Machine assistance device

Abstract

The invention provides a machine auxiliary device which can assist in supporting operation of a steam turbine. Wherein the metal grating is laid on the outer surface of a lower cylinder body of a cylinder of the steam turbine. And the electric heating belt is wound on the outer surface of the metal grating and can be electrified to heat the lower cylinder body. The heat conduction layer is laid on the outer surface of the metal grating and covers the electric heating belt. The machine auxiliary device can avoid the jigger jamming phenomenon by reducing the temperature difference between the upper cylinder body and the lower cylinder body, and therefore normal operation of a steam turbine is maintained.

Description

Technical Field

[0001] The present invention belongs to the field of steam turbines, and in particular, relates to a machine auxiliary device which can assist in supporting the operation of a steam turbine. Background Art

[0002] Steam turbines are widely used in many fields. For example, steam turbines can be used in air separation equipment to consume the work done by compressors. However, it is found during use that after the steam turbine is stopped, the cranking gear often becomes stuck. The cranking gear sticking will affect the subsequent operation of the steam turbine.

[0003] The inventors analyzed that this is because the upper and lower cylinders of the steam turbine have different heat dissipation, so there will be a temperature difference between the upper and lower cylinders. If the temperature difference is too large, it will cause the gap between the upper and lower cylinders to change, resulting in the cranking jam phenomenon.

[0004] Therefore, it is necessary to design a machine auxiliary device that can solve the above problems and assist in supporting the operation of the steam turbine. Summary of the invention

[0005] The purpose of the present invention is to provide a machine auxiliary device which can avoid the phenomenon of cranking jam by reducing the temperature difference between the upper and lower cylinders, thereby maintaining the normal operation of the steam turbine.

[0006] The present invention provides a machine auxiliary device for auxiliary support of the operation of a steam turbine, wherein the cylinder of the steam turbine has an upper cylinder body and a lower cylinder body. The machine auxiliary device comprises a metal grid, an electric belt and a heat-conducting layer. The metal grid is laid on the outer surface of the lower cylinder body. The electric belt is wound around the outer surface of the metal grid and is configured to be energized to heat the lower cylinder body. The heat-conducting layer is laid on the outer surface of the metal grid and covers the electric belt.

[0007] In one embodiment, the metal grid is only provided on the lower cylinder body, but not on the upper cylinder body.

[0008] In one embodiment, the cylinder has a low-pressure side and a high-pressure side in the axial direction. The electric belt comprises a low-pressure electric belt and a high-pressure electric belt which are separately arranged on the low-pressure side and the high-pressure side in the axial direction, and the heat-conducting layer comprises a low-pressure heat-conducting layer and a high-pressure heat-conducting layer which are separately arranged on the low-pressure side and the high-pressure side in the axial direction.

[0009] In one embodiment, each of the low-voltage electric belt and the high-voltage electric belt includes two parallel heating wires, each heating wire is a serpentine line extending along the circumference of the cylinder, and the amplitude of the serpentine line in the axial direction is greater than the distance in the circumferential direction.

[0010] In one embodiment, the minimum interval between the two heating wires of each heating belt is more than 20 mm. The amplitude of the serpentine line is 10 to 30 times the distance.

[0011] In one embodiment, the distance between each heating wire of the low-voltage electric belt is greater than the distance between each heating wire of the high-voltage electric belt.

[0012] In one embodiment, the low-voltage electric belt and the high-voltage electric belt are spaced 25 mm to 40 mm apart in the axial direction.

[0013] In one embodiment, the machine auxiliary device includes a controller and a temperature detection component, and the controller controls the switching of the electric belt according to the temperature detected by the temperature detection component.

[0014] In one embodiment, the machine auxiliary device includes a controller and a plurality of temperature sensors, and the plurality of temperature sensors are used to detect the temperature of the upper cylinder body on the low pressure side and the high pressure side, and the temperature of the lower cylinder body on the low pressure side and the high pressure side, respectively. When the first temperature difference between the upper cylinder body and the lower cylinder body on the low pressure side is above the first upper limit value, the controller sends a low pressure start signal to the low pressure electric belt to start the low pressure electric belt, and, when the first temperature difference is below the first lower limit value, the controller sends a signal to shut down the low pressure electric belt to the low pressure electric belt. Wherein, the first lower limit value is less than the first upper limit value. When the second temperature difference between the upper cylinder body and the lower cylinder body on the high pressure side is above the second upper limit value, the controller sends a high pressure start signal to start the high pressure electric belt to the high pressure electric belt, and, when the second temperature difference is below the second lower limit value, the controller sends a signal to shut down the high pressure electric belt to the high pressure electric belt. Wherein, the second lower limit value is less than the second upper limit value.

