Patent Application
20240042597
This disclosure relates to a mechanism for control and actuation of a device using cables or strings and related systems. Embodiments of this mechanism have applications for steering and tracking of interventional devices for cardiovascular procedures. Embodiments can relate to the control and navigation of interventional devices such as guidewires, catheters, needles, and imaging and ablative devices for cardiac and endovascular interventions. Further embodiments relate to steerable robotics for remote camera operation applications, continuum robotics applications, search and rescue applications, and confined space robotics.
Throughout this disclosure and claims, references to “cables” should be understood to broadly refer to any type of strings, wires, or similar manipulable components made of metal, fabrics, polymers, or crystals, for example.
Past approaches for controlling a cable-driven apparatus in medical interventional devices have often involved the use of motorized winches attached to the cables. These winches may utilize position and tension feedback to permit proportional adjustment of cable lengths to achieve the desired position of the end effector in a workspace. These winches may also be used to maintain optimal tensioning of the cables and avoid cable sagging (loss of tension). Typically, cable-driven mechanisms with a certain number of cables require use of an equivalent number of motors to control the end-effector position. For this approach, as the number of cables increases, so does the number of needed actuators, leading to increasing costs and complexity for control. Since all the cables are directly connected to the end effector, there is an inherent interdependence in the interaction of the cables. To achieve a required position, the motors must adjust all the cables to account for the interdependent motion. Also, these systems require a frame encompassing the available workspace to leverage the tension from the cables and allow for steering of the end effector. For example, there may be a cable-driven end effector with a two-dimensional planar workspace driven by four cables. Moving to any given position with one motor retracting cable may require the other three motors to release their corresponding cables. If this is not correctly accounted for, the increase in the cable tension could damage the system or jeopardize its performance and accuracy.
Robotics have been used in cable-driven systems in the past. In general, many robotic devices consist of master/slave systems in which the “master” represents the input, and the “slave” represents the output. In the context of this document, the “master” refers to the method of manipulating the cables, and the “slave” refers to the device being controlled and remotely manipulated. For intuitive control, it is essential that the input motion at the master resembles the output motion at the slave.
For a cable-driven system the cables may leverage an expandable structure as the frame that supports the cables for manipulation of a slave device by actuation of the master input unit. Various applications require the use of multiple cables connected to the slave. The mechanical coupling and interconnection of the cables require proportional adjustment of the cables at the input master unit for proper control and actuation of the slave. In a motorized system, this requirement can be accommodated by automatic proportional control of the motors that adjust the length of each cable at the desired tension. However, for a passive system, a solution is required that can account for the interdependence of these cables and allows for proportional adjustment of the lengths of the cables while reducing the system complexity. An appropriate solution is needed that will permit a passive manual slave arrangement while also possibly permitting simpler solutions for motorized configurations.
Accordingly, there is a desire for an improved apparatus or solution permitting the control and actuation of a cable-driven end effector of a desired device with enhanced effectiveness and convenience and which overcomes limitations of the past.
Embodiments described or otherwise contemplated herein substantially provide accurate control, actuation, and tensioning of cable-actuated end effectors of devices such as interventional devices. The embodiments disclosed herein relate to apparatuses, systems, and methods that allow for simultaneous actuation of multiple interacting cables to control the position of a device in a two-dimensional plane.
One embodiment relates to a cable driven parallel manipulator control mechanism that provides passive cable control. The control mechanism includes a control member, a motion stage, and a cable actuation mechanism. The control member includes a control surface defining a three-dimensional profile. The motion stage has at least two degrees of freedom (DOF) and is operably coupled to the control member. The cable actuation mechanism is located inferior to the control surface and includes at least one connector mechanism and a plurality of cables. The at least one connector mechanism constrained to contact the control surface. The plurality of cables each have a first end and a second end, wherein the first end is connected to one of the at least one connector mechanism and the second end provides coupled attachment to a device being controlled. Further, translation of the control member along a two-dimensional plane causes the at least one connector to travel perpendicularly to the two-dimensional plane resulting in cable displacements that actuate the device being controlled in proportion to translation of the control member.
One embodiment relates to a device control mechanism that controls a plurality of cables. The device control mechanism includes a control member with a control surface defining a three-dimensional conical recess in the bottom of the control member acting as a cam guide surface. The device control mechanism includes a motion stage operably coupled to the control member. The device control mechanism further includes a plurality of pistons, each including a spring and roller constrained to contact the guide surface from below. The device control mechanism also includes a plurality of cables, each having a first end and a second end, wherein the first end is connected to one of the plurality of pistons and the second end is connected to an end effector being controlled, such as an interventional device. The plurality of cables are maintained in tension and are anchored proximate the first ends and second ends as vertices of corresponding polygon shapes.
In certain embodiments, systems and methods incorporate a control surface (e.g., a three-dimensional conical surface) coupled to a two-degree-of-freedom motion stage to act as a master side for providing input to the system. In various embodiments, one end of each included cable is connected to a piston, which is constrained to contact the control surface (e.g., by utilization of springs). The other end of the cables is coupled to the slave device of interest to be controlled. As the control surface is translated along the two-dimensional plane, the pistons travel perpendicularly to the plane, resulting in cable displacements that actuate the slave end effector, such as the distal tip of a catheter, for example. Such systems and methods allow the user to directly adjust the position of the control surface, which results in a corresponding proportional adjustment of the catheter tip via the attached cables.
Some embodiments include a mechanism for actuation and control of an interventional device in two dimensions via a cable-driven mechanism. The mechanism includes multiple spring-loaded cam followers and a conical control surface acting as the cam. The two-degree-of-freedom translation of the conical cam results in the perpendicular linear motion of the cam followers. With the cables coupled to the cam followers from one end, and to the device of interest at the other end, the motion of the followers results in cable displacements that ultimately lead to the manipulation of the end effector, such as an interventional device. This approach allows for adjustment of the cable lengths with a proportion determined by the cam profile, which allows maintaining a set tension and while avoiding sagging. The resulting system can be an entirely passive mechanism that allows for accurate device position control, position estimation, and haptic feedback. Applications of such a device in interventional surgery and imaging, integration with continuum robots, remote camera operation, search and rescue applications, and confined space robotics are contemplated.
The above summary is not intended to describe each illustrated embodiment or every implementation of the subject matter hereof. The figures and the detailed description that follow more particularly exemplify various embodiments.
Subject matter hereof may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying figures, in which:
While various embodiments are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the claimed subject matter to particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the claims.
Embodiments disclosed herein include mechanisms for actuation and control of a cable-driven end effector. Proposed systems can comprise a variety of features, such as a control member with a control surface, motion stage system (i.e. axis system), and a cable actuation mechanism with at least one connector mechanism such as spring-actuated pistons or a lever. Furthermore, embodiments can also include modifications such as the addition of a gearbox and/or encoders to track cable displacements.
In various embodiments, control mechanism 100 includes a control member 110 having a control surface 112 (in a lower recess) and an input surface 114 (on top) mounted on a motion stage (specifically, a two-axis rail system 120 in
In some embodiments, pistons 133 are not present and instead, some other type of at least one connector mechanism is present. In some embodiments, at least one connector mechanism can be a lever or other mechanism for connecting the cables to the surface. For example, a lever could be used with a spring on one end and which is constrained by the control surface.
As control member 110 slides on the two-axis rail system 120, springs 134 keep rollers 135 in contact with its control surface 112. Control surface 112 defines a three dimensional profile. In this particular example, the three dimensional profile can be a three-dimensional conical recess and, accordingly, can generally act as a cam for the mechanism. The conical shape of control surface 112 provides a useful structure to ensure necessary cable displacements supplying tension and to communicate proportional adjustments to the device of interest. See
Rollers 135 can generally act as cam followers. Rollers 135 are free to rotate to reduce frictional wear on control surface 112. Pistons 133 have a lip to retain rollers 135. As pistons 133 translate in mounting block 132, the cables 131 are actuated by the relevant displacements. Cables 131 pass through cable guides 136 to actuate the end effector (or other feature of the interventional device attached at the end of the cable 131) to the required positions relevant to the embodiment.
The following description and
For purposes here, the end effector is manipulated by several cables, each using a single anchor as a leverage point. The control surface needs to change the lengths of the cables on the handle side to match the change of lengths of the cables on the end effector side. Here, the control surface is referred to as the master, and the end effector is referred to as the slave. Their corresponding coordinate systems are indicated by a superscript m, and s respectively.
Let α be the gear ratio between the slave and the master. That is, if a cable is retracted by 1 millimeter in the master side, the gearing system will result in a retraction of α millimeters at the slave side.
α=gear ratio (Eq. 1)
The coordinates of the ith anchor at the slave side will be called (xA
The displacement of the control surface is called (xm, ym) and is considered arbitrary. The resulting displacement of the catheter tip is called (xs, ys) and is a function of the fixed geometry (i.e. the anchor and piston position and the equation of the surface) as well as the current displacement of the surface.
The change of cable length on the slave side is calculated by taking the initial cable length (L0) at position 1 of the catheter (shown in
ΔLis=Lfs−L0s (Eq. 2)
Using Pythagoras' theorem, the initial (
ΔLis=√{square root over ((xA
The cables are individually constrained to the surface via the pistons. They are fixed in their x and y positions (like the anchors on the catheter side) so the z position of the cable is determined by the surface's height at that position. The surface is free to move along the x and y axes. The change in cable length is calculated by finding the initial vertical position (z0) of the cable (shown in
ΔLim=zfm−z0m (Eq. 4)
The initial (
ΔLim=z(xP
The relationship between ΔLis and ΔLim is due to the conservation of cable length. A negative relation occurs because increase in the length of cable in the handle must result in decrease in the length of cable at the catheter tip. Moreover, due to the gearing, an increase in cable length in the handle of α millimeters is required to cause a decrease in cable length of 1 millimeter at the catheter tip. Thus,
Accordingly, the following equation of the surface is well suited to elegantly matching up the two sides of this equality.
z(x, y)=H0−√{square root over (x2+y2)} (Eq. 8)
This is the equation of a cone with a slope of 1 as claimed. The height offset, H0, is arbitrary and has no bearing on the result. Thus, any height offset that is convenient may be used.
Moreover, this approach dictates that the geometry of the pistons in the handle should be a scaled-down version of the geometry of the anchors at the catheter tip.
Further, this explicitly describes that the catheter tip displacement is a scaled-up version of the control surface displacement.
(xs, ys)−α(xm, ym) (Eq. 10)
The slope of the cone may be changed to a number other than 1. For example, changing the slope to 2 would double the displacements of the cables, which can be combined with a gear ratio of one half in the tensioning system to leave the overall output unchanged. This can be useful because it can decrease the required width of the handle and improve ergonomics.
Accordingly, as demonstrated by this explanation and
Control mechanisms (such as 100 and 200, for example) have broad applicability to cable driven devices. Moreover, there are many applications for cable-driven master/slave systems. One application can be found in minimally invasive catheter-based procedures. These procedures are typically guided by flexible elongate members that can be manipulated from outside the body with two degrees-of-freedom, which limits the available workspace. A cable-driven end effector can be used in place of this to add extra degrees-of-freedom and allow the operator better control. Moreover, due to the direct mechanical connection, the operator can also receive haptic feedback from the end effector.
Other potentially relevant embodiments and applications of catheters and the like are in forward-looking imaging probes. One of the main limitations of miniaturizing imaging probes is that the limited space available at the tip of a miniaturized device constrains our ability to integrate sensors or transducers that permit a large field of view (FOV). Using a cable-driven catheter that leverages an expandable structure, the small FOV transducers or sensors can be steered to multiple positions to take readings. Position data taken from the sensors can be used to combine the numerous readings into a single, large FOV image. This can be applied to various imaging modalities such as ultrasound and optical coherence topography (OCT).
Another application lies in confined space robotics. In some embodiments, continuum robots can be used to access hard-to-reach areas while allowing for precise, remote control of an end-effector. Possible applications for confined-space robotics include search and rescue, industrial and nuclear maintenance robots, aerospace and automotive manufacturing, and endoscopy.
As previously noted, embodiments of the proposed systems and methods generally incorporate a control surface (e.g., a three-dimensional conical surface) coupled to a two-degrees-of-freedom motion stage to act as a master side for providing input to the system. In an embodiment, one end of each included cable is connected to a piston, which is constrained to contact the control surface (e.g., by utilization of springs). The other end of the cables is coupled to the slave device of interest to be controlled. As the control surface is translated along the two-dimensional plane, the pistons travel perpendicularly to the plane, resulting in cable displacements that actuate the slave end effector, such as the distal tip of a catheter, for example. This system allows the user to directly adjust the position of the control surface, which results in a corresponding proportional adjustment of the catheter tip via the attached cables.
In some embodiments, the cables may connect to a gearing system before transitioning to the slave. As discussed in the preceding, this has the effect of changing the geometry such that a proportionally smaller displacement of the control surface will be required for a given displacement of the end effector. This allows for the footprint of the master control to be adjusted for the application. In another embodiment, the system can be geared to increase the amount of force applied to the end effector of an interventional device. In addition, this may also be used to adjust the resolution between the master and the slave.
Control mechanisms (such as 100 and 200, for example) can be structured such that the dimensional displacement of the control surface is proportional in both direction and magnitude to the displacement of the end effector, for example. Moreover, the position and geometry of the pistons in the master are proportional to the geometry of the cable anchor points of a slave frame. Also, the position and geometry of the center of the cylinder, relative to the pistons in the master, is proportional to the position and geometry of the end effector relative to the expanded anchors on the slave. The proportionality constant is the gear ratio between the master and slave mechanisms.
In some embodiments, there may only be four cables used for the actuation of the device. Typically, in this scenario, the anchor points in the frame of the slave will be in the shape of a square. This allows the maximum possible coverage of the full area with just four anchor points for the cables. Correspondingly, there will then be four pistons moving perpendicular to the conical surface on the master side, arranged in the shape of a square as well. However, the system being proposed can be much more general and allow for an arbitrary number of anchors in arbitrary positions. For example, in some embodiments, anchors can be located at the vertices of regular polygons with an increasing number of sides. There will then be a corresponding number of cables, and the pistons in the master will be arranged in a corresponding polygon. This has the advantage of allowing the end effector to traverse a more significant proportion of the circular cross-sectional area as the number of vertices of the polygon increases.
In an embodiment, position sensors including devices like linear or rotary encoders, can be added in the master to track the position of the control surface or the displacement of the cables. In such embodiments, the sensor data can be used to visualize the position of the slave device or end effector relative to its available workspace and shown to the operator via a user interface.
In one embodiment, the control mechanism (such as 100 or 200, for example) can be applied to a cable-actuated steerable catheter with an expandable frame, such as the steerable catheter configuration disclosed in WO 2019/213215 A1 to Tavallaei et al. The expandable frame can be used as a rigid leverage point for the cables to actuate an end effector, such as the distal tip of a catheter. This allows for a fully mechanical solution to the master side of the catheter. Position sensors (including linear or rotary encoders, etc.) can also be used to track the catheter tip and provide feedback to the user.
Also, in an embodiment, a forward-looking imaging transducer can be mounted to the end effector. In such an embodiment, the end effector can be moved to various positions, and the imaging probe can be used with positioning data to reconstruct a large field of view (FOV) image. This can be applied to a catheter as discussed in the previous embodiment, or to robotics in a confined workspace for search and rescue applications or for imaging systems in hard-to-reach spaces. Various imaging modalities or sensors may be integrated into the system. Examples include but are not limited to optic-based sensors, ultrasound transducers, or radiation sensors. In such an embodiment, linear or rotary actuators or motors can be used to actuate the position of the control surface in the master. This is particularly useful for imaging probes as it will allow the probe to be swept across a cross-section to reconstruct an image autonomously.
In further embodiments, where the use of a motorized design is permissible, the use of the control surface can reduce the number of motors necessary to the two required to control the two-dimensional translation of the control surface.
Also, in an embodiment, the cables can be attached to the control surface at a single point. For example, a different type of design having three cables and a very elongated surface is possible. In this embodiment, the control surface will be a three-dimensional surface that corresponds to the changes in length required for the individual cables in a single attachment point. In such an embodiment, the cables would be constrained to the surface, and as the attachment point for the cables is moved on the three-dimensional surface the length of the cables on the surface would change in proportion such that the slave device would be controlled in the two-dimensional surface of interest. For other embodiments, alternate mounting methods can be used for the cables on either the end effector side or the control side. Various three-dimensional control surfaces can be used to account for the mounting methods, according to these embodiments.
The proposed method can also be used to actuate a continuum cable-driven manipulator that is actuated by a number of cables. For example, a deflectable catheter that is cable-driven and utilizes more than one cable to deflect its distal end can utilize the same strategy. Namely, a cam surface (also referred to at times herein as a “cam guide surface”) can be coupled to the cables such that the motion of the cam surface leads to the adjustment in length of the cables. This permits a passive remote actuation method and provides a mapping between the master unit manipulation and the catheter tip motion based on the profile of the cam surface.
Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the claimed subject matter. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations, and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the claimed subject matter.
Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features: rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted.
Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended.
Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein.
For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. § 112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.
The present application claims the benefit of U.S. Provisional Application No. 63/123,981 entitled “CABLE DRIVEN PARALLEL MANIPULATOR CONTROL MECHANISM AND RELATED SYSTEMS AND METHODS”, filed Dec. 10, 2020, which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/062391 | 12/8/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63123981 | Dec 2020 | US |
