ROBOTIC ARM

The disclosure relates to a robotic arm for use in surgery, microsurgery or supermicrosurgery, in particular for anastomosis, comprising: at least one instrument module comprising an instrument actuation submodule, wherein the instrument actuation submodule is configured to operate grasp and roll orientation of an instrument, wherein the instrument actuation submodule comprises a first motor and a first drivetrain for actuation of the instrument roll orientation, and wherein the instrument actuation submodule comprises a second motor and a second drivetrain for actuation of the instrument grasp orientation, at least one pitch module, and at least one yaw module.

TECHNICAL FIELD

The present disclosure relates to the technical field of robotic arms and robotic systems for use in surgery, microsurgery or super-microsurgery procedures.

For instance, the robot arm or robotic system can be used in performing anastomoses.

BACKGROUND

Anastomosis in microsurgery is a technique used to (re-)connect veins, arteries, and lymphatic vessels. This allows the flow of blood or lymphatic fluid to be restored in situations such as vascular congestion, (clinical)trauma, and tissue transplantation.

Microsurgeons perform anastomoses on vessels, which range in diameter from 2.5 mm down to 0.3 mm. These vessels are primarily connected end-to-end, by up to ten interrupted sutures around the circumference of the vessel. Classically, the surgeon places each suture by hand, using fine instruments to manipulate tissue, needle, and thread. The quality of an anastomosis depends on the precision of these fine manipulations, and the overall efficiency of the procedure. Experienced microsurgeons are able to efficiently suture on the micro scale, but this requires a high level of (fine motor) skill and long-term concentration. In particular, the inherent hand tremor makes fine instrument manipulations difficult, and this limits the manual operating precision to approximately 100 μm. Alternatively, robots can be used for precise surgical handlings on the submillimeter scale.

In particular, the use of robots facilitates accurate movements with micrometer precision without substantial tremor, thereby superseding the limitations of human hand manipulation.

SUMMARY

Robots for use in surgical, microsurgical or super-microsurgical procedures are known in the art.

EP3900650A1 discloses a surgical robotic system comprising a spherical wrist comprising a surgical instrument, which allows the surgical instrument to be actuated with high accuracy. The spherical wrist comprises a yaw axis, a pitch axis, and a roll axis to provide the surgical instrument with three rotational degrees of freedom, including a roll rotation about a longitudinal axis of the surgical instrument.

Since in anastomosis sutures are placed around the circumference of each vessel, the ideal instrument orientation changes throughout the procedure. New robot concepts may therefore improve on operating efficiency by a design that focuses on achieving high instrument dexterity and convenient repositioning. Such a robot can allow a robotic assisted surgeon to operate more naturally and to assume a favorable instrument pose throughout the procedure.

Another argument for a dexterous manipulator involves the invisibility of system boundaries when operating the robot. In manual procedures, surgeons directly hold the instruments and are constantly aware of the relative position and orientation of their hands and arms through the sense of proprioception. Using robotic assistance however, this sense of awareness is lost in the translation from the master to the robot. Since surgeons only see the tips of their instruments through the microscope, it is very challenging to keep track of the changes in the manipulator's posture brought about by a sequence of instrument manipulations. Consequently, this commonly causes the surgeon to unintentionally steer the robot away from its ideal configuration, unaware of this process until the system hits a mechanical boundary. Recovery typically requires the robotic arm to be manually repositioned to its starting configuration before resuming the procedure. One approach to increase the awareness of system bounds could be the implementation of haptic feedback in the masters. However, only considering the robot, an expansion of the manipulator's dexterous workspace appears most effective in limiting the interference with system bounds.

Most microsurgical procedures require the vessels to be dissected from surrounding tissue prior to anastomosis. For some, the orientation of these vessels is often not well known in advance. As a consequence, large rotations may still be required to bring the instruments into the correct orientation for suturing after the initial setup of the robotic system. These macro-adjustments in position and orientation are typically performed manually through the repositioning of the robot's support structure. Nevertheless, a design for a robot that prioritizes dexterity and maneuverability may minimize the need for manual adjustments of the support structure during the procedure.

Thus, it is necessary that robots provide the operator (e.g., a surgeon) with sufficient dexterity, so as to be able to perform complex movements in the microsurgical workspace and also avoid the risk of collision with other objects during manipulation.

It is an object of the present disclosure to provide an alternative robotic arm for use in surgery, microsurgery or super-microsurgery, in particular for anastomosis, with enhanced precision and dexterity.

The object is solved according to the present disclosure by a robotic arm. Accordingly, a robotic arm for use in surgery, microsurgery or supermicrosurgery, in particular for anastomosis, comprisingat least one instrument module comprising an instrument actuation submodule,wherein the instrument actuation submodule is configured to operate grasp and roll orientation of an instrument,wherein the instrument actuation submodule comprises a first motor and a first drivetrain for actuation of the instrument roll orientation,wherein the instrument actuation submodule comprises a second motor and a second drivetrain for actuation of the instrument grasp orientation,at least one pitch module, andat least one yaw module.

The disclosure is based on the basic idea that the robotic arm is designed to offer high dexterity and precise actuation of a surgical instrument. In particular, this is primarily achieved by the robotic arm comprising an instrument module, which in the essence serves two primary functions. On the one hand, it provides a universal interface to offer consistency in the attachment (also operation, and exchange) of various (custom) microsurgical instruments. On the other hand, the instrument actuation submodule is directly responsible for actuation of the instrument grasp operation and roll orientation, in particular as the module directly integrates the motors and drivetrains responsible for actuation of the instrument grasp operation and roll orientation. The latter serves to shift the transmission complexity for grasp and roll away from the spherical wrist mechanism. Previously, concepts for mechanical dexterous wrists were identified a bottleneck regarding instrument dexterity. In contrast, for the proposed active instrument module, these qualities can now be pursued separately for grasp and roll. Overall, a robotic arm with improved dexterity can be provided. Moreover, this effectively uncouples their implementation from the remaining five manipulator degrees of freedom of the robotic arm, and hence allows a relatively independent instrument actuation submodule.

In addition, the first drivetrain of the instrument actuation submodule may be configured and arranged for infinite instrument rotation.

The at least one pitch module may be configured and arranged for actuation of instrument pitch orientation.

In particular, the pitch module may comprise a pitch drive mechanism configured and arranged to actuate instrument pitch over an angular stroke of up to 150 degrees.

The at least one yaw module may be configured and arranged for actuation of instrument yaw orientation. In particular, the yaw module may comprise an inner tube and an outer tube, wherein the outer tube is also referred to as manipulator arm.

Further, the yaw module may comprise a yaw drive mechanism configured and arranged to actuate instrument yaw over an angular stroke of up to 150 degrees.

Overall, the instrument pitch and yaw may be operated over an angular stroke of up to 150 degrees, and when operated simultaneously they allow the instrument to dexterously orient to the workspace.

Altogether, high dexterity and precise actuation of a surgical instrument is enabled by the instrument actuation submodule and/or the pitch module and/or the yaw module.

The robotic arm may further comprise at least one instrument position module comprising at least three crank modules, wherein at least two crank modules are each linked to at least one strut. Linking the at least two crank modules each to at least one strut may enable restriction of freedom of movement to a defined movement, thus increases accuracy of the movement and rigidity of the robotic arm.

Three crank-modules of the instrument position module may serve to precisely control the manipulator arm, where the struts may directly control the instrument position.

Further, at least two crank modules may be linked to the same strut. In other words, at least two crank modules may be linked to one strut only. This structure can help define the motion and allows for a simple parallel kinematic structure.

In particular, the robotic arm may be a seven degree of freedom robotic arm, wherein the instrument actuation submodule may be a three degree of freedom module, the instrument submodule may be a one degree of freedom module and the instrument position module may be a three degree of freedom module. Thus, compared to a six degree of freedom robotic arm the end-effector pose can not only be reachable in a single configuration of the robotic arm.

Three degrees of freedom may correspond to the positioning of the instrument and arm in space. To this end, a parallel kinematic structure may be employed that is constructed. Here, the actuators may be mounted at the base of the robotic arm to reduce moving mass, with their drive stiffnesses acting in parallel rather than stacked in series. Two of the parallel linkages may be slender struts that attach to the tip of the manipulator arm. Each of these struts may be controlled by a direct drive balanced crank mechanism that prescribes one of the three actuated degrees of freedom at the manipulator arm. A similar crank mechanism may directly act on the rear of the arm and therein controls the third and last positioning degree of freedom. In addition, this latter crank constrains the remaining three passive degrees of freedom for the manipulator arm such that both its position and orientation in space may be fully defined.

In general, the robotic arm may comprise at least one parallel kinematic structure being formed by at least one of an instrument module and/or a yaw module and/or a pitch module and/or an instrument position module. Overall, this may enable high structural stiffness of the robotic arm.

The instrument module may be characterized by a modular structure. In other words, the instrument module may comprise at least one of a (sub-)module, an element, a joint, a drivetrains, a motor, etc. —all of which again my comprise several single elements. In particular, the instrument module may, in addition to the instrument actuation submodule, comprise an instrument submodule, wherein the instrument submodule may comprise an instrument retainer and an instrument. In other words, the instrument submodule may comprise a microsurgical instrument integrated into a matched retainer body.

The instrument may be a needle holder and/or forceps for surgery, microsurgery or supermicrosurgery, in particular for anastomosis, comprising two instrument beaks, at least one instrument hinge pin, at least two instrument handles and at least two handle joints.

In particular, the instrument may have length of less than 50 mm, in particular less than 30 mm, in particular 20 mm. Conventional traditional instruments, such as a traditional needle holder, have a length of about 150 mm. Thus, a sharp reduction in instrument length compared to the typical 150 mm for a traditional instrument/needle holder is achieved. This allows the instrument to be better suited for integration into the robot device, in particular the instrument retainer. Also, compared to conventional instruments for other robotic arms, the present instrument is more compact, with a length of approximately two thirds of the size of conventional instruments for robotic arms. In addition, the use of more compact instruments is motivated by the intended application of the robot in the upper range of precision procedures, such as anastomosis. Here, manipulations involve increasingly delicate tissue and sutures that pair well with the use of refined, compact instruments.

In particular, the beaks each may have a length of less than 20 mm, in particular less than 15 mm, in particular 10 mm. This dimension corresponds to the downscaling of the instrument to approximately two thirds of the size of conventional instruments for robotic arms. From a mechanical point of view, a reduced beak length serves to proportionally limit the maximum output arm for grasp. In turn, this again proportionally enables reduction of the required amount of force applied at the handle to clamp a needle with a force of e.g. over 5 N at the beaks. In addition, the use of compact instruments is motivated by the intended application of the robotic arm in the upper range of precision procedures. Here, manipulations involve increasingly delicate tissue and sutures that pair well with the use of refined instruments. Moreover, fine beaks appear less bulky at the enhanced levels of microscopic magnification that may be employed for a robotically steadied instrument.

Consequently, type-specific instrument functionality emanates predominantly from the beaks. These may be designed to preserve the shape of their traditional counterparts, which are already tailored to the microsurgical procedure. Moreover, this close correspondence in design may aim to facilitate the surgeon's transfer of skill from manual to robotic assisted surgery. Similar to their traditional counterparts, the custom instruments may be designed to be produced from surgical e.g. grade stainless steel, although e.g. titanium variants may be considered as well.

