Intelligent flexible drive unit for underwater applications

Abstract

A flexible origami actuator with embedded optical waveguide and an underwater manipulator application are disclosed. An underwater manipulator with a gripper driven by the same flexible origami actuator is also described. The main contributions of this disclosure include: 1) the elimination of stretch and bend coupling by combining origami flexible actuators with specially designed optical waveguides; 2) the optical waveguide is designed to not require cladding, greatly reducing manufacturing complexity; and 3) a hybrid underwater manipulator with redundant position feedback for precise and dexterous underwater applications is described.

Description

Technical Field

[0001] Disclosed are applications of flexible origami actuators and underwater manipulators with embedded optical waveguides. Background Art

[0002] Underwater manipulators are often used in scientific research on marine life. Compared with traditional rigid robots, soft robots offer new approaches. In particular, the inherent adaptability and waterproof properties of soft actuators are ideal for grasping delicate and flexible objects underwater, which inherits cable-driven and biomimetic approaches. In terms of continuum structures, hybrid structures, fluid elastomer actuators (FEAs) are also desirable for underwater applications.

[0003] Although soft robots have many advantages, one of the main challenges is reliable sensing feedback. Flexible materials have high elasticity, making many standard non-deformable sensing techniques inapplicable. In this context, flexible strain sensors are developed because they can undergo the same motion as flexible actuators. Examples include resistive strain sensors, capacitive strain sensors, and optical waveguide sensors. Many reported works have shown accuracy, robustness, and reliability, demonstrating the potential of this field. Summary of the invention

[0004] A simplified overview of the present invention is provided below to provide a basic understanding of some aspects of the present invention. This overview is not a broad overview of the present invention. It is neither intended to identify key or important elements of the present invention nor to describe the scope of the present invention. On the contrary, the sole purpose of this overview is to introduce some concepts of the present invention in a simplified form as a preface to a more detailed description below.

[0005] Flexible robots are ideal for underwater operational sampling and other service applications. Their unique compliance, adaptability and natural waterproofness enable compact and lightweight robot designs while achieving uncompromising flexibility and agility. However, the inherent elasticity and high nonlinearity of flexible materials also pose great challenges to the acquisition of sensory feedback for closed-loop control of flexible robots, especially in highly dynamic underwater environments. A popular solution to this problem is to measure the deformation of flexible robots using flexible strain sensors, but due to the characteristics of flexible materials, flexible robots are also prone to strong coupling of bending and stretching. In this paper, a new sensing flexible actuator "SOFA" based on origami flexible actuator structure and dedicated flexible optical waveguide sensor is proposed. Compared with the existing technology, the SOFA design brings two main advantages: 1) the decoupling of the bending and stretching motions of the actuator, which significantly improves the position measurement performance of the actuator under complex motion conditions through important geometric design; 2) the outer cladding of the optical sensor is removed by exploiting the interface effect between the flexible material of the sensor and the surrounding water, which significantly reduces the manufacturing complexity and realizes a new sensing mode of bending motion. A hybrid underwater manipulator with 3 degrees of freedom and an omnidirectional underwater platform with 6 degrees of freedom and 7 propellers were developed to demonstrate the performance of the proposed SOFA actuator using experimental results of the fabricated prototypes.

[0006] In one embodiment, this document describes a device for underwater applications made of a photodiode; an LED tube; a flexible origami fluid actuator between the photodiode and the LED tube; a plurality of optical waveguides configured to follow the movement of the flexible origami fluid actuator; and a plurality of sensors.

[0007] To achieve the above and related ends, the present invention includes the features fully described below and particularly pointed out in the claims. The following description and drawings set forth in detail certain illustrative aspects and implementations of the present invention. However, these are only a few of the various ways in which the principles of the present invention can be employed. Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the present invention when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 An underwater manipulator and a flexible origami fluid actuator with embedded optical waveguide according to embodiments are described.

[0009] Figure 2a Flexible origami fluidic actuators according to embodiments are described.

[0010] Figure 2b Three schematic diagrams of SOFA are described. Sc is the contact area between the upper and lower surfaces of the optical waveguide according to an embodiment.

[0011] Figure 2c An example of a flexible optical waveguide manufacturing process according to an embodiment is described.

[0012] Figure 2d SOFA exposure views and components according to embodiments are described.

[0013] Figure 3a A schematic diagram of SOFA is depicted, illustrating the relationship between the critical angle and the actuator orientation.

[0014] Figure 3b is a graphic illustration of the SOFA proof-of-concept test results.

[0015] Figure 3c is a graphical illustration of the SOFA bending test results in pitch.

[0016] Figure 3d The setup of the SOFA bending test platform is described.

