Pendulum type quasi-zero-stiffness vibration absorption energy harvesting system

Abstract

The invention relates to a pendulum type quasi-zero stiffness vibration absorption energy harvesting system, which belongs to the field of vibration absorption energy harvesting structures and comprises a horizontally arranged linear mounting shaft, a movable pendulum is arranged on the mounting shaft, the top end of the movable pendulum is rotatably arranged on the mounting shaft, a rotating shaft of the movable pendulum coincides with the axis of the mounting shaft, and the movable pendulum is naturally drooping. A sector-ring-shaped first permanent magnet is further embedded in the movable pendulum, and the first permanent magnet and the mounting shaft are coaxially arranged; a fixed pendulum is further fixedly arranged on the mounting shaft, a second permanent magnet corresponding to the first permanent magnet is arranged in the fixed pendulum, the second permanent magnet is in a sector ring shape with the axis coinciding with the axis of the mounting shaft, and the second permanent magnet is transversely aligned with the first permanent magnet; the second permanent magnet and the first permanent magnet are magnetized in the axial direction and repel each other. While efficient low-frequency vibration suppression is kept, part of vibration energy can be converted into electric energy to be recycled.

Description

Technical Field

[0001] The present invention relates to the field of vibration absorption and energy harvesting structures, and particularly to a pendulum-type quasi-zero stiffness vibration absorption and energy harvesting system. Background Art

[0002] With the rapid development of high-precision equipment technology towards the extreme and intelligent directions, the requirements for vibration environment control in fields such as aerospace vehicles, marine equipment, large-scale scientific research facilities, and intelligent robots are becoming increasingly stringent. During the service of equipment, when the vibration level of the structure exceeds the design threshold, effective vibration control measures must be taken in a timely manner to eliminate the potential threats posed by vibration to the functional integrity and operational reliability of the system.

[0003] As an important branch in the field of vibration engineering, dynamic vibration absorption technology has received extensive attention from the academic and engineering circles due to its unique mechanical control mechanism. This technology couples an additional dynamic system in the main structure and uses the phase reaction force generated by the mass-spring resonance unit to form a dynamic balance with the external excitation, thereby achieving targeted dissipation of the vibration energy of the main system. Compared with traditional vibration isolation technology, dynamic vibration absorption technology has three significant advantages: it can achieve compact vibration reduction without configuring a vibration isolation layer or a special support, and has good space adaptability; it has strong universality and can meet the requirements of various stiffness systems such as building steel structures, bridge engineering, and rotating machinery; it will not cause secondary interference due to the additional structure changing the original mechanical transmission path.

[0004] However, the existing mainstream linear dynamic vibration absorbers are constructed based on classical resonance theory, and they face the following technical bottlenecks in low-frequency vibration control: limited by the physical limit of linear stiffness, it is difficult to achieve the ultra-low stiffness design required for low-frequency (<20 Hz) and even ultra-low frequency (<5 Hz) vibrations.

[0005] Based on this, the present invention proposes a pendulum-type quasi-zero stiffness vibration absorption and energy harvesting integrated system, which breaks through the linear stiffness limit through a unique geometric nonlinear design and realizes efficient suppression of low-frequency and ultra-low frequency vibrations in the quasi-zero stiffness range. Summary of the Invention

[0006] The present invention provides a pendulum-type quasi-zero stiffness vibration absorption and energy harvesting system, which includes a horizontally arranged linear mounting shaft. A moving pendulum is arranged on the mounting shaft. The top end of the moving pendulum is rotatably arranged on the mounting shaft. The rotation axis of the moving pendulum coincides with the axis of the mounting shaft, and the moving pendulum is arranged in a natural hanging state. A fan-shaped first permanent magnet is also embedded in the moving pendulum, and the first permanent magnet is arranged coaxially with the mounting shaft. A fixed pendulum is also fixedly arranged on the mounting shaft. A second permanent magnet is arranged in the fixed pendulum corresponding to the first permanent magnet. The second permanent magnet is fan-shaped with its axis coinciding with the axis of the mounting shaft, and the second permanent magnet is horizontally aligned with the first permanent magnet. The second permanent magnet and the first permanent magnet are magnetized along their axial directions and repel each other.

