WO2005077102A2

WO2005077102A2 - Capacitance threshold sensor for a wheelchair lift or ramp

Info

Publication number: WO2005077102A2
Application number: PCT/US2005/004397
Authority: WO
Inventors: Jerome P. Sobota
Original assignee: The Braun Corporation
Priority date: 2004-02-11
Filing date: 2005-02-11
Publication date: 2005-08-25
Also published as: WO2005077102A3

Abstract

A system and method for detecting the presence of an object on the threshold of a vehicle wheelchair lift (10). An embodiment of the invention provides a capacitance sensor (100) for use in the vehicle wheelchair lift system. The sensor includes a first plate (102), a second plate (104), and a plurality of separators (106). The first plate is affixed to a baseplate (20) of the vehicle wheelchair lift, and referenced to ground potential. The second plate is parallel to the first plate, and is in communication with a controller (160). The separators are constructed and arranged between the first and second plates, and elastically couple the plates. Other embodiments may provide for alternative system and device configurations.

Description

CAPACITANCE THRESHOLD SENSOR FOR A WHEELCHAIR LIFT OR RAMP

FIELD [0001] This application claims the benefit of United States provisional Application No. 60/544,054, filed February 11 , 2004, the contents of which are incoφorated herein by reference.

[0002] Embodiments of the invention relate to safety systems for wheelchair lifts and ramps. More specifically, embodiments of the present invention relate to a sensor for detecting the presence of an object on the threshold of a vehicle wheelchair lift.

BACKGROUND [0003] Safety systems for vehicle wheelchair lifts are known, and have been employed to ensure the well-being of wheelchair lift users for many years. Safety systems for wheelchair lifts have been proposed that include mechanical, electrical, or electromechanical sensing. Existing sensing systems are costly and/or difficult to implement. Moreover, inexpensive sensing systems typically lack the sensitivity required to accurately detect the presence of an object on or near the lift. Therefore, it would be advantageous to provide a system for sensing an object on the threshold of a wheelchair lift that is inexpensive, sensitive, and straightforward to implement.

[0004] To prevent injury to a wheelchair lift user, it is important to warn the user of times when the lift is not at the vehicle threshold elevation so that the user does not accidentally fall out of the vehicle. In accordance with the National Highway Transportation Safety Administration ("NHTSA") Federal Motor Vehicle Safety Standard ("FMVSS") 403, "Except in cases where the platform is loaded over the vehicle floor such as with a personal rotary lift, a visual or audible warning is to activate: (1) if portions of a passenger's body or mobility aid is on the 'platforai threshold area' and (2) if the lift platform is more than 25 mm (1") below the 'floor reference plane.' Once a warning signal is activated, it must continue to operate until the 'platform threshold area' is vacated, or the lift is returned to the vehicle floor level."

[0005] Electromechanical sensing systems for detecting a threshold load have been primarily concerned with the installation of a mat switch which substantially covers the entire threshold area. If a sufficient load is present on the mat, switch contacts are closed and a signal is produced which may direct a controller to activate an alarm. While simple to install and implement, mat switches are expensive and prone to eventual failure due to wear. Tape switches, which are less expensive than mat switches, cannot easily cover the entire threshold area due to their substantially smaller size and are, therefore, disadvantageous. To overcome the expensive nature of such electromechanical sensor systems and provide a more reliable system, various electrical sensing systems have been proposed.

[0006] Electrical sensing systems include infrared, ultrasonic, radar, and other detection means. When employed for threshold sensing, such sensmg systems are easily integrated with the vehicle control system, such as the control system disclosed in U.S. Patent Application Serial Number 10/142,712 entitled "Electronic Controller for Vehicular Wheelchair Access," filed May 10, 2002 by applicant's assignee, which is incoφorated herein by reference in its entirety. However, when implemented for threshold sensmg as described above, the aforementioned electrical sensing systems generally require an object to break or otherwise interrupt a reflected beam in the threshold area. Moreover, placement of the beam is crucial to the sensitivity and reliable operation of the system. For example, if the beam is located substantially close to the vehicle threshold, the system may be unable to provide the user with sufficient advance warning to prevent the user from falling out of the threshold, especially if the user has built up momentum in anticipation of exiting the vehicle. Additionally, if the beam is located at a distance from the doorway, the system may provide a number of overly conservative warnings that a user may eventually ignore or disable altogether. Therefore, in view of the foregoing, a robust electrical sensmg system that does not rely on interruption of a beam is desirable for a threshold sensing application.