[0017] Figure 3e The setup of the SOFA proof-of-concept testbed is described. The setup for the stretching and shrinking tests is identical except that there are three optical waveguides in both the stretching and shrinking tests.

[0018] Figure 3f Graphical illustration of the results of the SOFA stretch and shrink tests are recorded.

[0019] Figure 3g Graphical illustration of the SOFA bend test results recorded for tumble.

[0020] Figure 4a A hybrid underwater robot according to an embodiment is described.

[0021] Figure 4b is a schematic diagram of the gripper. The actuator stretches to close the gripper.

[0022] Figure 4c A hybrid underwater manipulator joint assembly according to an embodiment is described.

[0023] Figure 4d is a schematic diagram of a hydraulic control system according to an embodiment.

[0024] Figure 4e A hydraulic control system according to an embodiment is described.

[0025] Figure 4f A gripping force test apparatus is described.

[0026] Figure 4g A hybrid underwater manipulator joint testing rig is described.

[0027] Figure 4h is a graphical illustration of the clamping force test results.

[0028] Figure 4i is a graphical illustration of the joint test results for pitch.

[0029] Figure 4j is a graphic illustration of the results of a tumble joint test.

[0030] Figure 5 a describes the onshore manipulator test, Figure 5 b describes the pick-and-place test in a water tank.

[0031] Figure 6 a corresponds to the underwater platform orientation of the motor; Figure 6 b describes the proposed omnidirectional underwater platform; Figure 6 c describes an underwater platform equipped with an underwater manipulator; Figure 6 d depicts the entire system tested in a water tank. DETAILED DESCRIPTION

[0032] The motion of many soft robots is achieved by stretching / bending of soft actuators, and stretching and bending occur simultaneously most of the time. One issue worth noting is that as the soft strain sensor is bound to the soft actuator, stretching and bending are measured simultaneously because they both have an impact on the output signal of the soft sensor.

[0033] As described in this paper, to solve the coupling problem, an underwater manipulator driven by a flexible origami fluid actuator (SOFA) with embedded optical waveguide is proposed. Figure 1 As shown. Each flexible origami actuator is embedded with three specially designed optical flexible waveguides, with photodiodes and LEDs placed on the top and bottom for sensing feedback. An underwater manipulator with a gripper is also proposed, driven by the same flexible origami actuator. The main contributions of the present disclosure include: 1) the stretching and bending coupling is eliminated by combining origami flexible actuators with specially designed optical waveguides; 2) the optical waveguides are designed to not require cladding, greatly reducing the manufacturing complexity; and 3) a hybrid underwater manipulator is described with redundant position feedback for precise and dexterous underwater applications.

[0034] Design Concept

[0035] The apparatus and method of the present invention provide at least one of the following three advantages: a) provide a feedback solution for flexible actuators for underwater manipulator applications; b) allow sensing methods to measure bending and stretching separately; and c) allow sensors to be robust, accurate and easy to manufacture. For the first advantage, since waterproofing is a key issue for underwater applications, an optical waveguide is used, because only the flexible waveguide needs to be exposed to water, and all electronic devices can be separated and well sealed, which greatly reduces the complexity of system design.

[0036] The second advantage is the decoupling of bending and stretching at two levels: 1) the actuator level and 2) the sensor level. First, we developed Figure 2a The flexible origami actuator shown. The unique folding structure can easily achieve contraction and extension. Similarly, the combination of different critical angles θc can achieve dual bidirectional motion ( Figure 2b ). Compared with conventional FEAs, when the proposed flexible origami actuator is bent, only the critical angle is changed and the stretching of the actuator is negligible (wall thickness < 0.7 mm). In this case, bending and stretching are decoupled at the actuator level. Secondly, an optical waveguide is designed that can fit snugly through the flexible origami actuator. The preformed buckling structure also ensures that the optical waveguide can follow the movement of the flexible origami actuator. In this case, bending and stretching are decoupled at the sensor level.

[0037] Typically, optical waveguides require at least two layers: a core layer to transmit light and a cladding layer that provides a lower refractive index and protection for the core layer. This approach has been well developed, but the manufacturing process is very complicated, especially when making flexible waveguides. In this case, modifications were made based on the following aspects:

[0038] 1) The waveguide molded with silicone rubber has only one layer. The refractive index of the material is greater than that of water (1.33), and water is considered as a cladding. In this case, the manufacturing process of the optical waveguide can be simplified.

[0039] 2) If Figure 2b As shown in Figure 1, as the critical angle decreases, the contact area Sc between the upper and lower surfaces of the optical waveguide increases. This area provides a "shortcut" for the light because the light can travel directly to the photodiode. In this case, the smaller the critical angle, the greater the output of the photodiode.

