CN117031070A - Quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design - Google Patents
Quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design Download PDFInfo
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
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Abstract
The invention discloses a quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design, and belongs to the technical field of quasi-zero stiffness accelerometers. The accelerometer comprises an accelerometer main body part based on a sensitive mass block and electrostatic negative stiffness comb tooth structures connected with four azimuth angles of the accelerometer main body part, wherein each independent electrostatic negative stiffness comb tooth structure is composed of a third fixed comb tooth array and a third movable comb tooth array, the third movable comb tooth array is connected with the azimuth angle of the sensitive mass block in the accelerometer main body part, and the third fixed comb tooth array is connected with an electrostatic negative stiffness comb tooth fixing anchor point sputtered with a metal electrode layer; the electrostatic force directions generated by the electrostatic negative stiffness comb tooth structures on the four azimuth angles are the same, and the electrostatic force directions are consistent with the moving directions of the accelerometer main body part and are used for counteracting the positive stiffness bending force generated by the straight beam structure, and the combination of the two forces enables the device to present quasi-zero stiffness characteristics at the initial position.
Description
Technical Field
The invention relates to the technical field of Quasi-Zero Stiffness (quick-Zero-Stiffness) MEMS (Micro-Electro-Mechanical System) accelerometers, in particular to a Quasi-Zero Stiffness MEMS accelerometer based on static negative Stiffness balanced straight beam positive Stiffness.
Background
The sensor is an instrument for sensing and transmitting signals, and the accelerometer is a more important type of sensor, and the wide application of the accelerometer lays the importance of the accelerometer. Applications of accelerometers are not available from watches, cell phones, automobiles, etc. in people's daily life to airplanes, rockets, satellites, etc. in the aerospace field. With the progress of technology, the status of integrated chips is gradually highlighted, the application of traditional accelerometers in the fields of wearable devices and high-end electronic products is limited, and with the development of key technologies such as low-frequency signal measurement and sensitivity improvement, micro-mechanical (MEMS) accelerometers are increasingly focused on.
A quasi-zero stiffness (QZS) MEMS accelerometer is a new type of micromechanical instrument, and unlike conventional accelerometers, the structural design of QZS accelerometers is generally divided into two parts, one of which is a common beam structure that provides support, which exhibits positive stiffness. In addition, there is a portion of the structure that is used to provide negative stiffness that counteracts the positive stiffness of the beam structure. Unlike large vibration isolation systems, in the MEMS field, many load generating mechanisms such as springs, magnet coils, etc. cannot be used. Therefore, the manner in which the negative stiffness is generated is critical. At present, a mechanism for generating negative rigidity generally adopts a bending beam or a rebound spring beam, and the statics of the beam structure can be briefly described as: as the magnitude of the midpoint load of the double-ended clamped beam is gradually increased, the rigidity of the beam is converted from positive rigidity to local negative rigidity to positive rigidity. The MEMS accelerometer combined can obtain a localized QZS due to the presence of localized negative stiffness characteristics and being approximately linear. However, the precondition for achieving such zero stiffness is that a certain amount of force needs to be pre-applied at the midpoint of the beam so that the beam is displaced to some extent, and for a beam made of silicon, it is difficult to withstand large deformation due to its brittleness.
In addition, an alternative QZS design approach is to apply an axial force primarily to the straight beam structure by reducing the positive stiffness of the support beam structure itself without introducing other negative stiffness. However, the experimental environment of the MEMS device is usually in a vacuum state to reduce the influence of air damping on the vibration response and quality factor of the device, the dielectric constant of the vacuum environment is very small, and in addition, the electrostatic force needs a considerable voltage for generating the electrostatic force. This approach is difficult to achieve in combination with the magnitude of axial critical pressure required for buckling of the straight beam.
Thus, it is a difficult and critical point to design a proper and convenient negative stiffness mechanism.