[0007] Further, a first mounting surface is formed on one side of the moving pendulum facing the fixed pendulum. The first mounting surface is perpendicular to the axis of the mounting shaft. A first electrode layer is fixedly arranged on the first mounting surface. The first electrode layer is a copper thin film layer after anodic oxidation treatment and covers the first mounting surface. A second mounting surface is formed on one side of the fixed pendulum facing the moving pendulum. The second mounting surface is parallel to the first mounting surface. A second electrode layer is fixedly arranged on the second mounting surface. The second electrode layer is a copper thin film layer and covers the second mounting surface. An FEP thin film layer is adhesively attached to the second electrode layer through an electrically conductive adhesive, and the FEP thin film layer covers the second electrode layer. The first electrode layer is in mutual contact with the FEP thin film layer.

[0008] Further, the first mounting surface is fan-shaped and coaxially with the mounting shaft, and the second mounting surface coincides with the first mounting surface in the horizontal direction.

[0009] Further, the mounting shaft is a cylindrical optical axis. A connecting cylinder is arranged at the top end of the moving pendulum corresponding to the optical axis, and the connecting cylinder is rotatably sleeved on the mounting shaft. A mounting cylinder is arranged at the top end of the fixed pendulum corresponding to the optical axis, and the mounting cylinder is sleeved on the optical axis and fixedly connected to the optical axis.

[0010] Further, a fixed cylinder is also fixedly sleeved on the optical axis, and the fixed cylinder is located on the side of the connecting cylinder away from the mounting cylinder.

[0011] Further, threaded mounting holes are provided on both end faces of the optical axis; one end of the mounting cylinder is sealed to form a first end cap. The mounting cylinder is sleeved on one end of the optical axis and the first end cap abuts against the end face of the optical axis. A first through hole is provided on the first end cap corresponding to the threaded mounting hole. The mounting cylinder is fixedly arranged on the optical axis through bolts that pass through the first through hole and the threaded mounting hole at the same time. A fixing cylinder is sleeved on the other end of the optical axis. One end of the fixing cylinder is sealed to form a second end cap. The second end cap abuts against the end face of the optical axis, and a second through hole is provided on the second end cap corresponding to the threaded mounting hole. The fixing cylinder is fixedly arranged on the optical axis through bolts that pass through the second through hole and the threaded mounting hole at the same time.

[0012] Further, a load block is further included, and a mounting groove for mounting the load block is provided on the moving pendulum.

[0013] Further, the moving pendulum and the first permanent magnet embedded therein are both symmetrically arranged with respect to the vertical plane where the axis of the mounting shaft is located; the number of mounting grooves on the moving pendulum is an even number, and the mounting grooves on the moving pendulum are symmetrically arranged with respect to the vertical plane where the axis of the mounting shaft is located.

[0014] The principle and effects of the present invention will be further described below in combination with the above technical solutions and the drawings: Through the innovative integration of the quasi-zero stiffness vibration absorption structure and the triboelectric energy harvesting unit, the present invention has achieved a double technological breakthrough in low-frequency vibration suppression and energy recovery. Based on the non-contact magnetic repulsion force coupling quasi-zero stiffness mechanism, the present invention forms a non-linear stiffness compensation mechanism through the optimized arrangement of the fan-shaped permanent magnet group, realizing the near-zero adjustment of the system equivalent stiffness near the equilibrium position, that is, reducing the system equivalent stiffness to the quasi-zero state in the low-frequency band, which can effectively suppress vibration in the low-frequency range, so as to achieve efficient suppression of low-frequency and ultra-low-frequency vibrations. At the same time, by integrating the triboelectric generator energy harvesting structure, part of the vibration energy can be converted into electrical energy for recovery while efficiently suppressing low-frequency vibrations.

[0015] In addition, the present invention adopts a pendulum structure to form a quasi-zero stiffness vibration absorption structure, which can effectively reduce the space size of the vibration absorber compared with the traditional linear vibration absorber, and is convenient for its installation in a compact space. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of the pendulum-type quasi-zero stiffness vibration absorption and energy harvesting system according to an embodiment of the present invention; Figure 2 It is an exploded structural diagram of the pendulum-type quasi-zero stiffness vibration absorption and energy harvesting system according to an embodiment of the present invention. REFERENCE SIGNS

[0017] 1 - Bolt, 2 - Fixed cylinder, 3 - Connecting cylinder, 4 - Optical axis, 5 - Fixed pendulum, 6 - Bolt, 7 - Second permanent magnet, 8 - Second electrode layer, 9 - FEP film layer, 10 - First electrode layer, 11 - Moving pendulum, 12 - First permanent magnet, 13 - Load block. Detailed implementation

[0018] For the convenience of those skilled in the art to understand, the present invention will be further described in detail below in conjunction with the drawings and embodiments: As Figure 1-2 , a pendulum - type quasi - zero - stiffness vibration - absorbing and energy - harvesting system includes a horizontally - arranged linear mounting shaft. A moving pendulum 11 is arranged on the mounting shaft. The top end of the moving pendulum 11 is rotatably arranged on the mounting shaft. The rotation axis of the moving pendulum 11 coincides with the axis of the mounting shaft, and the moving pendulum 11 is arranged in a natural hanging state. An annular - sector - shaped first permanent magnet 12 is also embedded in the moving pendulum 11, and the first permanent magnet 12 is coaxially arranged with the mounting shaft; A fixed pendulum 5 is also fixedly arranged on the mounting shaft. A second permanent magnet 7 corresponding to the first permanent magnet 12 is arranged in the fixed pendulum 5. The second permanent magnet 7 is annular - sector - shaped with its axis coinciding with the axis of the mounting shaft, and the second permanent magnet 7 is horizontally aligned with the first permanent magnet 12; The second permanent magnet 7 and the first permanent magnet 12 are magnetized along their axial directions and repel each other.

[0019] In the present invention, the pendulum - type quasi - zero - stiffness vibration - absorbing and energy - harvesting system is installed on the equipment that needs vibration reduction. It can fix the mounting shaft or the fixed pendulum 5 on the equipment to be vibration - reduced through methods such as threaded connection, welding, etc. to complete the installation of the pendulum - type quasi - zero - stiffness vibration - absorbing and energy - harvesting system. Among them, after the pendulum - type quasi - zero - stiffness vibration - absorbing and energy - harvesting system is installed, it is necessary to keep its mounting shaft horizontal. At this time, the moving pendulum 11 is in a natural hanging state, the first permanent magnet 12 in the moving pendulum 11 is horizontally aligned with the second permanent magnet 7 in the fixed pendulum 5, and the pendulum - type quasi - zero - stiffness vibration - absorbing and energy - harvesting system is in a static equilibrium position.

[0020] In the present invention, an installation shaft, a moving pendulum 11, a fixed pendulum 5, and first permanent magnets 12 and second permanent magnets 7 inside the moving pendulum 11 and the fixed pendulum 5 form a vibration absorption structure. The vibration absorption structure is used to generate a force opposite to the vibration direction when the device to be vibration-damped vibrates, effectively reducing its vibration amplitude. Among them, the fixed pendulum 5 is fixedly connected to the installation shaft, the moving pendulum 11 is rotatably arranged on the installation shaft, the second permanent magnets 7 and the first permanent magnets 12 in the fixed pendulum 5 and the moving pendulum 11 are horizontally aligned and repel each other. When the pendulum-type quasi-zero stiffness vibration absorption and energy harvesting system is in the working state, the moving pendulum 11 will deflect relative to the fixed pendulum 5. Due to the repulsive force of the first permanent magnet 12 therein, a negative stiffness is generated, and the negative stiffness will cancel out the torsional positive stiffness caused by the gravity of the moving pendulum 11, so that a lower dynamic stiffness can be achieved, that is, the quasi-zero stiffness characteristic is realized. The lower dynamic stiffness indicates that the pendulum-type quasi-zero stiffness vibration absorption and energy harvesting system has a lower natural frequency. At this time, the vibration absorption structure can respond to extremely low-frequency vibrations and can effectively suppress vibrations in the low-frequency range, thereby realizing the efficient suppression of low-frequency and ultra-low-frequency vibrations.

