EP1994363A1

EP1994363A1 - Micromechanical rotational speed sensor

Info

Publication number: EP1994363A1
Application number: EP07722020A
Authority: EP
Inventors: Bernhard Hartmann; Stefan GÜNTHNER
Original assignee: Conti Temic Microelectronic GmbH
Current assignee: Conti Temic Microelectronic GmbH
Priority date: 2006-03-10
Filing date: 2007-03-12
Publication date: 2008-11-26
Also published as: US8342022B2; CN101400969A; DE112007000303A5; JP2009529697A; KR20080113048A; WO2007104289A1; US20090031806A1

Abstract

The invention relates to a micromechnical rotational speed sensor comprising a substrate (9) and at least one base element (1) which is suspended on the substrate by means of at least one spring element (11, 11') and comprises at least one seismic mass (3), an excitation means (8) and a reading device (15). According to the invention, the spring element (11, 11') can be displaced perpendicularly to the direction of displacement (x, y) of the base element (1).

Description

Micromechanical rotation rate sensor

The present invention relates to a micromechanical rotation rate sensor according to the preamble of claim 1.

Yaw rate sensors are commonly used to determine an angular rate of rotation of an object about an axis. If the rotation rate sensor is micromechanically manufactured on the basis of silicon substrate, it offers, for example, the advantage over a precision industrial spinning top that it can be manufactured in very small dimensions at a relatively low cost. Furthermore, a relatively low measurement uncertainty and low energy consumption during operation are advantageous. An important field of application of rotation rate sensors is in automotive engineering, for example in vehicle dynamics control systems such as the Electronic Stability Program (ESP). An anti-lock braking system, an automatic braking force distribution, a traction control system and a yaw moment control act in such a way that lateral and longitudinal stabilization of the vehicle is achieved by targeted braking of individual wheels. This makes it possible to prevent the vehicle from turning about its vertical axis. Another application for yaw rate sensors is the so-called rollover detection of a vehicle in connection with airbag control units and restraint systems for vehicle occupants. Furthermore, gyroscopes are used for navigation purposes as well as for the determination of the position and the state of motion of vehicles of all kinds. Other Fields of application include image stabilizers for video cameras, dynamics control of satellites when exposed to the Earth orbit, and in civil aviation in back-up attitude control systems.

Micromechanically produced rotation rate sensors generally have a seismic mass, which is set in vibration via an excitation means. If the seismic mass moves radially inwards or outwards in a rotating system, then your orbit velocity will change. It thus experiences a tangential acceleration, which is caused by the Coriolis force. The reaction of the seismic mass to the rotation can be detected, for example, by means of a read-out device.

International Publication WO 03/104823 A1 discloses a multiaxial monolithic acceleration sensor with up to four seismic masses, which are designed in the form of paddles and are suspended on a frame via torsion springs. With this sensor, accelerations in the direction of the respective main sensitivity axes, but no rotation rates can be measured.

German Patent DE 196 41 284 Cl discloses a micromechanical rotation rate sensor with a substrate, a base element suspended on the substrate by a plurality of spring elements and comprising a seismic mass, an excitation means and a read-out device, in which the spring element is designed as a linear spring. Such micromechanically produced rotation rate sensors are preferably etched out of a silicon block. Even very small deviations in the manufacturing accuracy lead to flank angles of the respective structures. The flank angles cause an ner deflection of the spring elements, a movement of the base member perpendicular to the excitation, ie in the measuring direction of the rotation rate sensor. This leads to very high demands on the manufacturing accuracy or to a high rejection of, for example, etched from a silicon wafer structures. In addition, complex electronic evaluation circuits are required to compensate for the measurement inaccuracies caused by the flank angle.

The object of the present invention is to provide a micromechanical rotation rate sensor with a high measuring accuracy, which can be produced cost-effectively with a small scrap.

This object is achieved in that in a micromechanical rotation rate sensor with a substrate, at least one substrate element suspended by at least one spring element comprising at least one seismic mass, an excitation means and a read-out, the at least one spring element perpendicular to the direction of movement of the base member movable is. As a result, in the case of an excited movement of the base element, essentially only vertexes of the spring elements are raised or lowered in the rotation rate sensor according to the invention. Instead of a deflection of the base element perpendicular to the excitation direction, a movement of the spring elements takes place.