Disclosure of Invention
In order to solve the problems, the invention provides a quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design, wherein the static positive and negative stiffness balance refers to an electrostatic force with negative stiffness characteristic generated by static comb teeth, so that the direction of the electrostatic force is consistent with the moving direction of the accelerometer and is used for counteracting positive stiffness bending force generated by a supporting beam structure, and the combination of the two forces enables a device to present QZS characteristic at an initial position.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design comprises an accelerometer main body part based on a sensitive mass block and static negative stiffness comb tooth structures connected with four azimuth angles of the accelerometer main body part, wherein each independent static negative stiffness comb tooth structure is composed of a third fixed comb tooth array and a third movable comb tooth array, the third movable comb tooth array is connected with the azimuth angle of the sensitive mass block in the accelerometer main body part, and the third fixed comb tooth array is connected with a static negative stiffness comb tooth fixing anchor point sputtered with a metal electrode layer; the electrostatic force directions generated by the electrostatic negative stiffness comb tooth structures in the four azimuth angles are the same, and the electrostatic force directions are consistent with the moving directions of the accelerometer main body part.
Further, the accelerometer main body part comprises a sensitive mass block, a straight beam structure, a driving comb tooth structure and a detecting comb tooth structure; the sensitive mass block is positioned at the center of the accelerometer and is a receptor of inertial force of the accelerometer, a plurality of grooves are symmetrically arranged on two sides of the sensitive mass block, and each groove is supported by a straight beam structure; the driving comb tooth structure is arranged on the upper side and the lower side of the sensitive mass block, and the detecting comb tooth structure is arranged on the left side and the right side of the sensitive mass block. The straight beam structure is used as a supporting beam to support the sensitive mass block to achieve a suspended state, the movement of the sensing comb tooth structure represents the movement of the sensitive mass block, and the two driving comb tooth structures work in an intermittent mode to enable the device to move up and down in two directions.
Further, the sensing comb structure located on one side of the sensitive mass is located between a pair of straight beam structures.
Further, the motion direction of the sensitive mass block is one-dimensional, and in-plane motion is maintained.
Further, a strip-shaped empty groove is etched in the sensitive mass block along the central axis of the moving direction, and the center of the empty groove coincides with the mass center of the sensitive mass block.
Further, the length direction of the straight beam structure is perpendicular to the movement direction of the sensitive mass block, one end of the straight beam structure is connected with the bottom of the groove of the sensitive mass block, the other end of the straight beam structure is connected with a straight beam fixedly supporting anchor point sputtered with a metal electrode layer, and gaps are reserved between the two sides of the straight beam structure and the side walls of the groove.
Further, the ratio of the length of the straight beam structure to the depth of the groove is (1.1-1.5): 1.
Further, the number of teeth in the third movable comb tooth array in the electrostatic negative stiffness comb tooth structure satisfies the following formula:
wherein N is the number of movable comb teeth of the third movable comb tooth array in the static negative stiffness comb tooth structure, V is the direct current voltage difference value of the relative straight beam voltage required to be applied by the static negative stiffness comb tooth structure, and E, I, L is the Young modulus, the moment of inertia and the length of the straight beam structure respectivelyThe degrees a, b and d are respectively the comb tooth thickness, the comb tooth length and the comb tooth spacing in the static negative stiffness comb teeth,is a dielectric constant.
The static negative stiffness comb tooth structure is adopted to generate approximately linear negative stiffness so as to offset positive stiffness generated by the straight beam structure, and in a section with small deformation, the longitudinal loads of the electrostatic force and the end part of the mass are in direct proportion to the longitudinal displacement of the sensitive mass block, so that the quasi-zero stiffness is feasible. Because the size and the constraint mode of the mass are fixed in the manufacturing process, the static negative rigidity is necessarily adjustable, and the electrostatic force is adjusted only by adjusting the applied voltage, so that the mode is convenient to operate and accurate in adjustment. In order that the sensitive mass does not deflect around the centroid during movement, the electrostatic negative stiffness comb structure is symmetrical about a longitudinal axis passing through the centroid. Preferably, in order to generate larger electrostatic force, the length of a single comb tooth of the electrostatic negative stiffness comb tooth module is designed to be 200um, the distance between adjacent fixed comb teeth and movable comb teeth is 4um, and the number of comb teeth of each comb tooth array is 21. The rigidity of the device at the zero initial position can be guaranteed to be minimum, and the requirement of quasi-zero rigidity can be met in a left movable section and a right movable section.
