Sensors

Abstract

A sensor comprising a whisker shaft and a follicle is provided. The shaft has a root end and a tip end and the shaft tapers from the root end to the tip end so that the root end is wider and the tip end is narrower. The root end is pivotably mounted in the follicle.

Claims

1. An artificial whisker sensor comprising an elongate body having a root end and a tip end, in which the elongate body tapers from the root end to the tip end so that the root end is wider and the tip end is narrower, the root end is mounted in a hub, in which the hub is mounted in an elastomeric block so as to be in a suspended, free pivoting joint with a restoring force for the hub provided by the elastomeric block and being such that the pivot point of the whisker is at substantially the centre of the hub, a magnet is attached to the hub, the magnet is located axially above a magnetic field sensor for detecting the orientation of the magnet, in which deflection of the elongate body rotates the magnet about the pivot point such that it conveys the 2D angular pivot position of the elongate body.

2. The sensor according to claim 1, in which the hub is mounted in a polyurethane-filled follicle case.

3. The sensor according to claim 1, comprising a follicle case and a cast-in-place elastomeric block in the follicle case.

4. The sensor according to claim 3, in which the follicle case comprises an opening for the elongate body and an opening for the magnet.

5. The sensor according to claim 1, in which the magnetic field sensor is a tri-axis Hall effect sensor.

6. The sensor according to claim 1, in which the magnet is bonded to the hub.

7. The sensor according to claim 1, in which the tapering of the elongate body from the root end to the tip end is generally constant along the length of the elongate body.

8. The sensor according to claim 1, in which the hub comprises a flange.

9. The sensor according to claim 8, in which the elongate body is formed from a composite material.

10. The sensor according to claim 9, in which the elongate body is formed from GRP.

11. The sensor according to claim 1, in which the elongate body has a generally elongated cone shape.

12. The sensor according to claim 1, in which the elongate body is approximately 1.5 mm at the root end and approximately 0.7 mm at the tip end.

13. The sensor according to claim 1, in which an accelerometer is provided at or near the root end of the elongate body.

14. A vehicle provided with one or more artificial whisker sensors according to claim 1.

15. A method of exploration using one or more artificial whisker sensors according to claim 1.

16. The method according to claim 15, comprising the step of measuring and/or calculating and/or inferring whisker speed and/or material viscosity.

17. The method according to claim 15 comprising the step of moving the elongate body through material of interest and in doing so causing vortex-induced vibration; and measuring the frequency spectrum of the vibration.

Description

(1) The present invention is more particularly shown and described, by way of example, in the accompanying drawings, in which:

(2) FIG. 1 illustrates a general principle of a whisker assembly formed in accordance with embodiments of the present invention;

(3) FIG. 2 shows a whisker shaft is attached to a hub;

(4) FIG. 3 shows a whisker sensor formed in accordance with an embodiment of the present invention;

(5) FIG. 4 shows the variation of one measure of the spectrum (the frequency of the strongest peak) with speed for a particular tapered whisker in water;

(6) FIG. 5 shows the frequency spectrum at a low speed, below the sensitivity range of the whisker under test. No significant peak is visible;

(7) FIG. 6 shows the frequency spectrum at a higher speed, towards the bottom of the sensitivity range, where a distinct peak is detectable;

(8) FIG. 7 shows the frequency spectrum higher in the sensitivity range, where a very well-defined peak is visible; and

(9) FIG. 8 illustrates one application for a whisker module formed in accordance with the present invention.

(10) The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternative forms and should not be construed as limited to the examples set forth herein.

(11) Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

(12) Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealised or overly formal sense unless expressly so defined herein.

(13) In the description, all orientational terms, such as upper, lower, radially and axially, are used in relation to the drawings and should not be interpreted as limiting on the invention.

(14) FIG. 1 illustrates a general principle of a whisker assembly formed in accordance with embodiments of the present invention.

(15) The assembly has a machined Delrin (or other marine grade material) housing containing epoxy-potted electronics, an elastomeric whisker suspension, and a glass-reinforced plastic (GRP) whisker. It uses marine-grade materials and is designed to be submerged. Submerged depth is limited by the depth ratings of the cable and connectors used, and not the design of the whisker itself. The whisker design has no areas of pressure differences and is solid state in other parts, so is predicted to be functional at depths in the magnitude of kilometres deep.

(16) The sensing principle involves a permanent magnet attached to the whisker base and a magnetic sensor (for example Melexis MLX90333 or MLX90363) detects the position of the magnet, and hence the position of the whisker.

(17) In some embodiments the whisker assembly is designed so the whisker attaches to a hub with a flange, which sits inside a cylindrical recess with openings at top and bottom for the whisker shaft and the magnet. It allows testing of two kinds of suspension—either a pair of O-rings, or a cast-in-place elastomer. O-rings have the practical advantage that they are commercially available in a range of materials and Shore A hardness. Cast-in-place allows access to a different selection of materials, and also allows a slightly different mechanical behaviour, since it fills the cavity completely.

