GB2073890A - Capacitance force transducer - Google Patents
Capacitance force transducer Download PDFInfo
- Publication number
- GB2073890A GB2073890A GB8109201A GB8109201A GB2073890A GB 2073890 A GB2073890 A GB 2073890A GB 8109201 A GB8109201 A GB 8109201A GB 8109201 A GB8109201 A GB 8109201A GB 2073890 A GB2073890 A GB 2073890A
- Authority
- GB
- United Kingdom
- Prior art keywords
- plate
- moving plate
- force
- capacitance
- spider
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000003990 capacitor Substances 0.000 claims abstract description 5
- 241000239290 Araneae Species 0.000 claims description 30
- 230000000712 assembly Effects 0.000 claims description 22
- 238000000429 assembly Methods 0.000 claims description 22
- 125000006850 spacer group Chemical group 0.000 claims description 10
- 239000002184 metal Substances 0.000 claims description 7
- 229910052751 metal Inorganic materials 0.000 claims description 7
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 6
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 239000010949 copper Substances 0.000 claims description 6
- 239000011810 insulating material Substances 0.000 claims description 4
- 239000000463 material Substances 0.000 claims description 4
- 230000035945 sensitivity Effects 0.000 claims description 4
- 229910000906 Bronze Inorganic materials 0.000 claims description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 3
- 239000010974 bronze Substances 0.000 claims description 3
- KUNSUQLRTQLHQQ-UHFFFAOYSA-N copper tin Chemical compound [Cu].[Sn] KUNSUQLRTQLHQQ-UHFFFAOYSA-N 0.000 claims description 3
- 229920002430 Fibre-reinforced plastic Polymers 0.000 claims description 2
- 239000004677 Nylon Substances 0.000 claims description 2
- 238000006073 displacement reaction Methods 0.000 claims description 2
- 230000000694 effects Effects 0.000 claims description 2
- 239000011521 glass Substances 0.000 claims description 2
- 239000003365 glass fiber Substances 0.000 claims description 2
- 229920001778 nylon Polymers 0.000 claims description 2
- 238000005303 weighing Methods 0.000 claims description 2
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
- G01L1/142—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators using capacitors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G7/00—Weighing apparatus wherein the balancing is effected by magnetic, electromagnetic, or electrostatic action, or by means not provided for in the preceding groups
- G01G7/06—Weighing apparatus wherein the balancing is effected by magnetic, electromagnetic, or electrostatic action, or by means not provided for in the preceding groups by electrostatic action
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Electromagnetism (AREA)
- Measurement Of Force In General (AREA)
Abstract
A capacitance force transducer consists of a fixed plate 1 and a moving plate 8, forming 2 electrodes of a capacitor, wherein there is provided means for both constraining the motion of the moving plate and to provide a force related to the deflection of the moving plate from a zero load position tending to restore the moving plate to that position. In a preferred embodiment, the restoring and constraining forces are provided by a series of slots 7 cut in the moving plate so as to act as leaf springs. <IMAGE>
Description
SPECIFICATION
Improvements in or relating to force transducers
The present invention relates to force transducers that is to say, devices which can be used to provide output signals which are related to the magnitude of forces which are impressed upon them.
Capacitance force transducers consist of a fixed conducting plate and a moving conducting plate which is constrained to move relative to the fixed conducting plate under the action of an applied force so that the change in capacitance of the transducer is a measure of the applied force.
According to the present invention there is provided a capacitance force transducer of the type hereinbefore described wherein the means for constraining the movement of the moving plate relative to the fixed plate is arranged to provide a force related to the deflection of the moving plate from a zero load position tending to restore the moving plate to that position.
Preferably the constraining means consists of a plurality of leaf springs so disposed around the periphery of the moving plate that the moving plate can only move in a direction perpendicular to the plane of the fixed plate and the centre of the moving plate remains superimposed on that of the fixed plate.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which
Figure 1 is a plan view of an embodiment of the invention,
Figure 2 is an elevation of the embodiment of Fig. 1, and
Figure 3 is a plan view of a second embodiment of the invention.
Referring to the drawings, a capacitance force transducer which is suitable for use in the weighing of small objects, consists of an earthed metal plate 1 mounted on a stand 2.
Clamped to the underside of the metal plate 1 are two parallel spider assemblies 3 and 4.
The spider assemblies are separated by spacers 5. Each of the spider assemblies 3 and 4 is made of a glass reinforced sheet 6 one face of which has a layer 61 of copper deposited on it. Each of the spider assemblies 3 and 4 has an arrangement of slots 7 cut in it which form three sets of lead springs disposed regularly around the central region 8 of each of the spider assemblies 3 and 4 so as to constrain the central region 8 of each of the spider assemblies 3 and 4 to move so that the plane of the central region 8 of each of the spider assemblies 3 and 4 remains parallel to the outer region 9 of each of the spider assemblies 3 and 4. A tray 10 is attached to both of the spider assemblies 3 and 4 by means of three regularly spaced supports 11 and spacers 12, thus doubling the restoring force available from one spider assembly alone.The supports 11 pass through holes 11' in the earthed plate 1. The upper spider assembly 3 is clamped to the earthed plate 1 with its copper layer 6' facing downwards by means of three screws 1 3 which pass through its outer region 9 and into the spacers 5, which are of the same length as the spacers 1 2. The screws 1 3 are made of an insulating material such as nylon. The outer region 9 of the lower spider assembly 4 is clamped to the spacers 5 by means of insulating screws 14.
