US20080017486A1 - Acceleration sensitive switch - Google Patents
Acceleration sensitive switch Download PDFInfo
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- US20080017486A1 US20080017486A1 US11/823,196 US82319607A US2008017486A1 US 20080017486 A1 US20080017486 A1 US 20080017486A1 US 82319607 A US82319607 A US 82319607A US 2008017486 A1 US2008017486 A1 US 2008017486A1
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- electrode
- acceleration
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- variable capacitor
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- 230000001133 acceleration Effects 0.000 title claims abstract description 78
- 239000003990 capacitor Substances 0.000 claims abstract description 50
- 238000001514 detection method Methods 0.000 claims abstract description 7
- 125000006850 spacer group Chemical group 0.000 claims description 17
- 230000001960 triggered effect Effects 0.000 claims description 5
- 239000012212 insulator Substances 0.000 claims description 2
- 239000000758 substrate Substances 0.000 description 8
- 230000005684 electric field Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052755 nonmetal Inorganic materials 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 238000005459 micromachining Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
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Classifications
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- 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
- G01P15/0891—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 with indication of predetermined acceleration values
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- 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
- G01P15/125—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 capacitive pick-up
Definitions
- the invention relates to an acceleration sensitive switch, more particularly, to a switching arrangement with a variable capacitor that is sensitive to acceleration.
- Acceleration switches are designed to issue a signal when a threshold acceleration value is detected. Acceleration switches are widely used in air bag systems to detect the sudden deceleration of a vehicle during crash. Acceleration switches are usually mechanical switches having a spring-loaded mass that makes contact with an electrode, thus acting as a switch, when subjected to acceleration greater than a predetermined threshold value of acceleration. Today, acceleration switches are commonly manufactured using micromachining.
- U.S. Pat. No. 6,336,658B1 discloses an acceleration switch having a first and second inertia mass where the second inertia mass is lighter than the first inertia mass.
- a pair of torsion bars connect to the first inertia mass and act as a turning shaft for the first inertia mass.
- the acceleration switch also has a pair of electrodes formed on a substrate facing the second inertia mass. When acceleration of a predetermined value or greater is applied to the acceleration switch, the second inertia mass moves into contact with the pair of electrodes to act as a switch.
- U.S. Pat. No. 6,236,005B1 discloses an acceleration switch having an inertia mass and an electrode element that are pivoted about an axis of a spring element that connects the inertia mass and the electrode element to a housing.
- an electrical contact point on the electrode element touches a corresponding contact area in the housing, so that an electrical signal is provided to indicate that the predetermined value of acceleration is exceeded.
- the threshold value of acceleration will depend on the physical parameters of the switches such as the stiffness of the torsion bar or the spring element, the inertia mass, and the distance between the contacting electrodes.
- the threshold value of the switches described in these publications is generally difficult to adjust once the switches are made.
- the above switches involve at least one electrical contact that is formed with metal and may be subjected to problems such as micro-welding, arcing, and oxidation, which may cause failure of the switches.
- US Patent Application 2004/0161869A1 discloses a contactless acceleration switch without metal contacts as shown in FIG. 1 .
- the acceleration switch 100 comprises a mass 112 attached to a spring 114 , a substrate layer 102 with a threshold adjustment channel 108 located between a source 104 and a drain 106 thereon, and a gate insulating layer 120 located above the substrate layer 102 .
- the threshold adjustment channel 108 , the source 104 , and the drain 106 are implanted in the substrate layer 102 positioned at a predetermined distance from the mass 112 .
- the mass 112 operates as a moveable gate in combination with the source 104 and the drain 106 to form a field effect transistor (FET).
- FET field effect transistor
- an electric field may form between the mass 112 and the substrate layer 102 , creating an electrostatic force that attract the mass 112 to the substrate layer 102 .
- the mass 112 moves towards the substrate layer 102 to a position of critical distance at which point the electrostatic force exceeds a spring force created by the spring 114 .
- the mass 112 may suddenly contact the gate insulating layer 120 and the strength of the electric field reaches a maximum level, thus inverting the threshold adjustment channel 108 and allowing current to flow between the source 104 and the drain 106 , which turn on the FET.
- One problem with the switch 100 is that a substantially constant voltage in the range from less than five volts for low acceleration, to hundreds of volts for large acceleration range devices, has to be applied between the mass 112 and the substrate layer 102 .
- an acceleration sensitive switching arrangement comprising:
- the variable capacitor preferably comprises a base with at least one first electrode thereon and a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base.
- the spring applies a first force to the mass in a direction away from the base.
- the first electrode is preferably adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the electrode and the mass.
