Patent ID: 12228426

DETAILED DESCRIPTION

In the following description, numerous specific details are explained by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well-known methods, procedures, systems, components, and/or circuitry have been described at a high-level, without details, in order to avoid unnecessary obscuring aspects of the present teaching.

The present disclosure describes method, system, and programming aspects of an effective tactile sensor. The method and system as disclosed herein aim at improving a user's contact or touch detection experience.

A giant magnetoresistance (GMR) sensor, along with other magnetoresistance (AMR: anisotropic magnetoresistance; TGMR: tunneling giant magnetoresistance) sensors, provides an elevated level of precision in detecting magnetic field and its subtle variations. It has been used in magnetic storage devices, medical devices such as pacemakers, and in magnetic particle labelled biological or chemical process detection applications. When magnetic objects are in close proximity to these magnetic sensors, the magnetic field generated by them can be sensed by these sensors with exceedingly high precision. With a pre-configured sensor layout, the distance between the sensor and magnetic object as well as their relative position information can be derived by solving corresponding physics equations. An array of magnetic sensors can be placed on the same chip on a printed circuit board (PCB) hosting other electronic components to form a fully functional sensor device.

According to various embodiments of the present teaching, the method and system to create a tactile sensor is disclosed. A plurality of magnetic sensors is configured for sensing magnetic fields generated by ferromagnets present in close proximity to the magnetic sensors. Each of the ferromagnets is embedded in an elastomer matrix. When the elastomer matrices make physical contact with other solid surfaces, they deform and displace the ferromagnets embedded in them. The magnetic sensors detect the magnetic field change for each ferromagnet before and after contact occurs and send data to the processing device to quantify the contact. The device can provide contact direction, strength of encountered force, as well as their distribution information across the tactile sensors using predefined algorithms.

Furthermore, contact or touch detection device formation in the present teaching utilizes a typical semiconductor processing approach. There are at least two major advantages of this approach compared to others. The first advantage is manufacturability. Magnetic sensors are formed on generic substrates such as silicon or PET (polyethylene terephthalate), followed by spin-coating of two or more layers of elastomers with a ferromagnet formed in between. The height, width, and shape of the ferromagnet can be controlled as it is made in situ using either physical deposition techniques or electrochemical approaches (plating). The second advantage is the small footprint of the entire device. Unlike other methods by which magnets and elastomer matrices are typically assembled, which usually limit their sizes to the millimeter scale, the approach disclosed here can produce devices at the micrometer level or even the nanometer scale. These two advantages make it a good fit for large volume applications, such as for robotics, at a low cost.

Additional novel features will be explained in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings. The novel features of the present teaching may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations explained in the detailed examples discussed below.

FIG.1(PRIOR ART) depicts an exemplary structure and characteristic of a GMR sensor. A GMR sensor is one type of magnetic field sensors that utilize a giant magnetoresistance effect: when there are two magnetic layers separated by one thin nonmagnetic layer, their relative magnetization directions (parallel or antiparallel) result in different resistance states. As shown inFIG.1, a GMR sensor includes three layers: two ferromagnetic layers112,114comprised of cobalt (Co) separated by one nonmagnetic layer113comprised of copper (Cu). A resistance corresponding to parallel magnetization104is smaller than a resistance corresponding to antiparallel magnetization102.

To utilize the GMR effect, a spin valve structure is usually built by fixing one layer's magnetization and letting the other one rotate freely. The fixed layer is called the reference layer and the rotatable layer is called the freelayer. The reference layer may be confined by an antiferromagnetic layer (comprising PtMn or IrMn) directly or indirectly through a so-called SAF (synthetic antiferromagnetic) structure. When the spin valve GMR sensor senses a magnetic field, the freelayer will rotate so that GMR resistance is changed. Typically, a static biasing current is applied through the GMR structure, so a voltage change is measured instead of the resistance.

Preparation of current perpendicular to plane (CPP) GMR sensors may comprise bottom contact deposition, GMR multilayer stack deposition, top contact deposition, and sensor structure patterning involving photolithography, iron milling and insulator backfill, etc. Preparation of current in plane (CIP) GMR sensors may comprise GMR multilayer stack deposition, top contact deposition, and sensor structure patterning involving photolithography, iron milling and insulator back fill, etc.