Thus the outer regions 9 of the spider assemblies 3 and 4 are fixed in relation to the earthed plate 1 while the inner regions 8 are free to move in a direction perpendicular thereto in response to a force, or weight applied to the tray 10.
The earthed plate 1 and the copper layer 61 of the upper spider assembly 3 form the plates of a capacitor, and providing the leaf springs provided by the slots 7 are not stressed beyond their elastic limits, the change in capacitance of this capacitor as the spider assemblies 3 and 4 deflect in response to a force applied to the tray 1 0 will be a measure of that force. By applying known forces to the tray 10, the transducer can be calibrated to give an absolute measure of force.
If desired, the sensitivity of the force transducer can be increased by providing a second earthed plate as shown in dotted form in Fig.
2.
If it is desired to use the transducer to measure force absolutely then the use of a glass-fibre reinforced plastics material for the moving plate, or plates, is undesirable as such materials shown elastic hysteresis effects. This can be overcome by making the moving plate, or plates, of a metal with good elastic and conducting properties, such as phosphor bronze, and attaching a layer of an insulating material either to the underside of the fixed plate, or plates, or to the upper side of the moving plate, or plates.
Fig. 3 shows a plan view of a second embodiment of the invention. Components which correspond to those of the first embodiment of the invention, as shown in Fig. 1, have the same reference numerals.
The second embodiment of the invention has a greater central area for the same outer dimensions as the circular form used in the first embodiment of the invention. Thus the change in capacity with displacement of the upper plate 10 is increased, and hence the sensitivity of the device is increased also.
1. A capacitance force transducer of the type hereinbefore described wherein the means for constraining the movement of the moving plate relative to the fixed plate is
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (7)
1. A capacitance force transducer of the type hereinbefore described wherein the means for constraining the movement of the moving plate relative to the fixed plate is arranged to provide a force related to the deflection of the moving plate from a zero load position tending to restore the moving plate to that position.
2. A capacitance force transducer according tç claim 1 wherein the constraining means comprises a plurality of leaf springs so disposed around the periphery of the moving plate that the moving plate can only move in a direction perpendicular to the plane of the fixed plate and the centre of the moving plate remains superimposed upon that of the fixed plate.
3. A capacitance force transducer according to claim 1 or claim 2 wherein the leaf springs are integral with the moving plate.
4. A capacitance force transducer according to claim 3 wherein the conducting plate is made of a metal having good elastic and conducting properties.
5. A capacitance force transducer according to claim 4 wherein the moving plate is made of phosphor bronze.
6. A capacitance force transducer according to any preceding claim wherein the moving plate is circular in form.
7. A capacitance force transducer according to any preceding claim wherein the moving plate is square in form.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8109201A GB2073890A (en) | 1980-04-09 | 1981-03-24 | Capacitance force transducer |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8011759 | 1980-04-09 | ||
| GB8109201A GB2073890A (en) | 1980-04-09 | 1981-03-24 | Capacitance force transducer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2073890A true GB2073890A (en) | 1981-10-21 |
Family
ID=26275111
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8109201A Withdrawn GB2073890A (en) | 1980-04-09 | 1981-03-24 | Capacitance force transducer |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2073890A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2123157A (en) * | 1982-06-22 | 1984-01-25 | Peter Caleb Frederi Wolfendale | Load cells |
| WO1995020145A1 (en) * | 1994-01-21 | 1995-07-27 | The University Of Melbourne | Improvements in syringe pumps |
| AU690631B2 (en) * | 1994-01-21 | 1998-04-30 | University Of Melbourne, The | Improvements in syringe pumps |
-
1981
- 1981-03-24 GB GB8109201A patent/GB2073890A/en not_active Withdrawn
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2123157A (en) * | 1982-06-22 | 1984-01-25 | Peter Caleb Frederi Wolfendale | Load cells |
| WO1995020145A1 (en) * | 1994-01-21 | 1995-07-27 | The University Of Melbourne | Improvements in syringe pumps |
| GB2300926A (en) * | 1994-01-21 | 1996-11-20 | Univ Melbourne | Improvements in syringe pumps |
| GB2300926B (en) * | 1994-01-21 | 1998-02-18 | Univ Melbourne | Improvements in syringe pumps |
| AU690631B2 (en) * | 1994-01-21 | 1998-04-30 | University Of Melbourne, The | Improvements in syringe pumps |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |