WO2014177677A1

WO2014177677A1 - Capacitive proximity sensor system

Info

Publication number: WO2014177677A1
Application number: PCT/EP2014/058955
Authority: WO
Inventors: Hussein AL-SALLAMI
Original assignee: Al-Sallami Hussein
Priority date: 2013-05-02
Filing date: 2014-05-01
Publication date: 2014-11-06

Abstract

A capacitive proximity sensor system is disclosed. The capacitive proximity sensor system is connectable to a movable manipulator adapted to transfer samples between experimental station chambers. The capacitive proximity sensor system comprises a capacitive proximity sensor and a control system. The capacitive proximity sensor is mountable on the manipulator and adapted to provide a capacitance value based on a distance from the capacitive proximity sensor to an object with which contact is to be avoided. The control system is adapted to cause a stop of movement of the manipulator based on an alteration of the capacitance value. Corresponding method of guiding a movable manipulator inside an experimental station chamber is also disclosed.

Description

CAPACITIVE PROXIMITY SENSOR SYSTEM

TECHNICAL FIELD

The present invention relates in general to capacitive proximity sensors, and especially to a proximity detection system for manipulators in experiment stations operating, for example, in ultra-high vacuum, using a capacitive proximity sensor.

BACKGROUND

Closed chambers are often used in various types of experimental stations (e.g. electron microscopes, spallation plant stations, accelerator stations, etc.).

In an example scenario, an experimental station for angular- and spin resolved photoemission spectroscopy consists of several ultra-high vacuum (UHV) chambers of which two, the preparation chamber and the analysis chamber, are in continuous use during experiments. Operation includes repeated transfers of samples between these two chambers using a so-called manipulator. Due to different space constraints in various parts of the chamber(s) and/or in various parts of the transfer path between chambers, the risk of the manipulator being damaged (due to collision with chamber walls or any equipment inside the chambers), or the manipulator damaging any equipment is substantial. This risk may be even more pronounced if frequent change of the space constraints is experienced, e.g. due to extra

experimental equipment being mounted on, for example, a weekly basis.

Any damage typically results in extra work for the staff and high repair costs, as well as loss of experimental time.

Thus, finding a way to avoid the risk of damaging the manipulator and/or the other equipment is therefore highly sought after.

SUMMARY

An object of some embodiments is to provide a proximity sensing system, which seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages singly or in any combination.

If the manipulator collides with walls or equipment in the interior of the experimental station chamber, the affected walls or equipment, the sample, the sample holder, and/or the manipulator may be damaged. To change broken parts is time consuming and costly.

An aim of some embodiments is to minimize the risk of collision when operating a manipulator in an experimental station chamber.

An aim of some embodiments is to minimize the effect on the experimental sample and/or experimental result.

An aim of some embodiments is to provide a sensor that is suitable for demanding environments, such as high/extreme vacuum and/or high/low/extreme temperatures.

A first aspect is a capacitive proximity sensor system. The capacitive proximity sensor system is connectable to a movable manipulator adapted to transfer samples between experimental station chambers. The capacitive proximity sensor system comprises a capacitive proximity sensor and a control system.

The capacitive proximity sensor is mountable on the manipulator and adapted to provide a capacitance value based on a distance from the capacitive proximity sensor to an object with which contact is to be avoided.

The control system is adapted to cause a stop of movement of the manipulator based on an alteration of the capacitance value.

In some embodiments, the alteration of the capacitance value may be an increase in the capacitance value, indicating that the sensor is approaching an object/obstacle.

In some embodiments, the alteration may be a decrease in the capacitance value, indicating that the sensor is approaching an object/obstacle.

The manipulator may, for example, comprise of a movable rod (or shaft, or any other suitable tool) with means (e.g. a sample holder) for attaching a sample at or near the end of the rod extending into a chamber (e.g. a measurement chamber). The manipulator may typically be operated manually or by a computer.

The manipulator may be a multistage manipulator. A multistage manipulator may be moved in several directions/dimensions (e.g. in any of the X, Y, Z-directions as well as in a Theta (rotational) direction). The directions may, for example, be defined relative to a longitudinal or other suitable plane. In some implementations, the manipulator may only be movable in a Z-direction. The experimental chamber may be of various sizes and/or various interior geometries. Interior equipment of the chamber may e.g. comprise valves, beam shutters, detectors, cameras, and the like.

In some embodiments at least one of the experimental station chambers may be a vacuum chamber or an ultra-high vacuum chamber.