Further, a pair of driving comb tooth structures arranged on the upper side and the lower side of the sensitive mass block are composed of a first fixed comb tooth array and a first movable comb tooth array, the first movable comb tooth array is connected with the sensitive mass block, and the first fixed comb tooth array is connected with a driving comb tooth fixing and supporting anchor point sputtered with a metal electrode layer; each driving comb tooth structure is bilaterally symmetrical relative to the central axis of the sensitive mass block along the movement direction.
Further, a pair of detection comb tooth structures arranged on the left side and the right side of the sensitive mass block are composed of a second fixed comb tooth array and a second movable comb tooth array, the second movable comb tooth array is connected with the sensitive mass block, and the second fixed comb tooth array is connected with a detection comb tooth fixing and supporting anchor point sputtered with a metal electrode layer; the pair of second movable comb tooth arrays are bilaterally symmetrical about the central axis of the sensitive mass block along the movement direction, and the pair of second fixed comb tooth arrays are centrosymmetric about the center of mass center of the sensitive mass block.
The invention has the beneficial effects that: the invention provides a quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance, which greatly improves the space utilization rate and avoids electrostatic attraction with a straight beam structure by designing an electrostatic negative stiffness comb tooth structure on four azimuth angles of a sensitive mass block; the electrostatic force of longitudinal negative rigidity generated by the plurality of symmetrically distributed electrostatic negative rigidity comb tooth structures can be used for balancing positive rigidity longitudinal force generated by the straight beam structure, and the quasi-zero rigidity can be accurately achieved at the zero initial position of the device through fine adjustment of voltage; the invention widens the thought for the development of the quasi-zero stiffness MEMS accelerometer.
Drawings
FIG. 1 is an enlarged view of details of the whole and part of a quasi-zero stiffness MEMS accelerometer based on electrostatic positive and negative stiffness balance provided by an embodiment of the invention;
FIG. 2 is a power supply circuit diagram of the present invention;
FIG. 3 is a schematic structural diagram of a quasi-zero stiffness MEMS accelerometer based on electrostatic positive and negative stiffness balance according to an embodiment of the invention;
FIG. 4 is a graph comparing force versus displacement curves of straight beams before and after applying an electrostatic negative stiffness comb module voltage;
fig. 5 is an amplitude-frequency curve of the quasi-zero stiffness MEMS device obtained in the simulation experiment.
In the figure: the sensor comprises a 1-sensitive mass block, a 2-driving comb tooth structure, a 3-detecting comb tooth structure, a 4-static negative stiffness comb tooth structure, a 5-straight beam structure, a 6-straight beam solid support anchor point, a 7-driving comb tooth solid support anchor point, an 8-detecting comb tooth solid support anchor point, a 9-static negative stiffness comb tooth solid support anchor point and a 10-metal electrode layer.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention provides a quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance, which is used for accurately adjusting module voltage by designing a static negative stiffness mechanism with symmetry so as to achieve the effect of balancing positive stiffness of negative stiffness. In other words, the longitudinal electrostatic force generated by the electrostatic negative stiffness mechanism and the longitudinal force generated by the supporting straight beam are kept opposite in direction and consistent in magnitude, so that the whole device is in a force balance state, namely the stiffness is zero.
Referring to fig. 1 and 3, the invention comprises six modules, namely a sensitive mass module, a straight beam module, a driving comb tooth module, a detection comb tooth module, an electrostatic negative stiffness comb tooth module and a fixed support anchor point module.
The sensitive mass module is a main body and is composed of a sensitive mass block 1-1 positioned at the center of the accelerometer, the motion of the sensitive mass block 1-1 is one-dimensional, the motion direction is perpendicular to the length direction of the straight beam, and the in-plane motion is always kept, namely, the in-plane motion, namely, the sensitive mass block 1-1 does not deflect and translate out of the plane, only one in-plane motion exists, and the motion mode can avoid the complicated nonlinear dynamics problem.