SUMMARY [0007] The following summary describes a certain embodiment among those embodiments described below. It is not the only such embodiment, and is not limiting of embodiments of the invention.

[0008] An embodiment of the invention provides a pair of parallel plates that substantially cover the lift baseplate. The plates are separated by a foam adhesive and extend inwardly from the outboard edge of the vehicle. The first plate of the pair is affixed to the threshold and is referenced to ground potential, while the second plate is linked to the vehicle controller. The controller includes a charge transfer module that energizes the second plate to establish a capacitance between the plates. The plate capacitance changes if an object or obstruction contacts or otherwise comes in near proximity to the plates, and the charge transfer module detects the presence of the object by comparing the plate capacitance to a known capacitance. If an object is detected, the charge transfer module then outputs a signal to the controller. A platform sensor is operative to determine when the platform is at an elevation other than the threshold elevation, and outputs a signal to the controller. When the controller receives signals from both the platform sensor and the charge transfer module, an audible and/or visual alarm is actuated to indicate that the potential exists for an occupant to fall out of the vehicle threshold.

BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1 is a perspective view of an exemplary parallelogram-type lift for use with a capacitance sensor according to an embodiment of the present invention, showing the general arrangement of lift components.

[0010] FIG. 2 is a perspective view of an embodiment of a parallel plate arrangement for the threshold of a vehicle with the parallelogram-type wheelchair lift of FIG. 1.

[0011] FIG. 3 is a detail view of the parallel plate arrangement of FIG. 2 about Detail B.

[0012] FIG. 4 is a detail view of the parallel plate arrangement of FIG. 2 about Detail C.

[0013] FIG. 5 is a partial cutaway view of the parallel plate arrangement of FIG. 2.

[0014] FIG. 6 is a side view of the parallel plate arrangement of FIG. 2.

[0015] FIG. 7 is a close-up side view of the parallel plate aπangement of FIG. 6 about Detail A.

[0016] FIG. 8 is a block diagram of a system according to one embodiment. DETAILED DESCRIPTION [0017] FIG. 1 (Prior Art) shows a vehicle lift 10 for use with embodiments of a capacitance sensor described herein. A person using a personal transportation device (e.g., a wheelchair) may access a vehicle with this exemplary type of installed lift 10. Other types of lifts can also be used, h use, the lift platform 30 is unstowed, lowered to ground level, and is then raised to the threshold elevation or transfer level ("transfer level"). An inboard barrier 72 acts as a bridgeplate for a user to cross from the platform 30 to the vehicle threshold baseplate 20 inside the vehicle. Once the user is inside the vehicle, the lift 10 is typically folded or pivoted to a vertical position and stowed in the vehicle threshold area. To prevent the user from accidentally falling out of the vehicle, an alarm may be activated if the user is in the threshold area and the lift platform is at an elevation other than the transfer level. Additionally, a verification system to monitor the threshold area can be implemented to prevent accidental user injury or lift damage during a lift stowage operation, as the threshold area should be unoccupied and unobstructed while the lift 10 is in motion. The baseplate 20, as shown, is peraianently affixed to the floor of the vehicle interior. With reference to the axis of FIG. 1, the baseplate 20 has an outboard ("OB") edge coπesponding to the edge of the vehicle threshold, an inboard ("IB") edge and a width between lift support housings 18 to accommodate a wheelchair. A typical threshold depth (i.e., from the inboard edge to the outboard edge of the baseplate 20) is eighteen inches, hi other embodiments, the baseplate 20 can be configured for various threshold depths.