In particular, the instrument may be configured and arranged for an inverted hinge mechanism. Consequently, the beaks close instead of open upon the spreading of the instrument handles. This inversion serves the implementation of a knee mechanism for actuation of the instrument. The knee-mechanism is characterized by a non-linear input/output relation (linear input stroke at the knee, output at the instrument beaks). The non-linearity of the knee-mechanism serves in the design of the instrument module to increase the grasp clamping force and precision the further the beaks close. This allows the actuator effort for grasp to be concentrated where it matters most.

Therefore, the instrument retainer may comprise at least one knee mechanism central joint, at least two retainer guide pins, at least one stopper, at least one knee link pair, wherein the instrument retainer is configured to actuate the instrument by an inverted hinge mechanism. Overall, this enables a non-linear input/output relation (linear input stroke at the knee, output at the instrument beaks), as described above.

Further, the instrument actuation submodule may comprise a pushrod configured and arranged for actuating over the centerline of the instrument actuation submodule. The knee mechanism described above is in part selected for its short linear input stroke for grasp. Such motion may be convenient in the construction of a sterile barrier. In addition, this actuation stroke can be aligned along the roll centerline. This allows the operation of grasp to be conveyed independent from the instrument roll orientation. To this end, a pushrod is introduced, which acts over the centerline of the instrument actuation submodule. Moreover, a direct contact between this pushrod and the knee mechanism central joint serves to link the input motion at the drive to the operation of the beaks at the output. In particular, the pushrod may comprise a spherical tip configured for contacting a matching socket in the knee mechanism central joint.

Further, the instrument retainer may comprise at least one instrument preload band and at least one preload band guide pulley. This contributes to enabling a non-linear input/output relation (linear input stroke at the knee, output at the instrument beaks), as described above. In particular, the preload band is applied to both the instrument handle and the knee mechanism central joint, maintains the contact between pushrod and knee mechanism central joint and serves to remove play from the assembly. In particular, the instrument preload band is guided by the preload band guide pulley located on the knee-mechanism central joint as the band is applied at the handles and tensions them together, the preload force will always act through the links of the knee mechanism. Consequently, the joints of the knees are always in contact in the direction corresponding to a closing action, such that no play is traversed upon the clamping of an object.

The preload band may be produced from an elastomer, in particular an autoclave compatible elastomer, such as AFLAS.

Neither bacteria, nor viruses or spores should be transferred from the robotic system to the patient. To this end, parts of the robot may be covered by a physical sterile barrier impermeable to contaminants, such as a disposable drape, Drapes may be made application specific, produced in the required shape by bonding plastic sheets in a pattern. Moreover, physical components of different material may be incorporated in the sheets at an increase in complexity and cost. Although drapes are relatively flexible and strong, they remain vulnerable to mechanical contact stresses, which can cause punctures or tear the material. The drape should be kept clear from the microscope's and surgeon's field of view. Since surgical instruments come into direct contact with the patient they are themselves not suitable for draping. Therefore, these and any critical components outside the sterile barrier should be either cleanable and sterilizable, or be single use disposable. Sterilization is the process of destroying or inactivating the bacteria, viruses, and spores on critical components. It is preceded by cleaning, during which organic residue such as blood is removed. Autoclave pressurized steam-sterilization is the most common and cost-effective method that is available in all hospitals. This procedure is efficient, and as an indication takes a minimal of 4 minutes at 132° C. in a pre-vacuum sterilizer, or 30 minutes at 121° C. in a gravity displacement autoclave.

Components designed for autoclave sterilization must be heat tolerant, corrosion resistant, and non-absorbing. Moreover, cleaning and sterilization are generally facilitated by good exposure and smooth surfaces, without cavities or blind holes.

The robotic arm is characterized by a modular structure. The at least one instrument module, the at least one pitch module, the at least one yaw module as well as the instrument position module each comprise several elements or modules (such as a drivetrain and/or a joint—each again comprising several elements). The robotic arm may be designed sterilizable for all the joints and drivetrains regarding the orienting degrees of freedom and instrument grasp. In other words, the modular structure of the instrument module, and/or the pitch module and/or the yaw module and/or the crank module may be configured sterilizable for all the joints and drivetrains regarding the orienting degrees of freedom and instrument grasp. In particular, the instrument module (instrument actuation submodule and instrument submodule) and/or the pitch module and/or the yaw module and/or the crank module may comprise joints and/or elements for orienting the instrument and/or instrument grasp, wherein these joints and/or elements are configured sterilizable. In other words, parts of the instrument module, and/or the pitch module and/or the yaw module and/or the crank module may be configured for sterilization (in particular autoclave sterilization). This serves for minimal drape interference on instrument reorienting.

Overall, as described above, sterilizable elements and/or joints enable operation under sterile conditions, avoiding transfer of infectious microorganisms (such as bacteria, viruses, spores (of fungi) to the patient. In addition, single sterilizable elements of the robotic arm may enable the interchange of instrumentation during surgery. Afterwards, separation of parts serves once more to increase the exposure of inner surfaces for the process of cleaning and sterilization.

For efficiency in cleaning and sterilization the robotic arm may be designed to easily disassemble and thereby improves exposure of the submodule surfaces.

Medical robotics are subject to strict safety regulations, especially when they operate in direct contact with the patient. In case of the robotic arm, the focus must therefore always be on a safe and robust design that minimizes any risk to the patient and medical personnel. To this end, the following set of operational requirements is imposed on the robotic arm:The robot must be sterile in surgery (see above).The movement speed at the instrument tip is limited to 10 mms−1.The rotational velocity of the instrument is limited to π/2 rad s−1.Accelerations shall be low.The exerted force at the tip of the instrument may not exceed 5 N.The supply voltage is limited to 24V.

These requirements help limit the robotic arms potential to do damage. In addition to these operational safety requirements, the risks associated to abnormal conditions must be evaluated as well. These include events such as an unexpected power shutdown, or the failing of one or more components. Mechanical safety features may include inherent force limitation, back-drive-ability, redundancy in sensors, and weight compensation of the slave manipulator.

Inherent force limitation serves to limit the potential of the system to do harm in operation. To this end, actuators and control system in the slave may be no more powerful than required to produce a force of 0.5 N at the instrument tip.

Back-drive-ability allows the robotic system to be repositioned manually in case of a fault. This allows the robot to be cleared quickly away from the operating site in case of a hazardous situation, or when manual access is required. The yaw orientation and instrument position may be fully backdrivable to allow manual repositioning upon fault or convenience.

Redundancy in sensors serves to detect faults in the system by providing redundant measurement data for readout comparison. Upon the detection of a fault, the system may assume a safe state rather than that the controller continuous to drive the system based on an erroneous feedback signal. All but the grasp and roll drive may integrate a redundant pair of absolute position sensors for fault detection. These may also serve to provide instantaneous awareness of the robotic arm configuration on startup without requiring a homing procedure. In contrast, for grasp and roll no position sensors may be implemented as these drives are argued safe in open-loop control.

Weight compensation serves to balance the mechanical links of the robotic arm around the respective joints. This allows the arm to continuously operate in an equilibrium, such that upon fault (e.g. loss of power) the arm does not collapse on the patient. Moreover, a balanced arm requires minimal continuous actuator effort to maintain any given posture. In particular, the strut cranks may be balanced such that the arm/system does not collapse on loss of power.

The present disclosure further relates to a robotic system for use in surgery, microsurgery or supermicrosurgery, in particular anastomosis, comprising at least two robotic arms as described above. This enables performing complex surgeries requiring more than one robotic arm characterized by high dexterity.

Further details of the disclosure shall now be explained with reference to an example embodiment shown in more detail in the drawings.

DETAILED DESCRIPTION

FIG.1shows a needle holder106and forceps106as predominantly used by microsurgeons, to perform precision manipulations.

The needle holder106is shown on top ofFIG.1, whereas the forceps106are shown on the bottom ofFIG.1.

The needle holder106is the main instrument106for suturing, which holds the needle306while making the entry and exit bites.

It has a hinge approximately 15 mm from the tip, such that the instrument handle146acts as a lever. This allows the surgeon to firmly secure the needle in the beaks, exerting over 5 N of clamping force to prevent slippage.

FIGS.2-5together show an example of the procedure for microsurgical anastomosis.

An anastomosis starts with two vessels, surgically prepared to be (re-)connected by sutures.

Their vessel-ends are positioned and held relative each other in vascular clamps. The main suturing techniques for anastomosis are described below. They are primarily based on Acland's practice manual for microvascular surgery. Some of the corresponding illustrations are included to visualize the procedural steps.

FIG.2illustrates an example of picking-up the needle306: the needle306is grabbed with the needle holder106, just above half-height. It is oriented at a right angle to its beak, aided by the forceps106and the at sides on the base of the needle306.

FIG.3shows an example of the entry-bite (left site). The entry-bite is made such that the needle306punctures the vessel wall from the outside inwards. The forceps106are used simultaneously to push the edge of the vessel wall from the inside up. This allows the needle306to puncture approximately perpendicular to the vessel wall, while minimizing the risk of a through-stitch.FIG.3also shows an example of the exit-bite (right site). The exit-bite is subsequently made on the opposite vessel-end. Again, the forceps106are used to restrain the vessel and to curl its edge up for a perpendicular puncture, now from the inside out.

FIG.4shows an example of pulling the needle306and suture-thread through. The needle-tip, now protruding from the vessel wall, is grabbed by the forceps106and pulled through. Subsequently, the suture-thread is pulled along with the needle306, guided over the beaks of the needle holder to minimize stress on the vessel wall near the entry bite. Depending on the remaining suture-length, the needle306is dropped and the thread is grabbed and pulled through in multiple steps. This allows the manipulation to be performed within the microscope's limited field of view. However, care must be taken to preserve the integrity and tensile strength of the suture-thread. To this end, the suture should be clamped no more often than necessary, and may use only the forceps106instead of the needle holder106.

FIG.5shows an example of making the knot: three to four consecutive half-knots are tied to tension and secure the suture. A half-knot is initiated by grabbing the needle-side of the suture-thread with the forceps106, and wrapping a loop around the (spread) beaks of the needle holder106. Then, the needle holder106grabs the free end of the suture and pulls it back through the loop to form a half-knot. The surgeon tensions each half-knot by moving the instruments106apart, gently pulling on both ends of the suture-thread. The tension of the half-knot is assessed visually, as the forces involved are too small for humans to sense directly.FIG.5also shows an example of a cut suture-thread: The assistant cuts the suture-thread close to the knot using a micro-scissor. The remaining free ends of the knot are trimmed short and removed from the site. The result is a compact interrupted suture, that remains in place to be encapsulated in the patient's tissue.

The above steps disclosed inFIGS.2-5are repeated for each interrupted suture around the circumference of the vessel. The remaining length of the suture-thread decreases with each suture, but it is generally sufficient for one anastomosis.

The procedure and instruments106for robotic assisted anastomosis are similar to those for manual surgery as outlined above inFIGS.2-5. This close correspondence helps trained surgeons transfer their skills and techniques from manual to robotic assisted surgery.

Most manipulations in the procedure as shown inFIGS.2-5require the simultaneous use of both needle-holder106and forceps106. Therefore, the robot (also referred to as robotic system) features two robotic arms100, each operating one instrument106(cf.FIG.9). Through the masters, the surgeon controls both robotic arms100to co-operate within a shared workspace containing the vessel-ends.

This shared workspace is visualized inFIG.6, and can be subdivided into two segments.