Preferably, the spring element has at least two spring sections. The spring element is in particular U-shaped (three spring sections), V-shaped (two spring sections) or S-shaped (several spring sections). In the preferred embodiment of the present invention, a base member is suspended from four spring members. The spring elements are arranged in particular mirror-symmetrical siselement on Ba ^¬.

If there are several base elements, the spring elements benachbar ^¬ ter base elements advantageously by means of a coupling spring can be coupled.

As basic elements rigid base elements can be used, in which frame and seismic mass are rigidly connected. However, it is also possible according to the invention that a base element has a frame, a seismic mass and at least one suspension of the seismic mass on the frame. The seismic masses are then formed, for example, as a paddle.

Micromechanical rotation rate sensors according to the invention can be designed as x-axis sensor, z-axis sensor or as xz-axis sensor, which can sense rotational movements about the x-axis, the z-axis or both axes.

In the following description, the features and details of the invention in conjunction with the accompanying drawings with reference to embodiments will be explained in more detail. In this case, features and relationships described in individual variants can in principle be applied to all exemplary embodiments. In the drawings show:

1 is a schematic view of three examples of various base elements with paddle ausgebil ^¬ Deten seismic masses, 2 is a schematic view of a rigid base member,

3 is a schematic view of another form of a base element,

4 shows an embodiment of an excitation means with comb structure,

5 shows a schematic view of a read-out device via the movement in the substrate plane,

6 is a schematic view of a capacitive reading device,

7 shows a schematic view of a micromechanical rotation rate sensor with linear spring elements according to the prior art,

8 is a schematic view of the deflection caused by flank angle of the base member of Fig. 7,

9 is a schematic view of an embodiment of the present invention with spring elements according to the invention,

10 is a schematic view of the right part of FIG. 9 with reaction forces,

Fig. 11 in the upper part of a section along the line AA of Fig. 10 and in the lower part a section along the line BB and 12 is a schematic view of another embodiment of the present invention with coupled Federelementeen-

In Fig. 1 various embodiments of base elements 1 are shown, which can be used in the present invention. A base element 1 preferably comprises one or more seismic masses 3. The seismic masses are suspended in a frame 2. The suspension can be realized for example via bending beam 4 or torsion beam 5. Bending beam 4 have a linear spring characteristic, but the seismic masses 3 of the rotation rate sensors according to the invention can also be attached to the frame 2 via torsion beams 5. According to FIG. 1, one or more seismic masses 3 may be formed, for example, as a paddle with an opposite suspension 5.

The suspension 4, 5 allows a movement of the center of gravity of the seismic mass 3 only in the z-direction perpendicular to the plane of the frame 2. The plane of the frame 2 is parallel to the substrate or to the plane defined by the substrate (x / y plane).

In Fig. 2, a rigid base member 1 is shown, are rigidly connected in the frame 2 and seismic mass 3 as a unit.

According to FIG. 3, one or more seismic masses 3 can also be suspended on a rigid frame 2. This suspension, for example via torsion spring or spiral spring, allows a movement of the center of gravity SP of the seismic mass 3 only in a direction perpendicular to the frame plane (z-direction), the center of gravity SP of the seismic mass 3 outside the Frame level is. The frame plane (x / y plane) is parallel to the substrate.

According to FIG. 4, the excitation of the base element 1 can take place via a comb structure 6 against which a voltage Ü is present. An excitation means 6 is a device which can excite the base element 1 to vibrate along the first axis (y-axis), which can be done, for example, electrically, thermally, magnetically or piezoelectrically.

In Fig. 5 and 6, two different readout devices 15 are shown schematically. By means of the readout device 15, a deflection of the seismic mass or the base element 1 can be measured perpendicular or parallel to the frame plane, which can be capacitive, piezoresistive, magnetic, piezoelectric or optical. With the read-out device according to FIG. 5, a movement in the substrate plane and with the read-out device 15 according to FIG. 6 a movement perpendicular to the substrate plane can be measured.

Fig. 7 shows a known from the prior art, conventional concept for suspending base elements 1 in a substrate 9. The known suspension via linear spring elements 8. In the left side of Fig. 7, the spring element 8 in its neutral position and in the right half of the spring element 8 'is shown deflected. In general, suspension means an arrangement of spring elements which are fastened on the one hand to the base element 1, on the other hand to the substrate 9 or other elements. The spring elements allow a movement of the base element 1 in the direction of a first axis (y-direction) parallel to the substrate 9. If the flanks of the spring elements 8, 8 'are tilted as shown in FIG. 8, not only does the spring elements 8' move in the substrate plane along the first axis (y-direction), but also out of this (z-direction) , In the case of the conventional concept shown in FIG. 7, this results in the base element 1 being lifted out of the substrate plane more or less parallel. In the measuring principle shown in FIG. 6, in which the movement out of the plane is used to detect the inertial forces, this effect means the generation of a signal or a change in capacitance Δc even without a corresponding external force. This leads to a high measurement inaccuracy, so that too large flank angles 11 render the rotation rate sensor unusable.