In some embodiments, the capacitive proximity sensor may comprise at least two capacitive electrodes. According to some embodiments, the at least two capacitive electrodes may comprise two parallel metallic rings mounted in association with a sample holder of the manipulator. The metallic rings may, for example, comprise silver plated copper wires or any other suitable conductive material.

In some embodiments, the capacitive proximity sensor may be adapted to provide the capacitance value such that a first capacitance value is higher than a second capacitance value if a first distance associated with the first capacitance value is smaller than a second distance associated with the second capacitance value.

In some embodiments, the control system may be adapted to compare the capacitance value to a threshold value and cause the stop of movement of the manipulator when the capacitance value exceeds the threshold value.

Alternatively, the capacitive proximity sensor may be adapted to provide the capacitance value such that a first capacitance value is lower than a second capacitance value if a first distance associated with the first capacitance value is smaller than a second distance associated with the second capacitance value. Then, the movement of the manipulator will be stopped if the capacitance value falls below a corresponding threshold value.

The threshold value (or values) may be a fixed value or a dynamically adjustable value. The threshold value may be set by the operator and/or by the manufacturer.

Generally, one or more threshold values may be applied. Examples of several threshold values being used comprise one threshold value indicating to the operator that an obstacle is close by, one threshold value causing the stop of movement of the manipulator, and/or one threshold value causing only a decrease of the moving speed of the manipulator. The stop of movement of the manipulator may be a stop of movement in one or several dimensions/directions.

In some embodiments, the control system may comprise a processor adapted to compare the capacitance value to the threshold value and cause the stop of movement of the manipulator when the capacitance value exceeds the threshold value.

The processor may, for example, be a μϋοηίτοΙΙεΓ (microcontroller), or any other type of programmable device.

In some embodiments, the processor may be further adapted to cause rendering of an indication in a user interface when the capacitance value exceeds the threshold value.

The user interface may, for example, be a liquid crystal display (LCD) or any other type of screen or display suitable to display messages to an operator.

In some embodiments, the threshold value may be dynamically adjustable based on one or more of a chamber geometry, a sample holder geometry, a sample holder material, a sample geometry, and a sample material.

According to some embodiments, the control system may comprise a capacitance preparation unit adapted to measure the capacitance value. The capacitance preparation unit may also be referred to as a pre-processing unit.

The capacitance preparation unit may, for example, be a capacitance-to- digital converter and/or an amplifier.

In some embodiments, the control system may be further adapted to connect the capacitive proximity sensor to ground in an operational mode of the experimental station wherein the manipulator is stationary. In some embodiments, the control system may also disable the capacitance preparation unit by connecting it to ground.

A second aspect is a method of guiding a movable manipulator inside an experimental station chamber wherein the manipulator is adapted to transfer samples between experimental station chambers. The method comprises operating a capacitive proximity sensor system comprising a capacitive proximity sensor mounted on the manipulator and a control system.

The operation includes measuring a capacitance value provided by the capacitive proximity sensor, wherein the capacitance value is based on a distance from the capacitive proximity sensor to an object with which contact is to be avoided, and causing (by the control system) a stop of movement of the manipulator based on an alteration of the capacitance value.

According to some embodiments, the method may further comprise comparing the capacitance value to a threshold value. Then, the stop of movement of the manipulator may be caused when the capacitance value exceeds the threshold value.

In some embodiments, the method may further comprise dynamically adjusting the threshold value based on one or more of a chamber geometry, a sample holder geometry, a sample holder material, a sample geometry, and a sample material.

In some embodiments, the method may further comprise connecting the capacitive proximity sensor to ground in an operational mode of the experimental station wherein the manipulator is stationary.

A third aspect relates to capacitive proximity sensor system 200, which is mainly comprised of a capacitive proximity sensor 201 and a control system that will stop any movement of the manipulator 210 when it comes too close to any experimental equipment, chamber walls, valves, analyzer, and so on without actual contact.

A fourth aspect relates to a method for safely guiding a manipulator 210 inside a chamber using a capacitive proximity sensor system 200 mainly comprised of a capacitive proximity sensor 201 and a control system that will stop any movement of the manipulator 210 when it comes too close to any experimental equipment, chamber walls, valves, analyzer, and so on without actual contact.

In some embodiments, the second, third and fourth aspects may additionally have features identical with or corresponding to any of the various features as explained above for the first aspect.