Fine manipulations, such as making the needle306entry and exit bites, are done within a cylindrical volume of 20 mm in both diameter and height (first segment, referred to as precision workspace, represented by the lower cylinder with 20 mm diameter). Pulling the suture thread through and tying knots requires less precision, and a larger workspace can be utilized for efficiency. To this end, an additional cylindrical workspace is defined for suture handling (second segment, referred to as suture handling workspace). This volume has a diameter and height of 30 mm, and is stacked on top of the precision workspace. It is argued that further extensions to the workspace become less effective, as the surgeon must rely on visual feedback from the microscope to operate the instruments106. Here, the high level of microscopic zoom proportionally limits the field of view in radial direction, while the focal range is the limiting factor in axial direction.

For future reference, a fixed Cartesian coordinate frame is defined at the base of the workspace, where the z axis is assumed to coincides with the microscope's optical axis. Furthermore, roll indicates the instrument106rotation about its longitudinal axis, tilt the instrument angle with respect to the x-y plane, and approach its angular position around z, with respect to the x axis.

FIG.7shows de traditional instrument106grip on the forceps106(left) and needle holder106(right) during surgery. The arrows indicate the contact points through which the surgeon manually positions and actuates the instruments106. The grip is close to the tip for direct control, while the instrument106gains stability from the support point(s) at the back of the handle. Resting his hands either on the support table or directly on the patient, the surgeon can precisely position the instrument106, and attenuate tremor to some degree. Besides grasp, the maximum required force at the instrument tip is 0.5 N associated to the tensioning of a knot. This value is based on the suture breaking force. Moreover, it is assumed that the duration of this peak force is relatively short compared to the occurrence and interval of tightening consecutive half-knots.

FIG.8illustrates an embodiment of the robotic arm100according to the present disclosure.

The robotic arm100is configured for use in surgery, microsurgery or supermicrosurgery, in particular for anastomosis.

In this embodiment, the robotic arm100comprises an instrument module102(cf. e.g.FIGS.11-13) comprising an instrument actuation submodule104.

The instrument actuation submodule104is configured to operate grasp and roll orientation of an instrument106.

Not show in this embodiment is, that the instrument actuation submodule104comprises a first motor108and a first drivetrain110for actuation of the instrument roll orientation.

Also not shown in this embodiment is that the instrument actuation submodule104comprises a second motor112and a second drivetrain114for actuation of the instrument grasp orientation.

Further, the robotic arm100comprises a pitch module116(cf.FIGS.24-26).

Still further, the robotic arm100comprises a yaw module118(cf.FIGS.27-32).

In this embodiment, the robotic arm further comprises an instrument position module120(cf.FIGS.33-36).

In this embodiment, the instrument position module120comprises three crank modules122,254wherein two crank modules122are each linked to at least one strut124.

In this embodiment, the crank module254not linked to a strut124is referred to as central crank module254.

Alternatively, at least two crank modules122could be linked to the same strut124.

Not explicitly shown in this embodiment is, that the robotic arm100could be arranged without an instrument position module120.

Not explicitly shown in this embodiment is that the first drivetrain110of the instrument actuation submodule104is configured and arranged for infinite instrument106rotation.

Further not explicitly shown in this embodiment is that the pitch module116comprises a pitch drive mechanism202configured and arranged to actuate instrument106pitch over an angular stroke of up to 150 degrees, cf.FIG.26.

Further not explicitly shown in this embodiment is that the yaw module118comprises a yaw drive mechanism configured and arranged to actuate instrument106yaw over an angular stroke of up to 150 degrees, cf.FIG.38.

Still further not explicitly shown in this embodiment is, that the instrument module102comprises an instrument submodule126, the instrument submodule126comprising an instrument retainer138and the instrument106, cf.FIG.19.

In this embodiment, the robotic arm100is a seven degree of freedom robotic arm100.

In this embodiment, the instrument actuation submodule104is a three degree of freedom module and the instrument submodule is a one degree of freedom module.

In this embodiment, the robotic arm may comprise a parallel kinematic structure being formed by the instrument position module.

In general, the robotic arm can comprise at least one parallel kinematic structure being formed by at least one of an instrument module and/or a yaw module and/or a pitch module and/or an instrument position module.

In this embodiment, the instrument position module120is a three degree of freedom module.

Not explicitly shown is, that a robotic system according to the disclosure can comprise at least two robotic arms100as shown inFIG.9.

FIG.9shows an illustration of a robotic system comprising a pair of robotic arms100according to the present disclosure (as shown inFIG.8), cooperating in a shared work space.

The robotic arm geometry is designed to efficiently perform cooperative manipulations in the workspace for microsurgical anastomosis, cf.FIG.6.

A pair of robotic arms100(i.e. a robotic system comprising two robotic arms100) cooperating in this workspace from a top-view is illustrated, with an indication of the microscope's field of view on the anastomosis. The visualized configuration serves as an example that indicates how a dexterous robotic arm100allows the pair of instruments106to assume a wide range of orientations relative to the operating site.

High instrument dexterity, cf.FIGS.37and38. allows a more optimal orientation to be assumed for each manipulation at the benefit of the quality and efficiency of the operation,

Part of the robotic arm100may be draped, while other components remain exposed and hence are required sterile.FIG.10serves to distinguish between these two by visualizing the location of the drape128for the concept design.

Here, the drape128is applied away from the instrument106such that it poses minimal interference with the surgeon's line of sight and manual workspace. Those parts protruding outside the drape128are subject to autoclave steam sterilization.

Hence, it is apparent fromFIG.10that a substantial part of the robotic arm100must be designed suitable for sterilization. The added complexity of sterilizable modules is to be offset by an increase in instrument dexterity and precision.

Moreover, with sterilizable joints for grasp, roll, pitch, and yaw, none of these axes is affected by the disturbances or motion constraints typically imposed by the drape128.

FIG.11shows a first embodiment of the instrument module102with an instrument106, the pitch module116and the yaw module118, according to the present disclosure.

The instrument module102hinges directly on the yaw shaft270, for which the resulting hinge-line perpendicular to the shaft constitutes the pitch axis130. In addition, both the drivetrain and actuator for pitch are directly integrated into this yaw shaft as well (cf.FIG.24). The yaw orientation is imposed on the instrument106by a direct drive that controls the angular position of the shaft with respect to the concentric outer tube272. This outer tube272in turn constitutes the manipulator arm, which serves to position the assembly of revolute joints in space.

Also shown inFIG.11are the yaw axis132and the roll axis134.

FIG.12illustrates further an embodiment of the instrument module102according to the disclosure, holding an instrument106.

The instrument module102comprises an instrument actuation submodule104.

Further, the instrument module102comprises an instrument submodule126.

The instrument actuation submodule104may be understood as active part of the instrument module102, configured for actuation of instrument106grasp and roll.

The instrument submodule126may be understood as passive part of the instrument module102, configured for holding the instrument106.

Shown is also the pitch axis130.

The instrument module102is designed separable.

Disassembly of the instrument module102can be performed manually through the release of the quick-lock clips136, cf.FIG.13.

FIG.13shows a further illustration of the instrument module102(disassembled status).

Shown is the instrument submodule126and the instrument actuation submodule104, which are both part of the instrument module102.

The instrument submodule126comprises an instrument retainer138and an instrument106.

In this embodiment, the instrument submodule126further comprises a retainer shell140.

In this embodiment, the instrument retainer138holds the instrument106.

In particular, the inside of the instrument retainer138is shaped to hold the instrument106, cf.FIG.19.

Also, in this embodiment, the instrument actuation submodule102is configured for to operate grasp and roll orientation of the instrument106.

Further shown are the (two released) quick lock clips136.

Not explicitly shown inFIG.13is that the instrument actuation submodule102may remain connected to the yaw shaft270, such that the pitch transmission and electrical connections need not be detached.

The passive instrument submodule126in contrast features no such connections, and may therefore be swapped out freely for different types of instrumentation.

FIG.14illustrates an embodiment of a custom instrument106, designed for robotic operation.

The displayed instrument106is a needle holder106, in particular for surgery, microsurgery or super microsurgery, in particular for anastomosis, although other types (e.g. forceps) are largely similar in layout and/or dimensions.

In this embodiment, the instrument106comprises two compact instrument beaks142, an instrument hinge pin144, two instrument handles146and two handle joints148.

In an alternative embodiment, the instrument comprises more than one hinge pin144and/or more than two instrument handles146and/or more than two handle joints148.

In this embodiment, an effective beak142length of 10 mm is selected for the custom needle holder106. This dimension corresponds to the downscaling of the instrument106to approximately two thirds of a traditional needle holder106for a robotic arm100.

This reduced beak142length serves to proportionally limit the maximum output arm for grasp. In turn, this again proportionally reduces the required amount of force applied at the handle146to clamp a needle306with a force of over 5 N at the beaks.

In general, the instrument beaks142each may have a length of less than 20 mm, in particular less than 15 mm.

Also in general, the instrument106may have a length of less than 50 mm, in particular less than 30 mm, in particular 20 mm.

Moreover, the selected dimensions allow for a one-to-one transfer of grasp from the handle-joints to the tip of the beaks.

In further contrast with the traditional type of needle holder, the custom variant features an inverted hinge mechanism. In other words, the instrument is configured and arranged for an inverted hinge mechanism.

Consequently, the beaks now close instead of open upon the spreading of the handles. This inversion serves the implementation of a knee mechanism for actuation of the instrument, as is described in the following paragraph.

FIG.15shows an illustration of the instrument knee mechanism for symmetric actuation of the instrument106.

Shown is the instrument106according toFIG.14.

On the left side, the instrument106is shown in the open state, wherein on the right side ofFIG.15, the instrument106is shown in the closed state.

Additionally, shown are two retainer guide pins150, one knee link pair with two knee linkages152, one stopper154and a knee mechanism central joint156, which all are all comprised in the instrument retainer138.

In particular, the operation of grasp is conveyed from the instrument actuation submodule104to the instrument106via a knee mechanism.

Following, the instrument retainer138is configured to actuate the instrument106by an inverted hinge mechanism.

In an alternative embodiment, the instrument retainer138could comprise more than one central joint156, more than two retainer guide pins150, more than one stopper154and/or more than one knee link pair152.

The knee linkages152connect both instrument106halves to the central joint156. Symmetric actuation of the instrument106hereby reduces to the controlled translation of this central joint156over the module centerline.

Further, a pushrod158is introduced (as part of the instrument actuation submodule104), which acts over the centerline of the instrument actuation submodule104.

The pushrod158comprises a spherical tip configured for contacting a matching socket in the knee mechanism central joint156.

To this end, the instrument retainer138offers slots that serve as a straight-guide for the central joint's extended hinge pin150. This guide together with the instrument hinge pin144itself fully constrains the instrument mechanism with respect to the instrument retainer138, leaving only a single internal DOF for grasp.

Moreover, the second pin150on the central joint156serves to maintain the joint's156alignment with respect to the pushrod158to facilitate instrument106exchange.

The instrument knee mechanism is further illustrated inFIGS.16-18.

FIG.16shows an illustration of the relation of input/output of the instrument knee mechanism.

Here, a 2.2 mm linear input stroke suffices to fully close the instrument106from its maximum spread of 2 mm at the tip.

FIG.17illustrates the dimensioning of the knee-mechanism.

In particular, a schematic representation of one instrument106half is provided, including one of the linkages from the knee-mechanism. The other instrument106half and knee may be

considered their mirror image in the line A:A.

