Proximity detector comprising capacitive sensor

Translation of description of equivalent WO 2004023067 A2

"Proximity sensor capacitive sensor"

The present invention relates to a proximity sensor by capacitance sensor if.

In many industrial applications it is necessary to detect and measure the proximity between a machine and an obstacle, that it is other object or person, in order to deliver information of a proximity distance, warning signals and act result.

By way of example of industrial application of this type of detector include the management of an anti-collision function between mobile robots or stationary with an obstacle, running a function anti- burglary, and more generally any management implementing a proximity detection.

In the medical field many robots used for auscultation of patients need to know the patient's position relative to moving parts of the machine.

For example, for applications in radiology or imaging or for medical or surgical treatment is essential to provide the operator with equipment or automated control systems as accurate information as possible on the patient position to quickly and correctly position the auscultation elements.

X-ray radiology systems, knowledge and millimeter real time the position of a radiology equipment relative to a patient and his immediate physical environment would increase the speed of movement of the machine, of improve safety and to minimize the exposure time to x-rays

Increase the speed of movements of vascular positioners while ensuring no collision with the patient is a current wishes. However, the patient's appearance and position relative to the reference of the machine is not known, the travel speed of these robots are low so that the moving parts of the machine will not accidentally injure the patient. Usually an emergency stop consisting of mechanical switches stops any motion when the sensor or transmitter X arrive in contact with the patient or another part of the equipment however the kinetics of moving objects and low race contactors imposes small displacements speeds. Increasing the speed of the robot is then possible only if a wireless device detects the patient at a distance, said high threshold, sufficient to slow down the movements before arriving in contact with the patient. A minimum distance, said low threshold allows for the stop function anti-collision emergencies.

Consequently, there are a real need for non-contact proximity sensors providing information accurately and usable distance in specific environments such as medical imaging. Documents US 4987583, WO 9730633 and WO 97 19638 disclose proximity sensors suitable for this type of application.

Document US 5,952,835 discloses a contactless proximity sensor. The implementation is an electronic detector operating all or nothing with an oscillator FET transistor connected to an unguarded electrode.

Document US 5,442,347 discloses a capacitive proximity sensor controlled double-garde, operating in differential measurement phase by exploiting the constant RC generated with reference resistors. A guard is created by reproducing the sensor signal using a buffer (buffer). However, a major problem appears in principle to this concept as the buffer adds a parasitic capacitance to the capacitance to be measured. This parasitic capacitance is much greater than the ability to measure which causes measurement errors and significant instabilities.

Document US 5,554,973 discloses it a capacitive type electrostatic detector operating on a principle of operation switched capacitor without warning.

Document US 6,348,862 discloses a proximity sensor including a sensing electrode and a plurality of control electrodes located close to a spatial region in which is situated an object to be detected.

A main object of the present invention is to provide a capacitive sensor proximity sensor that provides an accurate measurement (typically millimeter) of the position of an object at a range of measurement (typically decimeter) greater than that permitted by the detectors close to the prior art, in particular with the effect of allowing to increase the X-ray machine travel speed and to provide a patient having topography to evaluate its thickness in order to optimize the transmission power of the beams X and so minimize the level of radiation required to produce an image. This object is achieved with a capacitive proximity sensor comprising:

- At least one detection antenna comprising a plurality of capacitive proximity sensors each having a measurement electrode, said antenna being placed close to an object or a body,

- Electronic means for exciting said measurement electrodes and to treat signals from said capacitive sensors, - digital means for controlling the electronic means and for calculating from the measuring signals thus processed, the distance between said electrodes and said object or said body.

According to the invention, the electronic means comprise, for each antenna to detect a floating bridge or floating capacitive excitation cooperating with scanning means for sequentially measuring the respective capacitance between each electrode of said antenna and the subject or body to measure. One can thus achieve the equivalent of a camera pixels in which each pixel is constituted by an electrode. This camera moved along the body of a patient will allow to achieve a topography of the patient to obtain a measurement of its thickness. The floating capacitive bridge can advantageously be of the type disclosed in FR2756048. One can also use a capacitive electrode of the type described in the document FR2640373, which implements a bias voltage source and a triaxial transformer. The proximity sensor according to the invention, consisting of a plurality of measurement electrodes orientated along several axes in order to cover all relevant areas can be achieved by several detection antennas. In an advantageous embodiment of a proximity sensor according to the invention, the detection antenna further comprises a single guard for one set of measuring electrodes of the antenna. But can also be provided a configuration in which the detection antenna further comprises several guards each provided for a portion of all the measuring electrodes of the antenna.

detection of the antennas can be made using a rigid or flexible circuit and connected to the electronic means.

Electronic means and the digital means for controlling and computation may cooperate to successively measure a distance to each electrode of an antenna according to a predetermined and alterable sequence.

detection antennas preferably have a test track located on the back or near the electrodes (guard plane side), which, in normal operation, is at the potential of the guard, and, test, shall be made mass.

Under these conditions, each electrode sees a parasitic capacitance simulating the presence of an object in order to verify one integrity of the proximity sensor.

