WO2019232198A1 - Haptic feedback sensor and method of making the same - Google Patents

Abstract

A normal force sensor includes first and second sensing surfaces including graphene and separated by an air gap, the first and second sensing surfaces electrically connected to first and second conducting elements. Methods of making a normal force sensor are also described.

Description

HAPTIC FEEDBACK SENSOR AND METHOD OF MAKING THE SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to ETS provisional patent application no. 62/677,709 filed on May 30, 2018, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

This invention was made with government support under Grant Number EBO 19473, awarded by the National Institutes of Health. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Tactile normal force sensors are essential in haptic feedback systems to reduce excessive grip force during robotic surgical operations. A human surgeon would easily be able to sense whether an instrument is meeting too much or too little resistance during surgery, and take corrective action. By contrast, an electromechanically guided instrument without the benefit of haptic feedback has no way to convey back to the operator the level of resistance it encounters.

Commercially available piezoresistive force sensors are expensive and cannot be readily used in biomedical applications and highly customized devices due to their standardized packaging, limited dynamic range, and limited resolution. Additive manufacturing technology (also sometimes referred to as 3D printing) provides for much greater customization of individual parts, as well as rapid prototyping. Although most often used to print plastic parts from ABS or other polymer filaments, recent advancements in 3D printing allow printing of objects from graphene filaments, which are slightly conductive.

Thus, there is a need in the art for a small, inexpensive, and customizable normal force sensor for use in robotic surgery applications, in order to make haptic feedback more widely available and provide for better patient outcomes. The present invention satisfies this need.

SUMMARY OF THE INVENTION

In one aspect, a normal force sensor comprises first and second sensing surfaces comprising graphene and separated by an air gap, the first and second sensing surfaces electrically connected to first and second conducting elements. In one embodiment,

the first and second sensing surfaces are configured to measure a force applied to any of the sensing surfaces based on an electrical resistance between the two conducting elements. In one embodiment, the relationship between the electrical resistance and the force applied is substantially logarithmic. In one embodiment, the relationship between the electrical resistance and the force applied is substantially linear. In one embodiment, the graphene comprises a conductive graphene filament. In one embodiment, the first and second conducting elements comprise copper. In one embodiment, the sensor further comprises an anchoring element configured to mount the normal force sensor to a surgical instrument.

In another aspect, a method of making a normal force sensor comprises the steps of depositing a quantity of a first filament having a first conductivity in a pattern comprising a base, an anchoring channel, and a partial first electrode layer, the partial first electrode layer including a first cavity; pausing the additive manufacturing device; inserting a first conducting member in the cavity; resuming the additive manufacturing device and printing over the cavity to envelop the first conducting member; printing a supporting structure surrounding an air gap; printing a partial second electrode layer including a second cavity; pausing the additive manufacturing device; inserting a second conducting member in the cavity; and resuming the additive manufacturing device and printing over the cavity to envelop the second conducting member; and printing a contact surface. In one embodiment, the first filament comprises graphene. In one embodiment, the first and second conducting members comprise copper. In one embodiment, the first and second conducting members comprise conductive foam.

In another aspect, a method of making a normal force sensor comprises the steps of depositing a quantity of a first filament having a first conductivity in a pattern comprising a base, an anchoring channel, and a partial first electrode layer, the partial first electrode layer including a first cavity; printing with a second filament having a second conductivity in a pattern comprising a first conducting member into the first cavity; printing with the first filament over the cavity to envelop the first conducting member; printing with the first filament a supporting structure surrounding an air gap; printing with the first filament a partial second electrode layer including a second cavity; printing with the second filament having a second conductivity in a pattern comprising a second conducting member into the second cavity; printing with the first filament over the second cavity to envelop the second conducting member; and printing a contact surface. In one embodiment, the first conductivity is less than the second conductivity. In one embodiment, the first filament comprises graphene. In one embodiment, the second filament comprises copper. In one embodiment, the second filament comprises Electrifi. BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing purposes and features, as well as other purposes and features, will become apparent with reference to the description and accompanying figures below, which are included to provide an understanding of the invention and constitute a part of the specification, in which like numerals represent like elements, and in which:

Figure 1 is a CAD model of an exemplary normal force sensor of the present invention;

Figure 2 is a photograph of an exemplary normal force sensor of the present invention;

Figure 3 is a photograph of an exemplary normal force sensor of the present invention;

Figure 5 is a diagram of a method of the present invention;

Figure 6 is a photograph of a testing procedure for devices of the present invention;

Figure 7 is a graph of measured ADC values vs. asserted force; and

Figure 8 is a graph of measured ADC values over time during a testing procedure.

