FR2621129A1 - ACCELERATION DETECTION DEVICE - Google Patents

Abstract

The device of the invention comprises a bar 11, elements 10, 12 supporting the two ends of the bar, a weight 15 for subjecting the bar to a twist in response to the application of an acceleration acting practically in the center of the bar, and a detector 16 of the value of the torsional deformation of the bar. When applying an acceleration to the detection device, the bar flexes and is deformed in proportion to the value of the acceleration. The deformation of the bar is detected by the detector and a signal, depending on the value of the acceleration, leaves the detector.

Description

1. The present invention relates to a device for

  acceleration detection to detect acceleration

ration or deceleration.

  The acceleration detection device described in Figure 17 is well known in the art. This device comprises a rod 1, one end of which is supported by a base 3 and the other end is free, and gauges of

  constraint 2 which are mounted on the bar 1.

  When the device is subjected to accelerated

  ration, there is displacement of the free end of the bar-

  reel 1 and this is subjected to bending. This bending is then transformed into an electrical signal by the gauges

of constraint 2.

  Furthermore, the bending to which the bar 1 is subjected is proportional to the absolute value of

  acceleration. Therefore, the electrical signal trans-

  formed by the strain gauges 2 becomes signal 2.

  certain in proportion to the absolute value of the access

  leration. Such a detection device is suggested in many applications, for example in the publication of Japanese patent 139758/1986 of June 27, 1986. This publication

  blication represents a semi-detection device

  conductor with the silicon bar and the gauges of

  constraint 2 in piezoelectric resistors.

  In this detection device, the bar 1

  must undergo significant bending during small accelerations

  so that they can be detected.

  To be amplified, the electrical signal trans-

  formed by the strain gauges 2 must be able to be used to allow the detection of low value accelerations. However, signal amplification

  electric is not desirable in this de-

  tection, because it not only amplifies the electrical signal

that but also the noises.

  In order for the bar 1 to be subjected to greater bending at low accelerations, it is necessary to

  reduce its mechanical resistance, for example by thinning

  health or by increasing the mass of its free end by

setting a weight in it.

  However, if one weakens the mechanical resistance

  bar 1, you can't always get a

  normal detection when applying an acceleration

  excessive tion. Indeed, the detection characteristics

  acceleration could be disturbed by rup-

  plastic structure or deformation of the bar 1.

  Accordingly, the object of the present invention is

  jet an improved acceleration detection device

  tion which overcomes the disadvantages just exposed

  which relate to conventional devices.

  The present invention also relates to the

  detection of low value accelerations.

  3. The object of the present invention is also to prevent the detection characteristics from changing after

  application of excessive acceleration.

  Another object of the present invention is to produce a precise electrical output signal. To achieve the foregoing objects, the present invention provides a bar, a means for supporting the

  two ends of the bar, a means to submit the bar-

  reau a torsion in response to the applied acceleration, the latter being practically in the center of the bar, and a means for detecting the value of the deformation of the bar

thus produced.

  The present invention will be clearly understood in general.

  its with the accompanying drawings in which: Figure 1 is a sectional view taken along

  line I-I of FIG. 16 of the first embodiment

  tion of the present invention; Figure 2 is a sectional view along line II-II of Figure 16 of the first embodiment of the present invention;

  Figure 3 is a sectional view for ex-

  pinpoint the source of the device error; Figure 4 is a processing circuit diagram

  signal for the first embodiment of the present

  the invention; Figure 5 is a sectional view taken along line I-I of Figure 16, showing the second embodiment of the present invention;

  Figure 6 is a sectional view along the line.

  gene II-II of FIG. 16, showing the second embodiment of the present invention; Figure 7 is a sectional view taken along line I-I of Figure 16, showing the third embodiment of the present invention; Figure 8 is a sectional view taken along line 4. II-II of Figure 16, showing the third embodiment of the present invention;

  FIG. 9 is a diagram of the milking circuit

  signal ment for the third embodiment of the present invention; Figure 10 is a sectional view taken along line II of Figure 16, showing the fourth embodiment of the present invention; Figure 11 is a sectional view taken along

  of line II-II of figure 16, representing the fourth-

  the embodiment of the present invention;

  Figure 12 is an oblique view of the fifth mo-

  of carrying out the present invention; Figure 13 is a sectional view taken along line I-I of Figure 16, showing the sixth embodiment of the present invention; Figure 14 is a sectional view taken along line II-II of Figure 16, showing the sixth embodiment of the present invention;

  FIG. 15 is a diagram of the processing circuit

  signaling for the sixth embodiment of the present invention;

  Figure 16 is an oblique view of the ex-

  of the pre-acceleration detection device

  invention; Figure 17 is a plan view of a device

  classic acceleration detection.