An advantage of some embodiments is that a capacitive proximity sensor is provided, which is suitable for experimental station chambers with demanding environments, such as, for example, high or ultra-high vacuum, extreme

temperatures (e.g. -250 °C to +250 °C), narrow passages and/or complex geometry. Another advantage of some embodiments is that a capacitive proximity sensor is provided, which is adapted to sense when it approaches an object in several dimensions/directions .

Another advantage of some embodiments is that a system is provided where an applied capacitive proximity sensor does not affects (or affects to a minimum degree) the sample during operation of the experimental chamber. For example, charging of the sample by the sensor may be avoided or minimized via connection of the sensor to ground when the manipulator is stationary.

Another advantage of some embodiments is that a capacitive proximity sensor is provided that may easily be adapted to operate in different types of experimental station chambers.

Another advantage of some embodiments is that a system is provided as a safeguard against computer malfunction.

Another advantage of some embodiments is that the risk of collision during operation of the manipulator is minimized.

Another advantage of some embodiments is that a system is provided that stops the manipulator even before the sensor touches a detected obstacle, thus ensuring that no damage or contact occurs. BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages will appear from the following detailed description, wherein embodiments will be described in more detail with reference to the accompanying drawings, in which:

FIG. la is a schematic view of an example capacitive proximity sensor system with a capacitive proximity sensor and a control system according to some embodiments;

FIG. lb is a schematic view of an example capacitive proximity sensor system with a capacitive proximity sensor and a control system according to some embodiments;

FIG. 2 is a block diagram of an example motion control system with safety system for multistage manipulator according to some embodiments; FIG. 3 is a schematic drawing illustrating an example implementation of the capacitive proximity sensor on a manipulator according to some embodiments;

FIG. 4 is a flow chart illustrating example method steps according to some embodiments;

FIGs. 5a, 5b, and 5c are block diagrams illustrating respective example architectures of the capacitive proximity sensor system according to some embodiments; and

FIGs. 6a-6k are schematic diagrams illustrating various examples associated with the threshold value according to some embodiments.

DETAILED DESCRIPTION

Embodiments presented herein relate, in general, to the field of proximity sensing systems. Some embodiments relate to a proximity sensing system using a capacitive proximity sensor, adapted for usage in a vacuum chamber with an ultra- high vacuum environment, for protecting a manipulator operating in said chamber from being damaged. However, it should be appreciated that some embodiments may be equally applicable to any type of manipulator operating in a chamber. However, for the sake of clarity and simplicity, most embodiments outlined in this specification are related to a manipulator operating in an ultra-high vacuum chamber.

Some embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which a number of various embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

With reference to Figures la, lb and 2, one way of avoiding the risk of damaging a manipulator operating in an ultra-high vacuum chamber is by using a capacitive proximity sensor system, exemplified by the capacitive proximity sensor systems 100a, 100b, 200, according to some embodiments.

The example capacitive proximity sensor system 200 is mainly comprised of a capacitive proximity sensor 201 and a control system that will stop any movement of the manipulator 210 when it comes too close to any objects with which contact should be avoided (e.g. experimental equipment, chamber walls, valves, analyzers, and/or any other interior of an experimental station chamber), without actual contact.

Figure la illustrates an example capacitive proximity sensor system 100a where a capacitive proximity sensor 101a is mounted at the end of a movable manipulator 110a which extends to the interior of an experimental chamber 102a and is adapted to transfer samples between different experimental chambers.

The capacitive proximity sensor 101a may, for example, comprise two or more capacitive electrodes that may be implemented as two parallel metallic rings.

The manipulator is movable in at least one direction/dimension. In the example of Figure la, the manipulator is movable in a Z-direction. Alternatively or additionally, the manipulator may, for example, be movable in one or more of an X- direction, a Y-direction, and a theta (TH) dimension, where the theta dimension represents a rotation of the manipulator around its Z-axis. The movement of the manipulator is typically controlled by a motion controller (Motion CNTR) 108a.

When the manipulator 102a approaches a physical object within the chamber 102a (e.g. the chamber wall 121a), the capacitance value sensed by the capacitive proximity sensor 101a is altered (typically increased). The capacitance value sensed by the capacitive proximity sensor 101a may depend on a distance 120a from the capacitive proximity sensor 101a to the physical object 121a with which contact is to be avoided.

The capacitive proximity sensor 101a provides the sensed capacitance value to a control system 130a, and the control system 130a causes a stop of movement of the manipulator 110a if the capacitance value indicates that the manipulator is approaching a physical object 121a with which contact is to be avoided. This may, for example, be indicated by an alteration (e.g. increase) of the capacitance value.