[0015] In one embodiment, when the first temperature difference still exceeds the predetermined value after the low-voltage start signal is sent for a predetermined time, the controller continues to send a signal to the high-voltage electric belt to start the high-voltage electric belt. When the second temperature difference still exceeds the predetermined value after the high-voltage start signal is sent for a predetermined time, the controller continues to send a signal to the low-voltage electric belt to start the low-voltage electric belt.

[0016] In the above-mentioned machine auxiliary device, the lower cylinder body can be heated by using the electric heating belt arranged in the lower cylinder body, thereby reducing the temperature difference between the upper and lower cylinder bodies, thereby avoiding the phenomenon of cranking jamming and ultimately maintaining the normal operation of the turbine.

[0017] Furthermore, in the above machine auxiliary device, by laying a heat-conducting layer, the heat generated by the electric belt can be evenly distributed on the outer surface of the lower cylinder body, thereby improving the heating efficiency. Moreover, by laying a metal grid under the electric belt and the heat-conducting layer, the two can be reliably fixed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The advantages and spirit of the present invention can be further understood through the following detailed description of the invention and the accompanying drawings.

[0019] Figure 1 is a schematic diagram of an exemplary machine assist device.

[0020] Figure 2 is a schematic diagram exemplarily showing the distribution of heating wires. DETAILED DESCRIPTION

[0021] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. However, the present invention should be understood to be not limited to the embodiments described below, and the technical concept of the present invention can be implemented in combination with other known technologies or functions, or other technologies that are the same as those known technologies.

[0022] For example, a first feature described later in the specification as being formed above or on a second feature may include an embodiment in which the first feature and the second feature are formed by direct connection, and may also include an embodiment in which an additional feature is formed between the first feature and the second feature, so that the first feature and the second feature may not be directly connected. Further, when a first element is described as being connected or combined with a second element, the description includes an embodiment in which the first element and the second element are directly connected or combined with each other, and also includes an embodiment in which one or more other intervening elements are added to indirectly connect or combine the first element and the second element.

[0023] The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by the ordinary skill in the art to which the invention belongs. It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with their meaning in the context of this specification and the related art, and should not be understood in an idealized or overly formal sense unless expressly provided herein. For the sake of brevity and / or clarity, well-known functions or configurations may not be described in detail.

[0024] The inventors have found that when the temperature difference between the upper and lower cylinders of the turbine cylinder is controlled within 10°C, the turbine cranking is normal. However, when the temperature difference between the upper and lower cylinders is greater than 20°C due to uneven heat dissipation, the cranking becomes stuck. Analysis shows that this is because when the temperature difference is too large, especially when the temperature of the upper cylinder is higher than that of the lower cylinder, the deformation of the upper cylinder is greater than that of the lower cylinder, resulting in a decrease in the radial clearance between the bottom of the lower cylinder and the impeller, increasing the friction between the impeller and the static cylinder part, resulting in increased friction of the rotor and jamming. Moreover, the temperature change of the upper cylinder is slower than that of the lower cylinder, so the overall deformation will cause the partition and the impeller to deviate from the normal vertical plane, and the axial clearance between the lower cylinder and the upper cylinder and the impeller will be inconsistent, which will further cause axial dynamic and static friction, resulting in high vibration and jamming of the unit. Therefore, it is particularly easy to have problems such as cranking jamming in general.

[0025] The machine auxiliary device 10 provided by the present invention is used to assist in supporting the operation of a steam turbine. The cylinder 80 of the steam turbine has an upper cylinder body 81 and a lower cylinder body 82. It is understood that the directional words "upper" and "lower" here refer to the relative position of the cylinder 80 when the steam turbine is operating normally. It is understood that the drawings in the text are only for example and are not necessarily drawn according to the conditions of equal proportion, and should not be considered to limit the actual protection scope of the present invention.