FIG.2illustrates an exemplary configuration of the tactile sensor setup according to an embodiment of the present teaching. As shown inFIG.2, at202, a set of magnetic sensors212are formed on the base201(only viewable at the cross-section view204). There are four magnetic sensors shown in this illustration, but it should be apparent to those skilled in the art that the quantity can be two, three or more depending on the detection algorithm. The sensors are covered by a basecoat elastomer layer203. Ferromagnet222sits on top of203and is covered by an overcoat elastomer layer205. Here205is conformally covering so it follows the ferromagnet's topography.204is the cross-section view of202for clarity.

Therefore, in202, there has been a ferromagnet222embedded in an elastomer matrix comprised of layers203and205. The magnetic sensor set212can detect the magnetic field generated by ferromagnet222, which is in proximity to the magnetic sensors. At202, the resistance or voltage signal at magnetic sensor set212is determined by the distances between ferromagnet222and the magnetic sensors, as well as the magnetic moment of the ferromagnet222itself.

The spacing between ferromagnet222and magnetic sensors is determined by the thickness of elastomer layer203, and the thickness of the seedlayer used to either sputter, evaporate, or plate the ferromagnet, and the lateral spacing between the magnetic sensors, as well as the size of the ferromagnet222itself. With the exception of the thickness of elastomer layer203, the other spacing elements are fixed so they can be considered constant during the touch or contact process and should have negligible impact to sensor signal change.

FIG.3illustrates another exemplary configuration of the tactile sensor setup, with magnetic sensor set312, elastomer basecoat layer303, elastomer overcoat layer305and ferromagnet322according to an embodiment of the present teaching. The main difference between the configurations inFIG.2andFIG.3is that the elastomer overcoat layer305has a flat top instead of following the topography created by the ferromagnet formation. This difference affects the device's sensitivity to compressive force and shear force, as explained in the following description.

FIG.4explains the working principle of the tactile sensor device described byFIG.2. When the device is freestanding as shown in402, the magnetic sensors detect the magnetic field generated by ferromagnet422and record it as the initial state. The initial state data can be stored by a non-transitory machine-readable medium through the printed circuit board440, which connects with or resides in a system such as a robotic arm450-1, a computer such as450-2, or a robot450-3.

In the case of a compressive force being applied to the tactile device, as shown by404, one object460touches the elastomer overcoat layer405from above, deforming both405itself as well as the elastomer basecoat layer403. Magnetic sensors sit within a rigid layer (typically made of alumina), so their positions are not affected by the compressive force. The deformation of405and403causes the ferromagnet422to move vertically downwards, bringing it closer to the magnetic sensors. The magnetic field sensed by the magnetic sensors412is then increased, causing them to report a stronger signal to the PCB440and the detection systems450.

In the case of a shear force being applied to the tactile device, as shown by406, another object470is touching the elastomer overcoat layer405from the left side, deforming405towards the right. The deformation of405causes the ferromagnet422to move laterally towards the right side, bringing it closer to some of the magnetic sensors while moving it away from the others. The magnetic field sensed by magnetic sensors412increases if their distance from the ferromagnet decreases and decreases if their spacing to the ferromagnet is increased. Therefore, the magnetic sensors412report different signal changes to the PCB440and the detection systems450.

FIG.4illustrates two simplified cases of applying compressive force and shear force, independently. It should be apparent to those skilled in the art that in many cases both compressive force and shear force co-exist or are applied with different ratios to the elastomer layers. The deformation of the elastomer layers and the displacement of the ferromagnet will be a combined result. That is one of the reasons why more than one magnetic sensor is needed to detect the magnetic field changes caused by the ferromagnet displacement, so compressive and shear components of the applied force can both be quantified.

InFIG.4the conformal formation of the elastomer overcoat layer405creates a protruded top right above the ferromagnet422. This helps to increase device sensitivity to shear force as illustrated in406, though may add noise when pure compressive force is applied if the overcoat layer405around the ferromagnet422is not uniformly deformed in404. The impact may be calibrated and saved in the non-transitory machine-readable medium.

FIG.5explains the working principle of the tactile sensor device described byFIG.3. When the device is freestanding as illustrated in502, the magnetic sensors detect the magnetic field generated by ferromagnet522and record it as the initial state. The initial state data can be stored by a non-transitory machine-readable medium through the printed circuit board540, which connects with or resides in a system such as a robotic arm550-1, or a computer550-2, or a robot550-3.

In the case of a compressive force being applied to the tactile device, as shown by504, one object560touches the elastomer overcoat layer505from above, deforming both505itself as well as the elastomer basecoat layer503. Magnetic sensors sit within a rigid layer (typically made of alumina), so their positions are not affected by the compressive force. The deformation of505and503causes the ferromagnet522to move vertically downwards so it gets closer to the magnetic sensors. The magnetic field sensed by the magnetic sensors512is then increased, so they report a stronger signal to the PCB540and the detection systems550.