The stop of movement may be achieved by inputting an indication, command, or the like to the motion controller 108a, which may or may not be comprised in the control system 130a

One way of determining when to stop movement of the manipulator is for the control system 130a to compare the capacitance value to a threshold value and cause the stop of movement of the manipulator when the capacitance value exceeds the threshold value. The comparison may be performed by a processor (PROC) 105a of the control system. The processor 105a may also input the indication, command, or the like to the motion controller 108a when the threshold value is exceeded. The processor may, for example, be a microcontroller.

Alternatively or additionally, the processor 105a may determine when to stop movement of the manipulator in any other suitable way and instruct the motion controller 108a accordingly.

The control system 130a (e.g. the processor 105a) may also cause rendering of an indication (e.g. an alarm) in a user interface (U/I) 104a when the capacitance value exceeds a threshold value. This threshold value may be the same or different than the threshold value for stop of movement of the manipulator.

The user interface 104a may also be used to input values to the control system 130a and/or to the motion controller 108a. For example, the user interface 104a may be used to dynamically adjust one or more of the threshold values based on one or more of a chamber geometry, a sample holder geometry, a sample holder material, a sample geometry, and a sample material. If the chamber geometry is to be used for dynamical adjustment of the threshold value, some means for tracking the position of the sensor and/or sample typically needs to be provided in association with the capacitive proximity sensor system. For example, the motion controller may have an encoder for reading the position of the sample during movement inside the chamber.

In some embodiments, the control system 130a may also comprise a capacitance preparation (or pre-processing) unit (PREP) 106a adapted to prepare/pre- process the capacitance value provided by the capacitive proximity sensor 101a for further processing (e.g. by the processor 105a). Preparation/pre-processing of the capacitance value by the capacitance preparation unit may, for example, comprise amplifying (or otherwise scaling) the capacitance value provided by the capacitive proximity sensor. Alternatively or additionally, preparation/pre-processing of the capacitance value by the capacitance preparation unit may, for example, comprise transforming the (typically analog) capacitance value provided by the capacitive proximity sensor to another format (typically a digital format). The capacitance preparation unit 106a may, for example, comprise one or more of an amplifier and a capacitance-to-digital converter.

Figure lb illustrates an example capacitive proximity sensor system 100b.

The reference numbers 101b, 102b, 104b, 105b, 106b, 108b, 110b, 120b, 121b, 130b represent units with the same or similar functionality as the corresponding units

101a, 102a, 104a, 105a, 106a, 108a, 110a, 120a, 121a, 130a of Figure la and will not be elaborated on further.

The control system 130b of the example capacitive proximity sensor system

100b further comprises disabling means 131, 132. When the manipulator 110b is stationary (e.g. during experimental mode of the chamber 102b), the control system

130b is able to connect the capacitive proximity sensor 101b to ground (or any other suitable potential) via the disabling means 131. This avoids any charging effect of the sample by the capacitive proximity sensor 101b during the experimental phase.

At the same time, the control system 130b may disable the capacitance preparation unit 106b.

Thus, in one example, the example control system 130a, 130b may comprise a capacitance preparation unit 106a, 106b which measures the capacitance value from the sensor 101a, 101b and converts the capacitance value to a digital signal. The digital signal is then passed on to a processor 105 a, 105 a which may compare the signal to a (predefined or dynamic) threshold value. If the signal exceeds the threshold value the processor 105a, 105b will indicate to the motion controller 108a, 108b (which controls the motion of the manipulator) to stop the manipulator 110a, 110b from moving in a certain direction (e.g. the X, Y, Z or theta/TH direction depending on in what direction an obstacle has been detected by the capacity proximity sensor). The processor 105a, 105b will also send, to an output/input device 104a, 104b, a flag indicating to the operator of the system that an obstacle was detected and that the manipulator will not move any further in a certain direction. The control system 130a, 130b may also keep track of the coordinates of the sample/manipulator inside the chamber and output them to the operator through the input/output device 104a, 104b. The operator may also control the motion of the manipulator 110a, 110b via the input/output device 104a, 104b. The capacitive proximity sensor may, in some embodiments, be

implemented using at least two Kapton coaxial cables as capacitive electrodes. The capacitive electrodes are adapted for high and ultrahigh vacuum environments withstanding large temperature differences, for example temperatures between 260°C and cryogenic -269°C. All conductors and braided shields (coaxial cable shields) may be silver plated copper wire; however other suitable conducting materials may also be used. The insulation may for instance be Kapton type-F film that is applied and heat treated to effectively minimize trapped volumes of gas and maintain mechanical strength. The capacitive electrodes (the wires) may in an embodiment of the present invention have a diameter of 0.25mm formed in a circular or straight shape. Other thicknesses or shapes of the capacitive electrodes may also be used with the same result.

