703. Positioned within a fixed tube 704, this setup allows for unrestricted linear motion when the clutch 700 is disengaged. Activating the adhesion between the clutch 700 and the tube 704 freezes their relative motion. Similar to planar designs, the presence of a soft layer 702 in this configuration facilitates the transfer of force to the inner surface 706 of the tube 704. In the illustration, electroadhesion (shown in window 710) is employed for switchable adhesion, but alternative switching mechanisms are applicable across all designs.

[0059] Moving to FIGS. 8A and 8B, another configuration of flexible linear clutches (e.g., clutch 800) is presented. Here, switchable adhesive flaps 809 are affixed to both sides of a rigid core 801 and inserted into a preloaded dual guide rail 808. The free-standing flaps 809 span a width greater than the space between the rails of the dual guide rail 808, allowing the flaps 809 to deform and maintain effective contact with the sides of the dual guide rail 808 upon insertion. These thin and flexible flaps 809, which may be made of thin metals, metalized films, and the like, adhere to the lining 803 of the dual guide rail when activated. The dual guide rail 808 can adopt a rigid structure with fixed walls, as shown in FIG. 8A, or a flexible design with preloaded walls ensuring constant contact of the flap 809, as shown in FIG. 8B. The flexible walls of the dual guide rail 808 provide greater compliance compared to the rigid wall design.

[0060] Thin, flexible clutches, such as clutch 800, deliver the compliance needed for secure adherence to rigid surfaces. While clutch flexibility may suffice for effective adhesion, enhancing the adhesion force involves incorporating a deformable adherent surface 910, as shown in FIG 9. This augmentation increases overall compliance and consequently boosts clutching force. For illustrative purposes in FIG 9, a balloonshaped object is depicted as the deformable adherent surface 910, which can be deformable but not extensible, thus resembling a liquid-filled thin shell.

[0061] The adhesion between counter surfaces and flexible clutches can be amplified by curving the surfaces that clutches adhere to, benefitting from the capstan effect. In one variation of the clutch design is depicted in FIG 10 with a round shaft (e.g., shaft 1011) and a flexible clutch 1000. When the clutch is off, the relationship between Thoid and Tioad can be expressed using the well-known capstan equation as:Tioad = Thoi^ e^0(2)

[0062] Here, Thoid represents the applied tension needed to counterbalance Tioad, the resultant force exerted on the opposite side of the clutch 1000. The coefficient of friction between the shaft 1011 and the clutch 1000 is denoted as p and 9 stands for the wrapping angle. This equation demonstrates force amplification based solely on the friction coefficient. Assuming that the adhesion between the clutch components can be adjusted using diverse physical principles, this force amplification can be further enhanced. Among many variations of switchable adhesion techniques, the capstan amplification is revised using electroadhesion. In this scenario, a voltage is applied between the adhesion layer of the clutch 1000 and the shaft 1011. A thin dielectric layer can be applied either to the shaft 1011 or the conductive side of the clutch 1000. The application of voltage across this dielectric layer generates an electroadhesion force. Considering this electroadhesion force, the updated equation is expressed as follows:where R is the radius of the shaft 1011, V is the voltage across the air gap between the clutch 1000 and shaft 1011, and d is the air gap. Recall that the first term of right-hand side of the equation comes from the pure Capstan where Thoid is applied to the clutch 1000. When this force is removed, ioad still exists thanks to the electroadhesion component which is simply:

[0063] Since the force capacity of these clutches increases exponentially with the wrapping angle, an approach to increase this angle is illustrated in FIG. 11 using one or more flexible but inextensible strings 1113 and 1114 that are connected to an electroadhesion (EA) clutch pad 1112 and are wrapped around the shaft 1111 several times. The string1113 can continue wrapping to the other side of the EA pad 1112 with the desired number of turns. The shaft 1111 can be connected to a motor that may rotate in any direction and depending on the rotation, one of the strings 1113 and 1114 is pulled and the other one is released. Although the pad 1112 itself can be extended to wrap around the shaft 1111, it covers a larger surface, thus turns of wrapping may be limited. The string 1113 or 1114 on the other hand can be wrapped several times without covering much area of the shaft 1111.