In one embodiment of the invention, through the SOI etching process, the oxide layer of the wafer is etched, the 30um device layer (sensitive mass block) is kept intermittent with the bottom silicon layer of the wafer, four grooves are symmetrically arranged on the left side and the right side of the device layer, and each groove is supported by a straight beam module, namely, the device layer is supported and suspended by the straight beam module only. The sensing mass block 1-1 is driven in a bidirectional manner through electrostatic driving force generated by the driving comb tooth module. Meanwhile, a strip-shaped empty groove is etched in the sensitive mass block along the central axis of the moving direction, so that on one hand, the weight of the mass block is reduced, the bearing pressure of the mass is reduced, on the other hand, the side wall perpendicular to the moving direction in the empty groove can provide illumination points for Doppler laser vibration measurement, a laser displacement measurement mode is added for an experiment process, the operation is convenient, the design cost of a displacement detection circuit is reduced, and meanwhile, the embarrassment of device reproduction caused by infeasibility of a single measurement mode in the experiment is avoided.
The straight beam module comprises four straight beam structures, one end of each straight beam structure is fixedly connected with the bottom of the groove of the sensitive mass block 1-1, the other end of each straight beam structure is fixedly connected to a straight beam fixedly supporting anchor point outside the sensitive mass block 1-1, and the straight beam fixedly supporting anchor points are fixedly restrained, and a metal electrode layer is sputtered on the straight beam fixedly supporting anchor points; taking a pair of straight beam structures positioned at the left side of the sensitive mass module as an example, the right end of the straight beam structures is fixedly connected with the sensitive mass block 1-1, and the left ends of the straight beam structures are fixedly connected to two straight beam fixing and supporting anchor points respectively. The right side of the sensitive mass block is opposite to the left side of the pair of straight beam structures, the left end of the pair of straight beam structures is fixedly connected with the sensitive mass block 1-1, and the right ends of the pair of straight beam structures are fixedly connected to two straight beam fixing and supporting anchor points respectively.
In one implementation of the invention, the length of each straight beam structure is 500um, the width is 4um, in order to reduce the space occupied by the device as much as possible, the straight beam structure is 400um inserted in the groove of the sensitive mass block, namely one end of the straight beam structure is fixed at the bottom of the groove of the sensitive mass block, and two sides of the straight beam structure are kept in clearance with the side wall of the groove and are not contacted with each other. When the sensor works, direct current is supplied to the metal electrode layers of one or more straight beam fixedly supported anchor points, so that initial voltage is set for the sensitive mass block 1-1.
The driving comb tooth module comprises driving comb tooth structures 2-1 which are positioned on the upper side and the lower side of the sensitive mass block 1-1. The driving comb structure actually comprises an upper comb array and a lower comb array, and is defined as a first fixed comb array and a first movable comb array according to the position relation. Taking a driving comb structure positioned on the upper side of the sensitive mass block 1-1 as an example, an upper comb array is used as a first fixed comb array, and is fixed on a driving comb fixed supporting anchor point which is fixed and restrained, and a metal electrode layer is sputtered on the driving comb fixed supporting anchor point; the lower comb tooth array is used as a first movable comb tooth array, is fixedly connected with the upper part of the sensitive mass block 1-1 and can move together with the sensitive mass block 1-1. Similarly, in the driving comb structure positioned at the lower side of the sensitive mass block 1-1, the lower comb array is used as a first fixed comb array, is fixed on a driving comb fixed supporting anchor point and is fixed and restrained, and a metal electrode layer is sputtered on the driving comb fixed supporting anchor point; the upper comb tooth array is used as a first movable comb tooth array, is fixedly connected with the lower part of the sensitive mass block 1-1 and can move together with the sensitive mass block 1-1.