Moreover, the solid lines inFIG.17represent the instrument106in fully opened position. Conversely, the configuration for closed instrument beaks142is displayed in dashed lines. The stroke leading from one configuration to the other is in addition visualized using dashed curves.

The properties of the instrument106have already been described in detail inFIG.14and/orFIG.15.

In surgery, it is not practical for the needle306to be grasped at the very tip of the instrument106. Neither will it be operated near the instrument106base close to the instrument hinge pin144.

It may therefore be assumed that for suturing the needle306will always be clamped somewhere in the 1 mm to 5 mm front section of the instrument beaks142.

Hence, it now follows from the graph that the mechanism input to output ratio is always greater than 2.275 in the relevant section.

Therefore, an actuation force of 2.2 N at the knee mechanism central joint156would suffice to realize a grasp force of over 5 N for any needle306used.

Furthermore, over 30% of the input stroke is used to close the instrument106over the last 15% of its spread, where the needles306and tissue are grasped.

As discussed already forFIG.14, the effective instrument beak142length Lbis scaled down to e.g. two-thirds of a traditional microsurgical instrument106.

Next, the length of the instrument handle146is selected equal to that at Lb=Lh=10 mm, in parallel consideration with the dimensioning of the knee mechanism and grasp drivetrain. Consequently, the required 2 mm maximum spread at the tip of the instrument106(St=1 mm) corresponds to an angular stroke of αb=5.7° for each instrument106half.

The instrument handle146is now set at an effective angle βh=17.5° to the instrument beak142, such that the spread at the knee ranges from 2 mm for the instrument106fully opened, to 3 mm for the beaks firmly closed.

Moreover, at βh=17.5°, there is sufficient space for the knee mechanism central joint156to move in between the instrument handles146, while αkneeds never be beneath a comfortable 42.5°. On the opposite end of the stroke, the knee angle is limited to a maximum value of αk=85°, as it is not desired for the knee linkages152to pass their unstable equilibrium position.

In addition, at least one mechanical end-stop/stopper154can be integrated into the instrument retainer138to block the knee linkages152before passing their critical angle.

In conclusion, for the dimensions listed above, a linear stroke Skof 2.2 mm now suffices as input for the knee-mechanism central joint156(to fully close the instrument beaks142), cf.FIG.16.

FIG.18shows an illustration of the instrument knee mechanism—preloading.

The illustration is based on the instrument(s)106properties disclosed inFIGS.14and15.

As inFIG.15, the instrument106is shown in its open position (left side), and in its closed position (right side).

The instrument106is shown here together with an instrument preload band160and a preload band guide pulley162.

In general, the instrument preload band160and the preload band guide pulley162may be comprised in the instrument retainer138.

Also, the instrument retainer138may comprise more than one preload band160and more than one preload band guide pulley162.

Due to the nature of the contact between the pushrod158and the knee mechanism central joint156, the pushrod158itself cannot exert a tensile force on the instrument106. Hence, an additional restorative force is required to spread the instrument beaks142and maintain the contact between pushrod158and knee mechanism central joint156.

To this end, the knee mechanism is preloaded by a preload band160, in particular an elastic preload band160, in particular a rubber band160, applied to both the instrument handles146and the knee-mechanism central joint156. This preload forces the instrument beaks142back into their open position, partly through the back-driving of the knee mechanism from the instrument handles146.

However, in case the preload is applied only at the instrument handles146, the resulting restorative force at the knee mechanism central joint156would strongly depend on the non-linearity of the knee.

Therefore, the preload band160is in addition looped around the preload band guide pulley162, which is in particular located around a retainer guide pin150, on the knee mechanism central joint156.

In addition to maintaining the contact between pushrod158and knee mechanism central joint156, the preload band160serves to remove play from the assembly.

As the preload band160is applied at the instrument handles146and tensions them together, the preload force will always act through the links of the knee mechanism. Consequently, the joints of the knees are always in contact in the direction corresponding to a closing action, such that no play is traversed upon the clamping of an object.

FIG.19shows an illustration of the instrument retainer holding the instrument.

The illustration is based on the embodiments disclosed inFIGS.13,14,15and18.

The instrument106attaches to the instrument retainer138via the instrument hinge pin144, which is situated directly at the base of the instrument beaks142.

In particular, the inside of the instrument retainer138is shaped to accept a specific type of instrument106.

In particular, the inside of the instrument retainer138comprises a specific instrument guide163to accept the instrument106.

In contrast, the instrument retainers138contours and dimensions are identical across the range of compatible instrumentation. This serves to provide a universal interface at the instrument retainer138that matches its counterpart on the instrument actuation submodule104and retainer shell140.

In addition, mechanical end stoppers154are integrated into the instrument retainer138that block the knees before passing their critical angle.

The instrument hinge pin144is convenient for attaching the instrument106to the instrument retainer138, as it is the only part of the instrument106that does not move upon actuation of grasp.

Moreover, the instrument guide163of the instrument retainer138and hinge pin144together serve to constrain the position of each instrument half with respect to the instrument retainer128as well as each other.

The instrument retainer138is in turn supported on two plain bearings in the retainer shell140of the instrument submodule126(cf.FIG.13).

To this end, the instrument106features a spherical surface at the instrument hinge pin144, such that it remains within bounds of the forward bearing upon operation of grasp. These plain bearings serve to reduce friction compactly, without complicating the process of cleaning and sterilization. As the retainer shell140attaches rigidly to the instrument actuation submodule104, it thereby positions and interfaces the instrument106and instrument retainer138with their respective drives.

For grasp, this interface amounts to establishing the preloaded contact between the pushrod158and knee mechanism central joint156. For roll, on the other hand, the instrument retainer138integrates an inner gear that meshes with its counterpart on the instrument actuation submodule104. Moreover, the resulting thickened end-section helps to preserve the circular shape of the torsion stiff retainer cone.

The instrument106in the instrument retainer138can be cleaned and sterilized disassembled from the instrument actuation submodule104. This serves to improve the exposure of the instrument submodule's126inner surfaces. Moreover, the disassembled instrument retainer138with instrument mechanism is designed to feature only pin-joints and compact mating surfaces. These are similar in construction to the hinge area in a traditional microsurgical needle holder. Consequently, for the custom instrument106, these contacts are assumed equally well suited to autoclave sterilization.

Furthermore, the instrument106and outer surface of the retainer (retainer shell)140may be brushed to remove organic contaminants such as blood prior to sterilization. The inside of the instrument retainer138in contrast is less prone to severe contamination and may be soaked and rinsed with cleaning agents. To facilitate this process, an anti-microbial coating can be applied to the instrument106, knee mechanism, and retainer138.

Moreover, this coating doubles in function to reduce friction in the mechanism joints and their contacts with the instrument retainer138. The instrument beaks142in contrast must remain free from such coating, e.g. to prevent the needle from slipping.

FIG.20shows an illustration of the instrument actuation submodule104.

As described previously, the instrument actuation submodule104comprises a first motor164and a first drivetrain166for actuation of the instrument roll orientation.

Further, the instrument actuation submodule104comprises a second motor168and a second drivetrain170for actuation of the instrument grasp orientation.

Further, the instrument actuation submodule104comprises a grasp instrument interface, a roll instrument interface, a compliant seal186, a front frame instrument module, a rear frame instrument module and a frame cap.

As also described previously, the instrument actuation submodule104is configured to operate grasp and roll orientation of an instrument106. In other words, the instrument actuation submodule104contains the actuators164,168and drivetrains166,170that allow full control over grasp and roll, when paired with the previously discussed instrument submodule126.

Furthermore, the instrument actuation submodule's104enclosure provides an interface to the manipulator arm250that doubles as the pitch axis130, as was already indicated inFIG.12.

FIG.21shows an illustration of the instrument module grasp drive.

Illustrated is inter alia the grasp drive motor168.

In this embodiment, the grasp drive motor168is a Stepper motor.

Further, there is a drive gear172and a motor pinion174.

Shown is also the pushrod158, a pushrod guide176, as well as a leadscrew nut178and a preload nut180.

Further, there is a bearing spacer182

The actuation of instrument grasp can be described as follows (reference is made toFIGS.15,18).

As discussed forFIG.15, the pushrod150positions the central joint of the knee mechanism156over a stroke of 2.2 mm along the instrument submodule126centerline.

The tip of the pushrod158is spherical and contacts a matching socket in the knee mechanism central joint156.

This contact is maintained only by the instrument preload force, such that no additional coupling is required that could otherwise hinder instrument exchange.

The knee-mechanism central joint156rotates along with the instrument106upon actuation of roll. In contrast, the angular position of the mating pushrod158is constrained with respect to this axis. Hence, in the absence of rotation, a compliant seal may be applied to the pushrod156that serves as a flexible sterile barrier over the 2.2 mm linear stroke.

First, focus is shifted to the linear actuation of the pushrod158. It is estimated that a force of 3.2 N would suffice, considering the knee-mechanism input-output relation and an estimate of an additional 1 N associated to friction and preload force.

Furthermore, the pushrod158is desired non-backdrivable, so no actuator effort is required for grasp once the instrument106is clamped. This measure serves to reduce heat generation in the instrument module102, such that the effects associated to temperature variations may be minimal.

In addition, the pushrod158is configured to traverse its full stroke within one second to fully open or close the instrument106.

Based on the consideration above, a M1.2 leadscrew with 0.25 mm pitch is selected for use in combination with a miniature Stepper motor168. The combination of leadscrew and motor168is commercially available from the supplier in direct drive.

For actuation of grasp however, an additional spur gear transmission is included in the drivetrain166.

A M1.2×0.25 mm stainless steel leadscrew serves to convert the rotation at the motor168to the required 2.2 mm linear grasp stroke at the pushrod150.

The M1.2×0.25 mm leadscrew is threaded directly on the rear-end-segment of the pushrod158to form a compact union. As the sterile barrier does not allow the pushrod158to rotate around its longitudinal axis, the leadscrew nut178is driven instead.

This configuration is illustrated inFIG.21where the leadscrew178nut is incorporated into the body of the driven spur gear172.

In turn, this body is suspended on a pair of miniature bearings184, preloaded using a Belleville washer. This washer is tensioned by tightening the adjacent nut, while the rotation of the body itself is temporarily constrained using a hex key.

For actuation of grasp and roll, both standard Stepper motors can be selected factory fitted with a twelve teeth module 0.12 motor pinion174(pinion is rated up to at least the stepper's boosted holding torque of 0.39 mN m). Therefore, this standard configuration provides a convenient starting point in the development of the miniature transmissions for both grasp and roll.

In case of the grasp transmission, the pitch-diameter of the driven spur gear172may be based on the center distance of 4 mm between the pushrod158and motor168. This results in a module 0.12 gear with 55 teeth, which corresponds to a transmission ratio of approximately 4.58:1 when paired with the motor pinion174.

The direct drive specs multiplied by this transmission ratio would result in an axial force of 3.2 N, available for speeds up to 2.6 mm s−1. This speed is sufficient to fully open or close the instrument106within one second, while the thrust can generate over 5 N of grasp force at the tip for all relevant instrument (needle) gauges.

In comparison to the M1.2×0.25 mm leadscrew, other variants have been considered as well. For example, a M2 leadscrew is commercially available with a smaller 0.20 mm pitch that allows twice the axial load and would increase grasp resolution. However, due to its larger diameter and reduced pitch, this variant offers only half the efficiency when compared to the M1.2×0.25 mm screw. Hence, as the stepper's torque is the limiting factor in the design, this reduction in efficiency would significantly reduce the available thrust at the pushrod158. Overall, the 0.25 mm pitch leadscrew is found most suitably balanced when considering its diameter, efficiency, and rated linear force.