DETAILED DESCRIPTION

It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in related systems and methods. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art. Unless defined otherwise, all 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. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, exemplary methods and materials are described.

As used herein, each of the following terms has the meaning associated with it in this section.

The articles“a” and“an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example,“an element” means one element or more than one element.

“About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate.

Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, 6 and any whole and partial increments therebetween. This applies regardless of the breadth of the range. Elements of the invention refer to additive manufacturing (AM) or 3D printing.

Although certain examples may be presented using fused filament fabrication (FFF) or fused deposition modelling (FDM), it is understood that some or all of the components of

embodiments of the present invention may be manufactured using other AM techniques, including but not limited to stereolithography (SLA), digital light processing (DLP), selective laser sintering (SLS), selective laser melting (SLM), electronic beam melting (EBM), digital manufacturing and laminated object manufacturing (LOM). These methods variously“build” a three-dimensional physical model, one layer at a time, providing significant efficiencies in rapid prototyping and small-batch manufacturing. AM also makes possible the manufacture of parts with features that conventional subtractive manufacturing techniques (for example CNC milling) are unable to create, such as internal channels or internal hollow spaces.

Similarly, although embodiments of the present invention may be described as printed from a polymer or graphene filament, alternative materials are also contemplated, including but not limited to polymers, including syntactic foam and ABS; metals, including copper, aluminum, stainless steel, and titanium; minerals, including marble, granite, or quartz; tissue, including muscle tissue, bone, or cartilage; or other materials, including ceramics, composite materials, biopolymers, or cells.

Referring now to Figure 1, a partial view of an exemplary sensor of the present invention is shown. The depicted 3D model may be printed for example with a mildly conductive filament, such as graphene filament. The model includes a first electrode layer 101, and a second electrode layer 102, separated by an air gap 105. The distal surface of the second electrode layer 102 includes a contact surface 103, which is the surface whose normal force will be measured by the sensor. The device further includes an anchoring channel 104, which is hollow and runs beneath the first electrode layer 101. The anchoring channel may be used to affix the sensor to a working surface of a robotic surgical instrument, for example one side of a pair of forceps. In one exemplary use case, the sensor of Figure 1 may be positioned on a pair of forceps such that the first gripping member of the pair of forceps runs through the anchoring channel 104, and the second gripping member of the pair of forceps, when closed, pushes against the contact surface 103. In this way, if a soft or spongy material is held between the forceps with the two gripping members separated by a given distance, the force measured by the sensor will be less than if a rigid material is held between the forceps with the two gripping members separated by the same distance.

In some embodiments, the pressures measured range from 0-20 Newtons. In other embodiments, the pressures measured range from 0-10 Newtons, 0-5 Newtons, or 0-40 Newtons. The measurement systems of the present invention may be configured to measure forces exerted on the sensor in increments of about 5 Newtons, about 1 Newton, about 0.5 Newtons, about 0.25 Newtons, or about 0.1 Newtons. The sensor may be configured to have a resistance between the first and second conducting members in a range from 10 W to 1 MW, 50 W to 100 kW, 100 W to 20 kW, or 300 W to 8 kW. Although certain force and resistance ranges and measurement granularities are listed, it is contemplated that larger ranges of force and resistance may be measured, at higher granularities.

Although the exemplary embodiment is described as configured for use with a forceps, for example a ProGrasp forceps for the Da Vinci Si robotic surgical system, it is contemplated that embodiments of the present invention may also be configured for use with other robotic surgical instruments, including but not limited to surgical instruments from Comidus Vascular Robotics, Hansen Medical, Intuitive Surgical, Mazorrobotics, Medrobotics, Smith & Nephew, Stereotaxis, Stryker, Titanmedical, Transenterix, Simmerbiomet, and RAVEN Surgical Robotic Systems.

With reference now to Figure 2, a prototype of an exemplary sensor is shown aside a penny for scale. The sensor is shown with contact surface 103 facing up, and with two conducting elements 201 and 202 electrically connected to the first and second electrode layers. The configuration of this exemplary embodiment is further illustrated with reference to Figure 3, in which a head-on view of the prototype sensor is shown. From this view, it is clear that the first conducting element 201 is partially embedded in, and electrically connected to first electrode layer 101, and that the second conducting element 202 is partially embedded in, and electrically connected to second electrode layer 102. In this configuration, the electrical resistance between the first conducting element 201 and the second conducting element 202 is measurably reduced when pressure is applied to the contact surface 103. Suitable materials for use in a conducting element of the present invention include, but are not limited to, copper, silver, conductive 3D printing filaments, or electrically conductive foam.

