Robotic gripper

Abstract

The application relates to the field of robot grippers, and provides a robot gripper which comprises at least two claw parts, each claw part comprising a body, a plurality of force applying members and an elastic member; the plurality of force applying members are slidably arranged in the body in the axial direction, the circumferential direction of the force applying members is provided with a medium containing chamber, the medium containing chamber covers the movable part of the force applying member and is filled with a phase change material, the phase change material can reversibly change between solid and liquid states to selectively lock or release the force applying member; the force applying member has a channel, and the channel is used for guiding in temperature control gas. The application combines the heat transfer medium and the mechanical buffering medium by introducing hot gas and cold gas into the channel, not only simplifies the internal space of the tooling, but also realizes synchronous and rapid regulation and control of the temperature and the support force of the force applying member by using the low thermal inertia of the gas.

Description

Technical Field

[0001] This invention relates to the field of robot end effector technology, specifically to a robot gripper, and more particularly to a robot gripper based on a solid-liquid phase change synergistic mechanism, which utilizes a temperature-controlled gas as both a heat exchange driving medium and a mechanical buffer medium to achieve efficient adaptive fitting and clamping of irregularly shaped curved workpieces. Background Technology

[0002] Robotic end effectors play a crucial role in automated machining, assembly, and material handling. Traditional dedicated fixtures are custom-designed for specific workpiece shapes, resulting in inherent drawbacks such as high development costs, lengthy changeover cycles, and low reusability, making them unsuitable for the growing demands of flexible manufacturing with diverse product types and small batches. For workpieces with free-form surfaces or irregular structures, the shape adaptability of general-purpose fixtures is particularly insufficient, often leading to localized false contact or stress concentration, which affects machining accuracy and may damage the workpiece surface.

[0003] Existing technologies include solutions that encapsulate low-melting-point alloys within a support device and achieve multi-point support through a heating-cooling cycle. However, these solutions typically rely on independent electric heating elements and natural convection cooling, resulting in high thermal inertia, slow response times, and a lack of claw-like robotic gripper configurations, making it difficult to meet the stringent requirements of rapid clamping in robots. Another approach involves clamping modules using bundles of elastic force-applying components combined with mechanical locking blocks. While these can adapt to the workpiece surface, the mechanical locking method struggles to provide the overall rigidity required for heavy-duty cutting, and the locking and releasing processes rely on manual adjustment, limiting automation and compromising repeatability.

[0004] In summary, how to achieve both efficient adaptive fitting of irregularly shaped curved workpieces and high-rigidity clamping under heavy-duty cutting conditions without the need for high-precision pneumatic control components and independent heating and cooling units, while simultaneously reducing the clamping cycle time exponentially, has become a pressing technical challenge in this field. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide a robotic gripper.

[0006] According to the present invention, a robotic gripper includes at least two claws, each claw including a body, a plurality of force-applying components, and an elastic component; Multiple force-applying components are slidably arranged in the body along the axial direction. Each force-applying component is circumferentially provided with a medium-containing chamber. The medium-containing chamber covers the movable part of the force-applying component and is filled with a phase change material. The phase change material is capable of reversible phase change between solid and liquid states to selectively lock or release the force-applying component. The force-applying component has a channel for introducing a temperature-controlled gas. The temperature-controlled gas serves both as a heat exchange medium for exchanging heat with the phase change material to drive its phase change and as a mechanical medium for forming a gas spring effect below the force-applying component to provide flexible support for the force-applying component. The elastic element is arranged circumferentially along the force-applying element and works in conjunction with the gas spring to provide flexible support force to the force-applying element when the phase change material melts.

[0007] Preferably, the phase change material in the medium containment chamber is distributed in a thin layer, and the phase change material is selected from any one of low melting point metals, paraffin wax, and water.

[0008] Preferably, the force-applying member is circumferentially configured with a sawtooth structure, which is arranged alternately along the length of the force-applying member, and a receiving groove for accommodating the phase change material is formed between adjacent sawtooths.