[0021] In addition, the present invention uses a pendulum structure formed by the moving pendulum 11 to constitute the vibration absorption structure. Compared with the traditional linear vibration absorption structure, the pendulum structure can effectively reduce the spatial size of the vibration absorption structure and facilitate its installation in a compact space.

[0022] In one embodiment, a first mounting surface is formed on the side of the moving pendulum 11 facing the fixed pendulum 5. The first mounting surface is perpendicular to the axis of the installation shaft. A first electrode layer 10 is fixedly arranged on the first mounting surface. The first electrode layer 10 is a copper thin film layer after anodic oxidation treatment and covers the first mounting surface; a second mounting surface is formed on the side of the fixed pendulum 5 facing the moving pendulum 11. The second mounting surface is parallel to the first mounting surface. A second electrode layer 8 is fixedly arranged on the second mounting surface. The second electrode layer 8 is a copper thin film layer and covers the second mounting surface. An FEP thin film layer 9 is adhesively attached to the second electrode layer 8 through a conductive adhesive. The FEP thin film layer 9 covers the second electrode layer 8; the first electrode layer 10 and the FEP thin film layer 9 are mutually attached.

[0023] In this embodiment, the FEP film layer 9 and the second electrode layer 8 are fixed to each other by conductive glue to form a composite layer, and the composite layer and the first electrode layer 10 are bonded to each other to form a friction generator energy capture structure, wherein the first electrode layer 10 is a copper film layer, fixed on the mobile pendulum 11, as the bottom electrode, and the composite layer formed by the FEP film layer 9 and the second electrode layer 8 are fixed to each other and fixed on the fixed pendulum 5, as the top electrode. When the pendulum-type quasi-zero stiffness vibration absorption and energy capture system is in a working state, the mobile pendulum 11 swings, and a relative angular displacement is generated with the fixed pendulum 5. Charge transfer will be formed at the contact interface due to the difference in electron affinity, thereby generating current, which can achieve low-frequency vibration energy capture. Therefore, the pendulum-type quasi-zero stiffness vibration absorption and energy capture system can convert part of the vibration energy into electrical energy for recovery while efficiently suppressing low-frequency vibration. Preferably, the first electrode layer 10 and the second electrode layer 8 are bonded to the first mounting surface, and after the FEP film layer 9 forms a microstructure surface by a nanoimprinting process, it forms a deformable composite layer with the second electrode layer 8 through a conductive silver paste.

[0024] In addition, by connecting an external circuit to the friction generator energy capture structure, the captured electrical energy can be converted into the equivalent damping force of the magnetorheological damper in real time, that is, the damping of the vibration absorption structure can be adjusted by using the recovered energy, so that the vibration absorption structure can maintain adaptive dynamic regulation within an ultra-wide frequency band (0.5-50Hz). Specifically, the pulse electrical energy output by the friction generator energy capture structure is converted into a DC signal using a bridge rectifier circuit, and then connected to a programmable resistor network to form an equivalent magnetorheological damper. By monitoring the time-frequency characteristics of the vibration response, the variable domain fuzzy control algorithm is used to adjust the equivalent damping coefficient in real time, so that the vibration absorption system can maintain the optimal dynamic vibration absorption ratio within an ultra-wide frequency band (0.5-50Hz).

[0025] In one embodiment, the first mounting surface is in the shape of a sector coaxial with the mounting axis, and the second mounting surface overlaps with the first mounting surface in the horizontal direction.

[0026] In this embodiment, the first mounting surface and the second mounting surface are fan-shaped and overlap with each other, and accordingly, the first electrode layer 10 and the composite layer are also fan-shaped and overlap with each other. The coaxial fan-shaped structure has a strong adaptability to the rotation angle and can cover a wide range of angular displacements, thereby improving the energy collection efficiency.

[0027] In one embodiment, the mounting axis is a cylindrical optical axis 4, and a connecting tube 3 is provided at the top of the movable pendulum 11 corresponding to the optical axis 4, and the connecting tube 3 is rotatably sleeved on the mounting axis; the top of the fixed pendulum 5 is provided with a mounting tube corresponding to the optical axis 4, and the mounting tube is sleeved on the optical axis 4 and fixedly connected to the optical axis 4.