In the case of a shear force being applied to the tactile device, as shown by506, another object570is touching the elastomer overcoat layer505and/or basecoat layer503from the left side, deforming505and503towards the right. The deformation of505and503mostly causes the ferromagnet522to move laterally towards the right side, bringing it closer to some of the magnetic sensors while moving it away from the others. The magnetic field sensed by magnetic sensors512increases if their distance from ferromagnet522decreases and decreases if their spacing to the ferromagnet is increased. Therefore, the magnetic sensors512report different signal changes to the PCB540and the detection systems550.

FIG.5illustrates two simplified cases of applying compressive force and shear force independently. It should be apparent to those skilled in the art that in many cases both compressive force and shear force co-exist or are applied with different ratios to the elastomer layers. The deformation of the elastomer layers and the displacement of the ferromagnet will be a combined result of these two forces.

InFIG.5the flat top of the elastomer overcoat layer505helps to improve the detection sensitivity and accuracy of detecting a compressive force as illustrated in504. However, without the protruded portion as shown inFIG.4by406, the tactile sensor device is less sensitive to shear force as illustrated in506. The impact may be calibrated and saved in the non-transitory machine-readable medium.

FIG.6illustrates an exemplary process flow of forming the tactile sensor as illustrated byFIG.2, according to an embodiment of the present teaching. At602, the base substrate611used to fabricate the tactile sensor can be made of rigid materials such as silicon, GaAs, AlTiC, or flexible substrates such as polyimide, polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN), polydimethyl siloxane (PDMS), etc.

At604, on base substrate611, a plurality of contact pads and magnetic sensors613are obtained to make a chip. In accordance with various embodiments, magnetic sensors613may be comprised of GMR sensors, AMR (anisotropic magnetoresistance) sensors, TGMR (tunneling giant magnetoresistance) sensors, Hall sensors, etc. The magnetic sensors are inside the chip and the plurality of contact pads are around the chip edges. In accordance with one embodiment, the chip is protected from the following process steps by coating it with a thin dielectric material such as alumina or other nonmagnetic protection layers.

At606, the chip with magnetic sensors is coated with an elastomer basecoat layer615. In accordance with various embodiments, elastomer basecoat material615may be comprised of natural rubbers, styrene-butadiene block copolymers, polyisoprene, polybutadiene, ethylene propylene rubber, ethylene propylene diene rubber, silicone elastomers, fluoroelastomers, polyurethane elastomers, and nitrile rubbers, etc.

At608, a thin layer of seed material is placed on the elastomer basecoat if electrochemical deposition is used to obtain the ferromagnet later. This seed layer provides a current conduction path during the electrochemical deposition process and may be removed from areas other than those under the ferromagnet.

At610, standard photolithography process is used to prepare for the electrochemical deposition of the ferromagnet. Holes in the size range of tens of nanometers to sub-millimeters are formed by patterning the photoresist layer with masks. The depth of the holes is in the range of hundreds of nanometers to tens of micrometers.

At612, ferromagnet617is obtained through electrochemical deposition or plating. It can be made of various different materials, such as soft magnetic materials including iron, cobalt, nickel, and their alloys or permanent magnetic materials such as NbFeB, SmCo5, FePt, CoPt, etc. The top-down view shape of the ferromagnet can be circular, rectangular, square, or other shapes.

At614, photoresist is removed to prepare for the next step. In case the photoresist material is used as the elastomer, it may stay as is or be trimmed to control its final thickness.

At616, an elastomer overcoat layer619is placed on top of the ferromagnet. This elastomer layer619may use the same material as the elastomer basecoat layer615or may be different from it. The coating process is chosen to be conformal so that the area directly above the ferromagnet is protruded over the other areas.

FIG.7illustrates another exemplary way of constructing the tactile device as illustrated byFIG.3, according to an embodiment of the present teaching. A major difference fromFIG.6is that the step of coating the elastomer overcoat may involve a planarization step to keep the finished top flat.

It should be apparent to those skilled in the art that the materials used inFIG.7may be the same or different from those inFIG.6. For example, the elastomer basecoat layer715and overcoat layer719may be different from the cases of615and619inFIG.6in order to optimize or modify device performance.

FIG.8illustrates an exemplary process of tactile sensor data collection and processing, according to an embodiment of the present teaching. The tactile sensor illustrated inFIG.2is used. A similar process can be used with the tactile sensor illustrated inFIG.3.