A block diagram of an example capacitive proximity sensor system 200 (compare with 100a, 100b) for protecting a multistage manipulator 210 (compare with 110a, 110b) is shown in Fig 2.

The example capacitive proximity sensor system 200 comprises a capacitive proximity sensor 201 (compare with 101a, 101b) comprising double circular capacitive electrodes (made for instance of Kapton coaxial cable) inside an ultra-high vacuum (UHV) chamber 202 (compare with 102a, 102b) for sensing the proximity of objects such as the walls of the chamber 202 (compare with 121a, 121b). In this case, the sensor 201 may be mounted as two rings in parallel (double-electrode capacitive sensor) near the sample holder 211 of the manipulator 210. The Kapton coaxial cables 221 extend from the sensor 201 to the exterior of the chamber 202 via a coaxial feed-through unit 220.

The example capacitive proximity sensor system 200 also comprises an input overvoltage protection circuit (Prot) 203, which protects the subsequent circuits from high voltages and/or voltage discharges/impulses/spikes that may occur, for example, when a measurement has been performed.

The example capacitive proximity sensor system 200 also comprises a liquid crystal display (LCD) 204 (compare with 104a, 104b) for monitoring and interfacing with the safety system 200. The LCD 204 may, for example, be used for displaying and/or setting an alarm (e.g. indicating to an operator of the manipulator 210 that an obstacle has been detected and that the motion of the manipulator 210 in a certain direction has been stopped), controlling the grounding (GND) (e.g. to ensure that no charging from the capacitive proximity sensor 201 and/or the capacitance preparation unit 206 will interfere with the sample during experiments), and/or changing sensor sensitivity and/or threshold values (e.g. for compensating for interior differences of the chamber, e.g. narrow passages and spacious areas, physical properties of the sample, e.g. large samples, small samples, heavy or light samples, etc.).

The example capacitive proximity sensor system 200 also comprises a μΰοηίΓθΙΙεΓ (or any other suitable processor) (μοηίτ) 205 (compare with 105 a, 105b) and a capacitance-to-digital converter (CDC) 206 (compare with 106a, 106b) that measures (and possibly amplifies or scales) the capacitance C_sens between the capacitive electrodes 201. The measured capacitance is compared with a defined threshold value (either set by the user of the system or by the manufacturer), which can be either fixed or dynamically adjusted (e.g. to suit the current location of the manipulator in the interior of the chamber, different chamber interiors and/or physical properties of the sample) by the μΰοηττοΙΙεΓ 205 according to a program. For example, a more narrow passage 209 for the manipulator may call for a lowered threshold value.

If the measured capacitance C_sens is altered by the presence of an object, such as the wall of the chamber 202, an output signal is generated which sets a flag or any other type of indication (and indicates it on the LCD 204 to the user) to signify that a threshold value has been or is about to be exceeded, thus indicating proximity, and the μΰοηίτοΙΙεΓ 205 or the user may stop the Χ,Υ,Ζ,ΤΗ-motors 207 driving the manipulator 210 via a motion controller 208 (compare with 108a, 108b), thus preventing the manipulator to get damaged.

In measuring mode and especially at very low temperature measuring applications in the ultra-high vacuum chamber 202, the μΰοηΐτοΙΙεΓ 205 may connect the capacitive electrodes 201 to ground and disable the CDC 206 to avoid any charging of the sample, temperature increase of the sample, or any other unwanted effect from the Kapton electrodes on the sample. When not measuring, the capacitive electrodes 201 and the CDC 206 are automatically de-grounded and start to work again, detecting the proximity to close by objects.

In some embodiments the position (i.e. how far the manipulator 210 has traveled from a defined position inside the chamber) may be determined by the μΰοηίΓθΙΙεΓ 20 . In combination with the measured capacitance C_sens of the capacitive proximity sensor 201, this provides for that the manipulator 210 may safely be guided along a path in the chamber 202 that changes dimensions (exemplified by the first narrow part of the chamber 209 and then the broader chamber 202 in Figure 2). For example, in the first narrower part 209, the threshold value that the measured capacitance C_sens is measured against is set to a first value which corresponds to the more narrow wall of the chamber 209, while when arriving at the much broader part in the chamber 202 the threshold value that the measured capacitance C_sens is measured against is set to a second value which corresponds to the more broader part where the chamber walls are further away from the manipulator 210 and the capacitive proximity sensor 201. The threshold value may be manually changed by an operator or automatically changed by the controller 205. Thus, in this way the manipulator may be safely guided through geometrical complex chamber environments without the risk of damaging the manipulator 210 or the test sample fixed to the manipulator 210.