(18) The O-ring design offers high quality and uniform material, but has been shown in experiments for this project to be unsuitable for sensing Vortex Induced Vibrations (VIV). To sense VIV the material must be compliant enough to allow movement by the small forces generated by the specific vortices shed by the specific whisker. The compliant material must also be elastic enough to restore to the centre position and not accumulate significant deformation. The compliant material used in some embodiments is polyurethane with a stiffness of approximately Shore A 20.

(19) The artificial whisker therefore may consist of a flexible shaft mounted into a polyurethane filled casing referred to as the whisker follicle. In some embodiments the end of the mounted whisker shaft is effectively a ball joint which is designed to pivot above a Hall Effect sensor IC.

(20) A small neodymium magnet is bonded to the mounted base of the whisker such that it conveys the 2D angular pivot position of the whisker shaft. This assembly is mounted into a follicle holder which houses the tri-axis Hall effect sensor IC (e.g. Melexis MLX90363, MLX90393 or MLX90333) which is aligned such that the magnet attached to the whisker shaft is suspended directly above the Magneto-Concentrator on the IC. This programmable sensor can be configured to generate digital signals or analogue output voltages, proportional to the degree of displacement of the magnetic field in the orthogonal axes from a calibrated zero position. The third axis, which is in-line with the whisker shaft, has been physically constrained. Therefore, any deflections of the whisker shaft can be measured as a proportional displacement vector at the base and captured using a computer or microcontroller or a standard Analogue to Digital Converter (ADC) at a maximum sample rate of, for example, up to 2 KHz, for example up to 1.5 KHz or up to 1 kHz.

(21) The whisker assembly may sense motion of the whisker shaft at the base of the shaft, where the magnet is located. Deflection of the shaft rotates the magnet about a pivot point. Utilisation of a magnet and Tri-axis Hall Effect sensor offers a 2 kHz sampling rate and a robust non-contact solution. In some embodiments the whisker can sense both AC and DC deflections, so therefore can sense a static deflection (i.e. force loading), and oscillating deflection (i.e. vibration).

(22) In some embodiments the sampling electronics consists of a custom-built Printed Circuit Board (PCB) and a dsPIC30f4011 micro-controller programmed to sample the analogue voltages across all 6 channels of a 3 whisker array at 500 Hz. The micro-controller relays this information via a Universal Asynchronous Receiver/Transmitter (UART) serial port in singular whisker mode, or via a combination of UART and Serial Peripheral Interface (SPI) to a FTDI FT232R USB bridge for high bandwidth communications. Both communications use a standard desktop computer as an end point for logging, live processing and offline analysis.

(23) As shown in FIG. 2 a whisker shaft is attached to a hub. The hub is suspended in a rubbery polyurethane block, which means it tends to pivot about a point at the centre of the hub (which may or may not be at the centre of a follicle).

(24) FIG. 3 shows a whisker sensor formed in accordance with an embodiment of the present invention.

(25) The whisker is tapered from its (narrower) tip end to its (wider) root end. The root end is mounted in a follicle case. The whisker root end is attached to a hub and the hub is suspended in an elastomeric block to provide a pivoting joint (i.e. not a cantilevered joint). The hub can move in X, Y and Z directions and the centre of rotation of the whisker is at the centre of the hub (and not, for example, at the base of the whisker). The whisker follicle arrangement includes a magnet which is located above a sensor for detecting movement.

(26) The whisker is attached to a stainless-steel hub, which is suspended in an elastomeric material to allow it to move. In this embodiment the root end of the whisker is not attached directly to the elastomer.

(27) The whisker can move smoothly over a range of angles, the centre of rotation is in the follicle, but there's a restoring force from the elastomer. The elastomer constrains the pivoting motion.

(28) FIG. 4 shows the variation of one measure of the spectrum (the frequency of the strongest peak) with speed for a particular tapered whisker in water.

(29) FIG. 4: When a whisker is moved through a fluid, vortex-induced vibration is caused. With a whisker of any shape, the frequency spectrum of this vibration varies with speed and viscosity, and so the spectrum can be used to infer speed. With a tapered whisker, this variation is a particularly useful measure.

(30) FIGS. 5-7 show spectra at three different speeds, illustrating how the spectrum changes with speed.

(31) FIG. 5 shows the frequency spectrum at a low speed, below the sensitivity range of the whisker under test. No significant peak is visible.

(32) FIG. 6 shows the frequency spectrum at a higher speed, towards the bottom of the sensitivity range, where a distinct peak is detectable.

(33) FIG. 7 shows the frequency spectrum higher in the sensitivity range, where a very well-defined peak is visible.

(34) FIG. 8 illustrates one application for a whisker module formed in accordance with the present invention. In this embodiment a whisker is provided on a module which in turn is mounted on a robot arm. The whisker shaft can, for example, be rotated to and fro, to cause it to pass through the sediment. When the shaft contacts an object this can be recorded and a picture of the environment can be built up.