In the instrument module102, the stepper motors168,164and leadscrew are integrated side-by-side for compactness. Consequently, the driven spur gear172is selected based on their center distance, and to match the factory fitted motor-pinion. This may result in a transmission ratio of 4.58 for a certain gear combination. A first conservative indication of performance indicates a force of 3.2 N to be produced at the pushrod158. This is based on the rated specs of the direct drive configuration of motor and leadscrew.

For validation, the following equation is now used to determine the required torque T to generate a linear force Ft based on the screw's lead L and efficiency e.

This computation shows that, neglecting other losses, a comfortable 0.1 mNm motor torque suffices for actuation of grasp. Taking into account the spur gear transmission, this torque serves to produce the maximal required push force of 3.2 N at the knee mechanism central joint156.

Moreover, screws with an efficiency e<35% can be self-locking.

This results in a non-backdrivable grasp drive for the robotic arm100upon integration of the M1.2×0.25 mm leadscrew. This self-locking property allows the continuous load associated to the clamping of the needle306to be born by friction in the screw instead of a holding torque at the actuator.

The Support Miniature Bearings

The leadscrew nut178is suspended on a pair of commercial miniature bearings184.

In one embodiment, these bearings have an inner diameter of 5 mm, an outer diameter of 8.2 mm, and width of 0.9 mm. They are available with a stainless steel retainer and ceramic balls, that are inserted between a split inner ring.

Instrument Handle Compliance

The instrument handles146of custom microsurgical instruments106feature a certain compliance that allows them to ex slightly upon the clamping of an object. This flexing offers a more gradual build-up of grasp force at the instrument beaks142, and in addition serves as a preload and buffer towards the drive. Hence, minor variations in the position of the pushrod158can be accepted elastically without loosing grip on the instrument106. Therefore, these variations do not require active compensation from the stepper motor168, which would otherwise need to provide a constant correcting torque on the non-backdrivable lead-screw. Moreover, for other custom instrument106types such as the forceps, a high handle compliance can serve to limit the attainable grasp force while offering more control over its application.

In the following, it shall be focused on instrument106roll.

Instrument106roll is actuated from the final joint in the manipulator wrist, such that it may be controlled directly and independently at all times. Moreover, this axis requires a maximum angular velocity of π=2 rad s−1over its revolute stroke of ≥540 degrees. The design effort for the associated transmission will focus on conveying instrument roll through the sterile barrier over large rotations.

FIG.22shows an illustration of the hypocyclic drive transmission.

A variant of the hypocyclic transmission mechanism is proposed. Here, a driven internal gear187is integrated into the instrument retainer138(cf. alsoFIG.19), and hence in extension it is directly linked to the orientation of the instrument106. Moreover, this driven gear meshes with its external (roll external gear188) counterpart on the instrument actuation submodule104(cf.FIG.23), which in turn prescribed the instrument roll orientation.

The internal gear187is concentric with the roll axis and has 74 teeth module 0.12. In contrast, the external gear188has three teeth less, and therefore requires an offset ax of 0.21 mm from the roll axis to properly mesh.

Operation of the hypocyclic drive transmission in the essence boils down to rolling the external gear188along the inner contours of the internal gear187. During this rolling motion, the center of the external gear188describes a circle around the hearth of the stationary internal gear187. Furthermore, over one such revolution, the relative orientation between the internal gear187and external gear188shifts by the difference in their respective number of teeth. For the non-backdrivable gear combination described above, this amounts to a transmission ratio of 1/24.7.

In case of the instrument module102however, it is desired that the internal gear187rotates while the external gear188does not. This is realized by constraining the rotation of the external gear188while still translating its center over the offset circle introduced above. In this configuration, the hypocyclic drive remains driven from the external188gear, but the rolling motion now occurs at the internal gear187concentric with the roll axis134.

Consequently, the sterile barrier is no longer required to seal a large rotation, but instead it now suffices to seal small in-plane translations. Consequently, a compliant seal186at the external gear188is able to convey an infinite angular stroke for roll.

In addition, a pair of relatively large open drive gears with only a small offset, allows sufficient space for integration of the pushrod158for grasp to pass through along the instrument module104centerline.

FIG.23shows an illustration of the roll drivetrain.

In particular, on the left side ofFIG.23, the roll drivetrain is illustrated from the outside, whereas on the right side ofFIG.23, a cross section of the roll drivetrain is illustrated.

Although the hypocyclic drive introduced above is a key feature of the roll drivetrain, it requires auxiliary transmission components to make it functional. In the essence, the rotary motion at the stepper motor164needs be converted to a translation of the external gear188over the offset circle.

In addition, the external gear188must be coupled torsion stiff to the instrument module102enclosure, while remaining sufficiently laterally compliant to allow the in-plane wobble.

Shown is the compliant seal186, the roll external gear188, the bellow190, the excenter shaft192, roll drive ball bearings184, the motor164, the balance mass198, the pushrod158and the motor pinion196, which are explained below.

The Bellow Coupling

A miniature metal bellow190is integrated into the design that acts as the torsion stiff laterally compliant coupling to the external hypocyclic gear.

The bellow190must offer a compact torsion stiff coupling with sufficient lateral compliance to allow the excursion imposed by the excenter drive. Due to the scale of implementation and exposure to autoclave sterilization, an electroformed metal bellow variant may be most suitable. These can be produced leak tight with wall thicknesses down to 5 μm, which allows for high exibility and force sensitivity.

Here, the module housing is made to enclose the bellow190as well, in order to protect it from damage upon handling.

Design Requirements

In operation, an effective roll torque of 1.5 mNm at the instrument tip suffices. Nevertheless, for robustness, the bellow190must withstand a minimum torque of 15 mNm, which corresponds to the application of a 5 N maximum force at the instrument tip. Furthermore, the bellow190is desired to offer an infinite rotary lifetime for a parallel offset of 0.21 mm between opposite ends. This offset corresponds to that of the roll drive excenter and is selected in parallel with the dimensioning of the hypocyclic transmission.FIG.39provides a schematic illustration of a standard bellow with the relevant design parameters indicated.

The Excenter

Furthermore, the in-plane wobble is generated by an excentre shaft192that passes through the bellow190.

On the drive side, the excenter shaft192features a 78 teeth internal gear that meshes directly with the standard motor pinion186on the motor164used.

Consequently, the transmission ratio from motor164to excenter shaft192is 6.5, which similarly to that of the grasp drive follows from their respective 4 mm center-distance.

On the opposite end of the excenter shaft192, it features an excenter with 0.21 mm offset that drives the external (hypocyclic) gear188.

The excentre shaft192assembly is laterally loaded by the bellow190, which produces a 1.4 N reaction force to the imposed excentre offset.

To minimize the friction in the roll drive associated to this load, (ceramic) ball bearings194are selected that support both the excentre shaft182and hypocyclic gear.

These bearings194are loaded predominantly radially, and some play is accepted in their application. This allows the hypocyclic gear to align itself to its meshing counterpart, while temperature variations can freely be accepted along the excenter shaft192.

Balancing the Roll Drive

To operate instrument roll at its maximum angular velocity of π/2 rad s−1, the excenter shaft192must rotate at close to 6.2 revolutions per second. However, none of the centers of mass for the external gear188, bearing190, and excenter shaft192will naturally be incident with the axis of rotation. Hence, operation of roll continuously shifts these masses around, which introduces vibrations in the system. Therefore, an additional balance mass198in integrated in the excenter shaft192that serves to balance out the drive to reduce vibrations in the system.

The Compliant Seal186

The contact between the knee-mechanism central joint156and pushrod158is maintained by a preload force. This allows the knee-mechanism to rotate freely with instrument roll, while the pushrod158remains stationary.

In the absence of rotation, a compliant seal186is applied to the pushrod158that exes to cover the 2.2 mm translation stroke.

As no relative motion is required between the compliant seal186and the pushrod158, they may be rigidly bonded to provide a robust barrier against the passing of any contaminants.

The other end of the compliant seal186is attached to the external (wobble) gear188of the roll transmission, where it is bonded similarly. Here, the compliant seal186must comply to the 0:21 mm in plane offset associated to the wobble drive excenter.

The compliant seal186can be produced from an elastomer, such that it is suitable for repeated autoclave sterilization. As opposed to the band in the preload mechanism, the grasp seal is designed for low strain, such that the stresses introduced in the barrier are minimal. This serves to increase the life-span of the barrier and thereby reduces the costs and downtime associated to servicing.

Nevertheless, the compliant seal186must be inspected prior to surgery for safety, to verify it remains adequately bonded and shows no punctures. If all is in order, the risk of damage to the compliant seal186during surgery is regarded low and no more than that associated to the application of a drape128, as is traditionally accepted.

Stepper Motor Control and Safety

Stepper motors allow for open-loop control, so no additional position sensors are required for operation of grasp and roll. The absence of such sensors contributes to the realization of a compact and robust design for the instrument actuation submodule104.

Moreover, an eight core electrical connection for both actuators combined suffices in this case. Currently, this connection is maintained over the pitch stroke through sliding contacts. Alternative solutions without relative motion between the contacts can however be used and may still be considered to improve robustness.

Regarding safety, upon a fault in the stepper motor164drive system it can either stall or start jittering. Stalling may occur due to a loss of power, or a short circuit causing the motor164to exert a holding torque. For the latter, safety features can be included in the control circuit that limit the available power and shutdown the drive on overcurrent detection. The scenario of jitter may result in the case of wire break or a malfunction in the control sequence. It is argued that neither of these failure modes could result in uncontrolled and harmful motion at the end-effector, as both grasp and roll are individually actuated independent axes.

Furthermore, due to the specific commutation pattern required to operate the stepper motor164, the fault scenario of runaway upon short circuit can be rejected. Single fault safety dictates that the fault conditions discussed above may not lead to an unsafe situation, neither directly nor due to an unawareness of the fault. Without position sensors on grasp and roll, the second condition must be satisfied. Here it is argued that the surgeon functions as an observer that may diagnose the loss of responsiveness for either of these axes. The surgeon controls the slave relative to the visual feedback provided through the microscope. Hence, he will act on the actual current state of the system with respect to the anastomosis, rather than attempt manipulations based on its supposed state.

Furthermore, it is argued that failure of roll does not lead to an unsafe situation, as there is no potential to do harm associated to this rotation. For grasp on the other hand, failure may occur with tissue or an object clamped stuck between the instrument beaks142. In this scenario, the instrument submodule126may be loosened by the quick-lock clips136, which simultaneously allows the instrument beaks142to spread. This proposed solution is considered equivalent to taking the instrument out of the actuation fingers upon fault.

No feedback is generated in the case of open-loop control and hence for grasp and roll no setpoint error is measured for the controller to act upon. Consequently, regarding safety, faults occurring in the instrument actuation submodule104are not communicated back to the controller and hence are argued not to have the potential to influence the control signal.

A mismatch between the controller input and actuator output occurs when the motor skips steps. Although this is generally undesired, it is not regarded unsafe behavior. Nevertheless, to prevent skipping steps, the available motor torque sits at a comfortable margin above that required for actuation of grasp and roll. Moreover, the required velocities and accelerations at the end-effector allow for a conservative motion profile. In addition, as neither the lead-screw nor the wobble drive is backdrivable, the actuators for both grasp and roll are relatively insensitive to disturbances at the end-effector.