[0040] Manufacturing Process

[0041] Flexible origami actuators such as Figure 2a It is manufactured by injection molding and has a wall thickness of 0.7 mm. Each actuator has, for example, three optical waveguide paths and a corresponding housing mechanism for mounting the flexible waveguides. The bottom of the actuator is permanently sealed, while the top has sealing sleeves as inlet and outlet.

[0042] The manufacturing process of flexible waveguide is as follows Figure 2c As shown. Transparent silicone rubber (VytaFlex 20, Smooth-On Inc) (n = 1.461) was selected as the flexible waveguide material. The mold was first 3D printed, and then silicone rubber was injected into the mold. After the silicone rubber was cured, the flexible waveguide was removed from the mold and cut into the desired shape. Finally, three flexible optical waveguides were placed on the flexible origami actuator.

[0043] like Figure 2d As shown, when the actuator with waveguide is ready, it is first sealed on the sealing sleeve. After that, the photodiode and LED are sealed in two acrylic tubes respectively. The photodiode and LED are placed perpendicular to the acrylic and the viewing angle of the LED is 18° to reduce propagation loss. Then two photodiodes and LED tubes are installed on the top and bottom of the actuator.

[0044] Sensing mechanism verification

[0045] As described in the previous section, the sensing mechanism is based on the contact area between the upper and lower surfaces of the optical waveguide. To demonstrate the feasibility of this approach, a validation test was first performed.

[0046] like Figure 3e As shown, a SOFA is mounted on the photodiode side, while the LED side can be moved axially. One optical waveguide is placed as usual, and the other optical waveguide has tin foil placed between the upper and lower surfaces so that there is no "shortcut" when the two surfaces are close. The last waveguide path is empty. A laser distance sensor (HG-C1100, Panasonic) is placed on the LED side to measure the changing length of the actuator. The test results are shown in Figure 3b As shown. The photodiode outputs on the empty waveguide path. The amplitude of the blocked optical waveguide signal is much smaller than the normal optical waveguide signal. In this case, it can be concluded that the sensing mechanism is effective.

[0047] SOFA Tension and Shrinkage Test

[0048] When the SOFA is stretched or contracted, the length of the actuator can be calculated from any of the three output signals of the three optical waveguides. Figure 3a As shown, the equation is:

[0049]

[0050] θc is the critical angle, H is the length of SOFA, L is the length of the folded edge, and h0 is the initial length of SOFA. The length that changes is

[0051]

[0052] The test bench setup was identical to the previous test, except that all three optical waveguides were properly installed. Figure 3f The measurement data of all optical sensors fit well with the laser measurement data, and the root mean square error (RMSE) of sensor 1, sensor 2, and sensor 3 are 0.59mm, 0.56mm, 0.5mm, and 0.47mm, respectively, as well as the average of the three sensors.

[0053] SOFA bending test

[0054] Given the three critical angles, the direction of SOFA can also be determined. Figure 3a As shown, the three points Pa, Pb, and Pc can be described as:

[0055] P a (-Lcosθ ca , 0, Lsinθ ca ); (3)

[0056]

[0057]

[0058] and

[0059] ab=P b -P a ; (6)

[0060] bc=P c -P b . (7)

[0061] The normal vector is

[0062]

[0063] Then the pitch and roll can be calculated as

[0064]

[0065]

[0066] Figure 3d The setup of the test platform is shown. The SOFA is fixed on the LED side and a 6-DOF inertial measurement unit (IMU) is mounted on top of the photodiode. The actuator is rotated manually and the data is captured. The test results are shown in Figure 3c and Figure 3g The RMS error of pitch is 2.2° and that of roll is 2.63°.

[0067] Robot design and system installation

[0068] A hybrid design of the underwater manipulator was conducted. On the one hand, flexible robots have inherent compliance advantages over traditional rigid robots in complex underwater environments. On the other hand, better accuracy and greater load can be achieved by applying rigid parts in the design. The hybrid underwater manipulator consists of two parts: the gripper and the joint. The gripper ( Figure 4b) is driven by a SOFA. The SOFA moves axially, and the gripper closes when the SOFA stretches, and vice versa. The maximum opening angle is 78°. The joint has two parts, each with three triangularly mounted SOFAs. The two photodiode circuits are sealed in the middle acrylic tube, and the two LED circuits are sealed in two tubes mounted on the top and bottom of the joint. The joint diameter is 108mm and the height is 114mm.

[0069] Underwater manipulator Figure 4d and Figure 4e The hydraulic control system shown is controlled. The hydraulic system consists of eight valves, two pumps and a control unit. For waterproofing and compactness, all electronic components are placed in acrylic tubes. There are six valves for the six actuators on the joint, and each valve is connected to two coupled actuators. The remaining two valves are used for the actuators on the gripper.