[0009] Preferably, the channel extends from the lower end of the force-applying member to the upper end and is disposed inside the force-applying member. The temperature-controlled gas is introduced from the lower end and transmitted to the upper end along the channel to heat or cool the medium-containing chamber.

[0010] Preferably, the elastic element is a helical spring, which is sleeved on the lower end of the force-applying element. The force-applying element extends circumferentially to form a functional part, and the two ends of the helical spring abut against the functional part and the bottom of the main body, respectively.

[0011] Preferably, a sliding cavity is provided around the center of the force-applying member, which allows the force-applying member to freely adjust its axial position when the phase change material is in a liquid state; The phase change material forms a rigid locking structure distributed around the movement path of the force-applying component in the solidified state, and the rigid locking structure provides structural support for the force-applying component under heavy load conditions.

[0012] Preferably, the system also includes a base, to which the main body is connected, and the base performs the functions of overall positioning, load-bearing, and connection with the robot.

[0013] Preferably, the two claws are arranged opposite each other. When the workpiece is pressed into the top of the plurality of force-applying components, each of the force-applying components generates a different displacement according to the surface contour of the workpiece, forming a support surface that matches the shape of the workpiece.

[0014] Preferably, it further includes a guide bushing, which is disposed between the force-applying member and the body, for guiding the axial sliding of the force-applying member.

[0015] Preferably, it further includes a sealing assembly disposed at the periphery of the medium receiving chamber to prevent leakage of the liquid phase change material.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs a hot gas and cold gas inlet channel, combining the heat transfer medium and the mechanical buffer medium into one. On the one hand, the hot gas directly convects and heats the medium-containing chamber, while the cold gas accelerates and forces convection to cool it, achieving rapid switching of phase change states. On the other hand, the introduced gas forms a controllable air cushion or air spring effect under the force-applying component, which not only simplifies the internal space of the tooling but also utilizes the low thermal inertia of the gas to achieve synchronous and rapid control of temperature and the supporting force of the force-applying component.

[0017] 2. In this invention, the phase change material in the medium containment chamber is a thin layer with a serrated structure, which greatly increases the heat exchange area between the phase change material and the temperature control gas. The heating melting time and cooling solidification time are both shortened exponentially, thereby greatly reducing the single clamping auxiliary time, effectively shortening the phase change time, and improving the processing efficiency.

[0018] 3. This invention utilizes the structural rigidity of solidified metal as a rigid locking structure, distributing liquid metal around the moving path of the force-applying component to increase the heat exchange area. After the phase change material cools and solidifies, the solid metal distributed around the force-applying component not only locks its axial position but also provides distributed structural support under heavy loads, effectively suppressing micro-displacement and vibration. Thus, based on efficient adaptive fitting of irregularly shaped curved workpieces, it further addresses the high rigidity clamping requirements under heavy loads.

[0019] 4. In this invention, each claw has multiple vertically floating force-applying components inside. When the phase change material is heated and melted, the force-applying components are in a freely adjustable state. When the workpiece is pressed into the top of the multiple force-applying components, each component will generate different displacements according to the workpiece surface contour, thereby forming a support surface that matches the workpiece shape. This multi-point adaptive fitting mechanism allows the same gripper to quickly adapt to different workpieces such as cylindrical parts, irregularly shaped parts, and free-form surfaces, without the need to redesign special fixtures for each type of workpiece, thus exhibiting good versatility.

[0020] 5. This invention uses temperature-controlled gas introduced through a channel as the sole energy medium, achieving forced heat exchange and phase change drive for the phase change material. Simultaneously, while providing heat exchange drive, the gas, together with the helical spring, provides flexible pneumatic support for multiple force-applying components. This design completely eliminates the need for high-precision pneumatic control components and independent heating and cooling units, significantly reducing system hardware costs and control complexity, and improving overall reliability.

[0021] 6. By adjusting the temperature, flow rate and pressure of the introduced gas, this invention can simultaneously achieve precise control of the phase change state of the phase change material and flexible adjustment of the supporting force of the force-applying component, thus meeting the process requirements under different working conditions. Attached Figure Description

[0022] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A cross-sectional view of the robot gripper when the two claws are separated. Figure 2 A cross-sectional view of the structure when the two claws of the robot gripper clamp the workpiece; Figure 3 This is a structural cross-sectional diagram of a force-applying component unit. The T-shaped dashed line in the diagram represents the cross-section of the channel. Figure 4 This is a schematic diagram of the robot gripper.