Electronic means and the digital means for controlling and calculating cooperate to deliver an alarm signal indicating an inconsistent measurement or dysfunction of the digital means for controlling and calculation.

One can also provide that the electronic means comprise one or more reference capabilities to control the calibration of electronic or perform an automatic recalibration. In a particular configuration of a proximity sensor according to the invention can be placed in proximity of the measurement electrodes, guard or ground surfaces arranged to modify the field lines of these electrodes. It is thus possible to create particular shapes of equivalent surface of the measurement electrodes.

In a particular embodiment, the proximity sensor according to the invention is disposed on the inner or outer surface of a dressing cover or housing for example the X imaging detector or the transmitter X.

Electronic means and the digital means for controlling and calculating cooperate to deliver proximity detection threshold of alarm signals. The distances measured between the electrodes and the detected objects are delivered in digital and analog form.

For controlling the displacements in six degrees of freedom, for example the antennas are disposed on five faces of the casing or cover.

In the case of a proximity sensor implemented in an X-ray radiologist equipment comprising a device for emitting an X-beam provided for irradiating an object or a body, an antenna, said antenna X, is then at least partially traversed by the beam X. In a simple configuration, the X antenna may for example include a bore for the passage of the beam X. This zone is not gauging because not provided with electrodes.

To overcome this drawback can then be provided that the antenna X is in the region X of the beam, made of materials at least partially transparent to X-ray

This embodiment is possible from a flexible printed circuit comprising a metallized insulator on both sides a by a very thin chromium layer constituting the adhesion layer with a layer of copper, the copper layer is removed by etching on the area that corresponds to the passage of the X-beam to leave on the insulating that the thin layer of chromium wherein the connecting tracks, the capacitive electrodes test track and the guard are formed (Fig. 5). Transmitter X may also be provided with antennas say X.

This latter configuration allows de completely cover the electrode sensor to increase the efficiency of this detector.

The proximity sensor according to the invention is distinguished from the detector disclosed in US 5,952,835 in that in the present invention, operating electronics for amplitude measurement with a guard, and that the oscillator has constant characteristics independent of the ability to measure. In addition, the detector of the invention operates in amplitude measurement and not a differential phase measurement.

This proximity sensor is designed to increase the movement speed of current radiology machines Security Detection (anti-collision), performing a coarse three-dimensional image of the patient, to evaluate the thickness of a patient to to optimize the power of X-ray to create images with minimal radiation and improve image quality.

The capacitive proximity sensor according to the invention is used to control the approach of a vascular positioner for medical application, by using multiple antennas, equipped with a plurality of capacitive electrodes, housed in the detector. This device performs real-time measurement of several absolute distances (a distance electrode) separating the cover surface of the detector and the surrounding objects such as a patient or the table.

proximity switches of the devices according to the invention may also be implemented in machines or robots moving, in particular of machine tools, industrial robots, transportation vehicles, etc. ... With the effect of increasing their speed of operation and to improve safety.

Other advantages and features of the invention will appear on examining the detailed description of a mode of implementation in no way limiting, and the appended drawings in which:

- Figure 1 is a schematic block diagram of X-ray equipment incorporating two proximity detectors according to the invention;

- Figure 2 illustrates the arrangement of an antenna within a proximity sensor according to the invention;

- Figure 3 illustrates an exemplary structure of an antenna of a proximity sensor according to the invention; - Figure 4 schematically shows the inputs and outputs of an electronic card equipping a proximity sensor according to the invention; and

- Figure 5 illustrates the structure of a flexible circuit used for the embodiment of an antenna within a proximity sensor; and

- Figure 6 illustrates the structure of a measurement system equipping a proximity sensor according to the invention.

will now be described with reference to Figure 1, an example of implementing proximity sensors according to the invention in an X-ray machine, for a vascular positioner. A first proximity sensor (1A) is disposed within an X detector device (5) equipping an X-ray machine (10), and comprises several antennas covering the five internal or external walls of the cover of the X-ray detector, each antenna having a plurality of electrodes Ei, j. A second proximity sensor (1B) is disposed on the inner surface of the X transmitter device (2) of the machine (10). The X transmitter device (2) and the X-ray detector device (5) are installed at both ends of a movable piece C shaped movable in rotation round an examination table (4) on which a patient (3 ) is elongated.

Referring to Figure 2, a according to the invention one proximity sensor includes an antenna 20 disposed on the inner surface of a face of the cap 22 and side faces 21, 22. The antenna 20 is constituted of a plurality electrodes arranged in a matrix consisting of the electrodes Ei, j fully located on one side of the electrodes E'i, j arranged in edges on both sides, and electrodes disposed wholly on the sides.

It should be noted that the antenna 20 could also be disposed on the outer surface of the detector cover.

will now be described with reference to Figure 3, an exemplary embodiment of an antenna 30 in the form of a flexible circuit. This antenna 30 lines the inner surface of a main face of a hood with electrodes 31 and the inner surfaces of side faces of the hood with electrodes 32, 33, 34. These electrodes are all connected to an electronic card via tracks drivers (not shown). The antennas with proximity sensors according to the invention can be realized in a multilayer technique, as illustrated schematically in Figure 5. To make the antenna called X can use a flexible printed circuit 50 consists of a metallic insulation I on both sides with a thin layer of chromium Cr and a thick layer of copper Cu, the two copper layers being removed on a ZX area which corresponds to the passage of the X-beam and wherein the connecting tracks, electrodes capacitive Ecr, a test track P, and a guard are made from two layers of chrome.