[0070] Gripping force and joint testing

[0071] First, the clamping force of the clamp was tested. Figure 4g As shown in Figure 1. The force sensor (FSR400, Interlink Electronics) is installed at the end of the gripper. Figure 4h As shown, when the pressure is 30 kPa, the clamping force reaches about 2.3 N.

[0072] As described in the previous section, given the three critical angles, the orientation of a SOFA can be calculated. In the manipulator joint, the normal vector of each section is parallel to the corresponding SOFA. In other words, the orientation of a part can only be obtained by one of the three SOFAs. Redundant sensor feedback can greatly improve the robustness and accuracy of the system. To verify the position feedback, an IMU is installed on the top photodiode as a reference ( Figure 4f ). The test results are as follows Figure 4i and Figure 4j The RMS error of pitch is 1.34° and that of roll is 5.1°.

[0073] Hybrid underwater manipulator verification

[0074] A series of tests were conducted to test the performance of the hybrid underwater manipulator. The hybrid underwater manipulator was first installed on a fixed platform and performed different tasks on land and underwater. Figure 5 a), the robot was mounted vertically and was controlled to grab a pen from an operator, rotate it clockwise for a count, and then return the pen to the operator. Figure 5 b), the robot is controlled to perform a pick-and-place task of a cylindrical object.

[0075] Omnidirectional underwater platform

[0076] Subsea Platform( Figure 6 b) It is controlled by 7 motors and can move in all directions. Compared with the cubic frame used by most existing underwater platforms, this underwater platform uses a triangular motion frame, which can reduce the overall weight while ensuring the thrust and carrying capacity remain unchanged. A total of 7 motors are used to control 6 degrees of freedom ( Figure 6 a): Three horizontal motors provide propulsion along the x-axis and y-axis individually; three vertical motors provide propulsion along the z-axis, pitch and roll; and a final motor mounted in the center provides yaw.

[0077] Verification test of the entire underwater platform

[0078] The manipulator system was installed on an underwater platform and tested in a water tank. Figure 6 As shown in Figure c, the manipulator is installed below the underwater platform. The connecting rod is 50 cm to prevent interference between the manipulator and the platform. Neutral buoyancy can be obtained by applying weight along the triangular frame and verified in a water tank ( Figure 6 d).

[0079] In this paper, a hybrid underwater manipulator with flexible origami actuators and embedded optical waveguides is proposed. By utilizing the unique structure of the flexible origami actuator, the bending and extension motions are first separated at the actuator level. Similarly, since the pattern of the embedded optical waveguide fits closely to the surface of the flexible origami actuator, the bending and extension are further decoupled at the sensor level. This new optical sensing method only requires a waveguide core layer, which greatly reduces the manufacturing complexity and cost. The feasibility of the method is also verified. The flexible origami fluid actuator SOFA with embedded optical waveguide is tested as a single unit and an assembly of a joint, and the results show a small RMSE. Finally, the hybrid underwater manipulator successfully performs different tasks on land, in a water tank, and on an underwater platform.

[0080] Unless otherwise indicated in the examples and elsewhere in the specification and claims, all parts and percentages are by weight, all temperatures are in degrees Celsius, and pressures are at or near atmospheric.

[0081] For any graph or numerical range for a given feature, a graph or parameter from one range can be combined with another graph or parameter from a different range for the same feature to generate a numerical range.

[0082] Except in the operating examples or where otherwise indicated, all numbers, values ​​and / or expressions concerning quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the word "about".

[0083] Although the present invention is explained with respect to specific embodiments, it should be understood that various modifications thereof will be apparent to those skilled in the art after reading the specification. Therefore, it should be understood that the invention disclosed herein is intended to cover such modifications within the scope of the appended claims.

Claims

1. A device for underwater applications, comprising: Photodiode; LED tubes; A flexible origami fluid actuator between the photodiode and the LED tube, wherein the flexible origami fluid actuator has a folded structure; a plurality of optical waveguides having preformed buckling structures, embedded in the flexible origami fluid actuator and conforming to the surface of the flexible origami fluid actuator, the plurality of optical waveguides being configured to follow the movement of the flexible origami fluid actuator, each of the plurality of optical waveguides not including a cladding; and Multiple sensors. 2 . The device for underwater applications according to claim 1 , wherein each of the plurality of optical waveguides comprises a core layer comprising transparent silicone rubber.

3. The device for underwater applications according to claim 1, wherein at least one of the plurality of sensors is an optical sensor.

4. The apparatus for underwater applications according to claim 1, further comprising a hydraulic control system and a gripper.

5. The device for underwater applications according to claim 1, comprising three optical waveguides.

6. Underwater robots, including: Device for underwater applications according to any one of claims 1 to 5.

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