[0023] The diagram shows: Ontology 1; Force-applying component 2; Sliding cavity 21; 22. Serrated structure; Functional section 23; Medium containment chamber 3; Receiving slot 31; Channel 4; Mechanical spring 5; Workpiece 6; Claw 7; Guide bushing 8; Sealing component 9. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0025] like Figures 1 to 3 As shown, this invention provides a robot gripper based on a solid-liquid phase change synergistic mechanism. This robot gripper employs a mechanism that uses phase change materials and springs to assist in adapting to the shape of a workpiece 6. It is a flexible gripper that utilizes the reversible solid-liquid phase change of the phase change material to achieve rapid adaptation and locking of irregularly shaped workpieces 6. The robot gripper includes a base, a body 1, and at least two elastic claws 7, as shown... Figures 1 to 4As shown, multiple force-applying components 2 that can float up and down are arranged inside each claw 7, and a sliding cavity 21 is provided around the center of the force-applying component 2. When the phase change material is heated and melted, the force-applying component 2 is in a freely adjustable state. When the workpiece 6 is pressed into the top of the multiple force-applying components 2, each force-applying component 2 will produce different displacements according to the surface contour of the workpiece 6, thereby forming a support surface that matches the shape of the workpiece 6. Then, heating is stopped and the phase change material is cooled and solidified. The rigidity of the solidified material is used to lock the position of the force-applying component 2 as a whole, forming a stable and reliable clamping.

[0026] The main body 1 bears the load and protects the internal functional components of the claw 7. The inner wall of the main body 1 is equipped with a guide structure to guide the axial sliding of the force-applying component 2, ensuring that the force-applying component 2 maintains the correct posture during floating. The guide structure is preferably a guide bushing 8. The guide bushing 8 is positioned between the force-applying component 2 and the main body 1 to precisely guide the axial sliding of the force-applying component 2, preventing it from tilting or jamming during floating. The base is fixedly connected to the main body 1, undertaking the functions of overall positioning, load-bearing, and connection with the robot. The lower end of the base may have a standard interface for quick docking with the flange at the end of the robotic arm, allowing the robot gripper to be detachably installed as an independent tooling module on the standard interface for easy changeover and maintenance.

[0027] like Figure 1 As shown, multiple force-applying components 2 are slidably arranged axially within the body 1, forming a force-applying component array. The force-applying components 2 are the actuating parts that directly contact and support the workpiece 6, and their number, arrangement density, and diameter are optimized according to the size and surface morphology characteristics of the workpiece 6. In this embodiment, the force-applying components 2 are uniformly arranged in an array on the top of the body 1, with appropriate spacing between adjacent force-applying components 2 to ensure dense support for the surface of the workpiece 6. A sliding cavity 21 is provided around the center of each force-applying component 2. The sliding cavity 21 allows the force-applying component 2 to freely adjust its axial position when the phase change material is in a liquid state, thereby achieving adaptive fitting to the surface contour of the workpiece 6.

[0028] The medium-containing chamber 3 covers a portion of the movable part of the force-applying component 2, serving to contain and constrain the phase change material. The medium-containing chamber 3 achieves adjustable and locked states through a solid-liquid phase change: when the phase change material is in a liquid state, the force-applying component 2 can freely adjust its axial position; when the phase change material cools and solidifies, the rigidity of the solidified material locks the position of the force-applying component 2 as a whole. The phase change material can be low-melting-point metals, paraffin wax, water, etc., preferably low-melting-point metals. Low-melting-point metals possess both high volumetric rigidity and excellent thermal conductivity, forming a stable load-bearing framework in the solidified state and allowing for free adjustment of the force-applying component 2 in the molten state.