- the detection circuit preferably comprises a voltage supply and a resistive load.
- the voltage supply is preferably an alternating voltage supply.
- the switching circuit preferably comprises a differential amplifier providing a first input voltage and a potentiometer providing a second input voltage to an electronic switch.
- the first input voltage corresponds to the detected capacitance and the second input voltage corresponds to the threshold value.
- the electronic switch is preferably triggered positive upon the second input voltage becomes larger than the first input voltage.
- the threshold value is preferably variable by adjusting the potentiometer to change the second input voltage.
- an acceleration sensitive variable capacitor comprising:
- the mass preferably includes at least one spacer formed on the surface facing the base.
- the spacer is preferably electrically insulated so as to prevent the mass to form electrical contact with the first electrode when the mass moved to the second predetermined distance.
- a layer of insulator is preferably formed on the first electrode separating the mass and the first electrode when the mass moved to the second predetermined distance.
- At least one third electrode is preferably formed on the base, adjacent to the first electrode, and having same electrically potential with the mass.
- the spacer preferably comes into contact with the third electrode when the mass moved to the second predetermined distance.
- the capacitance of the capacitor increases to a maximum upon the mass moved to the second predetermined distance, indicative of the capacitor undergoing a predetermined level of acceleration.
- the maximum capacitance of the capacitor being variable, most preferably by changing voltage supplied to the first electrode and the mass, so as to vary the level of acceleration required to move the mass to the second predetermined distance.
- the capacitance between the first electrode and the mass is preferably measured by a detection circuit comprising a voltage supply and a resistive load.
- FIG. 1 is a schematic view of a prior art acceleration switch
- FIG. 2 is a schematic block diagram representation of a switching arrangement according to the disclosure
- FIG. 3 is an electrical schematic diagram of the acceleration sensitive switching arrangement in accordance with a preferred implementation.
- FIGS. 4-6 are each schematic views of variable capacitors useful in the arrangement of FIG. 3 .
- FIG. 2 shows an acceleration sensitive switching arrangement 208 .
- the switching arrangement 208 comprises an acceleration sensitive variable capacitor 200 , a detector 202 , and a switching circuit 204 .
- the capacitance of the variable capacitor 200 is configured to change when the capacitor 200 is exposed to acceleration.
- the detector 202 includes a detecting circuit for detecting the capacitance of the capacitor 200 and outputting a corresponding electrical signal, such as voltage, to the switching circuit 204 .
- the switching circuit 204 compares the electrical signal to a threshold value. As such, when a value of capacitance corresponding to a threshold value of acceleration is measured by the detector 200 , the switching circuit 204 will be triggered to issue an output 206 , which is an electrical signal.
- the electrical signal may be sent to a controller for further processing.
- FIG. 3 shows an electrical circuit 225 in which a variable capacitor 210 , which will be discussed in more detail later, is connected to a detector 211 .
- the detector 211 includes an AC source 214 and a known load 212 , which is typically resistive.
- the voltage across the load 212 is related, according to Ohm's law, to the capacitance of the capacitor 210 .
- the voltage is input to a differential amplifier 216 to obtain a single output 217 , which is subsequently provided to a first input of an electronic switch 220 .
- the switch 220 also receives a second input signal, which is a predetermined threshold voltage 219 obtained from a potentiometer 218 .
- the switch 220 compares the two input voltage values, 217 and 219 , and will be triggered positive if the voltage 217 is larger than the threshold voltage 219 upon the second input.
- the threshold voltage 219 set by the potentiometer 218 can be adjusted so that the switch 220 will respond to a different value of maximum capacitance, which is associated to threshold value of acceleration experienced by the capacitor 210 .
- FIG. 4 shows a schematic view of a first configuration of an acceleration sensitive variable capacitor 230 .
- the variable capacitor 230 comprises a base 232 with an electrode 238 thereon and a proof mass 234 forming a second electrode resiliently suspended by a spring 240 .
- the spring 240 applies a spring force 242 to the mass 234 in a direction away from the base 232 .
- the spring force 242 varies linearly relative to the extension of the spring 240 .
- the AC source 214 in the detector 211 supplies an alternating voltage between the mass 234 and the electrode 238 , thereby forming a capacitor.
- the electric field formed between the mass 234 and the electrode 238 will create an electrostatic attractive force 244 that draws the mass 234 towards the base 232 .
- the electrostatic attractive force 244 increases exponentially as the space between the mass 234 and the electrode 238 reduces.