With reference now to Figure 4A - Figure 4C, another exemplary embodiment of a sensor is shown. In the perspective view shown in Figure 4A, the contact surface 401 is visible and first and second conductive elements 402 and 403 are shown positioned in corresponding cavities in sensor housing 400. The depicted conductive elements may in some embodiments be produced by 3D printing, and may therefore be fixedly attached to the sensor housing 400, although in some embodiments the conductive elements may be removable. In the head-on view of Figure 4B, contact hook 404 is shown, which may be used to mount the sensor assembly, for example to a surgical instrument. With reference to exploded view 4C, in the depicted embodiment, the conductive elements 402 and 403 include corresponding electrodes 412 and 413. In embodiments where the electrodes and conductive elements are removable, the sensor housing 400 may be produced with cavities from which the electrodes into which the electrodes may be inserted or removed. In embodiments where the electrodes and conductive elements are fixedly attached to the sensor housing, for example when the electrodes and/or conductive elements are 3D printed as a part of the sensor assembly, the electrodes may be printed directly on top of part of the sensor housing.

The change in resistance may be measured by a variety of means, including but not limited to running a small current through the resistance and measuring the voltage drop.

Induced voltage drops may in turn be measured over time by using an analog to digital converter (ADC). The measured voltages may be translated directly to an exerted mechanical force. In some embodiments, the relationship between the measured voltage and the exerted force is linear. In other embodiments, the relationship is logarithmic. In other embodiments, the measured voltage is compared to one or more thresholds to determine whether or not any force is being exerted on the contact surface.

Some embodiments of the present invention comprise a method of making an additive manufactured sensor. In one exemplary embodiment, shown in Figure 5, a method of the present invention comprises the steps of, with an additive manufacturing device, step 501, depositing a quantity of a first filament having a first conductivity in a pattern comprising a base, an anchoring channel, and a partial first electrode layer, the partial first electrode layer including a first cavity; step 502, pausing the additive manufacturing device and inserting a first conducting member in the cavity; step 503, resuming the additive manufacturing device and printing over the cavity to envelop the first conducting member; step 504, printing a supporting structure surrounding an air gap and a partial second electrode layer including a second cavity; step 505, pausing the additive manufacturing device and inserting a second conducting member in the cavity; step 506, resuming the additive manufacturing device and printing over the cavity to envelop the second conducting member; and step 507, printing a contact surface. The first and second conducting members may comprise any conductive material, including but not limited to copper and silver. By inserting the first and second conducting members during the

manufacturing process, the conducting members are assured secure adhesion with the printed filament. In some embodiments, the first and second conducting members comprise one or more anchoring elements, for example holes, which can be secured to printed pegs within the sensor and then covered over, in order to provide increased strain tolerance.

In some embodiments, the additive manufacturing device is a dual-extrusion additive manufacturing device configured to accept two different kinds of filament. In other

embodiments, the additive manufacturing device may be configured to accept three, four, five, or six filaments. In some embodiments where the additive manufacturing device is configured to accept multiple filaments, the additive manufacturing device is configured to switch substantially seamlessly between the filaments, therefore allowing for the printing or additive manufacture of objects comprising multiple filaments without needing to pause or manually switch filaments. Although the multi-material additive manufacturing device is described above as using filaments, it is envisioned that methods of the present invention may be used in conjunction with additive manufacturing devices using different processes, but still being configured to deposit multiple different materials without manual intervention.

In such multi-material embodiments of the present invention, a method of the present invention may instead include the steps of including a second material having a substantially higher conductivity than the first material, and printing, instead of inserting, the first and second conducting members into the sensor assembly. Examples of higher-conductivity materials for use with the present invention include, but are not limited to copper, silver, Electrifi conductive filament, Proto-pasta conductive PLA, Black Magic graphene composite PLA, Carbomorph, and F - electric by Functionalize, or any conductive 3D filament.

Although the invention is described herein as an addition to an existing robotic surgical instrument, in some embodiments of the invention the surgical instrument is itself made using an additive manufactured process, and the sensor is built into the surgical instrument at the time of manufacture.

EXPERIMENTAL EXAMPLES

The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the system and method of the present invention. The following working examples therefore, specifically point out the exemplary embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.

A prototype sensor is printed using the methods disclosed above, using conductive graphene fiber as the primary additive manufacturing material and two pieces of copper tape for the conductive members. The two pieces of copper tape are inserted during the printing process to ensure secure adhesion with the graphene material. The printed sensor is designed to fit on either of the two graspers on a set of Da Vinci Si ProGrasp forceps, and the contact point is at the circular top as seen in Figure 2. When the circular top is depressed, the copper wires are brought closer together, decreasing the resistance between the probing points, indicating that a force is being applied.