In one embodiment of the present invention, the horizontal spacing between adjacent teeth of the upper and lower arrays of teeth of the drive comb structure is 4um, the overlap length is 8um, and the distances between the upper and lower teeth to the bottom line of each other are 12um. When the driving comb module works, the device is controlled to move upwards by applying power to the fixed anchor point metal electrode layer connected with the driving comb structure at the upper side of the sensitive mass block 1-1, and the device is controlled to move downwards by applying power to the fixed anchor point metal electrode layer connected with the driving comb structure at the lower side of the sensitive mass block 1-1. The pair of driving comb structures 2-1 positioned on the upper side and the lower side of the sensing mass block 1-1 are bilaterally symmetrical about the longitudinal line of the mass center of the sensing mass block (namely, the central axis along the movement direction of the sensing mass block) so as to prevent the sensing mass block 1-1 from deflecting due to asymmetric electrostatic force. In addition, the voltage of the first fixed comb tooth array connected with the sensitive mass block 1-1 is consistent with the voltage of the sensitive mass block 1-1, the voltage of the sensitive mass block 1-1 is generally set to be zero or a smaller value is given, the voltage of the sensitive mass block 1-1 is given through a straight beam, for example, one end of the straight beam is connected with the sensitive mass block 1-1, the other end of the straight beam is connected with a fixed supporting anchor point of the straight beam, and the effect of setting the voltage for the sensitive mass block 1-1 can be achieved by applying specific voltage to a metal electrode layer on the fixed supporting anchor point of the straight beam. The other three straight beam structures can also apply voltage to the sensitive mass block 1-1 in the same way, and in actual operation, voltage can be applied to the sensitive mass block 1-1 through one or more straight beam structures. Therefore, the potential difference of the upper comb tooth array and the lower comb tooth array of the driving comb teeth can be controlled, and the driving force is controlled to simulate external acceleration under different magnitudes.
The detection comb tooth module comprises detection comb tooth structures positioned at the left side and the right side of the sensitive mass block 1-1, a pair of differential comb teeth are formed, the influences of feed-through signals, detection noise and parasitic capacitance can be effectively avoided, and the detection precision is improved. The detection comb structure is similar to the drive comb structure and also comprises a left comb array and a right comb array, and is defined as a second fixed comb array and a second movable comb array according to the position relation of the detection comb structure and the right comb array. Taking a detection comb tooth structure positioned at the left side of the sensitive mass block 1-1 as an example, the left comb tooth array is used as a second fixed comb tooth array, and is fixed on a detection comb tooth fixed support anchor point which is fixed and restrained, and a metal electrode layer is sputtered on the detection comb tooth fixed support anchor point; the right comb tooth array is used as a second movable comb tooth array, is fixedly connected with the left side of the sensitive mass block 1-1 and can move together with the sensitive mass block 1-1. Similarly, in the detection comb structure positioned on the right side of the sensitive mass block 1-1, the right comb array is used as a second fixed comb array, is fixed on a detection comb fixed support anchor point and is fixed and restrained, and a metal electrode layer is sputtered on the detection comb fixed support anchor point; the left comb tooth array is used as a second movable comb tooth array, is fixedly connected with the right side of the sensitive mass block 1-1 and can move together with the sensitive mass block 1-1.
In one embodiment of the invention, the sensing comb module is mainly used for sensing the displacement of the sensitive mass 1-1. For the force displacement curve of the static test device, the displacement obtained by detecting the comb tooth module can directly indicate the motion state of the sensitive mass block 1-1. For dynamic testing, the closed loop feedback control force needs to be calculated by the displacement amount obtained by detection, so that the detection part is crucial under static or dynamic work. The second movable comb tooth arrays in the pair of detecting comb tooth structures positioned at the left and right sides of the sensing mass block 1-1 are symmetrical about the longitudinal line of the mass center of the sensing mass block (namely, the central axis along the moving direction of the sensing mass block), and the second fixed comb tooth arrays are centrosymmetric about the mass center, so that the differential effect is achieved. When the comb teeth detection device works, if static displacement is measured, alternating current is required to be supplied to a metal electrode layer for detecting a fixed supporting anchor point of the comb teeth, so that the voltage output by the comb teeth is ensured to be changed; if the dynamic displacement is measured, direct current is required to be conducted on the metal electrode layer of the fixed supporting anchor point of the detection comb teeth.