[0029] like Figure 3As shown, the force-applying component 2 is circumferentially equipped with a serrated structure 22, which is alternately arranged along the length of the force-applying component 2. Adjacent serrations form a receiving groove 31 for accommodating the phase change material. In other words, one side of the phase change material in the medium receiving chamber 3 also forms a serrated structure. More importantly, the phase change material in the medium receiving chamber 3 is distributed in a thin layer, and this thin layer has a serrated structure, which is alternately arranged along the length of the force-applying component 2. This distributed thin-layer arrangement significantly increases the contact area between the phase change material and the heat exchange gas, resulting in an exponential reduction in both the heating / melting time and the cooling / solidification time. The thin-layer serrated structure of this invention reduces the phase change switching time for a single clamping operation from minutes to seconds, significantly improving the clamping cycle time.

[0030] Specifically, the body 1 is also equipped with a sealing component 9. The sealing component 9 is arranged around the force-applying member 2 and is located at both ends of the medium receiving chamber 3 to prevent leakage of the liquid phase change material in the molten state and ensure the sealing reliability of the medium receiving chamber 3.

[0031] like Figure 3 As shown, channel 4 extends upward from the bottom of claw 7, forming a blind-hole structure. Temperature-controlled gas enters from the bottom and is transferred upward along channel 4 to heat or cool the medium-containing chamber 3. The arrangement of channel 4 ensures heat is transferred upward along each channel, creating a uniform temperature field distribution and preventing localized overheating or undercooling in the medium-containing chamber 3. The temperature-controlled gas includes hot gas for heating the phase change material and cold gas for accelerating its cooling; these are alternately introduced into channel 4. The hot gas can be compressed air or an inert gas, while the cold gas can be ambient temperature compressed air or a cooled gas. By adjusting the temperature, flow rate, and duration of the hot and cold gases, the phase change process of the phase change material can be precisely controlled.

[0032] In this invention, the temperature-controlled gas introduced into channel 4 serves both as a heat exchange medium for the phase change material to drive its phase change and as a mechanical medium that forms a gas spring effect below the force-applying component 2 to provide flexible support for it. Specifically, the gas forms a controllable air cushion or gas spring effect below the force-applying component 2, providing basic support and reset force for it. This avoids the need for additional independent heating rods, cooling channels, and hydraulic buffer cylinders, simplifying the internal space of the tooling and utilizing the low thermal inertia of the gas to achieve synchronous and rapid control of temperature and the support force of the force-applying component.

[0033] like Figure 3As shown, the elastic element in the robot gripper is preferably a mechanical spring 5. The mechanical spring 5 works in conjunction with the gas spring to provide a restoring force for the force-applying element 2 when the phase change material melts. The mechanical spring 5 is preferably a helical spring, which is disposed in the sliding cavity 21. A functional part 23 extends circumferentially from the force-applying element 2. The two ends of the helical spring abut against the functional part 23 and the bottom of the body 1, respectively. The functional part 23 is preferably an annular thin plate extending radially outward from the force-applying element 2. Two annular thin plates are preferably arranged at intervals on the force-applying element 2. A medium receiving chamber 3 is disposed between the two annular thin plates, and a sealing component 9 is disposed between the medium receiving chamber 3 and the annular thin plates. When the phase change material melts, the force-applying element 2 is reset to its initial position under the combined action of the elastic restoring force of the mechanical spring 5 and the gas thrust of the gas spring, as shown. Figure 1 As shown, this prepares for the next clamping cycle. The coordinated design of the mechanical spring 5 and the gas spring ensures that the resetting process of the force-applying component 2 has both the reliability and certainty of the mechanical spring and the flexibility and adjustability of the gas spring, enabling it to adapt to workpieces 6 with different weights and surface morphologies.

[0034] At least two claws 7 are arranged opposite each other to form a clamping configuration for the workpiece 6. In one feasible embodiment, the robotic gripper includes two symmetrically arranged claws 7, with the force-applying elements of the two claws 7 arranged opposite each other, and the workpiece 6 located between the two claws 7. When the workpiece 6 is pressed against the tops of the multiple force-applying elements 2, each force-applying element 2 undergoes different displacements according to the surface contour of the workpiece 6, forming a support surface that matches the shape of the workpiece 6. The support surfaces of the two claws 7 together enclose the workpiece 6, achieving stable clamping of the workpiece 6, such as... Figure 1 , Figure 2 As shown.

