Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
  • G01L5/0052—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to impact
• • 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
  • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
  • G01L1/205—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using distributed sensing elements

Definitions

• the invention relates to a force-profile integrating sensor, in particular for use in in a collision detection system of an automotive vehicle, and a vehicle bumper comprising such force-profile integrating sensor.
• a force that is to be detected by the sensor due to the impact of the pedestrian generally has a rather high magnitude and is to be measured within a very short time period.
• a time-varying force profile will be applied on an impact area of the vehicle, mainly the bumper region in case of pedestrians, due to the initial linear momentum of the object with respect to the vehicle.
• This force profile leads to a deflection of the vehicle front structure.
• the force profile will depend on vehicle speed at time of impact, object mass, shape and material properties, as well as design and mechanical properties of the vehicle front structure.
• Typical pedestrian impact mitigation systems evaluate the impact by measuring characteristics of the force profile.
• Known implementations use a pressure-sensitive resistive sensor strip or a pressure-sensitive tube as sensing element, converting a deflection of the vehicle front structure into a measurable quantity.
• the measured quantity representing the deflection can be used to estimate the initial linear momentum of the impacting object by mathematically integrating the time-varying force profile during a duration of the impact. An estimation accuracy will depend on a correlation between a sensor output signal indicative of a force, a pressure or an acceleration profile and the force profile.
• European patent EP 1 899 997 B1 describes a foil-type switching element for use in collision detection systems that comprises a first carrier foil and a second carrier foil arranged at a certain distance from each other by means of a spacer having an active area. Electrode means are arranged within the active area and resistor means are associated with the active area in such a way that, in response to an activation pressure applied on the switching element, the electrode means are mechanically actuated and cause shunting of at least part of the associated resistor means.
• the active area includes at least two regions corresponding to open portions in the spacer. The regions have different sizes and, thereby, determine a different activation pressure threshold for each region.
• the electrode means are provided in each region.
• the resistor means comprise respective resistors, wherein at least one of the resistors is associated with each region, and the resistors are electrically connected in series.
• Prior art sensor systems including force-sensitive foil-type switching members having different force threshold values and being configured as a linear potentiometer (linear potentiometer foil-type switching members) are, for instance, described in European patent application EP 1 715 350 A1 .
• Fig. 1 depicts a temporal progression of a generic force profile being present at a vehicle bumper surface during a generic impact of an object along a longitudinal vehicle axis, centric to the bumper (z-axis: force, x-axis: time, y-axis: bumper segment representing location).
• n the number of sample sets taken during impact time.
• the area below the graph is the integral regarding variable x in (1 ), as observed by an ideal sensor system.
• Fig. 3 The inability to correctly determine the integral regarding variable x at a specific impact time as shown in Fig. 2 is exemplarily illustrated in Fig. 3 for a prior art sensor system including one foil-type switching member configured as a linear potentiometer having a lowest force threshold value (“linear pot”) for the applied mechanical pressure, and two force-sensitive foil-type switching members having a higher pre-determined threshold value (“low force threshold”) and a highest predetermined threshold value (“high force threshold”).
• linear pot lowest force threshold value
• low force threshold lower pre-determined threshold
• high force threshold highest predetermined threshold
• the linear potentiometer allows an approximation of the impact center and a portion of the force profile width exceeding the lowest force threshold value.
• the area below the graph of the force profile at force levels larger than the lowest force threshold value of the linear potentiometer remains unknown. Only the hatched area in Fig. 3 can be measured by the prior art sensor system.
• the additional information provided by an activation status of the two other foil-type switching members is limited. An activated status of the switching members is illustrated as a dashed line in Fig. 3. These only indicate that at a specific moment after the impact a specific force level has been exceeded somewhere along the sensor, and do not provide any information about the shape of the force profile.
• the object is achieved by a force- profile integrating sensor, in particular for use in a collision detection system of an automotive vehicle, including a first carrier foil carrying a contiguous electrically resistive layer,
• a second carrier foil carrying a plurality of electrode members, the second carrier foil being arranged at a specified distance from the first carrier foil by means of an electrically insulating spacer, wherein the spacer has a plurality of active cell areas, each active cell area being defined by one out of a plurality of openings in the spacer.