[0064] A convenient way of still taking advantage of capstan amplification but having the force acting in the axial direction to use multiple strands of thin film clutches that are helically wound on a shaft in a circular pattern, e.g., the strip-shaped clutches 1215 are wound around a shaft in opposite directions as shown in FIG. 12. This design, similar to the novelty toy known as a “finger trap,” comprises a braided mechanism that converts tension force along the strips to a compression force that squeezes the shaft 1211. Placing the strips 1215 in tension reduces the angle of the braid, which decreases the cylindrical diameter of the tube. The harder it is pulled, the tighter it gets. FIG. 13 shows an oblique and close-up view of multiple strands of thin film adhesives that are wound on two shafts 1311 in circular patterns and the shafts 1311 are connected through a spring 1316. The spring 1316 holds two shafts 1311 together and brings the moving shaft 1311 back to the initial position when the load is removed. When the adhesion is off the shafts 1311 are decoupled and move freely. When the adhesion is on the shafts 1311 are rigidly coupled and move together.

[0065] A segmented clutch 1400 can be placed on concentric counter-rotating shafts 1411a and 141 lb as shown in FIG. 14. These shafts 141 la and 141 lb can be connected to a single motor using a bevel gear design. By individually controlling the adhesion between a segment of the clutch 1400 and one of the shafts 1411a, the clutch 1400 can be moved in the direction of the engaged shaft 1411a. When engaged, the speed of the clutch 1400 matches with the engaged shaft 141 la instantly. However, both the speed and the direction of the clutch 1400 can be controlled by adjusting the time that it engages with each shaft 141 la and / or 141 lb. Assuming the first shaft 141 la rotates in the clockwise direction with a rotational speed of co, and the second shaft 1411b in the counterclockwise direction with the same speed, then the average rotational speed of the clutch 1400 can be expressed as:where T is the period of switching, ti is the time that the clutch 1400 engages with the first shaft 1411a, and t2 is the engagement time with the second shaft 1411b. For instance, if the clutch 1400 engages with the first shaft 141 la all the time, then t = T and (^average=<^o- If the clutch 1400 engages with two shafts 1411a and 1411b with the same amount of time, then the average clutch speed would be zero (i.e., it would be stationary).

[0066] Note that rapid switching between positive and negative rotational speeds implies very high acceleration. Time to switch clutch on and off may range from 10 ps to 100 ms, typically 1 ms. This would be problematic for clutches in the prior art due to their significant inertia which, coupled with high acceleration, would require very high forces and / or torques, leading to energy loss, rapid wear / degradation, and high vibration. The very low inertia of the thin film clutches described here enables rapid switching to occur without such deleterious effects. Additionally, if the load driven by the clutches is compliant, then the average speed described above will be converted into an average force or torque which may then be applied to a downstream load, including an inertial load.

[0067] While a clutch can be directly positioned on a shaft, as demonstrated in earlier FIGS. 10-14, the introduction of a bearing between the clutch and the shaft can minimize friction when the clutch is disengaged. FIGS. 15 A and 15B introduce a concept where a clutch 1500 incorporates a bearing design. The outer tube 1518 is connected to an inner shaft 1411 through two bearings 1517. In this setup, the clutch 1500 is permanently affixed to the interior of a rigid outer tube 1518, resting on the inner shaft 1511, facilitating free rotation when not actively engaged. The load is attached to the outer tube 1518. The inner shaft 1511, independently actuated for example by a motor, spins in the direction indicated by the arrow in FIG. 15 A. Engagement between the outer cylinder (e.g., the outer tube 1518) and the inner shaft 1511 is achieved by activating the clutch 1500, for instance, applying voltage to the clutch 1400 while electrically grounding the inner shaft 1511.

[0068] As depicted in FIGS. 16A-16C, another concept involves utilizing a clutch design to alter the speed and direction of a continuously rotating motor. The motor's output isdivided into two counter rotations via bevel gear 1621. These two rotating shafts 1622, having the same angular velocity (to), are concentric and connected to outer barrels 1609 through bearings. The clutches 1600 are permanently attached to the inner sides of these barrels and engage with the respective shafts. One clutch rests on one shaft, and the other clutch on the other shaft. A belt drive 1619 spans both barrels, linked to a remote joint 1620. By selectively turning on the clutches 1600, the belt can be driven, allowing control over speed and direction by toggling each clutch 1600 on and off within a specified timeframe. The formula previously provided for the design in FIG. 14 is also applicable in this context.

[0069] FIG. 17 outlines a method for crafting pre-curved thin film clutches. To introduce positive curvature, the adhesion layer 103 is pre-stretched and then laminated with the soft layer 102 and backing 101. Upon force release, the residual tensile stress in the adhesion layer 103 causes the soft layer 102 and backing 101 to pull, resulting in a curved geometry. The degree of pre-stretch determines the radius of curvature. The initial radius of curvature can be smaller than the radius of the shaft it wraps around. When placed on the shaft, it widens to encircle the shaft, applying slight pressure, aiding in clutch retention when clutch is inactive.