Regarding performance, the surgeon precisely controls the instrument roll angle relative to its current orientation using visual feedback obtained through the microscope. It is argued that due to clutching, there is no intuitive absolute link to be lost between the input at the master gripper and the output at the slave instrument. Furthermore, the surgeon can achieve any roll angle independent from the instrument's installation orientation, as there are no bounds on its angular stroke and no other degree of freedom are affected.

The actuation of instrument grasp does similarly not affect any of the other degree of freedom, but it is however bounded to the opening and closing stroke of the instrument106. Feedback on the motor current may be used for a homing procedure to define the bounds on a newly installed instrument. Homing is generally undesired, but this is accepted in case of grasp to deal with instrument variations. In addition, current sensing allows identification of the clamping point of the beaks around a needle, such that the motor may be shut down once the needle is firmly grasped. However, as lead-screw efficiency is relatively low, dedicated force sensing at the instrument may be considered to offer more detailed feedback. This could benefit the controller and surgeon.

The roll drivetrain must be able to offer a 0.5 N force at a maximum offset of 3 mm from the roll axis134(cf.FIG.11), due to the curvature of the instrument beaks142. This amounts to a minimal effective drive torque of 1.5 mNm.

In addition, the drivetrain is desired sufficiently robust to withstand a torque of up to 15 mNm, associated to a maximum force of 5 N applied at the instrument tip.

FIG.24shows an illustration of the pitch module200.

In particular, on the left side, the pitch module200is shown without the pitch module enclosure216, whereas on the right side, the pitch module200is shown coved with the pitch module enclosure216.

Overall, the pitch module200comprises a pitch drive mechanism202(cf.FIG.26), two flat cables204, a motor plus absolute encoder206, a plain bearing208, a pair of pitch belts210, a (forked) pull member212, a bellow type compliant seal214, a pitch module enclosure216, an assembly guide bushing218, a communication interface220and a yaw sensor magnet222,

Alternatively, the pitch module200comprises only a few of the mentioned elements.

The pitch module200is designed for a large angular stroke, such that surgeons may profit from the associated increase in instrument dexterity. To this end, a drive mechanism202is proposed that imposes the pitch orientation on the instrument actuation submodule104through a pair of flat metal pitch belts210. The pitch drive mechanism202is integrated into the cylindrical enclosure of the pitch module200/yaw shaft.

This pitch drive mechanism202serves to actuate instrument pitch over an angular stroke of up to 150 degrees.

The pitch belts210allow for a relatively compact pitch transmission, for which the short linear actuation stroke may be conveyed through a compliant sterile barrier.

Drive Stiffness

First, the effect of the pitch transmission ratio ipis discussed, here, pulley radius rpis set to 7.5 mm and the effective arm length rtfrom the pitch axis to the tip of the instrument106is 31.6 mm. These values correspond to those of the proposed instrument module104design, for which the formula evaluates to a transmission ratio of approximately ip=4.2.

The magnitude of a force applied at the instrument tip is multiplied by the above transmission ratio when acting at the smaller radius of the pulley. In addition, the resulting strain in the pitch drive system202is scaled up with the transmission ratio when experienced at the instrument tip.

These effects combined yield that the effective stiffness at the instrument tip is only a factor 1/17.75 of that offered at the pulley. This corresponds to a reduction in drive stiffness by the square of the transmission ratio.

The pitch module belt210is identified as the most critical member in its respective drivetrain.

Relevant Parameters in the Dimensioning of the Pitch Belt210

The considerations result a 1.5 mm wide titanium belt with 4.25 μm thickness, wrapped over a pulley with 15 mm diameter.

A 2.5 N preload is applied to the pitch belt210, which serves to increase the non-linear straightening stiffness and to remove play from the pitch drivetrain. Currently, the preload spring on the pitch belt210is applied in-line with the pull-member, but alternative solutions may still be considered to reduce its contribution to the overall drive compliance.

The effects of creep in the proposed pitch belt210can allow the angular position of the pulley to drift over time with respect to the pitch belt210when coupled only by friction. To prevent this discrepancy from forming, the pitch belt210is desired rigidly bonded to the pulley. This bond can be realized by small laser-welds, although these introduce stress-concentrations in the pitch belt210at the cost of a reduced load-rating and/or stroke.

Alternatively, adhesives may be considered that allow some stress relief over their contact area to reduce stress concentrations in the bond.

To this end, the pulley's theoretical maximum angular stroke of 180 degrees is reduced to 150 degrees, such that 3.9 mm of pitch belt210length is reserved for the bond.

Future development may produce a mechanical coupling between pulley and pitch belt210that can be disassembled more easily for servicing.

FIG.25shows an illustration of the forked pull member212and bellow type compliant seal214.

The forked pull member212and the bellow type compliant seal214have already been illustrated inFIG.24, but are here disclosed in more detail.

The parallel pitch belts210for pitch unite in a forked pull-member212on either end.

The cross-sectional area of the forked pull-member212is chosen significantly larger than that of the pitch belt210to compensate for their longer effective length.

Furthermore, the tensile forces in the pitch belt210are introduced in the forked pull member212to act along their center-plane, such that predominantly their in-plane stiffness is felt.

In plane bending moments at the base of the forked pull member212can however not be avoided, and hence the shoulders are designed wider to cubically increase their respective area moment of inertia. Consequently, the contribution of the pull-members212to the pitch drive compliance can be regarded insignificant in comparison to the parallel pitch belts210.

The forked pull members212are screwed directly onto the pull-rods224. This serves to adjust the drive preload and allows the forked pull-members212to be disassembled upon servicing of the compliant sterile barriers.

FIG.26shows an illustration of the pitch drive mechanism202.

In this embodiment, the pitch drive mechanism202comprises at least one of a linear ball bearing224, a non-locating ball bearing226, a ball screw228, a ball screw nut retainer230, a sensor scale232(as part of the enclosure), a ball screw locknut234, a preload spring236, a stopper238, a pull member212, an absolute linear position sensor242, a locating bearing support,244, a torsion stiff coupling246.

Alternatively, the pitch drive mechanism202could comprise not all of the mentioned elements.

Reference is also made toFIGS.24and25.

The Pitch Drivetrain

With the forked pull-member212is place, actuation of pitch reduces to the controlled translation of the members along their centerline. To this end, each forked pull-member212is supported in a pair of miniature linear bearing224, e.g. made of stainless steel with ceramic balls, suitable for exposure to the temperature cycle associated to repeated autoclave sterilization.

In operation, the upper and lower pull-member212move in opposite directions to maintain the pitch belt's210“straightening” preload over the pitch driven directly by a brushless DC motor.

A ball-screw228can be used featuring a section of both right-hand and left-hand thread. Similar to the linear ball bearings224in the pitch module200, the ball-screw228and ball screw nut234can be manufactured in stainless steel.

Furthermore, standard options for the ball screw nut234include ceramic balls without lubrication, to make the configurations suitable for repeated exposure to autoclave temperatures. Such ball screw nut234is featured on either threaded section of the ball screw228, moving symmetrically inward and outward between the pull-members212.

A compact body encapsulates each ball screw nut234and clamps the pull-member212between two cylindrical contacts to constrain the rotation of the ball screw nut234around the ball screw228.

In addition, stoppers238on the pull-members212constrain the axial position of the pull-member212with respect to the nut.

On one side, a preload spring236acts between stopper238and nut to preload the system to the selected tension of 2.5 N. Moreover, this preload spring236must correct the tolerances and thermal variations in the pitch drive for acceptable variations in the preload force. However, the preload spring236is also desired stiff, as it constitutes a serial link within the pitch drive mechanism. As stated above, alternative configurations to preload the pitch belt210may still be considered to improve the drive's overall stiffness.

The ball-screw228is located on one end in a matched pair of miniature precision ceramic angular contact ball bearings (in X-arrangement. In contrast, the opposite end is suspended floating in a ceramic deep-groove ball bearing. A standard bellow type torsion stiff coupling246is introduced between ball-screw228and motor such that any misalignment does not disproportionately stress the motor bearings.

For safety and performance the backdriving of pitch is argued to be non-essential, this could improve robustness of the drive during handling as it limits the maximum stress in the pitch belt210.

The Pitch Drive Actuator

The pitch drive actuator/motor206is integrated within the confinement of the enclosing yaw shaft116, cf.FIGS.8,24.

As there is significantly more space available here than in the instrument module102, the motor206may be selected from the range pre-qualified for autoclave sterilization.

Such a motor206does not require any additional modifications and hence can be cost effective while simultaneously minimizing the chance of complications.

Position Sensor Redundancy

Per revolution, the absolute encoder integrated into the motor206offers 4096 steps of angular position feedback. This sensor can however not determine the pitch angle at startup without performing a homing procedure.

Therefore, this functionality must emanate from a second absolute position sensor, that serves double to provide the controller with measurement data redundancy. To this end, an absolute linear position sensor242(miniature linear induction sensor) is integrated with the (TPLA32) sensor scale232in a parallel configuration along the ball-screw228.

This product offers a resolution down to 73 nm over an absolute stroke of up to 38.4 mm using the differential inductive sensing principle.

Although the absolute linear position sensor242is rated only for temperatures up to 100° C., the manufacturer has confirmed that both sensor242and scale232can withstand repeated exposure to autoclave temperatures when inactive.

FIG.27shows an illustration of the yaw module248.

Concisely, the yaw module248consists of a pair of concentric tubes270,272that together constitute the “manipulator arm”250.

The inner tube270integrates the drive mechanism for pitch and provides an interface for the instrument module102.

The outer tube272, on the other hand, is suspended by the pair of struts252in the front and the crank module254in the rear, which serve to position the tube assembly in space.

Consequently, variations in instrument yaw result from the controlled relative rotation of the inner tube270with respect to the outer tube272.

To this end, a direct drive motor is integrated in the outer tube that allows for an angular excursion of up to 150 degrees of instrument yaw, cf.FIG.38.

Furthermore, the entire yaw module248is subject to autoclave sterilization and requires disassembly to improve exposure of the inner surfaces.

The Actuation of Yaw

A limited angle torque motor is selected for actuation of yaw. This torquer allows for an angular excursion of up to 150 degrees, providing a continuous torque of up to 70 mNm at a nominal voltage of 21V.

Moreover, due to the arrangement of windings in the stator, the motor requires no commutation in positioning the two-pole rotor over its entire stroke. Consequently, this aids in the development of a simple and robust drive, designed for consistent performance over a large number of disassembly, cleaning, and sterilization cycles. The selected limited angle torque motor is of the moving magnet type, where the rotor sits concentrically within the outer coil.

This product is supplied as a kit, containing only the magnet core and two-wire stator, without any housing or bearings. Off the shelf however, this kit is not yet suitable for autoclave sterilization. Therefore, an alternative magnet material was proposed for which the rotor can be produced to withstand autoclave temperatures. In contrast, the shielding of the stator against the elements is to be designed a feature of the yaw module248concept itself.

To this end, the volume associated to the 1.14 mm air gap between the torquer's rotor and stator is considered for the implementation of physical shielding. This gap provides sufficient space to cover the inner diameter of the stator with a thin impermeable shell that shields off the windings. Here, an adhesive serves to hold the shell in place and also lends it rigidity from the structure of the stator itself.

Moreover, this solution is inspired by the canned rotor type of motors, such as are frequently applied in fluid pumps.