[0018] In the embodiment shown in FIG. 2, a capacitance threshold sensor 100 is sized and shaped to detect the presence of an object in or near the vehicle threshold area when installed. The capacitance threshold sensor 100 includes a first electrode plate 102 and a second electrode plate 104 (see FIG. 6). Although the electrode plates 102, 104 are shown to be substantially identical, plates 102 and 104 are not to be limited as such. As shown in FIG. 5, an exemplary threshold sensor 100 includes plates 102 and 104 that are generally rectangular, each measuring approximately 32.5" wide by 18" deep by 0.06" thick, to substantially cover a vehicle threshold baseplate 20, although the plates 102 and 104 are contemplated to be sized and shaped otherwise to adapt to various baseplates. The plates 102 and 104 can be made of metal such as steel or aluminum and may be coated with paint or the like to enhance durability and prevent coπosion. an exemplary embodiment, the metal plates are powder coated. There is no restriction on the shape, geometry, or size of the plates 102, 104, which, in alternate embodiments can be configured in a variety of ways (e.g., long and narrow strips, round, square, rectangular, or other random or iπegular shapes). In yet other alternate embodiments, the electrode plates may be substituted with a three-dimensional surface or object.

[0019] The sensitivity of the plates 102, 104 is related, for example, to surface area, orientation with respect to the object being sensed, object composition, and the ground coupling quality of both the sensor circuit and the sensed object. It will be apparent to persons knowledgeable in the art that smaller electrode plates will generally have less sensitivity than large ones. Therefore, sensitivity can be increased by using a larger electrode plate, reducing panel thickness, or altering panel composition in other possible embodiments.

[0020] In the embodiment shown, the electrode plates 102 and 104 are oriented substantially parallel and overlapping with each other. Each plate 102, 104 includes four holes 108, each hole located proximate to each corner of the plates 102, 104. The holes 108 provide a means to align the plates 102, 104 and attach the plates 102, 104 to the threshold baseplate 20. In other embodiments, more or less than four holes could be implemented as needed. As shown in the exemplary embodiment in FIG. 3, the holes 108 may include a countersink portion 108a. The countersink portion 108a can be a chamfered or otherwise depressed area coaxial with hole 108 that is sized and shaped to accept the head of a fastener 110. The illustrated fastener 110 is a screw; however, other fasteners such as bolts, rivets, and the like may also be suitable to affix the plates 102, 104 to the baseplate 20. When countersunk in the hole 108 (FIG. 4), the head of fastener 110 can be coplanar with the plate 102 to eliminate a raised impediment to a wheelchair-enabled vehicle occupant, or a trip hazard to an ambulatory vehicle occupant.

[0021] As shown in FIG. 5, plates 102, 104 are spaced apart by a plurality of separators 106. The separators 106 are aπanged between the plates 102, 104 to prevent upper plate 102 from contacting lower plate 104 during application of a compressive load or force (e.g., the weight of a wheelchair and wheelchair occupant) to upper plate 102, In the embodiment shown, the separators 106 are foam adhesive (e.g., double-stick tape) strips, and are somewhat elastic to allow the upper plate 102 to flex, or elastically deform, towards lower plate 104. However, the separators 106 may be manufactured from any suitable electrically neutral or dielectric material, and may be attached in a variety of different fashions. The illustrated foam adhesive strips are made of polyethylene foam, and are 0.5" wide, and 0.063" thick. Seven tapes extend the entire width of the plates 102, 104 and are spaced equally for even load distribution. Moreover, adhesive of the separators' 106 couples the plates 102, 104 together and can inhibit translation of the upper plate 102 with respect to the lower plate 104. In this way, a manufacturer may obviate the need for close tolerances when drilling, cutting, or otherwise forming the holes 108.

[0022] The plates 102, 104 in the above-described configuration form a parallel-plate capacitor when energized in an electric circuit. The noπnal capacitance of the parallel plates 102, 104 can be calculated, and is well known to be proportional to the plate area and inversely proportional to the distance between the plates. The effective (i.e., instantaneous) capacitance of the plates will change if, for example, an object compresses the upper plate 102. Changes in the effective capacitance may be detected by a vehicle controller, and acted upon to disable the vehicle lift, actuate an audible or visual warning, etc. In addition to variances in parallel plate geometry, the parallel plate capacitance may change due to proximity capacitive coupling. For example, the human body naturally has several hundred picofarads of "free space" capacitance. When a vehicle occupant is proximate the plates 102, 104, the occupant's capacitance can couple with the plates and provide a return (ground) path. The coupling causes a charge transfer which can be detected and acted upon.