- the spring force 242 is larger than the electrostatic attractive force 244 and thus, the mass 234 is resiliently suspended at a stable position away from the base 232 . If the capacitor 230 starts to move in a direction A, away from the plane of the base 232 towards the mass 234 , the capacitor 230 will experience acceleration in the same direction. An acceleration force 246 associated with the acceleration will act upon the mass 234 and move the mass towards the base 232 . When the mass 234 is moved by the acceleration force 246 a distance away from the stable position towards the base 232 , the spring force 242 of the spring 240 increases linearly while the electrostatic attractive force 244 increased exponentially relative to the distance.
- FIG. 4 also shows, arranged on the mass 234 , at least one spacer 236 formed on the surface facing the base 232 .
- the spacers 236 are electrically insulating and are configured to come into contact with the electrode 238 when the electrostatic attractive force 244 draws the mass 234 close to the electrode 238 .
- the insulated spacers 236 prevent the mass 234 from touching the electrode 238 so that the capacitor formed thereby will not short-circuit and to avoid any attractive binding between the mass 234 and the electrode 238 that might otherwise occur.
- the capacitance between the mass 234 and the electrode 238 reaches a maximum when the spacers 236 are in contact with the electrode 238 .
- a maximum voltage output from the differential amplifier 216 corresponding to the maximum capacitance will be detected as described earlier. As the maximum voltage is larger than the threshold voltage 219 obtained from the potentiometer 218 , the electronic switch 220 will be triggered.
- the mass 234 will stay at the position where the spacers 236 are in contact with the electrode 238 , even if the acceleration force is removed, because the electrostatic attractive force 244 is larger than the spring force 242 .
- the capacitance is always kept at a maximum and the electronic switch 220 is turned on continuously once the capacitor 230 has experienced acceleration larger than a threshold value, even if the acceleration only exceeded the threshold value for a short duration.
- a zero voltage is applied to the capacitor 230 via the source 214 , where the electrostatic attractive force 244 is removed.
- the spring force 242 will pull the mass 234 away from the base 232 , releasing the contact between the spacers 236 and the electrode 238 .
- the electrostatic attractive force 244 is a function of the voltage applied to the capacitor 230 , and also that the displacement of the mass 234 from the stable position is a function of the strength of the electrostatic attractive force 244 .
- This provides an alternative way to control the acceleration sensitivity of the capacitor 230 by changing the alternating voltage of the AC source 214 of FIG. 3 instead of adjusting the threshold voltage 219 obtained from the potentiometer 218 . This is achieved by connecting the source 214 to the potentiometer 218 through an AC-DC rectifying supply. A higher alternating voltage from the source 214 results in stronger electrostatic attractive force 244 , hence lower threshold value of acceleration. To obtain higher threshold value of acceleration, a lower voltage is therefore used for the AC source 214 .
- FIG. 5 shows another variable capacitor 250 .
- the variable capacitor 250 is similar to that of FIG. 4 except that the proof mass 234 has no spacers 236 on the surface facing the base 232 .
- an insulating layer 252 is deposited on top of the electrode 238 .
- the insulating layer 252 provides a non-metal contact between the mass 234 and the electrode 232 .
- the non-metal contact eliminates problems such as micro-welding, arcing, and oxidation.
- the thickness of the insulating layer 252 provides a minimum gap between the mass 234 and the electrode 232 , which gives a maximum capacitance when the mass 234 is in contact with the insulating layer 252 .
- FIG. 6 shows another variable capacitor 260 .
- the third electrode 262 in addition to the first electrode 238 and the proof mass 234 forming a second electrode, there is at least one third electrode 262 deposited on the base 232 adjacent to the first electrode 238 and facing the spacers 236 .
- the spacers 236 need not be insulated.
- the third electrodes 262 are electrically connected to the mass 234 so that the electrical potential of the third electrodes 262 and the mass 234 are the same.
- the electrostatic attractive force 244 draws the mass 234 towards the base 232
- the spacers 236 come into contact with the third electrodes 262 preventing contact between the mass 234 and the first electrode 238 and leaving an air gap in between the two. Since the spacers 236 are small, the contacting area is minimized and by having a same electrical potential with the mass 234 , the binding problem of FIG. 4 is avoided.
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- Switches Operated By Changes In Physical Conditions (AREA)
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Abstract
An acceleration sensitive switching arrangement (208) includes an acceleration sensitive variable capacitor (200), a detection circuit (202) for detecting a capacitance value of the variable capacitor (200), and a switching circuit (204) responsive to a comparison between the detected capacitance and a threshold value.
Description
- This application is a continuation of U.S. application Ser. No. 11/155,380, filed Jun. 17, 2005, which application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/666,411, filed Mar. 29, 2005, which are incorporated herein by reference in their entirety.
