3-dimensional pressure sensor

A method of measuring shear forces and normal forces produced by an elastomeric object using a single sensor array comprising the steps of

• a) disposing a piezoelectric material having a conductive surface on both sides and an axis of orientation on a substrate material to provide a high density array of piezoelectric material;
• b) covering said array with an elastomeric pad, said piezoelectric material, said substrate and said pad comprising said sensor array;
• c) contacting said sensor array with an elastomeric object;
• d) measuring tension and compression by the generation of opposite polarity voltages;
• e) calculating the tension and compression using stress constants defining the relationship of mechanical stress and generated voltage;
• f) stimulating said piezoelectric material ultrasonically and measuring a responsive ultrasonic signal indicating the amount of compression of the pad;
• and
• g) calculating said normal forces by the measuring the TOF of the signal and taking into account the stiffness of the elastomeric layer according to the formula
• d.sub.1 -d.sub.2 =1/2c(t.sub.1 -t.sub.2) (1)
• F=k(d.sub.1 -d.sub.2)=1/2kd(t.sub.1 -t.sub.2) (2)
• where:
• d1=the original thickness of the pad over the element
• d2=the thickness of the compressed pad
• t1=time-of-flight of ultrasound through he noncompressed rubber
• t2=time of flight of ultrasound through compressed rubber
• F=compressing force
• c=speed of sound in the elastomer, and
• k=elastomer stiffness;
• h) measuring piezoelectric voltages generated by contact of the elastomeric article with the sensor array;
• i) measuring shear forces by combining ultrasonic output with piezoelectric output such that the outputs cancel thereby providing a pure measure of shear force;
• and
• i) resolving the shear vector by the polarity of the voltage generated.

A method of measuring shear forces and normal forces produced by an elastomeric object using a single sensor array comprising the steps of

• a) disposing two layers of a piezoelectric material having a conductive surface on both sides and an axis of orientation on a substrate material such that each layer of the piezoelectric material has a different axis of orientation to provide a high density array of stacked piezoelectric material;
• b) covering said array with an elastomeric pad, said piezoelectric material, said substrate and said pad comprising said sensory array;
• c) contacting said sensor array with an elastomeric object;
• d) measuring tension and compression by the generation of opposite polarity voltages;
• e) calculating the tension and compression using stress constants defining the relationship of mechanical stress and generated voltage;
• f) stimulating said piezoelectric material ultrasonically and measuring a responsive ultrasonic signal indicating the amount of compression of the pad;
• g) calculating said normal forces by the measuring the TOF of the signal and taking into account the stiffness of the elastomeric layer according to the formula
• d.sub.1 -d.sub.2 1/2c(t.sub.1 -t.sub.2) (1)
• F=k(d.sub.1 -d.sub.2)=1/2kc(t.sub.1 -t.sub.2) (2)
• where:
• d1=the original thickness of the pad over the element
• d2=the thickness of the compressed pad
• t1=time-of-flight of ultrasound through the noncompressed rubber
• t2=time of flight of ultrasound through compressed rubber
• F=compressing force
• c=speed of sound in the elastomer, and
• k=elastomer stiffness;
• h) measuring piezoelectric voltages generated by contact of the elastomeric article with the sensor array;
• i) calculating shear forces by combining ultrasonic output with piezoelectric output such that the outputs cancel thereby providing a pure measure of shear force;
• j) resolving the shear vector of both axes by the polarity of the voltage generated;
• and
• k) orientating each sensor in said matrix to have a different orientation from an adjacent sensor to provide multiple axes of orientation for shear forces.

An apparatus for measuring shear forces and normal forces of an elastomeric object comprising

• a) at least one sensor comprising a piezoelectric material, having conductive surfaces on both sides thereof and an axis of orientation, and generating an electrical voltage in response to pressure contact;
• b) an ultrasonic pulsing source in proximity to said at least one sensor scuh that said pulsing source is capable of stimulating an ultrasonic echo in said sensor;
• c) means for measuring normal forces on said sensor using an ultrasonic echo;
• d) means for measuring shear forces and normal forces on said sensor by measuring a voltage generated by said sensor;
• and
• e) means for subtracting normal forces measured by ultrasonic means from total forces measured by said generated voltage to provide a measure of pure shear forces.

A method of measuring shear forces and normal forces in a tire footprint comprising the steps of:

• (a) providing a sensor comprising a layer of piezoelectric material having two conductive surfaces and shear orientation and converts mechanical stresses into voltage changes to provide a measure of shear forces created by said tire footprint;
• (b) using ultrasonic measuring means with said sensor for measuring normal forces of said tire footprint;
• (c) rolling a tire over said sensor;
• (d) measuring tension and compression created by said rolling tire using stress constants defining the relationship of mechanical stresses and generated voltage to measure said shear forces;
• and
• (e) mapping the results showing normal and shear pressures in a point by point analysis on a complete footprint in one operation.