[0035] In this invention, the phase change material, in its solidified state, forms a rigid locking structure distributed around the movement path of the force-applying component 2. This rigid locking structure provides structural support for the force-applying component 2 under heavy load conditions. Specifically, after the phase change material cools and solidifies, the solid metal distributed around the force-applying component 2 not only locks the axial position of the force-applying component 2, but also provides distributed structural support for the force-applying component 2 under heavy load conditions, effectively suppressing the micro-displacement and vibration of the force-applying component 2 under various forces and vibrations. This design, using solidified metal as a load-bearing skeleton, allows the robot gripper of this invention to maintain flexible adaptive capabilities while possessing the load-bearing capacity of traditional dedicated rigid clamps. Thus, based on the efficient adaptive fitting of the irregular curved workpiece 6, it further addresses the high-rigidity clamping requirements under heavy load conditions.

[0036] The working principle of this invention is as follows: The following is combined Figures 1 to 3 The working principle of the robot gripper of this invention is explained in detail.

[0037] First, the phase change material melting stage. Hot gas is introduced into channel 4, and the hot gas is transferred upward from the bottom of claw 7 along channel 4, convectively heating the medium containing chamber 3. Due to the thin-layer distribution of the phase change material and its serrated structure, the heat exchange area between the hot gas and the phase change material is greatly increased, and the phase change material melts rapidly in a short time. After the phase change material melts, the force-applying component 2 loses its axial constraint and gains free adjustment capability. At this time, the introduced gas forms a gas spring effect below the force-applying component 2, which, together with the mechanical spring 5, provides basic support force for the force-applying component 2, putting the force-applying component 2 in a ready state.

[0038] Secondly, the workpiece 6 is pressed in and adaptively fitted. The robot presses the workpiece 6 onto the top of multiple force-applying components 2. Each force-applying component 2 generates different displacements according to the surface contour of the workpiece 6. The force-applying components 2 slide freely within the sliding cavity 21, forming a support surface that matches the shape of the workpiece 6. During this process, the compliance of the gas spring allows the force-applying components 2 to smoothly adapt to the slight undulations and curvature changes on the surface of the workpiece 6, avoiding local false contact or stress concentration. The support surfaces of the two claws 7 together envelop the workpiece 6, achieving initial positioning and clamping of the workpiece 6.

[0039] Next, the cooling, solidification, and position locking stage. Hot gas is stopped, and cold gas is introduced into channel 4. The cold gas accelerates forced convection cooling, causing the liquid phase change material to rapidly cool and solidify. The solidified phase change material uses its material stiffness to lock the position of the force-applying component 2, forming a stable and reliable clamping. Simultaneously, the solidified metal is distributed around the movement path of the force-applying component 2, forming a rigid locking structure that provides structural support for the force-applying component 2 under subsequent heavy loads, greatly enhancing the overall rigidity of the tooling.

[0040] Fourth, the machining stage. After the position of the force-applying component 2 is locked and the rigid locking structure is formed, the robot gripper stably holds the workpiece 6, and the robotic arm or machine tool performs machining operations on the workpiece 6. Due to the auxiliary force-bearing effect of the solidified metal, the force-applying component 2 will not undergo micro-displacement or vibration under the action of cutting or grinding forces, ensuring machining accuracy and surface quality.

[0041] Finally, the phase change material remelting and the force-applying component reset stage. After processing, the multiple claws 7 separate from each other, and hot gas is introduced into the channel 4 again to remelt the phase change material. Under the combined action of the elastic restoring force of the mechanical spring 5 and the gas thrust of the gas spring, the force-applying component 2 resets to its initial position, and the workpiece 6 can be removed and enter the next clamping cycle.