• the electrode members of the plurality of electrode members are positioned on the second carrier foil to at least partially cover at least a majority of the plurality of openings in a direction perpendicular to the second carrier foil and to face the electrically resistive layer, and to electrically contact the electrically resistive layer upon exceeding a pre-determined threshold value for a mechanical pressure applied to one of the partially covered openings.
• the plurality of openings includes at least a first group of openings having a first opening area size and a second group of openings having a different second opening area size.
• the first opening area size and the second opening area size correspond to a first and a different second pre-determined threshold value for the applied mechanical pressure.
• the openings of the first group of openings are arranged along the specified direction in a spaced manner and the openings of the second group of openings are arranged along the specified direction in a spaced manner.
• the openings of the first group of openings and the openings of the second group of openings are spaced from each other in a direction perpendicular to the specified direction.
• the plurality of electrode members includes a first group of electrode members that at least partially cover openings of the first group of openings, wherein adjacently arranged electrode members of the first group are pairwise electrically connected by a resistor having a first resistance value.
• the plurality of electrode members includes at least a second group of electrode members that at least partially cover openings of the second group of openings, wherein adjacently arranged electrode members of the second group are pairwise electrically connected by a resistor having a second resistance value.
• At least one pair of connected electrode members of the first group and at least one pair of connected electrode members of the second group are aligned in the direction perpendicular to the specified direction to form, in combination with an opposing portion of the contiguous electrically resistive layer and a portion of the spacer that is adjacently arranged in between, a sensor segment.
• a plurality of sensor segments is arranged along the specified direction.
• mechanical pressure and "force”, are synonymously used in the present application and shall be understood such that a mechanical surface pressure that is applied to an opening of a specific opening area size will create a force acting in a direction perpendicular to the specific open area that is the mathematical product of the mechanical surface pressure and the specific opening area size.
• a mechanical pressure is applied to a sensor segment that exceeds the pre-determined threshold value of one group of openings and, in this way, activates the active cell area defined by the openings, pairwise electrically connected electrode members covering the openings will cause a partial short- circuit of the opposing portion of the contiguous electrically resistive layer.
• At least one out of the first carrier foil and the second carrier foil may be configured to deflect in a direction towards the opening of the spacer upon applying a mechanical pressure to the active cell area.
• a portion of the electrically resistive layer will at least partially be shunted by one of the resistors having the first resistance value upon exceeding the first pre-determined threshold value for the applied mechanical pressure, and a portion of the electrically resistive layer will at least partially be shunted by one of the resistors having the second resistance value upon exceeding the second pre-determined second threshold value for the applied mechanical pressure.
• At least two electrical terminals may be connected to ends of the electrically resistive layer, wherein at least one electrical terminal is connected to each of the ends that are opposing each other with regard to the specified direction, and wherein the at least two electrical terminals are accessible from outside the sensor.
• the partial short-circuit or degree of shunting will depend on the number of pairs of activated cell areas, the type of the activated cell areas, and their interconnecting resistors.
• the resulting total electrical conductance measured between the electrical terminals connected to the contiguous electrically resistive layer therefore represents an approximation of the integral of the force profile applied along the sensor at a specific time during the impact as described by (3).
• only active cell areas shunted by pairwise electrically connected electrode members contribute to a change of the total electrical conductance.
• a determined change of the total electrical conductance therefore represents a connection in series of the plurality of sensor segments, wherein in each of the sensor segments the portion of the contiguous electrically resistive layer is electrically connected in parallel to a resistor having the first resistance value, if the first pre-determined threshold value has been exceeded, and, in addition, is electrically connected in parallel to a resistor having the second resistance value, if the second pre-determined threshold value has also been exceeded, and so on, if further groups of openings having opening area sizes that correspond to a pre-determined threshold value are provided.
• One advantage of the invention lies in the fact that the sensor can provide a measurable physical quantity, namely a change of the total electrical conductance that is representative of the integral of the force profile at a point in time in the course of an impact.
• Another advantage of the invention is that this is accomplishable with a foil-type pressure sensor of relatively simple design.
• the portion of the contiguous electrically resistive layer of each sensor segment has a rectangular shape, the longer side being arranged in the specified direction. In this way, by arranging a plurality of sensor segments, a total length of the sensor in the specified direction can readily be accomplished that is suitable for use in a collision detection system of the automotive vehicle, for instance in a bumper member of the vehicle.