Figure 3 illustrates an example capacitive proximity sensor 301 mounted on a manipulator 303 in the vicinity of a sample holder 302. The example sensor 301 may, for example, be applied as any of the sensors 101a, 101b, and 201 of Figures la, lb, and 2, respectively. The example capacitive proximity sensor 301 may comprise two conducting wires, made e.g. of silver plated copper or any other suitable conductive material, around which Kaplan wires 304 are intertwined. The sensor is typically shaped around the sample holder 302 of the manipulator 303. The shaping may be circular, square, straight or any other suitable shape depending on the physical properties of the manipulator 303 and the sample holder 302.

Capacitive proximity sensors are, as such, known in the art. However, the prior art capacitive proximity sensors generally have one or more of the following problems. They may not be able to operate in high or ultra-high vacuum. They may not be able to operate in extremely high and/or extremely low temperatures. They may not be able to operate in large temperature spans. They may not be able to sense proximity to objects in two or more dimensions/directions. They may affect the sample (e.g. by charging) during the experimental phase.

Figure 4 illustrate an example method which may, for example, be carried out using any of the systems described in connection to Figures la, lb and 2.

The method may start in step 410 by mounting a capacity proximity sensor 101a, 101b, 201, 301 on a manipulator 110a, 110b, 210.

Then, the method comprises measuring, in step 420, a capacitance value provided by the capacity proximity sensor 101a, 101b, 201, 301. This step may, for example, be performed by a capacitance preparation unit 106a, 106b or a capacitance-to-digital converter 206.

The method comprises, in step 430, causing a stop of movement of the manipulator based on the capacitance value as has been explained and exemplified above.

The capacitance value may be passed on to a processor 105a, 105b, 205, and is compared it to a threshold value, as illustrated in sub-step 431. The threshold value may be dynamic or static. The threshold value may be set by an operator and/or a manufacturer.

If the capacitance value exceeds the threshold value (Y-step out from sub- step 432) the processor 105a, 105b, 205 may instruct the motion controller 108a, 108b, 208 to stop movement of the manipulator as illustrated in sub-step 433. The processor 105a, 105b, 205 may also display an indication in a LCD that the manipulator has been stopped.

If the capacitance value does not exceed the threshold value (N-step out from sub-step 432), the measuring continues in step 420.

More example features of a capacitive proximity sensor system will be explained hereafter with reference to Figures 5a-c and 6a-k. One example of a complete signal processing solution for capacitive proximity sensors is the AD7150 circuit from Analog Devices.

Figure 5a illustrates a block diagram of the AD7150. The AD7150 core comprises a high performance capacitance-to-digital converter (CDC) that allows for directly interfacing to a capacitive sensor, and it also houses other function that allows it to be used as a control system (compare with 130a, 130b, 205, 206) in a capacitive proximity sensor system.

In a typical scenario, the AD7150 provides signal processing for the capacitive proximity sensor and uses capacitance-to-digital converter (CDC) technology which combines features important for interfacing to real sensors. In this typical scenario, the internal registers of AD7150 (compare with 206) should be programmed by the microcontroller (compare with 205) with user-defined settings, and the data and status of the sensor can be read from the AD7150.

In this example, comparators compare the digitized signal with thresholds, either fixed or dynamically adjusted by the on-chip adaptive threshold algorithm engine. Thus, the outputs indicate a defined change in the input sensor capacitance.

The AD7150 also integrates an excitation source and an on-chip digital-to- capacitance converter (CAPDAC) for the capacitive inputs, an input multiplexer, a complete clock generator, a power-down timer, a power supply monitor, control logic, and an I2C®-compatible serial interface for configuring the part and accessing the internal CDC data and status, if required in the system. The internal registers of the AD7150 (compare with 206) can be programmed, for instance with user-defined settings, by a microcontroller (compare with 205).

The AD7150 is designed for floating capacitive sensors. Therefore, both Cx (wherein Cx corresponds to the previously mentioned C_sen_se) plates typically need to be isolated from ground or any other fixed potential node in the system.