The static negative stiffness comb tooth module comprises static negative stiffness comb tooth structures distributed on four azimuth angles of the sensitive mass block 1-1, the space utilization rate is greatly improved through a design mode on the four azimuth angles, and static attraction with the straight beam module is avoided. Each static negative stiffness comb tooth structure comprises a left comb tooth array and a right comb tooth array, and is defined as a third fixed comb tooth array and a third movable comb tooth array according to the position relation. Taking an electrostatic negative stiffness comb tooth structure positioned at the right upper azimuth angle of the sensitive mass block 1-1 as an example, the right comb tooth array is used as a third fixed comb tooth array, is fixed on an electrostatic negative stiffness comb tooth fixing and supporting anchor point and is fixed and restrained, and a metal electrode layer is sputtered on the electrostatic negative stiffness comb tooth fixing and supporting anchor point; the left comb tooth array is used as a third movable comb tooth array, is fixedly connected with the right upper part of the sensitive mass block 1-1 and can move together with the sensitive mass block 1-1.
In one embodiment of the present invention, each of the left and right comb arrays in the electrostatic negative stiffness comb structure has a length of 200um, two adjacent comb spaces have a spacing of 4um, and the overlap length is 180um. In order to avoid the influence of parasitic electrostatic forces on the direction of movement of the sensitive mass 1-1, the four electrostatic negative stiffness comb modules are symmetrical about a longitudinal line through the centroid. The movement of the sensitive mass block 1-1 drives the four straight beam structures to bend and deform, and the longitudinal force generated by the deformation of the straight beam structures is larger, so that any comb tooth array of each electrostatic negative stiffness comb tooth module comprises 21 comb teeth, and a larger electrostatic force is generated under a lower voltage to offset the longitudinal force of the straight beam.
The number of the comb teeth is not limited to the 21, and the design can be combined with a relational expression between the number of the movable comb teeth in the static negative stiffness comb tooth structure and the applied voltage, as shown in a formula (1):
wherein N is the movable of the third movable comb tooth array in the static negative stiffness comb tooth structureThe number of the comb teeth, V is the direct current voltage difference value of the relative straight beam voltage required to be applied by the static negative stiffness comb tooth structure, E, I, L is the Young modulus, the moment of inertia and the length of the straight beam structure respectively, a, b and d are the comb tooth thickness, the comb tooth length and the comb tooth spacing in the static negative stiffness comb teeth respectively,is a dielectric constant. In order to avoid excessive voltage applied to the electrostatic negative stiffness comb tooth structure, the number of comb teeth can be increased appropriately.
When the device works, equivalent direct current is required to be conducted on the metal electrode layers of one or more straight beam solid support anchor points, and the first-order natural frequency of the device is enabled to be as small as possible, namely the quasi-zero rigidity is achieved through accurate fine adjustment of the direct current voltage.
The fixed support anchor point module comprises a straight beam fixed support anchor point, a driving comb tooth fixed support anchor point, a detection comb tooth fixed support anchor point and an electrostatic negative stiffness comb tooth fixed support anchor point, wherein the power supply circuit diagram is shown in fig. 2, and all metal electrode layers on the fixed support anchor points are connected with a power supply. Various solid support anchor points are described in detail in the straight beam module, the driving comb tooth module, the detection comb tooth module and the static negative stiffness comb tooth module, and are not described herein.