The Measurement of Yaw

A pair of absolute encoders is implemented in the yaw module to measure the angular position of the limited angle torque rotor.

Similar to the pitch module, one sensor serves directly in the drive's control loop and is selected accordingly to offer high precision feedback.

The second sensor again operates in parallel to provide measurement redundancy, which improves system safety through fault detection. The performance of this redundant encoder is less critical and therefore allows more cost-effective and compact solutions to be considered.

FIG.28shows a further illustration of the yaw module248(disassembled).

In particular, the manipulator arm250, the inner tube270, the outer tube272, the rotor submodule256and the sensor submodule268of the yaw module248are shown.

To facilitate the process of cleaning and sterilization, the yaw module248is designed to allow for easy (dis)assembly between consecutive procedures.

Most contaminants are assumed to result from patient contact and will therefore be concentrated near the instrument tip.

For this reason, the yaw shaft270is suspended floating on a plain bearing on the open end near the struts252.

In addition, a pair of matched angular contact ball bearings in X-arrangement near the universal joint274serve to constrain the position of the yaw shaft270.

These bearings are of the open ceramic type, where their exposed surfaces aid the process of cleaning and sterilization. Moreover, the length and upward angle of the manipulator arm250hinders contaminants traveling up the tube, such that the bearings experience practically no ingress.

FIG.29shows an illustration of the yaw rotor submodule256.

This assembly contains the rotor258of the limited angle torque motor, as well as that of the inductive encoder260.

Both are passive components, concentrically bonded to a universal hollow shaft264, where an adhesive serves to lock their relative orientation and seal the edges.

In addition, a thin protective shell262encloses the outside of the rotor258. This protective shell262shields the rotor magnet258from corrosive agents and protects it against impact on handling. Moreover, the protective shell262provides smooth contours to the submodule that facilitates the process of cleaning and sterilization.

The yaw rotor submodule256can be mounted on the inner shaft/inner tube270of the yaw module248through the fastening of a single nut (anti-loss nut)266.

Conversely, loosening this anti-loss nut266allows the rotor258to be removed from the outer tube272, which simultaneously releases the yaw shaft270to be removed as well.

This disassembly step greatly increases exposure of the yaw module inner surfaces, and allows the manipulator arm250to be flushed through with cleaning agents.

To minimize the number of separate components upon disassembly, a retainer ring is glued in to the submodule that confines the anti-loss nut266nut to the rotor258in an anti-loss manner.

Upon assembly, a pin-in-slot construction prescribes the orientation of the rotor258relative to the yaw shaft270. In addition, the tightening of the anti-loss nut266serves to preload the axial bond between components.

The resulting friction in this bond serves to eliminate the traversion of angular play during fine yaw manipulations.

FIG.30shows an illustration of the yaw sensor submodule268, providing a top- and section view.

This assembly integrates the active halves for the pair of absolute encoders that provide feedback on the angular position of the yaw axis. To this end, it provides a housing for the inductive encoder, while it shields the sensor chip in an enclosed volume.

A sterilizable connector is featured on top of the submodule that allows communication with the sensors.

Disassembly of the sensor submodule268from the system opens up the rear end of the manipulator arm250, and thereby allows the rotor submodule268to be removed. To this end, the outer tube272contains a mounting rim that offers a precise fit with the inner diameter of the sensor housing.

Here, a pin and notch serve to prescribe the relative orientation of the sensors with respect to the manipulator arm250. The axial position of the sensor submodule268is constrained by tensioning it against a ridge in the outer tube272.

For convenient assembly, this tension is applied through the fastening of a quick-lock clip136on either side. An additional rubber ring on the mounting rim serves to seal the contact between the two components. This seal closes the sterile barrier and thereby prevents the spread of contaminants. Similar to the rotor, the sensor submodule268components may be sealed with adhesives to realize a compact and robust design without serviceable parts. Soft contours again assist in the efficiency of cleaning and sterilization.

FIG.31shows an illustration of the yaw shaft270radial electrical connections.

The electrical connections for grasp, roll, and pitch are all routed through the yaw shaft270for compactness and robustness.

This yaw shaft270however also rotates over the 150 degree yaw stroke relative to the stationary manipulator arm250. Consequently, the electrical connection between the two must be designed to function reliably regardless of this relative motion.

Moreover, as the connection passes through the sterile barrier of the manipulator arm250, the design has to be sterilizable itself as well.

For safety and robustness, a semi-fixed plug type connection may be used over the use of

sliding contacts that feature relative motion in operation. Here, the yaw shaft270integrates multiple-contact radial connector segments276, that face radially outward and are ground flush with the yaw shaft270itself.

To reduce the required length for the connector, three such radial connector segments276are spaced evenly over the circumference of the yaw shaft270in parallel.

The mating connector for the shaft-plug is displayed on the right ofFIG.31, and is directly suspended on the pair of angular contact bearings in the manipulator arm250. Consequently, upon assembly of the yaw shaft270, the plug automatically snaps in place and is secured there through the fastening of the rotor nut.

A at side on both the shaft and connector ensures that they can only be mated in the correct relative orientation.

Furthermore, the conductive patches in the connector280are placed on feathers between cuts that are sealed by a durable sterilizable rubber compound. This serves to make the patches slightly compliant in radial direction, which preloads the contacts while maintaining a smooth outer surface for robustness and to facilitate cleaning, and sterilization.

With the plug-type connection between the shaft and connector280defined, focus is now shifted to the relative rotation between the connector280and the outer tube272housing.

To this end, three sets of spiral flat cables278are designed to spiral outward from the central connector280.

Similar to the contact patches on the shaft, these are implemented in a parallel configuration to safe space in the axial direction.

Each of these cables278consists of twelve 28AWG multi-stranded cores with a flexx-Sil jacket.

When the yaw shaft270turns clockwise, the connection is maintained as the spiral flat cables278reduce their local radius and tighten closer around the plug. Vice-versa, for a counterclockwise rotation, the spiral flat cables278expand again.

Furthermore, to prevent over-stressing the spiral flat cables278, end-stops are implemented that contact a pin in the manipulator arm250that limits the rotation of the central connector280to the maximum stroke of 150 degrees.

The surfaces of the connector280and spiral flat cables278are relatively well exposed to steam sterilization in the autoclave. This may be further enhanced by moulding the cable base on either end in a compliant sterilizable rubber to fill the least exposed areas.

In addition, this helps smoothen the contours and serves as a strain-relief. The inner diameter of the spiral flat cable housing is designed to match that of the motor stator, such that they form one smooth continuous surface. For cleaning of the spiral flat cable assembly, it may again be flushed through with cleaning agents once the rotor258and yaw shaft270are removed.

Moreover, with the spiral flat cables278integrated behind the motor, they are relatively well shielded against accidental contact by an operator, which could otherwise damage the connection.

The disassembled yaw module248viewed from the rear is displayed inFIG.32.

FIG.32shows an illustration of the disassembled yaw module248, viewed from the rear.

In particular, the central connector280and the spiral flat cables278are shown.

InFIG.8, also the crank modules122,254of the instrument position module120are shown.

The crank modules122,254shall now be explained with regard toFIGS.8and33-36.

The two struts252attached to the manipulator arm250are each actuated by a crank module122and together control the instrument position in two degrees of freedom.

Here, a rotary Lorentz motor serves to position the crank over an angular stroke of 60 degrees.

The drive is controlled using feedback from a redundant pair of absolute position sensors. A protective cover in turn encloses the actuator and encoders to shield them off and prevent interference with the drape128.

The crank arm286protrudes from this cover to drive the strut124, which is attached to it via a spherical joint292.

A high level of symmetry in design allows identical modules to be used for the actuation of the struts124on either side of the base frame284.

Moreover, the crank module122may be assembled and tested independently as a functional subsystem of the robotic arm100.

The crank module122operates from inside the drape128during surgery, as previously indicated, such that it requires no sterilization afterwards. This serves to reduce the repeated effort associated to the cleaning and sterilization of the system in between procedures.

Moreover, the design constraints on the crank module122significantly relax when exposure to autoclave conditions is avoided.

The Crank Actuator:

A rotary voice coil actuator is integrated in the crank module122to offer direct drive actuation of the crank286.

The rotary voice coil actuator is of the moving coil type, with a stationary set of magnets and yoke. Both the coil arm and yoke are customized to better suit their integration into the crank module122.

While the yoke is made to accept the standard magnets, it provides additional pockets for the crank arm bearings282and a support structure for the position sensors. The crank arm286in turn directly integrates the standard motor coil288and is extended past its hinge to provide an interface for the strut124and encoder scale.

The concept design for the crank module122features an inline direct drive for high precision actuation of the strut124with minimal disturbances.

Moreover, this drive offers zero backlash while the rotary Lorentz motor allows cog free operation.

The crank286is supported on a pair of preloaded precision deep-groove ball bearings282that introduce only a small amount of friction. This friction however acts at a small radius and combined with a light and stiff design of the crank286this serves to minimize the effects of virtual backlash. Besides friction in the crank arm bearings282, relative motion between contacting surfaces is limited to the ball joint292at the strut124. Due to the small number of components and with minimal wear, the drive can be regarded relatively robust and low maintenance for consistent performance over its lifetime.

Furthermore, the motor288allows two-wire single phase operation, which serves to simplify control and the associated electronic circuits integrated in the system.

Precise control over the Lorentz motor requires feedback from a high resolution angular position sensor.

In case of the robotic arm100, this feedback system is required to provide an absolute reading with a redundant measurement signal for safety.

To this end, rotary encoder modules can be considered for measuring directly at the crank rotation axis. However, without any additional form of transmission, such sensors are limited to ⅙ of their measuring scale due to the 60 degree crank stroke.

Furthermore, actuation of the strut124at a crank arm286of 70 mm would already require a 19-bit encoder system to distinguish a 1 μm translation at the strut124. Such rotary sensors do not match well with a compact design for the crank module, that is desired especially slender near the crank and hinge to facilitate draping.

Consequently, the use of a limited angle arc shaped encoder is proposed, which measures away from the axis of rotation at a larger radius for increased resolution. Moreover, the implementation of such an encoder system pairs well with the construction of a balancing mass for the crank arm. The proposed arc shaped encoder system is based on a commercial product.

Here, the readhead may be stationary, such that no disturbances are introduced due to flexing of the data cable. The absolute scale is featured on a 0.15 mm thick stainless steel strip, which allows a curvature along its length down to a minimum radius of 50 mm. The arc segment298on the crank is in turn designed to accommodate this scale at the minimum radius, and it provides a slot to aid in its alignment and fixation.

For measurement redundancy, an identical pair of these optical encoder systems are integrated side-by-side within the crank module122. A more cost-effective solution could be implemented for the redundant sensor, as its performance is typically less critical. For the crank module122however, the symmetry and simplicity of two identical systems may be used for reasons of compactness and performance.

Although the arc segment298increases inertia of the crank286, it serves to balance its mass and that of the strut with respect to the axis of rotation. In addition, due to the large measurement diameter, the maximum resolution at the strut joint with this position sensor is 1.4 nm, depending on the read-head protocol selected.

The Crank:

The concept design for the crank module122is displayed inFIG.33. It directly integrates the rotor coil288from the Lorentz motor, which serves to position the crank arm286over its angular stroke of 30 degrees in either direction.

This coil is rigidly bonded to the crank arm286using an adhesive, such that the method of mounting is similar to that for a typical hard disk drive voice coil. The front end of the crank286features the interface for the strut124, while the arc segment with double encoder scale290is placed to the rear. Accurate positioning of the strut124benefits from a stiff design for the crank286, with low inertia.