• the plurality of openings further includes a third group of openings having a third opening area size that is different from the first opening area size and the second opening area size.
• the first resistance value, the second resistance value and a third resistance value are selected according to the following formulas for equivalent conductance values Gi to G 3 :
• k denotes a desired sensitivity factor, equivalent to the desired increase in electrical conductance of a sensor segment for reaching the first pre-determined threshold value for the applied mechanical pressure Pi .
• P m denotes the m-th predetermined threshold value in ascending order, so as to beneficially establish a linear relationship between an electrical quantity that is measurable at the electrical terminals and an applied mechanical pressure level.
• GFS denotes an electrical conductance of the portion of the contiguous electrically resistive layer of one of the sensor segments.
• a shape of the openings in the spacer is substantially rectangular with rounded edges. This configuration ensures that the electrode members can effectively be guided in the direction towards one of the opening of the spacer when a mechanical pressure is being applied to the active cell area.
• the specific electrical conductivity of the electrode members is at least ten times, more preferably at least twenty times, and, most preferably, at least fifty times the specific electrical conductivity of the electrically resistive layer.
• the at least partial electrical shunting of a portion of the electrically resistive layer is beneficially determined to a large extent by the known first, second and third resistance values of the resistors.
• the senor further comprises resistors having a fourth resistance value that interconnect at least two electrode members of the same group of electrode members of two different sensor segments that are adjacently arranged in the specified direction, for all the sensor segments, and
• At least two additional electrical terminals connected to the electrode members of the same group of electrode members of sensor segments that are arranged at outmost positions with regard to the specified direction, wherein the at least two additional electrical terminals are accessible from outside the sensor.
• the fourth resistance value is selected such that a time constant given by the product of a total electrical resistance resulting from summing up all the resistors having a fourth resistance value and a parasitic capacitance of the sensor, is lower than one tenth of a specified duration of an impact intended to be sensed. This ensures that an intended sensing of the impact will not be limited by the dynamic behavior of the sensor.
• the fourth resistance value is chosen to be substantially higher than the respective first, second or third resistance values associated with the same group of electrode members so as to not substantially influence the "normal" electrical conductance measurement.
• the fourth resistance value is chosen to be equal to the respective first, second or third resistance values associated with the same group of electrode members.
• the local resolution of the sensor is increased as the non-active zones between sensor segments are avoided.
• such a sensor would be inappropriate for discriminating a congiguous activation of e.g. three adjacent electrode members from an activation of only the two outermost electrode members of three adjacent electrode members.
• resistors having a fourth resistance value do not necessarily only interconnect adjacent sensor segments of one single group of electrode members.
• adjacent sensor segments of two or more groups of electrode members may be interconnected by respective resistors having a specific resistance value.
• respective additional electrical terminals are of course also provided for these groups of electrode members.
• a vehicle bumper in particular a bumper of an automotive vehicle, which comprises at least one embodiment of the force-profile integrating sensor disclosed herein.
• Fig. 1 in a 3D plot illustrates a temporal progression of a generic force profile being present at a vehicle bumper surface during a generic impact of an object
• Fig. 2 is a cross-section of the 3D plot pursuant to Fig. 1 at a specific point in time;
• Fig. 3 demonstrates a response of a prior art force-sensitive sensor to the force profile pursuant to Fig. 2,
• Fig. 4 is a schematic illustration of an embodiment of a force-profile integrating sensor in accordance with the invention.
• Fig. 5 is a schematic cross-section through a sensor segment of a force-profile integrating sensor, e.g. along the line A-A' in Fig. 4,
• Fig. 6 schematically shows a response of the force-sensitive integrating sensor pursuant to Fig. 4 to the force profile pursuant to Fig. 2, and
• Fig. 7 is a schematic illustration of the force-profile integrating sensor pursuant to Fig. 4 with an added slider function.
• FIG. 4 is a schematic illustration of an embodiment of a force-profile integrating sensor 10 in accordance with the invention and Fig. 5 is a shematic cross-section through a sensor segment of the sensor in Fig. 4 along the line A-A'.