[0070] A force output multiplexing technique using a set of thin film clutches is shown in FIG. 18. Clutches 100 on a rotating shaft 111 are attached to loads 123 on one side and linear or torsional springs 116 on the other. By selectively addressing target clutches 100 electrically, a single force output can be multiplexed to manipulate a higher number of loads. This technique may be adapted for applications requiring increased degrees of freedom.

[0071] In another approach to amplify the output of a displacement-limited actuator, as illustrated in FIGS. 19A and 19B, two sets of thin-film clutches 100 are employed. One clutch 100 is mounted to a fixed surface 125, and the other clutch 100 is attached to an oscillating structure 126. The clutches 100 engage and disengage with their counterparts. In each oscillation, the oscillating clutch 100 seizes the counterpart, pulling it forward with a small displacement. Subsequently, the grounded clutch 100 fixes this small displacement, while the oscillating clutch 100 returns to grasp the counterpart and pull it again. Utilizing a rapid actuator for clutch oscillation and swiftswitching between clutches 100 allows displacement of the counterpart over a larger range.

[0072] Fig. 20 depicts a single thin film clutch 100 draped over two independent shafts (a first shaft 2001 and a second shaft 2002), rotating at different angular velocities of a and to. The first shaft 2001 and the second shaft 2002 may have different properties such as high-speed low torque vs. low-speed high torque. The clutch 100 may have the speed of either shaft by continuously engaging or variable speed that can be controlled by adjusting the time it engages with either the first shaft 2001 or the second shaft 2002. The first shaft 2001 and the second shaft 2002 spin opposite each other to allow the clutch 100 to drive a low inertia load in two directions at different speeds, giving a transmission effect. The equation informed by FIG. 14 can be used in this case, as the first shaft 2001 rotates in the counterclockwise direction with a rotational speed of co, and the second shaft 2002 in the clockwise direction with speed a then the average rotational speed of the clutch 100 can be expressed as:where T is the period of switching, ti is the time that the clutch 100 engages with the first shaft 2001 and t2 is the engagement time with the second shaft 2002.

[0073] Low-inertia thin-film clutches may be used to distribute the mechanical power drawn from a source to multiple components or sub- systems. This approach, referred to as Switched Clutch Actuation (SCA), uses mechanical power sources (e.g., a rotating shaft or moving mass) to regulate and distribute power to target components. FIGS. 21A and 21B illustrate an analogy between electrical switches, such as MOSFETs in an H-bridge 2100 used for controlling current flow in a DC motor, and electromechanical switches in an SCA 2150 for regulating the speed and force of joints, end-effectors, or other mechanisms (e.g., a joint 2108 about an element 2107). In the electrical system, the switches 2102 manage voltage and current from the battery 2101 and adjust the motor’s 2103 torque and speed accordingly. Dashed arrows depict the current flow through the circuit and motor when switches SI and S4 are activated while S2 and S3 remain off. Similarly, the SCA circuit controls the velocity and force derived from mechanical power sources 2104 to govern the speed and force of the joint 2108 or other such endeffector. In essence, EA clutches (e.g., a clutch 2106a and a clutch 2106b) serve as themechanical analog to MOSFETs, engaging and disengaging to regulate power distribution between the source and target components. By varying the switching sequence and timing between S1-S2 and S3-S4 pairs, the speed and direction of the joint 2108 can be precisely controlled through a spring 2109. Although the spring 2109 may be replaced with, or supplemented by, other dynamic elements, such as a damper or an inertia element, an advantage that the spring 2109 provides is that the force developed depends on the the integral of the clutch velocities (e.g., the velocities of the clutch 2106a and the clutch 2106b). These velocities will exhibit rapid changes associated with switching, but integration has a smoothing effect which is useful in achieving smooth control of the output motion (e.g., the velocity of joint 2108). Notably, the low-inertia of the novel clutch designs makes this approach possible.

[0074] FIGS. 22A and 22B illustrate an illustrative construction of an SCA unit. The unit consists of a constantly rotating shaft (velocity source or V- source) 2201a and a second velocity source provided by the mechanical ground with zero velocity. Two concentric thin-film clutches 2207a and 2207b are mounted back-to-back on the shaft, with low- friction bearings 2202a and 2202b enabling their connection to the shaft. A load carrier tendon 2204a wraps around the bearings, transferring power between the clutches and the end-effector. In this design:• One clutch counter surface, which is a surface where the clutch engages, is fixed to the rotating shaft, while the other is fixed to the mechanical ground.• Force transfer to the end-effector occurs by engaging clutch 2207b with the rotating counter surface 2206b.• To hold the load, clutch 2207c engages the fixed counter surface 2205b while disengaging from the rotating counter surface.The zero-velocity source in this configuration improves energy efficiency during load holding by eliminating the need for continuous energy input.