[0026] The machine auxiliary device 10 includes a metal grid 1, an electric belt 2 and a heat-conducting layer 3. The metal grid 1 is laid on the outer surface of the lower cylinder 82. The electric belt 2 is wound around the outer surface of the metal grid 1 and is configured to be energized to heat the lower cylinder 82. The heat-conducting layer 3 is laid on the outer surface of the metal grid 1 and covers the electric belt 2.

[0027] In the above-mentioned machine auxiliary device 10, by laying the electric belt 2 on the outer surface of the lower cylinder 82, when the temperature of the upper cylinder 81 is much higher than that of the lower cylinder 82, the electric belt 2 can be energized, thereby heating the lower cylinder 82, reducing the temperature difference between them, thereby maintaining the distance between them and avoiding the wheel from getting stuck. Moreover, in the above-mentioned machine auxiliary device 10, by providing the metal grid 1, it is not only conducive to laying and fixing the electric belt 2, but also conducive to laying the heat conductive layer 3. The heat conductive layer 3 is not only conducive to further fixing the electric belt 2, but also can evenly disperse the heat to the entire covered surface.

[0028] See also Figure 1 The metal grille 1 is only provided on the lower cylinder 82, but not on the upper cylinder 81. This is because, according to the inventor's research and analysis, in actual design, various pipes are basically provided on the lower cylinder 82, such as Figure 1 The low-pressure side, medium-pressure side, high-pressure side shower pipes 91, 93, 92 and drain pipe 94 are shown. In addition, Figure 1 The figure also shows the upper and lower cylinder speed regulating valves 95 and 96 and the exhaust steam exhaust pipe 97. As shown in the figure, the lower cylinder body has multiple exhaust and condensation pipes, and the lower cylinder body is heavy and has a large heat dissipation area. Therefore, the lower cylinder body 82 dissipates heat faster than the upper cylinder body 81, which is an important reason for the temperature difference between the two. Moreover, the steam in the cylinder rises, the condensed water flows down, and the air in the cylinder convects after shutdown, and the high-temperature air gathers in the upper cylinder body, while the air temperature of the lower cylinder body is low. The thermal insulation protection of the outer surface of the lower cylinder body is not as strict as that of the upper cylinder body due to the influence of gravity. Therefore, the lower cylinder body cools down faster. Therefore, it is more reasonable to install electric belts only on the lower cylinder body, which is more helpful to control the temperature difference between the upper and lower cylinders. This can reduce the number of electric belts installed and save energy. Moreover, it can achieve the normal cooling rate of the cylinder body after shutdown to avoid slow cooling. Therefore, it is only necessary to set the metal grid 1 and the associated electric belt 2 and heat conductive layer 3 on the lower cylinder body 82, so as to avoid the jamming phenomenon at the most optimized cost.

[0029] See also Figure 1 The cylinder 80 has a low-pressure side Sa and a high-pressure side Sb along the axial direction X0. The axial direction X0 is also the extension direction of the rotor shaft 801 of the cylinder 80, or the central axis direction. The subsequent circumferential direction C0 is also the circumferential direction of the rotor shaft 801, or the rotation direction. The low-pressure side Sa and the high-pressure side Sb are also the exhaust side and the intake side of the cylinder 80, and are also often referred to as the low-temperature low-pressure side and the high-temperature high-pressure side.

[0030] The electric belt 2 includes a low-pressure electric belt 2a and a high-pressure electric belt 2b which are separately arranged on the low-pressure side Sa and the high-pressure side Sb along the axial direction X0. The heat-conducting layer 3 includes a low-pressure heat-conducting layer 3a and a high-pressure heat-conducting layer 3b which are separately arranged on the low-pressure side Sa and the high-pressure side Sb along the axial direction X0. The temperature difference of the cylinder 80 at the low-pressure side Sa and the high-pressure side Sb is different, and the above arrangement makes it possible to control them separately according to different areas, that is, zoning control. This can evenly heat the lower cylinder body, reduce the temperature difference, and has lower operating costs and higher efficiency.