At802, the magnetic sensors detect the magnetic field generated by the ferromagnet and save the initial state signal to a non-transitory machine-readable medium before contact or touch occurs. The data is transmitted to a computer822through a PCB840and displayed on a screen.

At804, when an object is touching the tactile device from the top, applying a compressive force to the elastomers, the magnetic sensors detect a stronger magnetic field, as the ferromagnet is displaced towards the sensors. Computer822processes the data together with other information (like ambient temperature) and translates magnetic field strength change into elastomer deformation. On the computer screen, the resistance values decrease, as GMR sensors have more parallel magnetizations at high field.

At806, when an object is touching the tactile sensor from the left side, a shear force is applied to the elastomers, so magnetic sensors on the left side detect a reduced magnetic field while magnetic sensors on the right side detect an increased magnetic field due to the ferromagnet being displaced towards the right side. Computer822processes the data together with other information (like ambient temperature) and translates magnetic field strength change into elastomer deformation. On the computer screen, the resistance values are reduced for magnetic sensors on the right side and increased for magnetic sensors on the left side, as their magnetizations are more antiparallel for a reduced magnetic field.

FIG.9illustrates a diagram of an exemplary system configuration of performing signal collection, processing, and storage, according to an embodiment of the present teaching. The tactile sensor device may have multiple magnetic sensors that are connected to a printed circuit board (PCB)950via the contact pads on the chip. The PCB transmits the magnetic sensor signal to a processor910, which also receives temperature information from a temperature sensor. There is a signal buffer that stores magnetic sensor signal versus time. The processed signals may be in the form of the ferromagnet's displacement vector (both magnitude and direction) and are transmitted to an external circuit930.

FIG.10is a flowchart of an exemplary process of performing signal collection, processing, data storage using the tactile sensor system. At1002, before contact or touch occurs, both the magnetic sensors and the temperature sensor collect their own initial state data and send it to the processor and a non-transitory machine-readable medium to process and store at1004. Upon contact or touch, magnetic sensors collect new signal levels at1006and send them to the processor to determine the displacement vector of the ferromagnet using elastomer temperature calibration curves at1008. Depending on the requirement of practical application, the system may receive a signal collection frequency request at1010and perform a remeasure of the signal levels from all the magnetic sensors as well as the temperature sensor at1012accordingly. The remeasured data is sent to1008and gets processed into the displacement vector of the ferromagnet as a function of time. The displacement versus time data is then transmitted to and stored at1014.

The above exemplary descriptions focus on one set of magnetic sensors to detect signals from one ferromagnet embedded in an elastomer matrix for contact or touch quantification. It should be apparent to those skilled in the art that the setup may be extended to arrays of tactile sensor devices on the same or different printed circuit boards (PCB's) to have multi-point contact or touch detection. The number of magnetic sensors and their layout on the substrates can be the same or different for each tactile device unit. Similarly, the materials used for the substrates, elastomer matrixes and the ferromagnets can be the same or different for each tactile device unit.

To implement the present teaching, computers or robotics may be used as the hardware platform(s) for one or more of the elements described herein. The hardware elements, operating systems, and programming languages of such computers are conventional in nature, and it is presumed that those skilled in the art are adequately familiar with them to adapt those technologies to implement the processes described here. A computer with user interface elements may be used to implement a personal computer (PC) or other types of workstations or terminal devices, although a computer may also function as a server if appropriately programmed. It is believed that those skilled in the art are familiar with the structure, programming, and general operation of such computer equipment and as a result the drawings should be self-explanatory.

All or portions of the software may at times be communicated through a network such as the Internet or various other telecommunication networks. Such communications, for example, may enable loading of the software from one computer or processor into another. Thus, other types of media that may bear the software elements include optical, electrical, and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air links. The physical elements that carry such waves, such as wired or wireless links, optical links, or the like, may also be considered as media bearing the software. As used herein, unless restricted to tangible “storage” media, terms such as computer or machine “readable medium” refer to any medium that participates in providing instructions to a processor for execution.

Those skilled in the art will recognize that the present teachings are amenable to a variety of modifications and/or enhancements. For example, although the implementation of various components described above may be embodied in a hardware device, it can also be implemented as a software only solution—e.g., an installation on an existing server. In addition, the units of the host and the client nodes as disclosed herein can be implemented as a firmware, firmware/software combination, firmware/hardware combination, or a hardware/firmware/software combination.

While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.