Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • 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
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/097—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by vibratory elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
  • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
  • G01C19/5719—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using planar vibrating masses driven in a translation vibration along an axis
  • G01C19/5726—Signal processing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • 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
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
  • G01P2015/0808—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate
  • G01P2015/0811—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate for one single degree of freedom of movement of the mass
  • G01P2015/0814—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate for one single degree of freedom of movement of the mass for translational movement of the mass, e.g. shuttle type

Definitions

• the invention relates to a method for measuring a physical quantity according to the preamble of claim 1 and a device for measuring a physical quantity according to the preamble of claim 7.
• a resonating structure is provided, the oscillation frequency of which varies as a result of a change in the physical quantity to be measured.
• the change in the oscillation frequency of the structure is detected by evaluation means and results in a frequency-analog signal, which indicates the size of the physical quantity to be measured.
• the resonating structure is formed by a spring-mass system, sensitivity depends on the geometric dimensions of the resonating structure.
• To evaluate the natural frequency shift of the oscillating structure it is connected as a frequency-determining element of an electronic oscillator circuit.
• the resolution essentially depends on the signal-to-noise ratio of the oscillator circuit and on the frequency measurement method used. In the course of the desired miniaturization of such measuring devices in the interest of inexpensive production, however, it is disadvantageous that this results in a deterioration in sensitivity or resolution.
• the method according to the invention with the features mentioned in claim 1 and the measuring device according to the invention with the features mentioned in claim 7 offer the advantage that the measuring sensitivity can be increased even with measuring devices with small dimensions. Because the structure vibrating at its resonance frequency is acted upon by an electrostatic force which preferably acts in the direction of vibration, it is advantageously possible to influence the sensitivity of the measuring device via the variables determining the electrostatic force. Thus, an operating point can preferably be made via the voltage, which also determines the electrostatic force and which is applied between the resonating structure and the counter structure assigned to it Measuring device can be set. The greater the voltage selected, the closer the working point comes to the point of mechanical instability of the measuring device.
• the sensitivity of the measuring device can be very advantageously adjusted via the level of the voltage that remains constant during the measuring process.
• the electrostatic force acting on the resonating structure can be varied very advantageously via the movably mounted counter structure, so that this is dependent solely on the change in distance due to the constant voltage.
• a natural frequency shift of the vibrating structure can be achieved.
• This natural frequency shift is greater with a physical quantity to be measured of the same size, the closer the working point of the measuring device is to the point of mechanical instability via the magnitude of the constant voltage.
• Even very small changes in the physical quantity to be measured lead to a relatively high natural frequency shift (resonance frequency shift), which can be evaluated accordingly with the evaluation means.
• Even the slightest geometrical shifts are sufficient, that is, Changes in the distance of the structure from the counter structure in order to produce relevant frequency differences.
• the counter-structure which causes the electrostatic force is a movably mounted component of a force sensor, in particular an acceleration sensor.
• the structure and the counterstructure are preferably arranged at an angle to a sensing direction of the acceleration sensor. This advantageously makes it possible to reduce the effect of the electrostatic force on the counterstructure and to increase the overall measuring accuracy of the measuring device according to the invention.
• a deflection of a seismic mass of the acceleration sensor to be detected can be divided very advantageously by the angular displacement, so that a more precise measurement is possible.
• Figure 1 is a schematic plan view of a basic structure of a measuring device according to the invention.
• FIG. 2 shows a frequency-voltage characteristic curve of the device according to FIG. 1;
• FIG. 3 shows a frequency-distance characteristic of the device according to FIG. 1 and
• Figure 4 is a schematic plan view of a