- The invention relates to an acceleration sensitive switch, more particularly, to a switching arrangement with a variable capacitor that is sensitive to acceleration.
- Acceleration switches are designed to issue a signal when a threshold acceleration value is detected. Acceleration switches are widely used in air bag systems to detect the sudden deceleration of a vehicle during crash. Acceleration switches are usually mechanical switches having a spring-loaded mass that makes contact with an electrode, thus acting as a switch, when subjected to acceleration greater than a predetermined threshold value of acceleration. Today, acceleration switches are commonly manufactured using micromachining.
- U.S. Pat. No. 6,336,658B1 discloses an acceleration switch having a first and second inertia mass where the second inertia mass is lighter than the first inertia mass. A pair of torsion bars connect to the first inertia mass and act as a turning shaft for the first inertia mass. The acceleration switch also has a pair of electrodes formed on a substrate facing the second inertia mass. When acceleration of a predetermined value or greater is applied to the acceleration switch, the second inertia mass moves into contact with the pair of electrodes to act as a switch.
- U.S. Pat. No. 6,236,005B1 discloses an acceleration switch having an inertia mass and an electrode element that are pivoted about an axis of a spring element that connects the inertia mass and the electrode element to a housing. When the switch is subject to acceleration greater than a predetermined value, an electrical contact point on the electrode element touches a corresponding contact area in the housing, so that an electrical signal is provided to indicate that the predetermined value of acceleration is exceeded.
- The threshold value of acceleration will depend on the physical parameters of the switches such as the stiffness of the torsion bar or the spring element, the inertia mass, and the distance between the contacting electrodes. The threshold value of the switches described in these publications is generally difficult to adjust once the switches are made.
- To overcome the limitation in adjusting the threshold value, various configurations of acceleration switch are proposed where the threshold value is adjustable by changing electrode voltage. U.S. Pat. No. 5,905,241 discloses an acceleration switch that uses snap-through buckling phenomenon of a bimorph beam to displace a movable electrode into contact with another electrode at a fixed distance when a threshold acceleration force is experienced. EP Patent Application 0924730A1 discloses an acceleration switch equipped with an inertial mass that is deflectable from a holding position to an actuated position in response to a predetermined acceleration force. A voltage controlled hold plate generates an electrostatic force that opposes the acceleration forces and holds the inertial mass in the holding position until overcome by the predetermined acceleration force. In both cases, the predetermined acceleration force necessary to trigger the switch can be adjusted by adjusting the electrode voltage or the voltage applied to the hold plate.
- However, the above switches involve at least one electrical contact that is formed with metal and may be subjected to problems such as micro-welding, arcing, and oxidation, which may cause failure of the switches.
- US Patent Application 2004/0161869A1 discloses a contactless acceleration switch without metal contacts as shown in
FIG. 1 . Theacceleration switch 100 comprises amass 112 attached to aspring 114, asubstrate layer 102 with athreshold adjustment channel 108 located between asource 104 and adrain 106 thereon, and agate insulating layer 120 located above thesubstrate layer 102. Thethreshold adjustment channel 108, thesource 104, and thedrain 106 are implanted in thesubstrate layer 102 positioned at a predetermined distance from themass 112. Themass 112 operates as a moveable gate in combination with thesource 104 and thedrain 106 to form a field effect transistor (FET). When acceleration level exceeds a threshold acceleration value, an electric field may form between themass 112 and thesubstrate layer 102, creating an electrostatic force that attract themass 112 to thesubstrate layer 102. Themass 112 moves towards thesubstrate layer 102 to a position of critical distance at which point the electrostatic force exceeds a spring force created by thespring 114. Themass 112 may suddenly contact thegate insulating layer 120 and the strength of the electric field reaches a maximum level, thus inverting thethreshold adjustment channel 108 and allowing current to flow between thesource 104 and thedrain 106, which turn on the FET. One problem with theswitch 100 is that a substantially constant voltage in the range from less than five volts for low acceleration, to hundreds of volts for large acceleration range devices, has to be applied between themass 112 and thesubstrate layer 102. - It is an object of the invention to provide an acceleration-sensitive switch that overcomes or ameliorates one or more of the disadvantages of the prior art or which at least provides a useful alternative.
- Accordingly, in a first aspect, the disclosure provides an acceleration sensitive switching arrangement comprising:
- an acceleration sensitive variable capacitor;
- a detection circuit for detecting a capacitance value of the variable capacitor; and
- a switching circuit responsive to a comparison between the detected capacitance and a threshold value.