• the force-profile integrating sensor 10 is designed for use in in a collision detection system of an automotive vehicle and includes a first carrier foil 22 carrying a contiguous electrically resistive layer 24 (e.g. made of a suitable graphite material), a second carrier foil 38 carrying a plurality of electrode members 40, 42, 44 (made e.g. of a printable silver material printed on respective areas of the second carrier foil 38), and an electrically insulating spacer 45.
• the first carrier foil 22, the second carrier foil 38 and the spacer have elongated rectangular shapes, with longer sides of the rectangles being aligned in parallel to a specified direction 16.
• Two electrical terminals 12, 14 are connected to ends of the electrically resistive layer 24.
• One of the electrical terminals 12, 14 each is connected to each one of the ends of the electrically resistive layer 24 that are opposing each other with regard to the specified direction 16.
• the two electrical terminals 12, 14 are accessible from outside the sensor 10, so as to enable carrying out electrical conductance measurements.
• the second carrier foil 38 is arranged at a specified distance from the first carrier foil 22 by means of the spacer 45.
• the spacer has a plurality of active cell areas, each active cell area being defined by one out of a plurality of openings 26, 28, 30 in the spacer.
• the electrode members 40, 42, 44 of the plurality of electrode members 40, 42, 44 are positioned on the second carrier foil 38 to completely cover all openings 26, 28, 30 of the plurality of openings 26, 28, 30 in a direction perpendicular to the second carrier foil and to face the electrically resistive layer 24.
• the second carrier foil 38 Upon exceeding a pre-determined threshold value for a mechanical pressure applied to one of the partially covered openings 26, 28, 30, the second carrier foil 38 is configured to deflect in the direction towards the opening 26, 28, 30 of the spacer far enough to let one of the electrode members 40, 42, 44 electrically contact the electrically resistive layer 24.
• the plurality of openings 26, 28, 30 includes a first group of openings 26 having a first opening area size, a second group of openings 28 having a different, smaller second opening area size, and a third group of openings 30 having again a different, smaller third opening area size.
• the openings 26, 28, 30 of the plurality of openings 26, 28, 30 in the spacer have a shape that is rectangular with rounded edges.
• the first, the second and the third opening area size correspond to a first 32, a different second 34, larger and again a different third 36, largest predetermined threshold value for an applied mechanical pressure that is sufficient to let the one of the electrode members 40, 42, 44 that covers the opening 26, 28, 30 electrically contact the electrically resistive layer 24.
• the openings 26, 28, 30 of the first 26, second 28 and third group 30 of openings are arranged along the specified direction 16 in a spaced manner.
• the openings 26, 28, 30 of the first 26, second 28 and third 30 group of openings are spaced from each other in a direction 18 perpendicular to the specified direction 16.
• the plurality of electrode members 40, 42, 44 includes a first group of electrode members 40 that completely cover openings of the first group of openings 26. Adjacently arranged electrode members 40 of the first group are pairwise electrically connected by a resistor 46 having a first resistance value such that each electrode member 40 is connected to only one resistor 46. Resistor 46 may e.g. be made of a printable resistive material, which is printed between the respective electrode members 40 onto the carrier foil 38.
• the plurality of electrode members 40, 42, 44 includes a second group of electrode members 42 that completely cover openings of the second group of openings 28. Adjacently arranged electrode members 42 of the second group are pairwise electrically connected by a resistor 48 having a second resistance value such that each electrode member 42 is connected to only one resistor 48. Resistor 48 may e.g. be made of a printable resistive material, which is printed between the respective electrode members 42 onto the carrier foil 38.
• the plurality of electrode members 40, 42, 44 includes a third group of electrode members 44 that completely cover openings of the third group of openings 30. Adjacently arranged electrode members 44 of the third group are pairwise electrically connected by a resistor 50 having a third resistance value such that each electrode member 44 is connected to only one resistor 50. Resistor 50 may e.g. be made of a printable resistive material, which is printed between the respective electrode members 44 onto the carrier foil 38.
• One pair of connected electrode members 40 of the first group, one pair of connected electrode members 42 of the second group and one pair of connected electrode members 44 of the third group are aligned in a centered manner in the direction 18 perpendicular to the specified direction 16 to form, in combination with an opposing portion of the contiguous electrically resistive layer 24 and a portion of the spacer that is adjacently arranged in between, a sensor segment 20.