[0023] In one exemplary embodiment, the lower plate 104 may be referenced to ground (earth) potential while the upper plate 102 is linked to the vehicle's controller (e.g., a microprocessor-based controller). The controller may include a capacitive module for energizing the upper plate 102 and sampling the capacitance thereof. The capacitive module samples the parallel plate capacitance and compares the sampled capacitance to a reference (e.g., setpoint) capacitance of the plates 102, 104. If the reference and sampled capacitances differ, the capacitive module may then output a signal to the controller. Other embodiments may include a similar interaction between the capacitive module and the controller, carried out in a different overall configuration.

[0024] A capacitance threshold sensor 100 according to embodiments of the invention may be employed for various safety interlocks. For instance, the threshold sensor 100 may defeat the lift from stowing if an object is sensed in the threshold area. Further, one or more capacitance sensors similar to the capacitance threshold sensor 100 may be employed for sensing an object on the lift platform, platform rollstops, handrails, or other various locations where object sensing may be desired to facilitate various other known safety interlocks.

[0025] FIG. 7 illustrates an exemplary embodiment where the lower plate 104 is referenced to ground (earth) potential, while the upper plate 102 is linked to a charge transfer sensor in communication with the vehicle's controller. An exemplary charge transfer sensor is the QProx QT320 2-channel programmable advanced sensor integrated circuit (IC) available from the Quantum Research Group of Pittsburgh, PA. The QT320 charge transfer sensor is a self-contained digital IC capable of detecting proximity to or touching of an element on two sensing channels.

[0026] In the embodiment shown, the plates 102, 104 linked to the QT320 sensor act as a threshold sensor. Each sensing input channel of the QT320 sensor includes a low cost, non-critical capacitor that facilitates direct-to-digital capacitance acquisition using a charge- transfer method, in a process using a capacitance-to-digital converter. Typical values of these capacitance ranges from 2nF to lOOnF. Sensitivity of the capacitance threshold sensor 100 may be adjusted as required for near proximity sensing. Upon detecting an obj ect proximate to or in contact with the plates 102, 104, the QT320 sensor is operative to output a digital signal that endures for the length of time that the object is detected. When the controller receives the output signal, the controller may be programmed to perform one or more various functions. The functions performed by the controller may include, but are not limited to, disabling vehicle components (e.g., interlocks), activating a warning or indicator, and activating/polling additional sensors, hi an exemplary embodiment, the controller is operative to control the functions of the lift 10 (e.g., raise, lower, stow, deploy) in coordination with vehicle functions (e.g., power locks, sliding doors), hi other embodiments, various models of capacitor sensors can be used, and other sensor/controller configurations can be employed.

[0027] The controller can communicate with a platform elevation sensor or other sensing means to provide a vehicle occupant with a warning indication that the lift's platform 30 is at an elevation other than the transfer level. The platform elevation sensing means may be located on the platform 30, on or in the vehicle, or any other suitable location. The platform elevation sensing means may include, for example, a cammed switch, an inclinometer, an encoder, or other position indexing device operative to output a digital or analog signal. Moreover, the lift platform elevation sensing means can be configured to discriminate elevation changes of less than or equal to 1 inch below the vehicle floor.

[0028] As previously described, the controller may receive an enduring output signal from the capacitance sensor 100 indicating the presence of an object on or proximate to the vehicle threshold. Upon receiving the capacitance sensor's output signal, the controller may poll, query or otherwise communicate with the platform elevation sensing means to determine the lift platform elevation. At this time, if the controller determines that the platform elevation is below the transfer level, the controller can activate an audible or visual alarm warning as notification that the threshold has been exceeded and the lift is not in the proper location. The visual warning may be a flashing red beacon, or the like, having a minimum intensity of 20 candela and a frequency from 10 to 2 Hz, for example. Furthermore, the visual warning can be installed such that it does not require more than plus or minus 15° side-to-side head rotation as viewed by a user backing onto the platform from the interior of the vehicle, or loading onto the platfoπn in a forward direction from the vehicle interior. An audible warning can also be incoφorated. In one embodiment, an audio signal with an intensity of a minimum of 85 dBa, and a frequency between 500 and 3,000 Hz can be used. Other configurations of both visual and/or audio alerts can be implemented, h an embodiment, the alarm will endure until one of the following occurs: 1) the lift platform 30 reaches the transfer level, or 2) the capacitance threshold sensor 100 no longer senses an object on or proximate to the vehicle threshold.