[0075] FIGS. 23 A and 23B illustrate a system 2300 of the application of the SCA system with two opposing velocity sources 2303a and 2304a. These velocity sources are both powered by a single motor operating at a constant speed, with the output from the motor reversed to generate a second velocity source, maintaining the same speed. The system includes two concentric thin-film clutches 2306a and 2306b, mounted back-to-back and connected to each velocity source via low-friction bearings (e.g., bearings 2310a). Aload-bearing tendon 2302b couples the outputs of the two SCAs and is linked to two springs (e.g., spring 2301a). This configuration allows for antagonistic control of a robotic joint or end-effector, providing precise control over movement and force in applications requiring complex motion control. The integration of the springs allows for greater flexibility and responsiveness in regulating the motion of the robotic system. This set of figures and their descriptions highlights the use of SCAs for precise, scalable control of robotic joints and end-effectors, employing mechanical clutches to regulate both force and velocity.

[0076] It should be emphasized that FIGS 22A, 22B, 23A and 23B are only exemplary and that many variations are possible without altering the fundamentals described herein. For instance, the rotating velocity sources may be replaced by sources that translate, oscillate, or move in other directions. The sources need not be velocity sources, but may be torque sources or hybrid sources that exhibit more complex torque- speed relationships. The number of sources may be one, two, or three as in the examples above, or any other number. The clutch outputs need not connect to tendons, but may connect to any other power transfer mechanism, such as a belt or linkage. In addition to springs, other dynamic elements such as masses and dampers, may be used to smooth the output motion.

[0077] As described herein and for use in applications such as the illustrative examples, a low- inertia thin film clutch may include a switchable adhesion layer, a soft interlayer, and a backing layer formed from a flexible and mostly inextensible material, where force is transmitted across a clutch surface via the soft interlayer. The adhesion layer of the illustrative low-inertia thin film clutch may be based on one of an electrostatic mechanism, an electromagnetic mechanism, a thermal mechanism, a light-responsive mechanism, and a gecko-inspired mechanism. The low-inertia thin film clutch may further include an extended adhesion layer extending beyond the soft interlayer. In some cases, the low-inertia thin film clutch may be disk-shaped and may transmit inplane forces and torques. This disk-shaped low-inertia thin film clutch may include an extended adhesion layer creating a brim, where an adhesion force between a clutch plate and the brim resists a complex loading force.

[0078] In some cases, the low-inertia thin film clutch may include a patterned surface wherein patterning of the patterned surface comprises one or more of: one or more pocketsembedded in one or more of the adhesion layer, the soft interlayer, and the backing layer, one or more wells in one or more of the adhesion layer, the soft interlayer, and the backing layer; an array of thru-holes through the adhesion layer, the soft interlayer, and the backing layer; and protuberances formed from the soft interlayer and adhesion layer. In some cases, a counterpart of the low-inertia thin film clutch may be a deformable and inextensible object that increases force capacity of the low-inertia thin film clutch. In some cases, the counterpart may be a cylindrical object. In some cases, the low-inertia thin-film clutch may further include inextensible strings attached to the low-inertia thin film clutch and that may wrap around the counterpart. In some cases, the counterpart may be made of two or more components and may be attached via a spring. In some cases, the low-inertia thin film clutch is a cylindrical clutch comprising a stiff core wrapped with the soft interlayer coated with the switchable adhesion layer, wherein a counterpart of the clutch is a fixed tube.

[0079] Aspects of this disclosure describe a mechanical power transfer system that may include a first velocity source comprising a first rotatable shaft operating at a first velocity, a second velocity source operating at a second velocity, and two or more low-inertia thin film clutches wherein a first surface of a first low-inertia thin film clutch is fixed to the rotatable shaft of the first velocity source and wherein a second surface of a second low-inertia thin film clutch is fixed to a surface of the second velocity source. The mechanical power transfer system may further include low-friction bearings that enable connection of the two or more low-inertia thin film clutches with the rotatable shaft. The mechanical power transfer system may further include a load carrier tendon that transfers power between the two or more low-inertia thin film clutches and an end effector. In some cases, the first velocity source of the mechanical power transfer system may be a constant velocity source and / or a direct current (DC) motor. In some cases, the second velocity source may be a source of zero velocity. In some cases, the first velocity source may be a motor comprising the first rotatable shaft rotating at a first constant velocity in a first direction of rotation and the second velocity source may be a second rotatable shaft operating at a second velocity in a second direction of rotation. In some cases, the first velocity source and the second velocity source may be powered by a same motor operating at a constant speed.