Figure 2 and Figure 3 show the overall structure of the 3D printed graphene sensor.

Figure 3 shows the size and copper tape placement in between the layers of the sensor. The CAD design in Figure 1 indicates features of the sensor and the layers where the copper tape is manually applied. The sensor was mounted to a set of appropriate forceps and a test was performed using an apparatus as shown in Figure 6. The test included a board 605 comprising a plurality of pegs 604, as well as three triangular prisms 603 with holes extending through the center from face to face. In the test, an operator directed a set of forceps 602 having a sensor 601 to pick up each of the three prisms 603 and move them from one peg to another.

Figure 7 shows the value measured from the ADC graphed against the measured force exerted on the sensor in Newtons. A force gauge test was conducted with a Mark- 10 M3- 10 Digital Force Gauge, wherein a sequence of known forces was applied to the sensor and the ADC measurements recorded. As shown in the graph, the relationship is roughly logarithmic. In addition to the measured values (indicated by dots) a rough logarithmic curve is shown, suggesting a relationship between ADC value (y) and force in Newtons (x) of approximately y = 55.351 ln(x) + 805.72

Figure 8 shows the fluctuation of the resistance (measured as an ADC value) during a trial of six peg transfers which demonstrates that the sensor is properly detecting when force is applied, but the baseline is noisy. This may be due to unstable adhesion between the graphene and copper layers.

The results demonstrate that sensors of the present invention can effectively detect normal force with good resolution. Each printed sensor costs about 35 cents, which is significantly cheaper than purchasing an industry -manufactured normal force sensor. Along with the low cost, the design flexibility of the sensor allows for various applications, even outside of the medical field. 3D printable sensors can provide a cheap and efficient alternative to industry- grade normal force sensors for haptic feedback systems. Since these are made simply through 3D printing, creating a sensor is quick and simple for anyone with access to a 3D printer. These factors will stimulate a wider acceptance for sensor-equipped biomedical devices since cheaper sensors will significantly reduce the cost of making these devices.

The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.

Claims

CLAIMS What is claimed is:

1. A normal force sensor, comprising:

first and second sensing surfaces comprising graphene and separated by an air gap, the first and second sensing surfaces electrically connected to first and second conducting elements.

2. The normal force sensor of claim 1, wherein the first and second sensing surfaces are configured to measure a force applied to any of the sensing surfaces based on an electrical resistance between the two conducting elements.

3. The normal force sensor of claim 2, wherein the relationship between the electrical resistance and the force applied is substantially logarithmic.

4. The normal force sensor of claim 2, wherein the relationship between the electrical resistance and the force applied is substantially linear.

5. The normal force sensor of claim 1, wherein the graphene comprises a conductive graphene filament.

6. The normal force sensor of claim 1, wherein the first and second conducting elements comprise copper.

7. The normal force sensor of claim 1, further comprising an anchoring element configured to mount the normal force sensor to a surgical instrument.

8. A method of making a normal force sensor, comprising the steps of:

depositing a quantity of a first filament having a first conductivity in a pattern comprising a base, an anchoring channel, and a partial first electrode layer, the partial first electrode layer including a first cavity; pausing the additive manufacturing device;

inserting a first conducting member in the cavity;

resuming the additive manufacturing device and printing over the cavity to envelop the first conducting member;

printing a supporting structure surrounding an air gap;

printing a partial second electrode layer including a second cavity;

pausing the additive manufacturing device;

inserting a second conducting member in the cavity;

resuming the additive manufacturing device and printing over the cavity to envelop the second conducting member; and printing a contact surface.

9. The method of claim 8, wherein the first filament comprises graphene.

10. The method of claim 8, wherein the first and second conducting members comprise copper.

11. The method of claim 8, wherein the first and second conducting members comprise conductive foam.

12. A method of making a normal force sensor, comprising the steps of:

depositing a quantity of a first filament having a first conductivity in a pattern comprising a base, an anchoring channel, and a partial first electrode layer, the partial first electrode layer including a first cavity;

printing with a second filament having a second conductivity in a pattern comprising a first conducting member into the first cavity;

printing with the first filament over the cavity to envelop the first conducting member; printing with the first filament a supporting structure surrounding an air gap;

printing with the first filament a partial second electrode layer including a second cavity; printing with the second filament having a second conductivity in a pattern comprising a second conducting member into the second cavity; printing with the first filament over the second cavity to envelop the second conducting member; and printing a contact surface.

13. The method of claim 12, wherein the first conductivity is less than the second conductivity.

14. The method of claim 12, wherein the first filament comprises graphene.

15. The method of claim 12, wherein the second filament comprises copper.

16. The method of claim 12, wherein the second filament comprises Electrifi.