[0028] In this embodiment, the moving pendulum 11 is rotatably connected to the optical axis 4 through the connecting cylinder 3 at its top end. Here, the connecting cylinder 3 can be rotatably connected to the optical axis 4 through a bearing structure or can be rotatably connected to the optical axis 4 through a sliding fit structure; the fixed pendulum 5 is fixedly connected to the optical axis 4 through the mounting cylinder at its top end. Here, the mounting cylinder can be fixedly connected to the optical axis 4 through a welding structure or can be fixedly connected to the optical axis 4 through a welding structure.

[0029] In one embodiment, a fixed cylinder 2 is also fixedly sleeved on the optical axis 4, and the fixed cylinder 2 is located on the side of the connecting cylinder 3 away from the mounting cylinder.

[0030] In this embodiment, the mounting cylinder and the fixed cylinder 2 are respectively fixed on both sides of the connecting cylinder 3, which can play a blocking role on the connecting cylinder 3 to prevent the connecting cylinder 3 from coming out of the optical axis 4 during use. Correspondingly, when the connecting cylinder 3 is rotatably sleeved on the optical axis 4 through a sliding fit structure: the inner side wall of the connecting cylinder 3 abuts against the outer side wall of the optical axis 4 and is slidably matched with the outer side wall of the optical axis 4. At the same time, both ends of the connecting cylinder 3 respectively abut against the mounting cylinder and the fixed cylinder 2 and are slidably matched with the mounting cylinder and the fixed cylinder 2 respectively.

[0031] In one embodiment, threaded mounting holes are provided on the end faces at both ends of the optical axis 4; one end of the mounting cylinder is sealed to form a first end cover. The mounting cylinder is sleeved on one end of the optical axis 4 and the first end cover abuts against the end face of the optical axis 4. A first through hole is provided on the first end cover corresponding to the threaded mounting hole. The mounting cylinder is fixedly arranged on the optical axis 4 through a bolt 6 that simultaneously passes through the first through hole and the threaded mounting hole; a fixed cylinder 2 is sleeved on the other end of the optical axis 4. One end of the fixed cylinder 2 is sealed to form a second end cover. The second end cover abuts against the end face of the optical axis 4, and a second through hole is provided on the second end cover corresponding to the threaded mounting hole. The fixed cylinder 2 is fixedly arranged on the optical axis 4 through a bolt 6 that simultaneously passes through the second through hole and the threaded mounting hole.

[0032] In this embodiment, the mounting cylinder is tightened against the end face of the optical axis 4 by the bolt 6 installed in the threaded mounting hole, so as to realize the fixed connection with the optical axis 4. Similarly, the fixed cylinder 2 is tightened against the end face of the optical axis 4 by the bolt 1 installed in the threaded mounting hole, so as to realize the fixed connection with the optical axis 4. Among them, two symmetrical hole structures can be provided on the equipment to be vibration-damped. By making the bolt 6 / 1 pass through the hole structure and the first through hole / second through hole at the same time, the pendulum-type quasi-zero stiffness vibration absorption and energy capture system can be fixedly installed on the equipment to be vibration-damped while fixing the mounting cylinder and the fixed cylinder 2.

[0033] In one embodiment, a weight block 13 is further included, and a mounting groove for installing the weight block 13 is provided on the moving pendulum 11.

[0034] In this embodiment, by increasing or decreasing the weight blocks 13 in the installation grooves, the weight of the moving pendulum 11 can be adjusted, so that the natural frequency can be adjusted according to the usage requirements, and the vibration isolation frequency band can be optimized. Furthermore, the pendulum-type quasi-zero stiffness vibration absorption and energy capture system can have a wider range of applications.

[0035] In one embodiment, the moving pendulum 11 and the first permanent magnet 12 embedded therein are both symmetrically arranged with respect to the vertical plane passing through the axis of the installation shaft; the number of installation grooves on the moving pendulum 11 is an even number, and the installation grooves on the moving pendulum 11 are symmetrically arranged with respect to the vertical plane passing through the axis of the installation shaft.