- The variable capacitor preferably comprises a base with at least one first electrode thereon and a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base. The spring applies a first force to the mass in a direction away from the base.
- The first electrode is preferably adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the electrode and the mass.
- The detection circuit preferably comprises a voltage supply and a resistive load. The voltage supply is preferably an alternating voltage supply.
- The switching circuit preferably comprises a differential amplifier providing a first input voltage and a potentiometer providing a second input voltage to an electronic switch. The first input voltage corresponds to the detected capacitance and the second input voltage corresponds to the threshold value. The electronic switch is preferably triggered positive upon the second input voltage becomes larger than the first input voltage.
- The threshold value is preferably variable by adjusting the potentiometer to change the second input voltage.
- In a second aspect, the disclosure provides an acceleration sensitive variable capacitor comprising:
- a base with at least one first electrode thereon;
- a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base, the spring applying a spring force to the mass in a direction away from the base; and
- the first electrode being adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the first electrode and the mass,
- wherein the attractive force overcomes the spring force and draws the mass towards the base upon the mass being moved, due to acceleration, to within a second predetermined distance from the base.
- In a first aspect of the capacitor, the mass preferably includes at least one spacer formed on the surface facing the base. The spacer is preferably electrically insulated so as to prevent the mass to form electrical contact with the first electrode when the mass moved to the second predetermined distance.
- In a second aspect of the capacitor, a layer of insulator is preferably formed on the first electrode separating the mass and the first electrode when the mass moved to the second predetermined distance.
- In a third aspect of the capacitor, at least one third electrode is preferably formed on the base, adjacent to the first electrode, and having same electrically potential with the mass. The spacer preferably comes into contact with the third electrode when the mass moved to the second predetermined distance.
- Preferably, the capacitance of the capacitor increases to a maximum upon the mass moved to the second predetermined distance, indicative of the capacitor undergoing a predetermined level of acceleration.
- The maximum capacitance of the capacitor being variable, most preferably by changing voltage supplied to the first electrode and the mass, so as to vary the level of acceleration required to move the mass to the second predetermined distance.
- The capacitance between the first electrode and the mass is preferably measured by a detection circuit comprising a voltage supply and a resistive load.
- At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
-
FIG. 1 is a schematic view of a prior art acceleration switch; -
FIG. 2 is a schematic block diagram representation of a switching arrangement according to the disclosure; -
FIG. 3 is an electrical schematic diagram of the acceleration sensitive switching arrangement in accordance with a preferred implementation, and -
FIGS. 4-6 are each schematic views of variable capacitors useful in the arrangement ofFIG. 3 . -
FIG. 2 shows an accelerationsensitive switching arrangement 208. The switchingarrangement 208 comprises an acceleration sensitivevariable capacitor 200, adetector 202, and aswitching circuit 204. The capacitance of thevariable capacitor 200 is configured to change when thecapacitor 200 is exposed to acceleration. Thedetector 202 includes a detecting circuit for detecting the capacitance of thecapacitor 200 and outputting a corresponding electrical signal, such as voltage, to theswitching circuit 204. Theswitching circuit 204 compares the electrical signal to a threshold value. As such, when a value of capacitance corresponding to a threshold value of acceleration is measured by thedetector 200, theswitching circuit 204 will be triggered to issue anoutput 206, which is an electrical signal. The electrical signal may be sent to a controller for further processing. -
FIG. 3 shows anelectrical circuit 225 in which avariable capacitor 210, which will be discussed in more detail later, is connected to adetector 211. Thedetector 211 includes anAC source 214 and a knownload 212, which is typically resistive. The voltage across theload 212 is related, according to Ohm's law, to the capacitance of thecapacitor 210. The voltage is input to adifferential amplifier 216 to obtain asingle output 217, which is subsequently provided to a first input of anelectronic switch 220. Theswitch 220 also receives a second input signal, which is apredetermined threshold voltage 219 obtained from a potentiometer 218. Theswitch 220 compares the two input voltage values, 217 and 219, and will be triggered positive if thevoltage 217 is larger than thethreshold voltage 219 upon the second input. Thethreshold voltage 219 set by the potentiometer 218 can be adjusted so that theswitch 220 will respond to a different value of maximum capacitance, which is associated to threshold value of acceleration experienced by thecapacitor 210. -
FIG. 4 shows a schematic view of a first configuration of an acceleration sensitivevariable capacitor 230. Thevariable capacitor 230 comprises a base 232 with anelectrode 238 thereon and aproof mass 234 forming a second electrode resiliently suspended by aspring 240. Thespring 240 applies aspring force 242 to themass 234 in a direction away from thebase 232. Thespring force 242 varies linearly relative to the extension of thespring 240. TheAC source 214 in thedetector 211 supplies an alternating voltage between the mass 234 and theelectrode 238, thereby forming a capacitor. The electric field formed between the mass 234 and theelectrode 238 will create an electrostaticattractive force 244 that draws themass 234 towards thebase 232. The electrostaticattractive force 244 increases exponentially as the space between the mass 234 and theelectrode 238 reduces. - When the