The Crank Arm286

The strut124attaches directly along the hearth line of the crank arm286, such that the resulting torsional moment introduced in the crank is minimal under load. Furthermore, due to the manipulator geometry, the main component of the force acting through the strut will always be in plane with the Lorentz motor rotation.

Nevertheless, depending on the sideward sway of the strut124, a smaller bending moment is also introduced in the horizontal plane of the crank286.

Consequently, a closed box structure is employed for the crank arm286that offers high stiffness in both planes, while mass and inertia remain relatively low.

To this end, the inner material may be removed from the crank by machining its bottom surface away, and gluing in a matching cover afterwards. This cover serves to close the box and thereby lends it stiffness through the suppression of the internal degrees of freedom associated to an open box. Moreover, less material toward the tip of the crank286requires less mass for balancing towards the rear, and hence this serves double to reduce inertia.

Attachment of the Drape128:

For the closed box design of the crank286, as introduced above, the most profound effect on stiffness is gained through an increase in the effective height of its side-walls.

Nevertheless, the crank286is simultaneously slender at the hinge to minimize interaction with the drape128upon repositioning. In case the drape128is hindered in this regard, it introduces disturbances in the crank286and may even restrict its range of motion.

As discussed previously, the relative motion in the drape128between the operated crank286and stationary base frame284is desired minimal. Therefore, it is desired that a well-defined interface from crank286to drape128is provided, as well as one from drape128to base frame284. Regarding the drape128as a sheet, it is most compliant when loaded in out-of-plane bending instead of an in-plane tensile force.

To this end, the drape128is proposed to be applied in a plane perpendicular to the crank286and fastened close to its hinge. There it can be cost-effectively held in place by bands294, e.g. disposable sterile rubber bands, such as are well available commercially. This concept is illustrated inFIG.35, in parallel to the sealing of the drape around the strut.

The Coil Support Structure300and Arc Segment298(Cf.FIG.33):

To the rear of the hinge, the crank286is loaded in the plane of rotation by the Lorentz force at the rotor coil288, and the inertial force of the arc-segment298.

These loads are transferred through the slots of the Lorentz motor by the coil support structure300. This structure consists of two parallel plates, which are situated inline with the side walls of the crank286to offer high in-plane stiffness. The coil support structure300is illustrated inFIG.33.

Moreover, this coil support structure300and arc-segment298move between the magnets of the Lorentz motor. For electrical conductors such as aluminum, Eddy currents will be generated as the structure experiences a change in magnetic field upon rotation of the crank286.

Therefore, the material for the coil support structure300is selected an electrical insulator, such that no prohibitive Eddy currents are generated.

The aluminum nitride machinable ceramic is selected for the coil support structure300. It is an electric insulator with high thermal conductivity of 180 W=mK and low thermal expansion of 4 μm=mK.

In this capacity, the coil support structure300allows heat generated at the rotor coil288to be dissipated to the crank286, which may in turn serve as a thermal buffer and simultaneously increases the surface area for heat loss.

The crank arm286and arc-segment298are both machined from aluminum to limit production costs. The aluminium nitride in contrast is more expensive, and hence it is integrated such that the support structure300can be cut out of thin sheet material. The difference in thermal expansion between aluminum and ceramic could introduce hysteresis in the crank286.

Therefore, the crank286is assembled with its components permanently bonded using adhesives. Permanent bonding is allowed here as the resulting crank286may be integrated as a single submodule during the assembly of the Lorentz motor.

Direct Drive Considerations:

A consequence of a direct drive is that the required forces must be realized directly by the actuator, without further reduction associated to a transmission. Consequently, continuous holding forces result in a higher heat dissipation in the actuator. The Lorentz motor considered is a moving coil variant.

To improve heat dissipation to the frame, a moving magnet with stationary coil may be considered.

Alternatively, a thin thermal strap could be considered to offer a thermal path for cooling the coil to the frame. For future developments, the collection of data representing the force required during surgery may provide additional insight into heat generation at the actuator.

FIG.34shows an illustration of the struts124.

The struts124constitute the links between the manipulator arm250and the pair of drive cranks286overhead (see alsoFIG.8)

In this capacity, the struts124transfer the input motion at the crank module122directly to their interface at the tip of manipulator arm250.

Correspondingly, each of the crank modules122can actively control the manipulator arm250by prescribing a single degree of freedom to its position in space. Moreover, this manipulation directly translates to control over the position of the spherical wrist, and hence in extension prescribes the position of the instrument106itself.

Moreover, each strut124may only link the crank286to the manipulator arm250in one degree of freedom to prevent overconstraining the system.

To this end, the strut124features a spherical joint292on either end, that allow the strut's124body to orient itself along the line of operation.

Hence, the struts124will predominantly experience axial loads, with only small bending moments resulting from friction in the joints.

To transfer this axial load, a slender stainless-steel tube efficiently serves as the body for the strut124to provide high stiffness for a lightweight design. In addition to stiffness, the tubes are dimensioned primarily for robustness. This serves to minimize the chance of damaging the struts during handling or transport in the autoclave trays.

Here, the edges are sealed and smoothed to prevent the ingress and buildup of contaminants. Moreover, the use of corrosion resistant materials combined with a simple and smooth design makes the strut suitable for repeated autoclave sterilization.

Consequently, the ability to operate the struts124outside the sterile barrier serves to significantly reduce visual obstruction by the drape128, as previously described. Although the struts124need to be detached from their cranks286upon sterilization, they may remain attached to the manipulator arm250to reduce the effort of (dis)assembly.

Closing the Sterile Barrier Around the Strut124:

As illustrated inFIG.35, the crank modules254operate from within the sterile barrier during surgery.

Hence, the struts124must pass through this barrier to interact with the manipulator arm250on the outside. Consequently, it is important for safety that the sterile barrier is well sealed to the struts124such that no contaminant may pass through in operation.

To this end, the drape128is designed with a tapered extension at the end of the sleeve covering the crank286. This tapered extension in turn ends in a perforated hole that allows the spherical joint292of the strut124to be fed through.

In addition, the strut124contains a spherical end-stop302(cf.FIG.34) that cannot pass through the hole, thereby locking the drape128in position.

Closing the sterile barrier now amounts to fixating and scaling the drape128around the strut124using surgical tape296.

Subsequently, the drape128can be inverted to fold back up away from the strut124to cover the crank286after the attachment to the spherical joint292has been secured, cf.FIG.35.

The Spherical Joints292:

The strut124uncouples from the crank286at the spherical joint292for disassembly upon sterilization.

Spherical joints292where the socket can snap-on to the ball-stud allow a simple coupling procedure and good access to the contact surfaces during sterilization. A consequence is that separation often requires increased tolerances, reduced stiffness, or a spring preload which could increases friction or play. Moreover, such spherical joints292may lead to high forces being exerted on the crank during (un)coupling by an operator.

Therefore, the spherical joint292itself is selected non-separable, so it may be produced to tight tolerances for smooth operation without a high preload.

A two-side open socket is selected to reduce the inaccessible surfaces, and an antibacterial sterilizable Teon coating may be applied to the socket to reduce friction.

The spherical joints292of the struts124are semi-permanently fixed to the manipulator arm250via metal pins, as they require no separation upon cleaning and sterilization.

On the side of the cranks286however, the struts124must be detached between procedures for installation of the drape128among others. Here, an anti-loss hand-screw serves to tension the spherical joint292against a spherical contact on the opposite face such that the spherical joint292is rigidly locked in position.

The Central Crank Module254for the Manipulator Arm250:

An additional third crank module254serves to control the seventh and last degree of freedom at the instrument106by actuating the manipulator arm250directly in its center of mass.

This third crank module254can be referred to as central crank module254.

Moreover, this central crank module254also passively constrains the manipulator arm250in three degrees of freedom, such that it is now fully constrained.

Consequently, the design of this third (central) crank module254/crank arm286is different from the crank modules122interacting with the struts124.

Nevertheless, the correspondence of the central crank module254ends at the crank arm286, which integrates a universal joint304for the fixation of the manipulator arm250, as is illustrated inFIG.36.

In contrast with the crank modules122for the struts124, balancing of the crank286is not desired for the central crank module254, as this would nearly double the moving mass of the manipulator arm250.

Instead, the integration of a weight compensation mechanism is suggested to balance the central crank over its 60 degree stroke.

FIG.37andFIG.38illustrate the extreme orientations for the pitch (FIG.37) and yaw axis (FIG.38) respectively.

Both joints allow for an angular variation of 150 degrees, and when operated simultaneously they allow the instrument106to dexterously orient to the workspace.

On the contrary, the roll axis allows infinite rotation and can therefore assume any required orientation.

CONCLUSION

A novel concept design for a seven degree of freedom robotic arm/manipulator dedicated to assist microsurgeons in small-scale anastomoses is proposed. This medical robot sets out to provide superhuman operating precision to facilitate the fine manipulations essential in achieving high quality anastomosis.

The concept is build on the identification and reevaluation of user requirements to tailor

the solution to the field of microsurgery.

Manual access to the operating site and a direct line of view both through and underneath the microscope are preserved. From user preferences and procedural conveniences, high instrument dexterity and direct control are identified high potential aspects to improve the precision and efficiency of fine manipulations. The proposed design for the seven degree of freedom robotic system is composed of a three degree of freedom structure for the positioning of the manipulator arm; a three degree of freedom serial spherical wrist to orient the instrument; and a seventh degree of freedom to operate grasp at the instrument beaks.

Moreover, this instrument is designed a custom variant of the needle holder, that is compactly integrated into the manipulator and may be interchanged during the procedure. It allows any of the microsurgical needles to be grasped with over 5 N of clamping force, while the beaks fully close within one second, symmetrically from a maximum spread of 2 mm at the tip. In addition, both instrument pitch and yaw may be operated over an angular stroke of up to 150 degrees, while instrument roll is unbounded and hence allows for infinite rotation.

Moreover, the grasp, roll, pitch, and yaw drives are all designed sterilizable. In particular, the instrument module, the pitch module and/or the yaw module and/or the crank module comprise joints for orienting the instrument and/or instrument grasp, wherein these joints are configured sterilizable.

This allows the drape to be situated further from the instrument such that it causes minimal interference and visual obstruction.

Three crank-modules serve to precisely control the manipulator arm, where the slender struts act close to the center of the wrist for direct control over the instrument position. These cranks are operated in direct drive for high precision, although the central crank requires an additional mechanism to be designed for weight compensation.

For safety, the yaw orientation and instrument position are fully backdrivable to allow manual repositioning upon fault or convenience. In addition, the manipulator arm and strut cranks are balanced such that the system does not collapse on loss of power.

In addition, all but the grasp and roll drive integrate a redundant pair of absolute position sensors for fault detection. These also serve to provide instantaneous awareness of the manipulator configuration on startup without requiring a homing procedure.

In contrast, for grasp and roll no position sensors are implemented as these drives are argued safe in open-loop control.

In addition, sterile barriers are implemented exclusively in configurations where the seal may

bond rigidly to the respective components, without relative motion between mating surfaces. These local seals and the drape together significantly reduce the number of components directly exposed to autoclave conditions and thereby allow more compact and precise drives to be constructed. For efficiency in cleaning and sterilization the slave manipulator is designed to easily disassemble and thereby improves exposure of the submodule surfaces.

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