• the portion of the contiguous electrically resistive layer 24 of each sensor segment 20 has a rectangular shape, the longer side being aligned parallel to the specified direction 1 6.
• a plurality of e.g. twenty identical sensor segments 20 may be arranged along the specified direction 1 6 in a juxtaposed way, which generates a sensor geometry matching a size of the vehicle bumper. For clarity reasons, only three of the twenty identical sensor segments 20 are shown in Fig. 4.
• the level of shunting of the electrically resistive layer 24 is effectively given by the electrical resistances of the resistors 46, 48, 50, as the electrical conductance of the electrode members 40, 42, 44 is selected to be fifty times the electrical conductance of a portion of the contiguous electrically resistive layer 24 in electrical contact to one of the electrode members 40, 42, 44.
• the corresponding portion of the electrically resistive layer 24 will partially be shunted by the resistor 46 having the first resistance value upon exceeding the first predetermined threshold value 32 for the applied mechanical pressure, and will be further shunted by the resistor 48 having the second resistance value upon exceeding the second, larger pre-determined threshold value 34 for the applied mechanical pressure, and will be further shunted by the resistor 50 having the third resistance value upon exceeding the third, largest pre-determined threshold value 36 for the applied mechanical pressure.
• the total electrical conductance of the sensor segment will be 1 ' GFS-
• a total electrical conductance of the sensor segment 20 will be 2 " GFS, which means that the difference with respect to the inactive sensor is 1 ' GFS-
• P2 is exceeded at the sensor segment 20
• the total electrical conductance of the sensor segment 20 will be 3 ' GFS, which means that the difference with respect to the inactive sensor is 2 GFS-
• P3 is exceeded at the sensor segment 20
• the total electrical conductance of the sensor segment 20 will be 4 " GFS, which means that the difference with respect to the inactive sensor is 3 ' GFS- AS this is the same for all twenty sensor segments 20, a linear relationship is established between a change of electrical quantity, namely the total electrical resistance that is measurable between the two electrical terminals 1 2, 14, and the applied mechanical pressure level.
• Fig. 6 schematically shows a response of the force-sensitive sensor 10 pursuant to Fig. 4 to the force profile pursuant to Fig. 2.
• a drop in total resistance RACTIVE measured between the two electrical terminals 1 2, 14 of the force-profile integrating sensor 10 in response to applying the force profile will contain information about the force profile integral (normalized for GFS or 1 /RFS respectively):
• RINACTIVE denotes the total resistance between the two electrical terminals 1 2, 14 of the force-profile integrating sensor 1 0 in a mechanically unloaded condition.
• Fig. 7 is a schematic illustration of the force-profile integrating sensor 1 0 pursuant to Fig. 4 with an added slider function.
• the force-profile integrating sensor 1 0 shown in Fig. 7 is further equipped with resistors 56 that have a fourth resistance value and that interconnect electrode members 40 of the same group of electrode members 40 of two different sensor segments 20 that are adjacently arranged in the specified direction 16, for all the sensor segments 20.
• the force-profile integrating sensor 10 includes two additional electrical terminals 52, 54 connected to the electrode members 40 of the first group of electrode members 40 of sensor segments 20 that are arranged at outmost positions with regard to the specified direction.
• the two additional electrical terminals 52, 54 are accessible from outside the sensor 10 to enable electrical measurements.
• the fourth resistance value is selected such that a time constant given by the product of the total electrical resistance resulting from summing up all the resistors 56 having a fourth resistance value and a parasitic capacitance of the force-profile integrating sensor 10 is lower than one tenth of a specified duration of an impact intended to be sensed.
• the fourth resistance value is for instance selected to be substantially higher than the respective first resistance values of resistors 46. In an alternative embodiment, the fourth resistance value is chosen to be equal to the respective first resistance values of resistors 46.

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• Force Measurement Appropriate To Specific Purposes (AREA)

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Citations (2)

• 2015
  • 2015-08-21 LU LU92804A patent/LU92804B1/en active IP Right Grant
• 2016
  • 2016-08-18 WO PCT/EP2016/069579 patent/WO2017032680A1/en active Application Filing

Patent Citations (2)

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