capacitor 230 is not in motion or there is no acceleration, thespring force 242 is larger than the electrostaticattractive force 244 and thus, themass 234 is resiliently suspended at a stable position away from thebase 232. If thecapacitor 230 starts to move in a direction A, away from the plane of the base 232 towards themass 234, thecapacitor 230 will experience acceleration in the same direction. Anacceleration force 246 associated with the acceleration will act upon themass 234 and move the mass towards thebase 232. When themass 234 is moved by the acceleration force 246 a distance away from the stable position towards thebase 232, thespring force 242 of thespring 240 increases linearly while the electrostaticattractive force 244 increased exponentially relative to the distance. There is a critical distance away from the stable position where thespring force 242 and the electrostaticattractive force 244 increase at a same rate. Below the critical distance, theelectrostatic force 244 increases at a lower rate than thespring force 242, resulting a positive effective spring force. If theacceleration force 246 is less than the positive effective spring force, themass 234 will be pulled back to the stable position by the positive effective spring force once theacceleration force 246 is removed. If theacceleration force 246 is large enough to move themass 234 to the critical distance, theacceleration force 246 will continue to move themass 234 further towards the base 232 into a position where the electrostaticattractive force 244 overcomes thespring force 234 and draws themass 234 towards theelectrode 238. -
FIG. 4 also shows, arranged on themass 234, at least onespacer 236 formed on the surface facing thebase 232. Thespacers 236 are electrically insulating and are configured to come into contact with theelectrode 238 when the electrostaticattractive force 244 draws themass 234 close to theelectrode 238. Theinsulated spacers 236 prevent the mass 234 from touching theelectrode 238 so that the capacitor formed thereby will not short-circuit and to avoid any attractive binding between the mass 234 and theelectrode 238 that might otherwise occur. The capacitance between the mass 234 and theelectrode 238 reaches a maximum when thespacers 236 are in contact with theelectrode 238. A maximum voltage output from thedifferential amplifier 216 corresponding to the maximum capacitance will be detected as described earlier. As the maximum voltage is larger than thethreshold voltage 219 obtained from the potentiometer 218, theelectronic switch 220 will be triggered. - The
mass 234 will stay at the position where thespacers 236 are in contact with theelectrode 238, even if the acceleration force is removed, because the electrostaticattractive force 244 is larger than thespring force 242. The capacitance is always kept at a maximum and theelectronic switch 220 is turned on continuously once thecapacitor 230 has experienced acceleration larger than a threshold value, even if the acceleration only exceeded the threshold value for a short duration. To turn off or reset the switchingarrangement 208, a zero voltage is applied to thecapacitor 230 via thesource 214, where the electrostaticattractive force 244 is removed. Thespring force 242 will pull themass 234 away from thebase 232, releasing the contact between thespacers 236 and theelectrode 238. - It is known that the electrostatic
attractive force 244 is a function of the voltage applied to thecapacitor 230, and also that the displacement of the mass 234 from the stable position is a function of the strength of the electrostaticattractive force 244. This provides an alternative way to control the acceleration sensitivity of thecapacitor 230 by changing the alternating voltage of theAC source 214 ofFIG. 3 instead of adjusting thethreshold voltage 219 obtained from the potentiometer 218. This is achieved by connecting thesource 214 to the potentiometer 218 through an AC-DC rectifying supply. A higher alternating voltage from thesource 214 results in stronger electrostaticattractive force 244, hence lower threshold value of acceleration. To obtain higher threshold value of acceleration, a lower voltage is therefore used for theAC source 214. -
FIG. 5 shows anothervariable capacitor 250. Thevariable capacitor 250 is similar to that ofFIG. 4 except that theproof mass 234 has nospacers 236 on the surface facing thebase 232. To prevent themass 234 and theelectrode 232 from short-circuit, an insulatinglayer 252 is deposited on top of theelectrode 238. The insulatinglayer 252 provides a non-metal contact between the mass 234 and theelectrode 232. The non-metal contact eliminates problems such as micro-welding, arcing, and oxidation. The thickness of the insulatinglayer 252 provides a minimum gap between the mass 234 and theelectrode 232, which gives a maximum capacitance when themass 234 is in contact with the insulatinglayer 252. -
FIG. 6 shows anothervariable capacitor 260. In this arrangement, in addition to thefirst electrode 238 and theproof mass 234 forming a second electrode, there is at least onethird electrode 262 deposited on the base 232 adjacent to thefirst electrode 238 and facing thespacers 236. Thespacers 236 need not be insulated. Thethird electrodes 262 are electrically connected to themass 234 so that the electrical potential of thethird electrodes 262 and themass 234 are the same. When the electrostaticattractive force 244 draws themass 234 towards thebase 232, thespacers 236 come into contact with thethird electrodes 262 preventing contact between the mass 234 and thefirst electrode 238 and leaving an air gap in between the two. Since thespacers 236 are small, the contacting area is minimized and by having a same electrical potential with themass 234, the binding problem ofFIG. 4 is avoided. - Although the invention has been described with reference to preferred embodiments, it will be appreciated by those persons skilled in the art that the invention may be embodied in many other forms.