FIGS. 9 and 10 show a micromechanical rotation rate sensor according to the invention. In the left side of FIG. 9, the spring elements 11 are in their neutral position, in the right side, the spring elements 11 'are shown deflected. The spring elements 11, 11 'are suspended at the point 12 on the substrate 9 and over the point 13 on the base element 1. 10 shows the reaction forces F _R acting on the base element 1.

The essential advantage of the present invention will be explained in more detail in connection with FIG. 11. Here, the upper half of Fig. 11 is a sectional view taken along the line AA of Fig. 10 and the lower half is a sectional view taken along the line BB. First with tilting about the 1st axis (y-axis). The movements of the spring elements 11, 11 'extend in the substrate plane perpendicular to the movement of the seismic mass or of the base element 1. In this configuration, substantially only the vertices of the spring elements 11, 11' are raised or lowered. According to FIG. 10, there is a preferred spring arrangement of four folded spring elements 11, 11 ', the at the respective corners of the base element 1 engage each other mirror-symmetrically. Thus, the vertices of the spring elements 11, 11 'move in opposite directions on each edge, when the base member 1 moves in one direction. The resulting reaction forces F _R on the center of gravity of the base member 1 cancel each other in ideal symmetrical arrangement, when the base member 1 is sufficiently rigid. Thus, according to the invention, there is no movement of the base element 1 and of the seismic masses, since the spring element 11, 11 'is movable perpendicular to the movement direction (x, y) of the base element 1, in contrast to the prior art shown in FIGS. 7 and 8. In this case, the geometry of the spring elements 11, 11 'is designed so that production-related shape variations are not or only slightly disturbing effects on the sensor behavior.

Preferably, the spring element 11, 11 'according to the invention has at least two spring sections. The spring element 11, 11 'is in particular U-shaped (three spring sections, as shown in FIGS. 9 and 10), V-shaped (two spring sections) or S-shaped (a plurality of spring sections).

When tilted about the second axis or x-axis, the cross section of the springs of the spring elements 11, 11 'remains unchanged, so that no movement occurs out of the substrate plane. Although the cross-section of the coupling spring 14 is tilted in the configuration shown in FIG. 12 as a two-mass oscillator, the influence of the total tilting is drastically reduced by the spring concept according to the invention in comparison with the prior art.

The principle of the rotation rate sensor according to the invention as a two-mass oscillator will be explained in more detail in connection with FIG. 12. The movement of the base elements 1, which over the top and arranged below spring elements 11 'are coupled, 180 ° out of phase with each other, along the 1st axis. The coupling sets a common resonance frequency of the two oscillators.

The advantage of the two-mass oscillator as a rotation rate sensor k lies in the fact that linear accelerations cause a movement of both seismic masses or basic elements in the same direction. Coriolis forces acting on the elements depend on their direction of motion and thus force out-of-phase deflections. Thus, disturbing linear accelerations can be eliminated from the outside by signal subtraction and signals due to rotational movements are added.

Furthermore, the focus of the entire arrangement is always at rest. Thus, the internal driving forces, which excite the base elements 1 for antiphase oscillation, cancel each other and the substrate remains at rest. Ideally, therefore, influences of sensor mounting, z. B. hard or soft bond, do not couple to the moving masses.

The functional principle as yaw rate sensor is explained below. Definition: X- and Y-direction are in the substrate plane, Z-direction is perpendicular to the substrate plane.

x-axis sensor:

The base element is excited to periodic oscillations along the 1st axis (y-axis). During a rotational movement of the sensor about the 2nd axis (x-axis, in the substrate plane and perpendicular to the first axis), a Coriolis force occurs perpendicular to the 1st and 2nd axis (z-axis). This affects both the frame and the seismic mass suspended in it. The suspension of the frame is so basic element 2 so specifies that a movement in z-direction is possible. In base element 1 and 3, the suspension of the frame is mainly rigid for movement in the Z direction, only the seismic mass is deflected in the direction of this axis. The deflection of the base element configurations in the z-direction is detected with the read-out device, as shown in FIG. 6, and is a measure of the rotational speed which has occurred.