Figure 5b shows a simplified functional block diagram of an example capacitance-to-digital converter. The converter consists of a second-order sigma delta (Σ-Δ), charge balancing modulator and a third-order digital filter. The measured capacitance Cx is connected between an excitation source and the Σ-Δ modulator input. The excitation signal is applied on Cx during the conversion, and the modulator continuously samples the charge going through Cx. The digital filter processes the modulator output, which is a stream of 0s and Is containing the information in 0 and 1 density. The data is then processed by the adaptive threshold engine and output comparators (compare with Figure 5a). In some embodiments, the data can be also read and/or written through the serial interface, with or without using the output comparators of the AD7150. Figure 5c illustrates an example use of CAPDAC. The AD7150 CDC core maximum full-scale input range is 4 pF. However, the system can accept a higher capacitance on the input, and an offset (non-changing component) capacitance of up to 10 pF can be balanced by the programmable on-chip CAPDAC. The CAPDAC can be understood as a negative capacitance connected internally to the CTN pin. The CAPDAC has a 6-bit resolution and a monotonic transfer function. Figure 5 c shows how to use the CAPDAC to shift the CDC 4 pF input range to measure capacitance between 10 pF and 14 pF.

Figures 6a-6d illustrate comparator and threshold modes. The AD7150 comparators and their thresholds can be programmed to operate in several different modes. In an adaptive mode, the threshold is dynamically adjusted and the comparator output indicates fast changes and ignores slow changes in the input (sensor) capacitance. Alternatively, the threshold can be programmed as a constant (fixed) value, and the output then indicates any change in the input capacitance that crosses the defined fixed threshold.

The AD7150 logic output (active high) indicates either a positive or a negative change in the input capacitance, in both adaptive and fixed threshold modes (see Figure 6a illustrating a positive threshold mode that indicates positive change in input capacitance and Figure 6b illustrating a negative threshold mode that indicates negative change in input capacitance).

Additionally, for the adaptive mode, the comparators can work as window comparators, indicating input either inside or outside a selected sensitivity band (see Figure 6c illustrating in-window (adaptive) threshold mode and Figure 6d illustrating out-window (adaptive) threshold mode).

In an adaptive mode, the thresholds may be dynamically adjusted, ensuring indication of fast changes (for example, an object moving close to a capacitive proximity sensor) and eliminating slow changes in the input (sensor) capacitance, usually caused by environment changes such as humidity or temperature or changes in the sensor dielectric material over time (see Figure 6e illustrating adaptive threshold indicating fast changes and eliminating slow changes in input capacitance).

The adaptive threshold algorithm may be based on an average calculated from previous CDC output data. The response of the average to an input capacitance step change (more exactly, the response to the change in the CDC output data) may be an exponential settling curve, which can be characterized by the following equation: Average ( ) = Average ( 0 ) + Change ( l-exp( N TimeConst ) ), where Average ( N ) is the value of averaging over N complete CDC conversion cycles after a step change on the input, Average ( 0 ) is the value before the step change, TimeConst can be selected in the range between 2 and 65,536, in steps of power of 2, by programming the ThrSettling bits in the setup registers (see figure 6f illustrating a data average response to data step change).

In adaptive threshold mode, the output comparator threshold may be set as a defined value (sensitivity) above the data average, below the data average, or both, depending on the selected threshold mode of operation (see Figure 6g). The sensitivity value may be programmable in the range 0 to 255 LSBs of the 12-bit CDC converter.

In adaptive threshold mode, the comparator may feature a hysteresis function (see figure 6h). The hysteresis may be fixed to one-fourth of the threshold sensitivity and can be programmed on or off. The comparator typically does not have any hysteresis in the fixed threshold mode.

In case of a large, long change in the capacitive input, when the data average adapting to a new condition may take too long, a timeout can be set. The timeout may become active (counting) when the CDC data goes outside the band of data average ± sensitivity. When the timeout elapses (a defined number of CDC conversions is counted), the data average (and thus the thresholds), is forced to follow the new CDC data value immediately (see Figure 6i). The timeout can be set independently for approaching (for change in data toward the threshold) and for receding (for change in data away from the threshold). See Figure 6j and Figure 6k.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" "comprising," "includes" and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should be regarded as illustrative rather than restrictive, and not as being limited to the particular embodiments discussed above. The different features of the various embodiments of the invention can be combined in other combinations than those explicitly described. It should therefore be appreciated that variations may be made in those embodiments by those skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims

1. A capacitive proximity sensor system (100a, 100b, 200) connectable to a movable manipulator (110a, 110b, 210, 303) adapted to transfer samples between experimental station chambers (102a, 102b, 202), the capacitive proximity sensor system comprising:

a capacitive proximity sensor (101a, 101b, 201, 301) mountable on the manipulator and adapted to provide a capacitance value based on a distance (120a, 120b) from the capacitive proximity sensor to an object (121a, 121b) with which contact is to be avoided; and

a control system (130a, 130b, 205, 206) adapted to cause a stop of movement of the manipulator based on an alteration of the capacitance value.