Claims (20)
1. A switching arrangement sensitive to acceleration, the switching arrangement comprising:
an acceleration sensitive variable capacitor;
a detection circuit for detecting a capacitance value of the variable capacitor; and
a switching circuit responsive to a comparison between the detected capacitance and a threshold value.
2. The switching arrangement of claim 1 , wherein the variable capacitor comprises a base with at least one first electrode thereon and a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base.
3. The switching arrangement of claim 2 , wherein the spring applies a first force to the mass in a direction away from the base.
4. The switching arrangement of claim 2 , wherein the first electrode is adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the electrode and the mass.
5. The switching arrangement of claim 1 , wherein the detection circuit comprises a voltage supply and a resistive load.
6. The switching arrangement of claim 5 , wherein the voltage supply is an alternating voltage supply.
7. The switching arrangement of claim 1 , wherein the switching circuit comprises a differential amplifier providing a first input voltage and a potentiometer providing a second input voltage to an electronic switch.
8. The switching arrangement of claim 7 , wherein the first input voltage corresponds to the detected capacitance and the second input voltage corresponds to the threshold value.
9. The switching arrangement of claim 8 , wherein the electronic switch is triggered positive upon the second input voltage becoming larger than the first input voltage.
10. The switching arrangement of claim 8 , wherein the threshold value is variable by adjusting the potentiometer to change the second input voltage.
11. An acceleration sensitive variable capacitor comprising:
a base with at least one first electrode thereon;
a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base, the spring applying a spring force to the mass in a direction away from the base, wherein the mass includes at least one spacer formed on the surface facing the base; and
the first electrode being adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the first electrode and the mass,
wherein the attractive force overcomes the spring force and draws the mass towards the base upon the mass being moved, due to acceleration, to within a second predetermined distance from the base.
12. (canceled)
13. The acceleration sensitive variable capacitor of claim 12 , wherein the spacer is electrically insulated so as to prevent the mass from forming electrical contact with the first electrode when the mass moves to the second predetermined distance.
14. The acceleration sensitive variable capacitor of claim 11 , wherein a layer of insulator formed on the first electrode separating the mass and the first electrode when the mass moved to the second predetermined distance.
15. The acceleration sensitive variable capacitor of claim 11 , wherein at least one third electrode is formed on the base, adjacent to the first electrode, and having same electrically potential with the mass.
16. The acceleration sensitive variable capacitor of claim 15 , wherein the spacer comes into contact with the third electrode when the mass moved to the second predetermined distance.
17. The acceleration sensitive variable capacitor of any one of claims 11 to 16 , wherein the capacitance of the capacitor increases to a maximum, indicative of the capacitor undergoing a predetermined level of acceleration, upon the mass moving to the second predetermined distance.
18. The acceleration sensitive variable capacitor of claim 17 , wherein the maximum capacitance of the capacitor is variable so as to vary the level of acceleration required to move the mass to the second predetermined distance.
19. The acceleration sensitive variable capacitor of claim 18 , wherein the maximum capacitance of the capacitor is variable by changing voltage supplied to the first electrode and the mass.