  Figures 1, 2 and 16 show the first mo-

  of the present invention. As is

  illustrated in figure 16, the detection device is assembled

  tee in a shoemaker 17. As illustrated in Figures 1 and 2, the

  detection device according to this first embodiment

  tion includes a bar 11, two bases 12 and 13 for support

  carry the two ends of the bar 11, a weight 15 to cause the bar 11 to twist in response to 5.

  the application of an acceleration, this being sensitive

  in the center of the bar, and two strain gauges

  te 16 for detection of the bar twist value

  reau. The two ends of the bar 11 are supported by the two bases 12 and 13, respectively. A projecting element 14 is fixed to the center of the bar 11. The element 14 is perpendicular to the side 11a of the bar 11. The weight 15

  is fixed to one end of the projecting element 14.

  On the other hand, two strain gauges 16 are mounted on either side of the weight 15. The gauges are fixed to the bar 11 so as to detect the stress exerted in a direction making an angle of 45 relative to the longitudinal direction of the bar 11. The gauges 16 are connected to a signal processing circuit 21 by

  conductive wires (not shown).

  The bar 11 and the bases 12 and 13 are mounted

  in the housing 17. Two stops 18 are fixed to the

  inner tie of the housing 17. Two interstices 20 are formed

  between the stops 18 and the weight 15. It is preferable that the dimensions of the spaces 20 are a function of the mechanical resistance of the bar 11, but in the present embodiment, the dimensions of the interstices 20 are established in accordance with the accepted value for the

errors.

  Now in connection with FIG. 3, we give

  ra a general explanation of the origin of the errors. The

  force F, proportional to the absolute value of the acceleration

  ration, is produced when an acceleration a is applied

  quée the detection device 10. At this time, the weight 15 is rotated about the longitudinal axis

  llb of the bar 11 under the effect of deformation by tor-

sion of this bar.

  If the force F produced by the acceleration must be maintained at a constant value, the stress f 6. linked to the deformation due to torsion decreases during

  the rotation of the weight 15. Consequently, the more the deformation

  torsion, the greater the acceleration

  the higher the applied value, the larger the errors

  your. Consequently, the dimensions of the interstices 20 are established in accordance with the admissible value for the

  errors in this first embodiment.

  Now in connection again with the fig-

  res 1 and 2, we will explain the operation of the device

detection 10.

  The force proportional to the absolute value of

  the acceleration acts on the weight 15 when the acceleration

  tion is applied in the X-X direction of the detection device 10 illustrated in FIG. 2. The force exerted

  on the weight 15 causes the bar 11 to twist and

  develops a torsional deformation which is proportional-

  the to the absolute value of the acceleration. At this point, the de-

  torsional formation to which the bar 11 is subjected

  is distributed uniformly in its longitudinal direction

  dinal. When the torsional deformation is produced, the bar 11 is subjected to a stress proportional to the value of the deformation. The value of the constraint

  to which the bar 11 is subjected is transformed into si-

  general electrical by the strain gauges 16.

  Incidentally, the detection device of the first embodiment of the invention proceeds to detect the acceleration by using the torsional deformation of the bar 11. The compression stress and the stress

  are produced in bar 11 in di-

  rections intersecting at right angles, when the

  torsional deformation of the bar. The constraints of

  pressure and expansion thus produced cut to 45

  of the longitudinal direction of the bar 11, respectively-

  is lying. Consequently, if a single strain gauge 16 is fixed to the bar 11 in such a direction 45 7. from the longitudinal direction of the bar, one of the

electrical signal constraints.

  Furthermore, in the first embodiment of

  the invention the torsional deformation is produced symmetrically

  three times relative to the weight 15 acting on the bar

  11, because the weight is fixed at its center.

  Therefore, the detection device of this first embodiment can be used with a bridge

  of Wheatstone because the two strain gauges 16 are fi-

  attached to both sides of the weight 15, parallel to the other

  tre, and in the direction at 45 from the longitudinal direction of the bar-

  reau 11. The compression stress is detected by a

  gauge 16 and the extension constraint by the other gauge 16.

  Now in connection with FIG. 4, we explain

  that the signal processing circuit 21 of the first embodiment of the invention. Regarding the bridge of

  Wheatstone, we omit to describe it because it

  this is a well known circuit. However, the detection device 10 using the Wheatstone bridge compensates for the changes in the detection characteristics of strain gauges 16 due to variations in temperature etc. and

  becomes more precisely sensitive to small accelerations.