• FIG. 1 shows a generally designated 10 measuring device.
• the measuring device 10 is only shown schematically in a top view and is intended to illustrate the measuring method according to the invention.
• the measuring device 10 has a structure 12 which is formed by a bending beam 14 which is movably clamped between two bearings 16.
• the bearings 16 can be part of a frame 18 which is part of a substrate 20, not shown here.
• the bending beam 14 spans a window 22 formed by the frame 18.
• the structure 12 is assigned a drive device 24, which is formed, for example, by an electrostatic comb drive 26.
• the drive device 24 also has an electronic oscillator circuit, not shown here.
• the Structure 12 is also assigned a counter structure 28 which is arranged on the side of the bending beam 14 opposite the drive device 24.
• the counter structure 28 is movably supported in the direction of oscillation of the bending beam 14 indicated here by a double arrow 30. Both the structure 12 and the counter structure 28 are connected to a DC voltage source in a manner not shown in FIG. 1, the structure 12 being connected to the negative pole or ground of the DC voltage source and the counter structure 28 being connected to the positive pole of the DC voltage source or vice versa (polarity not important) .
• the measuring device 10 shown in FIG. 1 performs the following functions:
• the structure 12 is set in its oscillation direction 30 into a resonant oscillation with a resonance frequency fg (without external load). If an external physical variable, for example an acceleration or a pressure, now acts on this structure 12 (bending beam 14) vibrating at the resonance frequency fg, mechanical stresses are coupled into the structure 12, which lead to a natural frequency shift of the resonance frequency f with which the structure 12 swings. By detecting the frequency shift between the resonance frequency f and the resonance frequency fg, the size of the physical quantity acting can be inferred in a frequency-analog measurement method.
• the sensitivity of the measuring driving essentially depends on the geometric dimensions of the structure 12. The following applies to the pure bending vibration of the bending beam 14:
• the resonance frequency fg applies to the unloaded state of the structure 12.
• F is the force applied to the structure 12,
• E the modulus of elasticity and ⁇ the density of the material used (material constant) of the bending beam 14.
• 1 is the length, with b the width in Direction of vibration 30 and h the height of the bending beam 14 specified.
• an electrostatic force Fg is exerted by the counter-structure 28 on the structure 12 which oscillates in the idle state with the resonance frequency fg.
• the vibration behavior can be influenced in a targeted manner by the action of the electrostatic force Fg on the structure 12.
• the mechanical spring force of the structure 12 (bending beam 14), which also determines the resulting resonance frequencies f, is superimposed by the electrostatic force Fg, so that the effective spring stiffness c e ff of the structure 12 changes.
• This change in the effective spring stiffness affects the resonance frequency f, with the following relationship:
• the electrostatic force F and thus the resonance frequency f of the structure 12 can be influenced by a size of the voltage U and a size of the distance d.
• the structure 12 and the counter-structure 28 form a capacitor, so to speak, the structure 12 and the counter-structure 28 representing the capacitor plates.
• the other sizes, such as length 1, width b and height h of structure 12 and length lg and height h j of the counter structure 28 are predetermined and fixed by the design of the measuring device 10.
• FIG. 2 shows the resonance frequency-voltage characteristic of the measuring device 10 assuming a fixed distance d between the structure 12 and the counter structure 28. It becomes clear that the resonance frequency f drops with increasing voltage U.
• a working point of the measuring device 10, in particular a distance of the working point from a point of mechanical instability of the structure 12 of the measuring device 10 can be set via the voltage U. The closer the operating point is placed to the point of mechanical instability, the sensitivity of the measuring device 10 can be increased, since even smaller deviations in the resonance frequency f, due to a physical variable to be measured from the outside, lead to a higher signal deviation.
• FIG. 3 shows a resonance frequency-distance characteristic of the measuring device 10. It becomes clear that the resonance frequency f decreases as the distance d between the structure 12 and the counterstructure 28 becomes smaller.
• the resonance frequency f is limited on the one hand by the resonance frequency fg, which corresponds to the oscillation frequency of the structure 12 in the unloaded state, and the value 0 on the other.
• the resonance frequency f assumes the value 0 when the electrostatic force Fg corresponds exactly to the restoring force of the bending beam 14, so that the sum of the forces on the bending beam becomes 0.
• the point Pg of the mechanical instability of the measuring device 10 lies at the point where the resonance frequency f takes the value 0.
• a constant voltage U is applied between the structure 12 and the counter structure 28.