A conductive layer G custody copper + chromium, the Ecu electrodes + cr copper + chromium, and Esquire electrodes chromium, are made following an industrial process using flexible circuits multi-layer type "Adhesiveless", that have on polyimide support a thin layer of chromium coated copper. This industrial process is controlled by the flexible circuit manufacturers.

An electronic card equipping a proximity sensor according to the invention comprises, with reference to Figure 4, 64 connections to the electrodes of three sensing antennas, a test input connected to a test electrode for each antenna, a reset input of reset, and a DC voltage supply input.

This circuit provides an alarm signal "Watchdog" five alarm threshold detection signals (objects or too near patients), a detection signal from the transmitter X, five analog output signals corresponding to the five faces of the hood, an analog output signal detecting the transmitter X, an excitation signal to the test electrode, and a digital serial link for communicating with the central unit of the equipment.

The alarm signal "Watchdog" is placed at the lowest level in case of inconsistent measurements, lack of electrode or software failure. The analog outputs are image minimum distances from the face of the detector, the sides of the detector or the transmitter. The reset signal is a reset signal from the microcontroller. Digital link 64 provides the measured distances and the good working of the proximity sensor. The sensor is connected directly to the CPU IF equipment without interface card.

As illustrated in Figure 6, an antenna A of a proximity sensor according to the invention is connected via a flexible connecting cable CL to an electronic card 60 includes an analog multiplexer for scanning an input, a capacitive floating bridge multi implementing a technology disclosed in FR2756048 corresponding to French patent No. 96 13992 of 15 November 1996, an a / D conversion module and a digital module for calculating distance, control of functioning and communication with SI system in raining and machine control. We will now describe the operation of a proximity sensor according to the invention, with reference to the aforementioned figures. The proximity sensor measures a distance successively on each electrode in an order that may be modified simply in the software. The proximity sensor has a test electrode in normal operation is at the potential of the guard and when grounding can test the proper functioning of the sensor and the good condition of all connections + antenna.

By acting on the test command, it will also test the operation of the measuring chain for each sensor.

If a measured distance on one of the electrodes reaches a predefined threshold logic low output corresponding to the antenna that supports the electrode goes low state, it will return to the high state when the distance exceeds the threshold again . The alarm output "watchdog" goes low state if any of the n measurements is inconsistent (test failure) or the microcontroller is blocked or fails.

Initially, the digital outputs are images of the distances measured for each electrode, but treatment may then become more complex, so it should be a calculation of reserve power in the microcontroller (DSP).

We will now describe a practical example of manufacturing a proximity sensor according to the invention. In this practical example, the power module is disposed on a 160 mm length of map and width 100 to 160 mm, and comprises a connector for analog outputs (shielded twisted), a connector for input / output logics, a connector for food, and a plurality of connectors for the electrode signals.

Antennas which occupy the edges of the detector will have half of their surface on the side and one on the large face. There are 33 electrodes distributed on the four antennas: antenna 3 to the detector and an antenna for the transmitter X electrodes 13 are located on the air side of the detector 16 of the X and antenna 2 on the transmitter X .

The range of the sensors is greater than 100 mm with millimeter resolution, which optimizes control sensor approach speed to the patient (maximum speed with minimum risk of impact).

The cables that connect the electronic antennas on the side of the issuer X undergo motions and must accept in practice a 50mm bend radius dynamically.

To allow replacement of the antenna transmitter side X or electronics without removing the cable, the latter is for example equipped with a side dish and a side connector electronic connector. One can also provide a guard band on the sides of the detector to change the electrodes of the field lines to change the equivalent surface of the electrodes and measuring range and scope. As this is a safety device, the detection distance must be very reliable and the system must be notified in case of failure. In real terms the outskirts of the equipment are very congested. The objects to be detected are of different natures: human body (patient lying on the mattress of the table or doctor standing next to the table), metal parts to ground or not, non-metallic parts but slightly conductive. The detection must be done in any direction. Detection is performed on the entire active surface of the detector and on its edges, corresponding to five surfaces of a box.

The antenna X should be almost transparent to X-rays, which means for the realization of the electrodes and the guard using a metal thin. Doctors usually install a lightweight plastic cover on the sensor (charlotte). The magnitude of the time in which a complete proximity must be detected is 50 ms for an antenna 64 electrodes. Size objects to be detected is variable: the patient's abdomen to his hand, a finger or nose.

Of course, the invention is not limited to the examples just described and numerous adjustments can be made to these examples without exceeding the scope of the invention. More generally, the proximity switches according to the invention can be implemented in any industrial application, in the case of detecting a presence or complex shapes using multi-antennas electrodes. proximity sensors can thus be provided according to the invention fitted mobile robots or vehicles, to improve security around these facilities. proximity switches of the invention can also be implemented in anti-intrusion and anti-collision devices devices.