  Furthermore, in the first embodiment of

  the invention, the stress developed is distributed in a manner

  re uniform over the entire length of the bar 11 because the

  torsion formation is itself in the long sense

  tudinal of this bar. Therefore, if the position of

  fixing the strain gauges 16 varies, the characteristics

  Detection ticks will not be modified when the gauges 16 are placed parallel to each other and in the direction making an angle of 45 with the longitudinal direction of the bar. Consequently, the detection device 10 according to the first embodiment can be mass produced with characteristics

identical detection.

  8. In connection with FIGS. 5 and 6, we describe the

  second embodiment of the present invention. The the-

  ment projecting 14 of the first embodiment is sup-

  awarded and the weight 15 is fixed directly to the bar 11 in this second embodiment. In addition, the stops 18 are also removed, and the gaps 20 are

  between weight 15 and shoemaker 17. The dimensions of the in-

  terstices 20 are established according to the accepted value

  for errors as in the first embodiment.

  The rest of the construction of the device 10 of this second embodiment is identical to that of the first. By

  Therefore, we will not proceed to its detailed description-

  lée. In connection now with FIGS. 7, 8 and 9, the third embodiment of the present invention will be described. The detection device of this third embodiment uses four strain gauges 16a, 16b, 16c and 16d in place of the two gauges 16 of the first embodiment.

  The mounting of the four gauges 16a-16d is the following

  boast. The gauges 16a and 16c are fixed to a surface of the bar

  reau 11 on both sides of the weight 15, parallel to each other and in the direction making an angle of +45 with the longitudinal direction of the bar. In addition, the gauges

  16b and 16d are fixed to a surface of the bar

  reau 11, on both sides of the weight 15, parallel to each other and in the direction making an angle of -45 with the longitudinal direction of the bar. The four gauges

  16a-16d are connected to the processing circuit

  signal 22 by conductive wires (not shown

  your). We will not proceed to the detailed explanation of the

  circuit 22 because it includes a well-connected Wheatstone bridge

  naked in technique. However, the processing circuit 22 with the four strain gauges 16a-16d compensates for the 9. changes in the detection characteristics of the gauges.

  due to variations in temperature, etc. and is more pre-

  cis in the case of small value accelerations.

  The rest of the construction of this third embodiment is identical to that of the first embodiment. By

  Therefore, we will omit its detailed explanation.

  In connection now with FIGS. 10 and 11, the fourth embodiment of the present invention will be described. The bar 11 of the fourth embodiment has been rotated 90 about the longitudinal axis 11b relative to the position of the bar of the third embodiment. Therefore, the position of the weight 15

  on the bar 11 is different from that of the third mo-

of achievement.

  In the fourth embodiment, the weight 15 protrudes in a direction such that it is difficult to bend the bar 11. Consequently, the value of the bending of the bar is low, in the event of acceleration in the direction YY and the direction ZZ illustrated in FIG. 10. Consequently, the detection device 10 of the fourth embodiment has a sharp directivity. Consequently, only the acceleration in the X-X direction is

  detected by the device 10 of this fourth embodiment

  station. In addition, the device 10 has a high endurance against excessive accelerations occurring in

  direction Y-Y or in direction Z-Z.

  The rest of the construction of this fourth mode

  is identical to the third embodiment.

  tion. Therefore, it will not be explained.

detailed tion.

  Now in connection with FIG. 12, we describe

  ra the fifth embodiment of the present invention

  tion. This fifth mode is an example of simplification of the fourth embodiment. In the fifth embodiment of the invention, the bar 11, the element at 10. projection 14 and the weight 15 form the same assembly by micromachining of a silicon wafer 23. The strain gauges 16a-16d are formed directly on the rod 11 in the form of a silicon diffusion resistance. Consequently, the positions of the gauges 16a-16d can be determined very precisely. As a result, the fifth embodiment can be mass produced

  with identical detection characteristics.

  In addition, the bar 11 can be thinned by gra-

  in this fifth embodiment. Consequently, the thickness of the bar 11 can be freely established as a function of the smallest values of the acceleration

that we have to detect.

  The rest of the construction of the fifth embodiment is identical to the fourth embodiment and we

will omit the description.

  Now in connection with FIG. 13, we de-

  will write the sixth embodiment of the present invention

  tion. In this sixth embodiment, a light detector consisting of a light-emitting diode 24 and a semiconductor position detection device 26 is used as a means for detecting the value of the torsional deformation of the bar 11 to the place of the strain gauges 16a-16d used in the fourth mode of

production.