[0031] Preferably, the heat conductive layer 3 is diatom mud. Diatom mud can perfectly adapt to the application scenarios in the text. By using diatom mud, heat can be transferred to the lower cylinder 82 more evenly in a short time for heating, and heat can be dissipated into the air more evenly for a long time to dissipate heat. Moreover, static electricity can be eliminated. The electric belt 2 cannot fit the surface of the cylinder well in some parts, so static electricity will be generated, and the external environment may also have static electricity. In addition, the porous structure of diatom mud can effectively absorb the high-frequency noise generated by the operation itself, which helps to achieve the noise reduction effect. Diatom mud can also automatically adjust the moisture according to the changes in the humidity on the surface of the lower cylinder to maintain a relative balance of humidity. It is worth noting that condensation water is easily formed in the lower cylinder, and as mentioned earlier, there are multiple condensation water drainage pipes, so the humidity on the surface of the cylinder is high.

[0032] See also Figure 2 Each of the low-voltage electric heating belt 2a and the high-voltage electric heating belt 2b, for example, 2a, includes two parallel heating wires 21. Each heating wire 21 is a serpentine line extending along the circumferential direction C0 of the cylinder 80, and the amplitude a0 of the serpentine line (or, the heating wire 21) in the axial direction X0 is greater than the distance g0 in the circumferential direction C0. The serpentine line is a wavy line with a periodic cycle of crests, troughs, crests, and troughs. As shown in the figure, the amplitude a0 is the distance between the crest point and the trough point in the direction perpendicular to the extension direction (that is, the axial direction X0), and the distance g0 is the distance between the crest point and the corresponding crest point in the extension direction (that is, the circumferential direction C0). The structure of the above-mentioned electric heating belt can make the layout convenient and the heating effect is good. The electric heating belt, electric heating wire, etc. in the text are often referred to as heating belts, heating wires, etc. in engineering.

[0033] See also Figure 2, the minimum interval m0 between the two heating wires 21 of each electric heating belt 2a is more than 20mm, for example, 25mm. The amplitude a0 of the serpentine trace 21 is 10 to 30 times the distance g0. The minimum m0 is the smallest of the interval distances between all corresponding points of the two heating wires 21 in the direction of the line connecting the two. The above structure allows the heating wire to be arranged basically parallel to the rotor axis, which can help reduce the curvature of the heating wire, balance the heat generated by the resistors at each point, and avoid large local temperature deviations. Moreover, it can be easily arranged and the heating effect is guaranteed.

[0034] See also Figure 1 , the distance g0 of each heating wire 21 of the low-voltage electric belt 2a is greater than the distance of the heating wire of the high-voltage electric belt 2b. This is an optimized arrangement based on the difference between the low-voltage side Sa and the high-voltage side Sb. The mesh size of the metal grid 1 can be less than 1 / 4 of the distance g0 of the serpentine wiring 21, for example, 1 / 10, to facilitate the arrangement and support of the electric belts 2a and 2b.

[0035] See also Figure 1 The low-voltage electric heating belt 2a and the high-voltage electric heating belt 2b are spaced 25 mm to 40 mm apart in the axial direction X0. Figure 1 As shown in p0. In this way, the independent effects and cooperative effects of the low-pressure side Sa and the high-pressure side Sb can be balanced. It can be understood that the range values ​​in the text include the endpoint values.

[0036] See also Figure 1 The machine auxiliary device 10 includes a controller 4 and a temperature detection component 5. The controller 4 controls the switch of the electric belt 2 according to the temperature detected by the temperature detection component 5.

[0037] The controller may be one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. The temperature detection component may include, for example, various sensors, such as thermocouples.

[0038] See also Figure 1 The machine auxiliary device 10 includes a controller 4 and a plurality of temperature sensors such as 51a, 51b, 52a, 52b. The plurality of temperature sensors 51a, 51b, 52a, 52b are used to detect the temperature of the upper cylinder 81 at the low pressure side Sa and the high pressure side Sb, and the temperature of the lower cylinder 82 at the low pressure side Sa and the high pressure side Sb. Figure 1 Although the controller 4 is shown as two separate parts, it can be integrated into one. The aforementioned plurality of temperature sensors 51a, 51b, 52a, 52b can be considered to constitute the aforementioned temperature detection component 5.