(35) This arrangement can be used as part of a tactile sensing system and to measure viscosity and flow speed across the whisker.

(36) If the whisker is swept at a known speed it is possible to calculate viscosity of the medium through which the whisker is being moved. If the whisker is being moved through a medium of known viscosity it is possible to calculate the velocity.

(37) Further examples of aspects and embodiments are listed in the following numbered paragraphs.

(38) 1. An artificial whisker sensor comprising an elongate body having a root end and a tip end, in which the body tapers from the root end to the tip end so that the root end is wider and the tip end is narrower, the root end is mounted in a hub, with the hub being in a suspended, pivoting joint, and the pivot point of the body is at substantially the centre point of the hub.

(39) 2. A sensor as claimed in paragraph 1, in which the hub is mounted in elastomeric material.

(40) 3. A sensor as claimed in paragraph 1 or paragraph 2, in which the tapering is generally constant along the length of the body.

(41) 4. A sensor as claimed in any preceding paragraph, in which the body is formed from a composite material.

(42) 5. A sensor as claimed in paragraph 4, in which the body is formed from GRP.

(43) 6. A sensor as claimed in any preceding paragraph, in which the body has a generally elongated cone shape.

(44) 7. A sensor as claimed in any preceding paragraph, in which the body is approximately 1.5 mm at the root end and approximately 0.7 mm at the tip end.

(45) 8. A whisker sensor assembly comprising a whisker sensor mounted in a housing, a magnet is attached to the whisker and a magnetic sensor is provided in the housing to detect the position of the magnet and hence the whisker.

(46) 9. An assembly as claimed in paragraph 8, in which the whisker is mounted on a hub and the hub is mounted in an elastomeric suspension.

(47) 10. An assembly as claimed in paragraph 8 or paragraph 9, in which an accelerometer is provided at or near the base of the whisker.

(48) 11. A whisker array comprising a plurality of whiskers and a local processor.

(49) 12. An array as claimed in paragraph 11, in which the array consists of three whiskers.

(50) 13. A whisker array comprising a cluster of three whiskers and a local processor.

(51) 14. An artificial whisker sensor comprising an elongate body having a root end and a tip end, in which the body tapers from root end to the tip end.

(52) 15. A sensor comprising a whisker shaft and a follicle, the shaft having a root end and a tip end, in which the shaft tapers from the root end to the tip end so that the root end is wider and the tip end is narrower, the root end is mounted in the follicle so as to provide a uniformly suspended pivot.

(53) 16. A sensor comprising a whisker shaft and a follicle, the shaft having a root end and a tip end, in which the shaft tapers from the root end to the tip end so that the root end is wider and the tip end is narrower, and the root end is pivotably mounted in the follicle.

(54) 17. A sensor as claimed in paragraph 15 or paragraph 16, in which the root end is attached to a hub, and the hub is mounted in an elastomeric block provided in the follicle.

(55) 18. A sensor as claimed in paragraph 17, in which the whisker tends to pivot about a point generally at the centre of the hub.

(56) 19. A sensor as claimed in paragraph 17 or paragraph 18, in which the pivot point of the body is at substantially a centre point of the follicle.

(57) 20. An artificial whisker sensor for taking angular measurements, comprising a beam-like body having a root end and a tip end, in which the body tapers from the root end to the tip end so that the root end is wider and the tip end is narrower, the root end is mounted in an artificial follicle, and the beam-like body can pivot in the follicle.

(58) 21. A sensor as claimed in paragraph 20, in which the whisker root end can move smoothly over a range of angles.

(59) 22. A sensor as claimed in paragraph 20 or claim 21, in which a centre of rotation of the whisker is in the follicle.

(60) 23. A sensor as claimed in any of paragraphs 20 to 23, in which the follicle includes elastomeric material for providing a restoring force for the whisker.

(61) 24. An underwater vehicle provided with one or more whisker sensors and/or whisker assemblies and/or whisker arrays according to any preceding paragraph.

(62) 25. A remotely operated vehicle provided with one or more whisker sensors and/or whisker assemblies and/or whisker arrays according to any of paragraphs 1 to 23.

(63) 26. A method of tactile exploration comprising: providing one or more artificial whisker sensors, the or each sensor comprising a tapered, elongate body; moving the whisker through material of interest and in doing so causing vortex-induced vibration; and measuring the frequency spectrum of the vibration.

(64) 27. A method as claimed in paragraph 26, comprising the step of measuring and/or calculating and/or inferring whisker speed and/or material viscosity.

(65) 28. A method as claimed in paragraph 26 or paragraph 27, comprising the step of measuring motion of the sensor/s at the root end thereof.

(66) 29. A method as claimed in any of paragraphs 25 to 28, performed using one or more whisker sensors and/or whisker assemblies and/or whisker arrays and/or a vehicle according to any of paragraphs 1 to 25.

(67) Combinations of different aspects and embodiments may be made.

(68) Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.