[0042] As can be seen from the above working principle, this invention uses the temperature-controlled gas introduced through channel 4 as the sole energy medium to achieve forced heat exchange and phase change drive of the phase change material. Simultaneously, while providing heat exchange drive, the gas, together with the pre-installed mechanical spring 5, acts as a flexible pneumatic support for multiple force-applying components 2, essentially functioning as a gas spring. By distributing liquid metal around the movement path of the force-applying components 2 in a way that increases the heat exchange area, it not only solves the industry pain points of large thermal inertia and slow cycle time of traditional phase change fixtures, but also creatively utilizes the structural rigidity of solidified metal as a rigid locking structure. Thus, while completely eliminating high-precision pneumatic control components and independent heating and cooling units, it simultaneously meets the requirements of efficient adaptive fitting of irregularly shaped curved workpieces 6 and high-rigidity clamping under heavy-duty cutting conditions.

[0043] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the tooling or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0044] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A robotic gripper, characterized in that, It includes at least two claws (7), each of the claws (7) including a body (1), multiple force-applying elements (2) and an elastic element; Multiple force-applying components (2) are slidably arranged in the body (1) along the axial direction. A medium-containing chamber (3) is arranged circumferentially on the force-applying component (2). The medium-containing chamber (3) covers the movable part of the force-applying component (2) and is filled with a phase change material. The phase change material can reversibly change phase between solid and liquid to selectively lock or release the force-applying component (2). The force-applying component (2) has a channel (4) for introducing a temperature-controlled gas. The temperature-controlled gas serves as both a heat exchange medium for the phase change material to drive its phase change and a mechanical medium for forming a gas spring effect below the force-applying component (2) to provide flexible support for the force-applying component (2). The elastic element is arranged circumferentially along the force-applying element (2) and works in conjunction with the gas spring to provide flexible support force to the force-applying element (2) when the phase change material melts.

2. The robot gripper according to claim 1, characterized in that, The phase change material in the medium containing chamber (3) is distributed in a thin layer, and the phase change material is selected from any one of low melting point metal, paraffin, and water.

3. The robot gripper according to claim 1, characterized in that, The force-applying member (2) is circumferentially arranged with a sawtooth structure (22), which is alternately arranged along the length of the force-applying member (2), and a receiving groove (31) for accommodating the phase change material is formed between adjacent sawtooths.

4. The robot gripper according to claim 1, characterized in that, The channel (4) extends from the lower end of the force-applying member (2) to the upper end and is disposed inside the force-applying member (2). The temperature-controlled gas is introduced from the lower end and transmitted to the upper end along the channel (4) to heat or cool the medium-containing chamber (3).

5. The robot gripper according to claim 1, characterized in that, The elastic element is a helical spring, which is sleeved on the lower end of the force-applying element (2). The force-applying element (2) extends circumferentially to form a functional part (23), and the two ends of the helical spring abut against the functional part (23) and the bottom of the body (1), respectively.

6. The robot gripper according to claim 1, characterized in that, A sliding cavity (21) is provided around the middle part of the force-applying component (2), and the sliding cavity (21) allows the force-applying component (2) to freely adjust its axial position when the phase change material is in a liquid state; The phase change material forms a rigid locking structure distributed around the movement path of the force-applying component (2) in the solidified state, and the rigid locking structure provides structural support for the force-applying component (2) under heavy load conditions.

7. The robot gripper according to claim 1, characterized in that, It also includes a base, the main body (1) is connected to the base, and the base undertakes the functions of overall positioning, bearing and connection with the robot.

8. The robot gripper according to claim 1, characterized in that, The two claws (7) are arranged opposite each other. When the workpiece (6) is pressed into the top of the plurality of force-applying members (2), each force-applying member (2) generates different displacements according to the surface contour of the workpiece (6) to form a support surface that matches the shape of the workpiece (6).

9. The robot gripper according to claim 1, characterized in that, It also includes a guide bushing (8), which is disposed between the force-applying member (2) and the body (1) to guide the axial sliding of the force-applying member (2).

10. The robot gripper according to claim 1, characterized in that, It also includes a sealing assembly (9) disposed at the periphery of the medium receiving chamber (3) to prevent leakage of liquid phase change material.

Images