[0039] When the first temperature difference dT1 between the upper cylinder 81 and the lower cylinder 82 on the low-pressure side Sa is above the first upper limit, for example, 5°C, the controller 4 sends a low-pressure start signal H1 to the low-voltage electric belt 2a to start the low-voltage electric belt 2a. And, when the first temperature difference dT1 is below the first lower limit, for example, 2°C, the controller 4 sends a signal to shut down the low-voltage electric belt 2a. Among them, the aforementioned first lower limit is less than the aforementioned first upper limit. It can be understood that "above" and "below" in the text can be actually implemented as greater than, less than, and can also be actually implemented as greater than or equal to, less than or equal to.

[0040] When the second temperature difference dT2 between the upper cylinder body 81 and the lower cylinder body 82 on the high-pressure side Sb is above the second upper limit, for example, 5°C, the controller 4 sends a high-voltage start signal H2 to the high-voltage electric belt 2b to start the high-voltage electric belt 2b. And, when the second temperature difference dT2 is below the second lower limit, for example, 2°C, the controller 4 sends a signal to shut down the high-voltage electric belt 2b to the high-voltage electric belt 2b. The aforementioned second lower limit is less than the aforementioned second upper limit. Starting the electric belt, for example, turning on the electric belt to start heating, and shutting down the high-voltage electric belt, for example, turning off the electric belt to stop heating.

[0041] The above settings can realize automatic control. By default, the electric heating belt can be in the off state. It can be understood that the terms "first" and "second" are only used for descriptive purposes, and do not refer to the limitation of time sequence, quantity, or importance. They cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated, but are only for distinguishing one technical feature from another technical feature in the technical solution. Therefore, the features defined as "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more than two (that is, more than two), unless otherwise clearly specified. Similarly, the qualifier similar to "one" that appears in the text does not refer to the limitation of quantity, but describes the technical features that have not appeared in the previous text. Similarly, unless it is a noun modified by a specific quantitative quantifier, the text should be regarded as including both singular and plural forms, and the technical solution can include both singular and plural technical features. Similarly, modifiers such as "about" and "approximately" that appear before a numeral in a text usually include the number itself, and their specific meaning should be understood in the context.

[0042] Further, when the first temperature difference dT1 still exceeds the predetermined value after the low-voltage start signal H1 is sent for a predetermined time, for example, 5 minutes, the controller 4 continues to send a signal to the high-voltage electric belt 2b to start the high-voltage electric belt 2b. When the second temperature difference dT2 still exceeds the predetermined value after the high-voltage start signal H2 is sent for a predetermined time, the controller 4 continues to send a signal to the low-voltage electric belt 2a to start the low-voltage electric belt 2a. The aforementioned predetermined value may be, for example, higher than the previous upper limit, such as 10°C. The above setting can make full use of the electric belts on both sides in some extreme cases, such as when the heat dissipation of the lower cylinder is particularly fast and the temperature difference is not easy to reduce, and quickly control the temperature difference within a controllable range.

[0043] During actual installation, the cylinder insulation structure can be removed after the turbine is shut down and the cylinder body cools down to a temperature below 150° C. Preferably, the upper and lower cylinder bodies are removed at the same time to avoid too fast removal on the same side, too large temperature difference, and stress deformation and damage to the turbine.

[0044] Then, clean the impurities on the cylinder surface, fix the rivets with argon arc welding, and fix the stainless steel grille as the metal grille on the outer wall of the rivets. At the curved surface, bend and correct the metal grille to ensure that the metal grille fits completely with the cylinder wall.

[0045] Afterwards, two heating wires are connected in parallel and fixed tightly to the grid mesh, and the minimum spacing between the heating wires is set at 25mm to ensure that they do not interfere with each other.

[0046] Thermocouples used as temperature sensors can be fixed on the same vertical plane (that is, perpendicular to the central axis) of the upper and lower cylinder surfaces and do not contact the heating wire. The heating wire is evenly covered with diatom mud.

[0047] Conduct loop resistance test on heating wire, thermocouple, etc., and confirm again that the heating area of ​​heating wire is consistent with the power wiring of control cabinet. Finally, repair the insulation layer on the outer surface of cylinder body, and ensure that the insulation layer fits tightly with the diatom mud on the outside of heating wire to reduce the heat diffusion loss of lower cylinder body. After installation, conduct reliability test, the result is qualified, and there is a sign of weakened magnetism.