2. The capacitive proximity sensor system (100a, 100b, 200) of claim 1 wherein at least one of the experimental station chambers (102a, 102b, 202) is a vacuum chamber or an ultra-high vacuum chamber.

3. The capacitive proximity sensor system (100a, 100b, 200) of any of claims 1 through 2 wherein the capacitive proximity sensor (101a, 101b, 201, 301) comprises at least two capacitive electrodes.

4. The capacitive proximity sensor system (100a, 100b, 200) of claim 3 wherein the at least two capacitive electrodes comprises two parallel metallic rings (201, 301) mounted in association with a sample holder (211, 302) of the manipulator.

5. The capacitive proximity sensor system (100a, 100b, 200) of any of claims 1 through 4 wherein the capacitive proximity sensor (101a, 101b, 201, 301) is adapted to provide the capacitance value such that a first capacitance value is higher than a second capacitance value if a first distance associated with the first capacitance value is smaller than a second distance associated with the second capacitance value.

6. The capacitive proximity sensor system (100a, 100b, 200) of any of claims 1 through 5 wherein the control system (130a, 130b, 205, 206) is adapted to compare the capacitance value to a threshold value and cause the stop of movement of the manipulator when the capacitance value exceeds the threshold value.

7. The capacitive proximity sensor system (100a, 100b, 200) of claim 6 wherein the control system comprises a processor (105 a, 105b, 205) adapted to compare the capacitance value to the threshold value and cause the stop of movement of the manipulator when the capacitance value exceeds the threshold value.

8. The capacitive proximity sensor system (100a, 100b, 200) of claim 7 wherein the processor (105a, 105b, 205) is further adapted to cause rendering of an indication in a user interface (104a, 104b, 204) when the capacitance value exceeds the threshold value.

9. The capacitive proximity sensor system (100a, 100b, 200) of any of claims 6 through 8 wherein the threshold value is dynamically adjustable based on one or more of a chamber geometry, a sample holder geometry, a sample holder material, a sample geometry, and a sample material.

10. The capacitive proximity sensor system (100a, 100b, 200) of any of claims 1 through 9 wherein the control system (130a, 130b, 205, 206) comprises a capacitance preparation unit (106a, 106b, 206) adapted to measure the capacitance value.

11. The capacitive proximity sensor system (100a, 100b, 200) of any of claims 1 through 10 wherein the control system (130a, 130b, 205, 206) is further adapted to connect the capacitive proximity sensor (101a, 101b, 201, 301) to ground (131) in an operational mode of the experimental station wherein the manipulator (110a, 110b, 210, 303) is stationary.

12. A method of guiding a movable manipulator (110a, 110b, 210, 303) inside an experimental station chamber (102a, 102b, 202), wherein the manipulator is adapted to transfer samples between experimental station chambers, the method comprising operating a capacitive proximity sensor system (130a, 130b, 205, 206) comprising a capacitive proximity sensor (101a, 101b, 201, 301) and a control system (130a, 130b, 205, 206) by:

measuring (420) a capacitance value provided by the capacitive proximity sensor mounted on the manipulator, wherein the capacitance value is based on a distance (120a, 120b) from the capacitive proximity sensor to an object (121a, 121b) with which contact is to be avoided; and

causing (430), by the control system, a stop of movement of the manipulator based on an alteration of the capacitance value.

13. The method of any claim 12 further comprising comparing (431) the capacitance value to a threshold value, and wherein the stop of movement of the manipulator is caused (433) when the capacitance value exceeds the threshold value (432).

14. The method of claim 13 further comprising dynamically adjusting the threshold value based on one or more of a chamber geometry, a sample holder geometry, a sample holder material, a sample geometry, and a sample material.

15. The method of any of claims 12 through 14 further comprising connecting the capacitive proximity sensor to ground in an operational mode of the experimental station wherein the manipulator is stationary.