20. The acceleration sensitive switch of claim 19 , wherein the capacitance between the first electrode and the mass is measured by a detection circuit comprising a voltage supply and a resistive load.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/823,196 US20080017486A1 (en) | 2005-03-29 | 2007-06-26 | Acceleration sensitive switch |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US66641105P | 2005-03-29 | 2005-03-29 | |
US11/155,380 US7284432B2 (en) | 2005-03-29 | 2005-06-17 | Acceleration sensitive switch |
US11/823,196 US20080017486A1 (en) | 2005-03-29 | 2007-06-26 | Acceleration sensitive switch |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/155,380 Continuation US7284432B2 (en) | 2004-06-18 | 2005-06-17 | Acceleration sensitive switch |
Publications (1)
Publication Number | Publication Date |
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US20080017486A1 true US20080017486A1 (en) | 2008-01-24 |
Family
ID=46062811
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/155,380 Expired - Fee Related US7284432B2 (en) | 2004-06-18 | 2005-06-17 | Acceleration sensitive switch |
US11/823,196 Abandoned US20080017486A1 (en) | 2005-03-29 | 2007-06-26 | Acceleration sensitive switch |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
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US11/155,380 Expired - Fee Related US7284432B2 (en) | 2004-06-18 | 2005-06-17 | Acceleration sensitive switch |
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US (2) | US7284432B2 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20110009773A1 (en) * | 2006-02-04 | 2011-01-13 | Evigia Systems, Inc. | Implantable sensing modules and methods of using |
US8242392B1 (en) | 2011-11-01 | 2012-08-14 | John Ondracek | Multi-directional momentum-change sensor and methods of use |
CN108469535A (en) * | 2018-03-26 | 2018-08-31 | 温州大学 | Micro-acceleration gauge based on Electrostatic Absorption effect |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
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US7999201B2 (en) * | 2008-11-06 | 2011-08-16 | Shandong Gettop Acoustic Co. Ltd. | MEMS G-switch device |
US8322216B2 (en) * | 2009-09-22 | 2012-12-04 | Duli Yu | Micromachined accelerometer with monolithic electrodes and method of making the same |
CN103502059B (en) * | 2011-05-12 | 2015-07-01 | 丰田自动车株式会社 | Collision detection device for vehicle |
US10422813B2 (en) * | 2015-09-02 | 2019-09-24 | Circor Aerospace, Inc. | Miniature hermetic acceleration detection device |
CN113203939B (en) * | 2021-04-26 | 2022-03-18 | 中国科学院地质与地球物理研究所 | Detection method and device for MEMS acceleration sensor chip |
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US5417111A (en) * | 1990-08-17 | 1995-05-23 | Analog Devices, Inc. | Monolithic chip containing integrated circuitry and suspended microstructure |
US5353641A (en) * | 1992-08-07 | 1994-10-11 | Ford Motor Company | Digital capacitive accelerometer |
US5447068A (en) * | 1994-03-31 | 1995-09-05 | Ford Motor Company | Digital capacitive accelerometer |
DE4423396C2 (en) * | 1994-07-04 | 2001-10-25 | Fraunhofer Ges Forschung | Method for producing a micromechanical surface structure |
DE59607318D1 (en) * | 1995-01-24 | 2001-08-23 | Infineon Technologies Ag | MICROMECHANICAL COMPONENT |
JPH10334778A (en) | 1997-05-30 | 1998-12-18 | Hyundai Motor Co Ltd | Critical microswitch and its manufacture |
EP0924730A1 (en) | 1997-12-15 | 1999-06-23 | Trw Inc. | Acceleration switch |
JP2000088878A (en) | 1998-09-09 | 2000-03-31 | Tokai Rika Co Ltd | Acceleration switch and its manufacture |
EP0997920B1 (en) | 1998-10-29 | 2002-06-12 | Sensonor A.S. | Micromechanical acceleration switch |
US6388299B1 (en) * | 1998-12-10 | 2002-05-14 | Honeywell Inc. | Sensor assembly and method |
US20020114058A1 (en) * | 2000-12-19 | 2002-08-22 | Dereus Dana Richard | Light-transmissive substrate for an optical MEMS device |
US6720634B2 (en) | 2002-01-07 | 2004-04-13 | Honeywell International Inc. | Contactless acceleration switch |
-
2005
- 2005-06-17 US US11/155,380 patent/US7284432B2/en not_active Expired - Fee Related
-
2007
- 2007-06-26 US US11/823,196 patent/US20080017486A1/en not_active Abandoned
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20110009773A1 (en) * | 2006-02-04 | 2011-01-13 | Evigia Systems, Inc. | Implantable sensing modules and methods of using |
US8242392B1 (en) | 2011-11-01 | 2012-08-14 | John Ondracek | Multi-directional momentum-change sensor and methods of use |
CN108469535A (en) * | 2018-03-26 | 2018-08-31 | 温州大学 | Micro-acceleration gauge based on Electrostatic Absorption effect |
Also Published As
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US7284432B2 (en) | 2007-10-23 |
US20060219536A1 (en) | 2006-10-05 |
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