[0048] In general, the use of the above-mentioned machine auxiliary devices can assist the normal operation or shutdown of the steam turbine, reduce the temperature difference between the upper and lower cylinders of the steam turbine, and improve reliability.

[0049] Unless clearly indicated to the contrary, each aspect or embodiment defined herein may be combined with any other aspect or embodiments. In particular, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0050] The preferred specific embodiments of the present invention are described in this specification. The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Any technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments according to the concept of the present invention should be within the scope of the present invention.

Claims

1. A machine auxiliary device for assisting the operation of a steam turbine, wherein the cylinder of the steam turbine has an upper cylinder body and a lower cylinder body, characterized in that: The machine auxiliary device comprises: A metal grille is laid on the outer surface of the lower cylinder body; An electric belt, wound around the outer surface of the metal grid, configured to be energized to heat the lower cylinder; and The heat-conducting layer is laid on the outer surface of the metal grid and covers the electric heating belt.

2. The machine-assisted device according to claim 1, characterized in that: The metal grille is only arranged on the lower cylinder body, but not on the upper cylinder body.

3. The machine-assisted device according to claim 1, characterized in that: The cylinder has a low-pressure side and a high-pressure side in the axial direction; The electric belt includes a low-pressure electric belt and a high-pressure electric belt which are axially separated and arranged on the low-pressure side and the high-pressure side, and the heat-conducting layer includes a low-pressure heat-conducting layer and a high-pressure heat-conducting layer which are axially separated and arranged on the low-pressure side and the high-pressure side.

4. The machine-assisted device according to claim 3, characterized in that: Each of the low-voltage electric heating belt and the high-voltage electric heating belt includes two parallel heating wires, each heating wire is a serpentine line extending along the circumference of the cylinder, and the amplitude of the serpentine line in the axial direction is greater than the distance in the circumferential direction.

5. The machine-assisted device according to claim 4, characterized in that: The minimum distance between the two heating wires of each heating belt is more than 20mm; The amplitude of the serpentine routing is 10 to 30 times the distance.

6. The machine-assisted device according to claim 4, characterized in that: The distance between each heating wire of the low-voltage electric belt is greater than the distance between the heating wires of the high-voltage electric belt.

7. The machine-assisted device according to claim 3, characterized in that: The low-voltage electric belt and the high-voltage electric belt are spaced 25 mm to 40 mm apart in the axial direction.

8. The machine-assisted device according to claim 1, characterized in that: The invention comprises a controller and a temperature detection component. The controller controls the switch of the electric belt according to the temperature detected by the temperature detection component.

9. The machine-assisted device according to claim 1, characterized in that: It includes a controller and a plurality of temperature sensors, wherein the plurality of temperature sensors are used to respectively detect the temperature of the upper cylinder body at the low pressure side and the high pressure side, and the temperature of the lower cylinder body at the low pressure side and the high pressure side; When the first temperature difference between the upper cylinder body and the lower cylinder body on the low-pressure side is above a first upper limit value, the controller sends a low-pressure start signal to the low-pressure electric belt to start the low-pressure electric belt, and when the first temperature difference is below a first lower limit value, the controller sends a signal to the low-pressure electric belt to shut down the low-pressure electric belt, wherein the first lower limit value is less than the first upper limit value; When the second temperature difference between the upper cylinder body and the lower cylinder body on the high-pressure side is above the second upper limit value, the controller sends a high-pressure start signal to the high-pressure electric belt to start the high-pressure electric belt, and when the second temperature difference is below the second lower limit value, the controller sends a signal to the high-pressure electric belt to shut down the high-pressure electric belt, wherein the second lower limit value is less than the second upper limit value.

10. The machine-assisted device according to claim 9, characterized in that When the first temperature difference still exceeds a predetermined value after the low-voltage start signal is sent for a predetermined period of time, the controller continues to send a signal to the high-voltage electric belt to start the high-voltage electric belt; When the second temperature difference still exceeds a predetermined value after the high-voltage start signal is sent for a predetermined period of time, the controller continues to send a signal to the low-voltage electric belt to start the low-voltage electric belt.

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