[0080] In some cases, a mechanical system may include a low-inertia thin film clutch including a switchable adhesion layer and a soft interlayer, and two rotating counterparts, where an engagement time of the switchable adhesion layer of the low-inertia thin film clutch on a surface of one of the two rotating counterparts defines a speed and a direction of the mechanical system.

Claims

What is claimed is:

1. A low-inertia thin film clutch, comprising: a switchable adhesion layer; a soft interlayer; and a backing layer formed from a flexible and mostly inextensible material, wherein force is transmitted across a clutch surface via the soft interlayer.

2. The low-inertia thin film clutch of claim 1, wherein the adhesion layer is based on one of an electrostatic mechanism, an electromagnetic mechanism, a thermal mechanism, a light-responsive mechanism, and a gecko-inspired mechanism.

3. The low-inertia thin film clutch of claim 1, further comprising an extended adhesion layer, wherein the extended adhesion layer extends beyond the soft interlayer.

4. The low-inertia thin film clutch of claim 1, wherein the low-inertia thin film clutch is disk-shaped and transmits in-plane forces and torques.

5. The low-inertia thin film clutch of claim 4, further comprising an extended adhesion layer creating a brim, wherein an adhesion force between a clutch plate and the brim resists a complex loading force.

6. The low-inertia thin film clutch of claim 1, further comprising a patterned surface wherein the patterning comprises one or more of: one or more pockets embedded in one or more of the adhesion layer, the soft interlayer, and the backing layer, one or more wells in one or more of the adhesion layer, the soft interlayer, and the backing layer; an array of thru-holes through the adhesion layer, the soft interlayer, and the backing layer; and protuberances formed from the soft interlayer and adhesion layer.

7. The low-inertia thin film clutch of claim 1, wherein a counterpart of the low- inertia thin film clutch is a deformable and inextensible object that increases force capacity.

8. The low-inertia thin film clutch of claim 1, wherein a counterpart is a cylindrical object.

9. The low-inertia thin film clutch of claim 8, further comprising inextensible strings attached to the low-inertia thin film clutch and wrap around the counterpart.

10. The low-inertia thin film clutch of claim 9, wherein the counterpart is made of two components and attached via a spring.

11. The low-inertia thin film clutch of claim 1, wherein the low-inertia thin film clutch comprises a cylindrical clutch comprising a stiff core wrapped with the soft interlayer coated with the switchable adhesion layer, wherein a counterpart of the clutch is a fixed tube.

12. A mechanical power transfer system comprising: a first velocity source comprising a first rotatable shaft operating at a first velocity; a second velocity source operating at a second velocity; and two or more low-inertia thin film clutches wherein a first surface of a first low-inertia thin film clutch is fixed to the rotatable shaft of the first velocity source and wherein a second surface of a second low-inertia thin film clutch is fixed to a surface of the second velocity source.

13. The mechanical power transfer system of claim 12, further comprising low- friction bearings enabling connection of the two or more low-inertia thin film clutches with the rotatable shaft.

14. The mechanical power transfer system of claim 12, further comprising a load carrier tendon that transfers power between the two or more low-inertia thin film clutches and an end effector.

15. The mechanical power transfer system of claim 12, wherein the first velocity source comprises a constant velocity source.

16. The mechanical power transfer system of claim 12, wherein the first velocity source comprises a direct current (DC) motor.

17. The mechanical power transfer system of claim 12, wherein the second velocity source comprises a source of zero velocity.

18. The mechanical power transfer system of claim 12, wherein the first velocity source comprises a motor comprising the first rotatable shaft rotating at a first constant velocity in a first direction of rotation and the second velocity source comprises a second rotatable shaft operating at a second velocity in a second direction of rotation.

19. The mechanical power transfer system of claim 12, wherein the first velocity source and the second velocity source are powered by a same motor operating at a constant speed.

20. A mechanical system, comprising: a low-inertia thin film clutch comprising: a switchable adhesion layer; and a soft interlayer; and two rotating counterparts wherein engagement time of the switchable adhesion layer of the low-inertia thin film clutch on a surface of one of the two rotating counterparts defines a speed and a direction of the mechanical system.

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