  The light emitting diode 24 is arranged as

  light source, at the outlet of the housing 17. The light pro-

  the light emitting diode 24 is transmitted to the

  semiconductor position detector 26 by optical fiber

  that 25. One end of the fiber 25 is fixed to the light-emitting diode 24, and the other end to the weight 15.The

  light produced by diode 24 is introduced into the

  support 26 which constitutes the element converting the position

  incident light in voltage or electric current.

  In the sixth embodiment of 11.

  the invention, when the bar 11 is subjected to a tor-

  By applying acceleration, the position of the incident light is detected. At this stage, the electric voltage proportional to the applied acceleration is present at the output of the device 26. The rest of the construction of this sixth embodiment is identical to the fourth mode and we

  will therefore omit the description.

  Now in connection with FIG. 14, we

  will explain the seventh embodiment of the invention.

  In this seventh embodiment, a primary coil

  re 27 and a pair of secondary coils 28 are used

  as means for detecting the value of the

  torsion of the bar 11 in place of the gauges

  13 of constraint 16a-16d of the fourth embodiment.

  The primary coil 27 is wound around the weight 15 and excited by an alternating current voltage of predetermined frequency. Furthermore, the two secondary coils 28 are wound near the weight 15 opposite the two ends of the primary coil 27. The secondary coils 28 are fixed to the case 17 by means (not shown). In addition, gaps are

  formed between the weight 15 and the secondary coils 28.

  Therefore, the weight 15 does not interfere with the coils

  secondary 28 when subjected to displacement in

  tion of the deformation of the bar 11.

  In the seventh embodiment of the present invention, when the bar 11 is subjected to a

  torsion as a function of the applied acceleration, the tens

  induced in the secondary coils 28 are modified

  trusted by the variation of mutual inductance between the

  primary coil 27 and secondary coils 28 in response

  se at the value of the torsional deformation of the bar 11.

  The two secondary coils 28 are connected to the signal processing circuit 29 illustrated in FIG. 15, 12. respectively, and a voltage proportional to the value

  acceleration is obtained at the output of circuit 29.

  The rest of the construction of this seventh embodiment is identical to the fourth embodiment and will therefore not be described. Incidentally, we know in the art that the stress necessary to cause the bar to twist

  It is established whatever the total length of this bar-

  reau. Consequently, the bending tension of the bar 11

  can be reinforced using a short length bar

  without reducing the detectable value of the acceleration.

  Furthermore, according to the present invention, the bar-

  reau 11 can undergo a great deformation and the weight 15 is protruding on the bar. Therefore, the position of

  stops 13 can be determined easily.

  The present invention is not limited to the examples

  ples of realization which have just been described, it is on the contrary susceptible of modifications and variants

  which will appear to those skilled in the art.

13.

Claims (8)

  1 - Acceleration detection device, characterized in that it comprises: - a bar (11), - means (10, 19) for supporting at least the two ends of the bar; - a means (15) for subjecting a twist to the   bar in response to the application of accelerated action   being substantially at the center of the bar; and - means (16) for detecting the value of the   torsional deformation of the bar.   2 - Device according to claim 1, charac-   terized in that the means (12) supporting the two ex-   bars of the bars further comprise: - means for fixing said ends and - means (18) for stopping the torsion of the bar.   3 - Device according to claim 1, charac-   terrified in that the means causing the bar to twist   includes a weight (15) projecting in a direction pendulum to the bar.   4 - Device according to claim 1, character-   laughed at in that the means allowing the detection of the   torsional formation of the bar further comprises: - means (16) for transforming the value of the torsional deformation into an electrical signal; and   - a means (21) for processing this electrical signal   than. - Device according to claim 2, characterized in that the means for fixing the two ends of the   bar comprises a pair of bases (10, 12).   6 - Device according to claim 3, charac-   characterized in that the weight is a projecting element (15).   7 - Device according to claim 4, character-   laughed at in that the means of transformation of the value 14.   of torsional deformation includes gauge gauges bust (16).   8 - Device according to claim 4, character-   in that the means for transforming the value of the torsional deformation comprise: - means (26) for transforming the position of an incident light into an electrical signal; - a light source (24) producing the incident light;   - an optical fiber (25) connected to the light source miner and attached to the bar.   9 - Device according to claim 4, character-   laughed at in that the means transforming the value of the   torsion formation comprises two coils (28) on the ends.