[0029] FIG. 8 shows an embodiment of a vehicle lift system 145. The system 145 includes a capacitance sensor 150, a charge transfer sensor 155, a lift system controller 160, a platform elevation sensor 165, and a warning indicator 175. Object information is gathered by the capacitance sensor 150, which is linked to a charge transfer sensor 155. It should be understood that the term link can be used to describe both direct and indirect connections, for example, wireless and wired connections. The charge transfer sensor 155 conditions the signal received from the capacitance sensor 150 and outputs a conditioned signal to the lift system controller 160. The lift system controller 160 can be configured to receive and transmit a plurality of input/output (I/O) signals. The platform elevation sensor 165 provides the lift system controller 160 with information regarding the platform elevation with respect to the platform transfer level. The lift system controller 160 utilizes the input signals to produce output signals including general control information 170 and control information 173 for the warning indicator 175. General control information 170 includes signals that activate, deactivate, or otherwise control the lift or components thereof. Example implementations of the various components of the system 145 are provided above.

[0030] The use of examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. Narious embodiments of this invention are described herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above- described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

WHAT IS CLAIMED IS:

1. A vehicle wheelchair lift, comprising: a capacitance sensor configured to output a signal indicative of the presence of a person or object on a plate of the wheelchair lift; and a lift system controller configured to be in communication with the capacitance sensor and to control at least one operation of a wheelchair lift based upon the signal output by the capacitance sensor.

2. The lift of claim 1, further comprising a charge transfer sensor configured to be in communication with the capacitance sensor, the charge transfer sensor configured to charge the capacitance sensor.

3. The lift of claim 2, wherein the charge transfer sensor is configured to output a signal to the controller indicative of the presence of a person or object on a plate of the wheelchair lift, based at least in part on the signal output by the capacitance sensor.

4. The lift of claim 1, wherein the plate is a baseplate configured to be mounted on a floor of a vehicle.

5. The lift of claim 1, wherein the controller is configured to be in communication with multiple vehicle components and to send a signal to the components after the capacitance sensor outputs the signal indicative of the presence of a person or object on a plate of the vehicle wheelchair lift.

6. The lift of claim 5, wherein the vehicle components include vehicle interlock systems, vehicle ignition controls, or vehicle transmission controls.

7. The lift of claim 1, wherein the capacitance sensor comprises: a first plate configured to be affixed to a baseplate of the vehicle wheelchair lift; a second plate parallel to the first plate and configured to be in communication with the controller; and a plurality of separators configured to be aπanged between the first plate and the second plate to space the first plate from the second plate, and elastically couple the plates to one another.

8. The lift of claim 7, wherein the first plate and the second plate comprise a metal.

9. The lift of claim 7, wherein the second plate is constructed and arranged to allow for elastic deformation towards the first plate.

10. The lift of claim 7, wherein the separators comprise foam and adhesive.

11. The lift of claim 10, wherein the foam is polyethylene.

12. The lift of claim 1, further comprising a warning indicator in communication with the controller, the warning indicator being configured to output a warning based on a signal received from the controller, wherein the controller is configured to send a signal to the warning indicator based on the signal output by the capacitance sensor.

13. The lift of claim 12, wherein the warning is audible.

14. The lift of claim 1, further comprising a platform elevation sensor configured to output, to the controller, a signal indicative of a sensed elevation of a platform of the wheelchair lift.

15. The lift of claim 14, wherein the platform elevation sensor is configured to sense elevation changes of less than or equal to about one inch.

16. The lift of claim 1, wherein the plate of the wheelchair lift comprises the capacitance sensor.

17. The lift of claim 16, wherein the charge transfer sensor is configured to condition the signal output by the capacitance sensor.

18. The lift of claim 1 , wherein the controller is configured maintain communication with the capacitance sensor for the duration that the capacitance sensor is producing an output signal.