As z-axis sensor:

The base element is excited to periodic oscillations along the 1st axis (y-axis). During a rotational movement of the sensor about the 3rd axis (z-axis, perpendicular to the substrate plane and perpendicular to the first axis), a Coriolis force perpendicular to the 1st and 3rd axis occurs (x-axis). This affects both the frame and the seismic mass suspended in it.

Variant 1: The suspension of the frame is designed so that movement in the x-direction is possible, so that the seismic mass is deflected along this axis. The deflection can be measured, such. B. shown in Fig. 5

Variant 2: For base element 3, a frame movement in the x direction is possible, but not necessary. About the outsourced center of gravity (SP) is the Coriolis force acting in the x direction, decomposed into a force in the x and z direction. Thus, the seismic mass is moved in the z-direction and a measuring device, as in the case of the x-axis sensor, can be applied as shown in FIG. However, it is important that the torsion axis (suspension of the mass on the frame) is parallel to the first axis and perpendicular to the Coriolis force. This deflection, either in the z or x direction, is proportional to the rotational speed that occurs.

As xz-axis sensor:

Variant 1: combination of the above sensor

Variant 2: Base element 3 contains 2 masses in a frame, which are oriented 180 ° to each other.

In the case of a yaw rate in the x direction, a Coriolis force occurs in the z direction, which has the consequence that both masses are deflected in the same z direction (+ z or -z). The addition of both signals provides the total signal, the subtraction returns 0.

In the case of a yaw rate in the z direction, a Coriolis force occurs in the x direction, which has the consequence that a mass is deflected in the + z direction and a mass is deflected in the - z direction. The addition of the individual signals gives 0, the subtraction gives the total signal.

LIST OF REFERENCE NUMBERS

1 base element

2 frames

3 seismic mass

4 Suspension of the seismic mass or bending beam

5 Suspension of the seismic mass or torsion beam

6 excitation means or comb structure

7 counter electrode

8 spring element according to the prior art

8 'spring element according to the prior art, deflected

9 substrate

10 flank angles

11 spring element

11 'spring element, deflected

12 suspension point of the spring element on the substrate

13 suspension point of the spring element on the base element

14 coupling spring

15 readout device

A-A cut

B-B cut

Δc capacity change

F _R reaction force

SP focus

Ü voltage x direction (substrate plane) y direction (substrate plane) z direction (perpendicular to the substrate plane)

Claims

claims

1. Micromechanical rotation rate sensor with a substrate

(9), at least one on the substrate (9) by at least one spring element (11, 11 ') suspended base element

(1), which comprises at least one seismic mass (3), an excitation means (8) and a read-out device

(15), characterized in that the spring element

(11, 11 ') perpendicular to the direction of movement (x, y) of the base element (1) is movable.

2. Micromechanical rotation rate sensor according to claim 1, characterized in that the spring element (11, 11 ') has at least two spring portions.

3. Micromechanical rotation rate sensor according to claim 2, characterized in that the spring element (11, 11 ') is U-shaped, V-shaped or S-shaped.

4. Micromechanical rotation rate sensor according to one of the preceding claims, characterized in that a base element (1) on four spring elements (11, 11 ') is suspended.

5. Micromechanical rotation rate sensor according to claim 4, characterized in that the spring elements (11, 11 ') are arranged mirror-symmetrically on the base element (1).

6. A micromechanical rotation rate sensor according to claim 4 or 5, characterized in that spring elements (11, 11 ') of adjacent base elements (1) by means of a coupling spring (14) can be coupled.

7. A micromechanical rotation rate sensor according to claim 1, characterized in that a base element (1) has a frame (2), a seismic mass (3) and at least one suspension (4, 5) of the seismic mass on the frame (2).

8. A micromechanical rotation rate sensor according to one of the preceding claims, characterized in that the rotation rate sensor is designed as an x-axis sensor, which can sense rotational movements about the x-axis.

9. micromechanical rotation rate sensor according to one of claims claim 1 to 7, characterized in that the rotation rate sensor is designed as a z-axis sensor, which can sense rotational movements about the z-axis.

10. Micromechanical rotation rate sensor according to one of claims 1 to 7, characterized in that the rotation rate sensor is designed as xz-axis sensor, which can sense both rotational movements about the x-axis and rotational movements about the z ~ Ach.se.