The using method of the MEMS accelerometer is as follows:
the early test stage comprises the following steps 1-3:
step 1, applying equivalent direct current to a metal electrode layer of one or more straight beam fixedly supported anchor points, and striking an illumination point on a side wall perpendicular to the movement direction in an empty slot in a sensitive mass block by using a Doppler laser vibration meter for measuring displacement of the sensitive mass block;
step 2, alternating current with an indefinite frequency of fixed value is supplied to a fixed anchor point metal electrode layer connected with any driving comb structure to sweep frequency, and the alternating current enables alternating potential difference to be generated between the fixed comb teeth and the movable comb teeth in the driving comb structure, so that driving force is applied to the sensitive mass block;
and 3, supplying direct current to the metal electrode layers of the fixed anchor points connected with the static negative stiffness comb tooth structures on four azimuth angles of the sensitive mass blocks, and finely adjusting the direct current from small to large, so that the sweep frequency range of alternating current applied to the metal electrode layers of the fixed anchor points driving the comb teeth in the step 2 can be adjusted simultaneously, and the change of the natural frequency of a device is observed through the output of a Doppler laser vibrometer, so that the first-order natural frequency of the device is as small as possible, namely the quasi-zero stiffness is achieved, and the voltage difference value of the relative straight beam voltage required to be applied by the static negative stiffness comb tooth structures is obtained.
The actual application stage comprises the following steps 4-6:
step 4, mounting the tested MEMS accelerometer on equipment to be tested, and electrifying equivalent direct current on the metal electrode layer of one or more straight beam solid support anchor points; meanwhile, according to the voltage difference value of the relatively straight beam voltage required to be applied by the static negative stiffness comb tooth structure obtained in the test stage, direct current which accords with the voltage difference value is conducted on the fixed anchor point metal electrode layer connected with the static negative stiffness comb tooth structure on four azimuth angles of the sensitive mass block, so that the direction of static force generated by the static negative stiffness comb tooth structure is consistent with the moving direction of the accelerometer and is used for counteracting positive stiffness bending force generated by the supporting beam structure;
step 5, applying equivalent direct current to the metal electrode layers of the two detection comb teeth fixed support anchor points for measuring dynamic displacement (in special cases, for example, measuring a constant acceleration, applying equivalent fixed-frequency alternating current to the metal electrode layers of the detection comb teeth fixed support anchor points);
and 6, calculating the acceleration in real time. Here, the acceleration calculation process is consistent with the conventional accelerometer, and is common knowledge in the art, and will not be described here again.
In order to ensure that the electrostatic driving force of the driving comb tooth module does not change along with the displacement change of the sensitive mass block, the invention adopts constant-pressure driving. To verify the quasi-zero stiffness interval, a force-displacement curve needs to be plotted. The driving force is obtained by calculating parameters such as the number of the teeth of the driving comb structure, wherein the driving voltage, the number of the driving teeth and the like are known, so that the driving force can be obtained easily. The displacement detection is obtained by detecting the comb tooth structure, and the displacement can be accurately calculated by adopting differential capacitance detection. Fig. 4 is a force displacement curve of a device before and after the electrostatic negative stiffness comb module is electrified, only four straight beam structures generate longitudinal force along with the movement of the sensitive mass block 1-1 before electrification, and the longitudinal force generated by the four electrostatic negative stiffness comb structures is added after the electrification. Before power is applied, the rigidity of the device is equal to the sum of the rigidity of the four straight beam structures, and the rigidity is high; after the static negative stiffness comb tooth structure is electrified, in a small range of movement, the electrostatic force generated by the static negative stiffness comb tooth structure and the electrostatic force generated by the straight beam structure can be almost completely counteracted, and the device is basically in a zero stiffness state. Fig. 5 is a frequency curve of the quasi-zero stiffness MEMS device obtained in the early simulation experiment, wherein the black solid line is a frequency curve after the electrostatic negative stiffness force is applied, and the dotted line is a frequency curve without the electrostatic negative stiffness force, so that it can be clearly seen that the natural frequency of the electrostatic negative stiffness force is directly reduced from original 1805Hz to 2Hz, and the effect of quasi-zero stiffness is achieved.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. The quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design is characterized by comprising an accelerometer main body part based on a sensitive mass block (1) and static negative stiffness comb tooth structures (4) connected with four azimuth angles of the accelerometer main body part, wherein each independent static negative stiffness comb tooth structure (4) is composed of a third fixed comb tooth array and a third movable comb tooth array, the third movable comb tooth array is connected with the azimuth angle of the sensitive mass block (1) in the accelerometer main body part, and the third fixed comb tooth array is connected with a static negative stiffness comb tooth fixing anchor point (9) sputtered with a metal electrode layer; the electrostatic force directions generated by the electrostatic negative stiffness comb tooth structures (4) in the four azimuth angles are the same, and the electrostatic force directions are consistent with the moving directions of the accelerometer main body part.