19. A vehicle wheelchair lift system, comprising: means for controlling at least one operation associated with a wheelchair lift; capacitive means for generating a signal indicative of the presence of an object on or proximate to a component of the wheelchair lift; and means for conditioning the generated signal for use by the controlling means.

20. A vehicle having a wheelchair lift, the wheelchair lift comprising: a controller; a capacitance sensor coupled to the controller and configured to generate an output signal; a charge transfer sensor coupled between the capacitance sensor and the controller, the charge transfer sensor configured to output a signal to the controller indicative of the presence of a person or object on a plate of the wheelchair lift, based at least in part on the signal output by the capacitance sensor; a platform elevation sensor coupled to the controller and configured to output a signal indicative^'of an elevation of a platform of the wheelchair lift; and a warning indicator coupled with the controller that outputs a warning signal based on information received by the controller from the charge transfer sensor and the platform elevation sensor.

21. The vehicle of claim 20, wherein the capacitance sensor comprises: a first plate affixed to a baseplate of the vehicle wheelchair lift; a second plate parallel to the first plate and configured to be in communication with the controller; and a plurality of separators configured to be aπanged between the first plate and the second plate to space the first plate from the second plate, and elastically couple the plates to one another.

22. The vehicle of claim 21, wherein the first plate is coupled to a reference potential, and the second plate is coupled to second potential that is greater than the reference potential.

23. The vehicle of claim 22, wherein the controller is coupled to multiple vehicle interlocks and outputs a signal to the interlocks after receiving a signal indicative of the presence of an object on a plate of the wheelchair lift.

24. The vehicle of claim 21 , wherein the first plate and the second plate comprise a metal.

25. The vehicle of claim 21 , wherein the second plate is constructed and aπanged to allow for elastic deformation towards the first plate.

26. The vehicle of claim 21, wherein the separators comprise foam and adhesive.

27. The vehicle of claim 26, wherein the foam is polyethylene.

28. A wheelchair lift comprising: a controller; a capacitance sensor coupled to the controller and configured to output a signal indicative of the presence of a person on a plate of the wheelchair lift; and a platform elevation sensor coupled to the controller and configured to output a signal indicative of a sensed elevation of a platform of the wheelchair lift.

29. The wheelchair lift of claim 28, wherein the controller is coupled to multiple vehicle interlocks and outputs a signal to the interlocks after receiving the output signal of the capacitance sensor.

30. The wheelchair lift of claim 28, wherein the capacitance sensor comprises: a first plate coupled to a baseplate of the vehicle wheelchair lift; a second plate parallel to the first plate and configured to be in communication with the controller; and a plurality of separators aπanged between the first plate and the second plate to space the first plate from the second plate, and elastically couple the plates to one another.

31. The wheelchair lift of claim 30, wherein the first plate and the second plate comprise a metal.

32. The wheelchair lift of claim 30, wherein the second plate is constructed and aπanged to allow for elastic deformation towards the first plate.

33. The wheelchair lift of claim 30, wherein the separators comprise foam and adhesive.

34. The wheelchair lift of claim 33, wherein the foam is polyethylene.

35. The wheelchair lift of claim 28, further comprising a warning indicator in communication with the controller, the warning indicator being configured to output a warning based on a signal received from the controller.

36. A method of controlling a wheelchair lift, the method comprising: associating a capacitive sensor with a baseplate of a wheelchair lift: charging the capacitive sensor; sensing the presence of a person or object on the wheelchair lift based on an output of the capacitive sensor; and controlling an operation of the wheelchair lift based on whether the presence of a person or object on the wheelchair lift is sensed.

37. The method of claim 36, further comprising controlling an operation of a vehicle component selected from the group an interlock system, an ignition system, and a transmission control based on an output of the capacitance sensor.

38. The method of claim 37, further comprising configuring the capacitance sensor to have a first plate configured to be affixed to a baseplate of the vehicle wheelchair lift; a second plate parallel to the first plate and configured to be in communication with the controller; and a plurality of separators configured to be aπanged between the first plate and the second plate to space the first plate from the second plate, and elastically couple the plates to one another.