• the greater this voltage U is chosen, the closer the operating point of the measuring device 10 comes to the point Pg of mechanical instability, and the greater is a shift in the resonance frequency f for a given change in the distance d between the structure 12 and the counterstructure 28 from one another .
• the electrostatic force Fg is only dependent on the distance d.
• a change in the distance d corresponds to a movement on the curve shown in FIG. 3.
• the closer one gets to the point Pg of mechanical instability the softer the structure 12 becomes and the lower the resonance frequency f.
• the steepness of the curve and thus the sensitivity to a geometric change in the distance d increases. Even the slightest geometrical shifts are sufficient to produce relevant differences in the resonance frequency f.
• the increase in the sensitivity of the measuring device 10 is only limited here by the fact that the structure 12 itself must still oscillate in order to detect a change in the resonance frequency f.
• the vibration of the structure 12 leads to an additional variation in the distance d between the Structure 12 and the counterstructure 28.
• the non-linearity of the characteristic curve resulting from the oscillation of the structure 12 and the resulting variation in the distance d is electronically compensated in an evaluation circuit in a manner not to be considered in more detail here.
• FIG. 4 shows a possible form of use of the measuring device 10 in a schematic plan view.
• an acceleration sensor designated 32 is shown here.
• the same parts as in Figure 1 are provided with the same reference numerals and not explained again.
• the acceleration sensor 32 has a seismic mass 34, which is softly suspended by springs 36 in a planar vibration plane 38.
• the springs 36 are connected to a foot 40 on the substrate 42 on the one hand and the seismic mass 34 on the other hand.
• the springs 36 are also connected to the counter structure 28.
• the counter-structure 28 is in turn part of the measuring device 10 (FIG. 1), which also has the structure 12 and the drive device 24.
• the counter structure 28 is coupled to the seismic mass 34 via the springs 36.
• the counter structure 28 is connected to the positive pole of a direct voltage source 44 via the springs 36 and the foot 40.
• the structure 12 is connected to the negative pole via the frame 18 or the substrate 42. as the ground of the DC voltage source 44 connected.
• the DC voltage source 44 is switched on, the voltage U is therefore present between the counter-structure 28 and the structure 12.
• the measuring device 10 is arranged at an angle ⁇ to a sensitivity direction 46 of the acceleration sensor 32.
• the acceleration sensor 32 shown in FIG. 4 performs the following function:
• the mass 34 When used as intended, the mass 34 is set into a planar oscillation in the planar oscillation plane 38 due to an acceleration acting in the sensitivity direction 46 from the outside.
• the acceleration causes a force on the seismic mass 34 which, depending on the spring constant of the springs 36 on which the seismic mass 34 is suspended, leads to a deflection with a certain amplitude.
• this deflection is divided down over the lifting effect of the springs 36, so that the counter-structure 28 experiences a correspondingly reduced deflection (change in the distance d).
• the deflection is divided down again, so that finally a deflection of the seismic mass 46 leads to a much smaller change in the distance d.
• the change in the distance d with a constantly applied voltage U leads to a variation in the resonance frequency f with which the structure 12 is excited by the drive device 24.
• the change in the resonance frequency f can be detected by an evaluation means (not shown here) and a frequency-analog signal can be determined which corresponds to the magnitude of the acceleration acting.
• the seismic mass 34 can oscillate with an amplitude in its sensitivity direction 46, which is limited by an overload stop (not shown). Even at maximum amplitude, the division of the deflection would prevent the counter structure 28 from striking the structure 12 on the one hand via the springs 36 and on the other hand via the inclined position at an angle.
• Another advantage in the arrangement of the structure 12 and the angle ⁇ is that a reaction of the electrostatic force Fg to the counter structure 28 can be reduced.
• the proportion of the electrostatic force Fg acts on the direction of movement of the counter structure 28, which corresponds to the sine of the angle ⁇ .

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Citations (8)

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• 1996
  • 1996-10-21 DE DE19643342A patent/DE19643342A1/de not_active Ceased
• 1997
  • 1997-10-15 WO PCT/DE1997/002353 patent/WO1998018011A1/de active IP Right Grant
  • 1997-10-15 US US09/284,907 patent/US6324910B1/en not_active Expired - Lifetime
  • 1997-10-15 DE DE59707374T patent/DE59707374D1/de not_active Expired - Lifetime
  • 1997-10-15 JP JP51879498A patent/JP4129060B2/ja not_active Expired - Fee Related
  • 1997-10-15 EP EP97912049A patent/EP0932833B1/de not_active Expired - Lifetime

Patent Citations (8)

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