2. The quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design according to claim 1, wherein the accelerometer main body part comprises a sensitive mass block (1), a straight beam structure (5), a driving comb structure (2) and a detecting comb structure (3); the sensing mass block (1) is positioned in the center of the accelerometer, a plurality of grooves are symmetrically formed in two sides of the sensing mass block (1), and each groove is supported by the straight beam structure (5); the driving comb structure (2) is arranged on the upper side and the lower side of the sensitive mass block (1), and the detecting comb structure (3) is arranged on the left side and the right side of the sensitive mass block (1).
3. A quasi-zero stiffness MEMS accelerometer based on electrostatic positive and negative stiffness balance design according to claim 2, characterized in that the detection comb structure (3) at one side of the sensitive mass (1) is between a pair of straight beam structures (5).
4. The quasi-zero stiffness MEMS accelerometer based on electrostatic positive and negative stiffness balance design according to claim 2, wherein the direction of motion of the sensitive mass (1) is one-dimensional, maintaining in-plane motion.
5. The quasi-zero stiffness MEMS accelerometer based on the static positive and negative stiffness balance design according to claim 4, wherein a strip-shaped empty groove is etched at the central axis of the sensitive mass block (1) along the motion direction, and the center of the empty groove is coincident with the mass center of the sensitive mass block (1).
6. The quasi-zero stiffness MEMS accelerometer based on the electrostatic positive and negative stiffness balance design according to claim 4, wherein the straight beam structure (5) is perpendicular to the motion direction of the sensitive mass block (1), one end of the straight beam structure (5) is connected with the bottom of the groove of the sensitive mass block (1), the other end of the straight beam structure is connected with a straight beam solid supporting anchor point (6) sputtered with a metal electrode layer, and gaps are reserved between two sides of the straight beam structure (5) and the side walls of the groove.
7. The quasi-zero stiffness MEMS accelerometer based on electrostatic positive and negative stiffness balance design of claim 6, wherein the ratio of the length of the straight beam structure (5) to the depth of the groove is (1.1-1.5): 1.
8. The quasi-zero stiffness MEMS accelerometer based on electrostatic positive and negative stiffness balance design of claim 6, wherein the number of teeth in the third moving comb array in the electrostatic negative stiffness comb structure satisfies the following formula:
；
wherein N is the number of movable comb teeth of the third movable comb tooth array, V is the direct-current voltage difference value of the relative straight beam voltage required to be applied by the static negative stiffness comb tooth structure, E, I, L is the Young modulus, the moment of inertia and the length of the straight beam structure respectively, a, b and d are the comb tooth thickness, the comb tooth length and the comb tooth spacing in the static negative stiffness comb teeth respectively,is a dielectric constant.
9. The quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design according to claim 2, wherein a pair of driving comb structures (2) arranged on the upper side and the lower side of the sensitive mass block (1) are composed of a first fixed comb array and a first movable comb array, the first movable comb array is connected with the sensitive mass block (1), and the first fixed comb array is connected with a driving comb fixing anchor point (7) sputtered with a metal electrode layer; each driving comb tooth structure (2) is bilaterally symmetrical relative to the central axis of the sensitive mass block (1) along the movement direction.
10. The quasi-zero stiffness MEMS accelerometer based on static positive and negative stiffness balance design according to claim 2, wherein a pair of detection comb structures (3) arranged on the left and right sides of the sensitive mass block (1) are composed of a second fixed comb array and a second movable comb array, the second movable comb array is connected with the sensitive mass block (1), and the second fixed comb array is connected with a detection comb fixing anchor point (8) sputtered with a metal electrode layer; the pair of second movable comb tooth arrays are bilaterally symmetrical with respect to the central axis of the sensitive mass block (1) along the movement direction, and the pair of second fixed comb tooth arrays are centrosymmetric with respect to the center of mass center of the sensitive mass block (1).
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