[0036] In this embodiment, the moving pendulum 11 and the first permanent magnet 12 therein are symmetrically arranged. At the same time, the installation grooves therein and the weight blocks 13 in the installation grooves are also symmetrically arranged, which can ensure the symmetry of the pendulum-type quasi-zero stiffness vibration absorption and energy capture system, thereby avoiding generating lateral static forces on the support structure and reducing friction and energy loss.

[0037] The above embodiments only illustrate several implementation manners of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A pendulum-type quasi-zero stiffness vibration absorption and energy capture system, characterized in that: It includes a horizontally arranged linear installation shaft, a mobile pendulum is arranged on the installation shaft, the top end of the mobile pendulum is rotatably arranged on the installation shaft, the rotation axis of the mobile pendulum coincides with the axis of the installation shaft, and the mobile pendulum is naturally hanging, a first permanent magnet in the shape of a fan ring is also embedded in the mobile pendulum, and the first permanent magnet is coaxially arranged with the installation shaft; a fixed pendulum is also fixedly arranged on the installation shaft, a second permanent magnet is arranged in the fixed pendulum corresponding to the first permanent magnet, the second permanent magnet is in the shape of a fan ring with an axis coincident with the axis of the installation shaft, and the second permanent magnet is arranged transversely aligned with the first permanent magnet; the second permanent magnet and the first permanent magnet are magnetized along their axial direction and repel each other.

2. A pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to claim 1, characterized in that: A first mounting surface is formed on the side of the movable pendulum facing the fixed pendulum, the first mounting surface is arranged perpendicular to the axis of the mounting shaft, a first electrode layer is fixedly arranged on the first mounting surface, the first electrode layer is a copper film layer after anodizing treatment and is arranged covering the first mounting surface; a second mounting surface is formed on the side of the fixed pendulum facing the movable pendulum, the second mounting surface is arranged parallel to the first mounting surface, a second electrode layer is fixedly arranged on the second mounting surface, the second electrode layer is a copper film layer and is arranged covering the second mounting surface, an FEP film layer is adhered to the second electrode layer by conductive adhesive, and the FEP film layer covers the second electrode layer; the first electrode layer and the FEP film layer are bonded to each other.

3. A pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to claim 2, characterized in that: The first mounting surface is in the shape of a sector coaxial with the mounting axis, and the second mounting surface overlaps with the first mounting surface in a horizontal direction.

4. A pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to any one of claims 1 to 3, characterized in that: The installation shaft is a cylindrical optical axis, and a connecting tube is provided at the top of the movable pendulum corresponding to the optical axis, and the connecting tube is rotatably sleeved on the installation shaft; the top of the fixed pendulum is provided with a mounting tube corresponding to the optical axis, and the mounting tube is sleeved on the optical axis and fixedly connected to the optical axis.

5. A pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to claim 4, characterized in that: A fixing tube is also fixedly sleeved on the optical axis, and the fixing tube is located on a side of the connecting tube away from the mounting tube.

6. A pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to claim 5, characterized in that: Threaded mounting holes are provided on both end surfaces of the optical axis; one end of the mounting tube is sealed to form a first end cover, the mounting tube is sleeved on one end of the optical axis and the first end cover abuts against the end surface of the optical axis, a first through hole is provided on the first end cover corresponding to the threaded mounting hole, and the mounting tube is fixed to the optical axis by a bolt that passes through the first through hole and the threaded mounting hole at the same time; the other end of the optical axis is sleeved with a fixing tube, one end of the fixing tube is sealed to form a second end cover, the second end cover abuts against the end surface of the optical axis, and a second through hole is provided on the second end cover corresponding to the threaded mounting hole, and the fixing tube is fixed to the optical axis by a bolt that passes through the second through hole and the threaded mounting hole at the same time.

7. The pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to claim 6, characterized in that: It also includes a weight block, and the mobile pendulum is provided with an installation groove for installing the weight block.

8. The pendulum-type quasi-zero stiffness vibration absorption and energy capture system according to claim 7, characterized in that: The movable pendulum and the first permanent magnet embedded therein are symmetrically arranged about the vertical plane where the axis of the mounting shaft is located; the number of mounting grooves on the movable pendulum is even, and the mounting grooves on the movable pendulum are symmetrically arranged about the vertical plane where the axis of the mounting shaft is located.

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