Instrument articulation

A robotic instrument comprising an arm extending between a robot arm connection and an attachment for an end effector, the arm comprising: a first arm part; a second arm part distal of the first arm part; and a joint whereby the first and second arm parts are coupled together, the joint permitting the first and second arm parts to rotate relative to each other about at least two mutually offset axes; a control rod attached to the second part of the arm at a location spaced from the first and second axes, the control rod extending distally of that location along the first arm part; and a drive mechanism for driving the control rod to move relative to the first arm part and thereby alter the attitude of the second arm part relative to the first arm part.

This is a United States national phase application of PCT/GB2015/050019 filed Jan. 8, 2015 entitled “Instrument Articulation,” which claims priority from United Kingdom Application No. 1400569.8 filed Jan. 14, 2014 entitled “Instrument Articulation” and United Kingdom Application No. 1418255.4 filed Oct. 15, 2014 entitled “Instrument Articulation,” the entire disclosures of which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to articulations, for example for surgical robots.

BACKGROUND

A typical robot arm comprises a series of rigid links, each of which is connected to the next by a respective articulation. Each articulation is designed to have appropriate characteristics of strength, range of motion, size etc. for the purpose the arm is to perform.

One particular application of robots is for performing or assisting in surgery.FIG. 1illustrates a typical surgical robot arm. A patient1is lying on a bed2. The robot arm3extends from a base4towards the patient. The arm has a series of rigid links5,6,7, which are connected to each other and to the base by articulations8,9,10. The articulations provide a sufficient range of motion that the arm can approach the patient in different ways so as to perform a range of surgical procedures. The links can be made to move about the articulations by motors11which are under the control of a surgeon. The final link7of the arm terminates in a wrist articulation12to which a surgical instrument13is attached. The surgical instrument is designed for insertion into the patient and, for example, could be an endoscope or could terminate in a cutting or pinching tool.

It is desirable for the tip of the surgical instrument to be articulated and hence mobile, so that it can be placed in a wide range of orientations relative to the remainder of the surgical instrument. That assists in allowing the surgical instrument to perform a wide range of surgical procedures, and in allowing a surgeon to place multiple arms close to a surgical site. It is also desirable for the surgical instrument articulation to be kinematically well-functioning, without there being any attitudes in the core of its range of motion that are difficult to reach or where there could be poor control over the motion of the end effector.

U.S. Pat. No. 4,257,243 describes a constant velocity joint for coupling a tractor drive shaft to an agricultural machine. U.S. Pat. No. 3,470,712 describes a similar arrangement for serving as a constant velocity coupling.

SUMMARY

According to the present invention there is provided a robot, robot arm or articulation as set out in the accompanying claims.

DETAILED DESCRIPTION

FIG. 2shows the terminal part of a surgical instrument. The surgical instrument is attached to a robot arm which is generally of the type shown inFIG. 1, with a base and a number of inter-articulated rigid links. The end-most part of the terminal link of the surgical instrument is shown at20inFIG. 2. The terminal link of the surgical instrument ends in a wrist joint21which carries an attachment22to which a surgical end effector can be attached, for example a cutting or pinching tool. The joint21articulates the attachment22relative to the terminal link20of the surgical instrument.

The terminal link of the surgical instrument is a rigid shaft, defined by a stiff outer tube23. At the distal end of the tube is a spherical joint21. Spherical joint21comprises a part-ball24which is captive in a part-cup25. The part-cup is fast with the terminal link20of the surgical instrument. The part-ball is fast with the attachment22. The spherical joint allows the attachment to move with three degrees of rotational freedom, but no translational freedom, relative to the terminal link of the surgical instrument.

On the interior of the part-ball24is a Hooke's or universal joint35. The Hooke's joint is offset from the centre of rotation of the spherical joint21and connects the part-ball24to a control rod26. The control rod runs through the interior of the tube23towards the proximal end of the terminal link20of the surgical instrument. The universal joint35connects the control rod to the tube so that it has two degrees of rotational freedom relative to the part-ball.

A pantograph mechanism27couples the control rod26to the tube23. The pantograph comprises a pair of hinged two-part links28,29which terminate in collars30,31through which the control rod26runs. The pantograph permits the control rod to have three degrees of translational freedom relative to the tube23, and to rotate relative to the tube about its longitudinal axis by spinning in the collars, but prevents the control rod from yawing about its transverse axes. The control rod is preferably rigid.

With this mechanism, when the control rod translates laterally relative to the tube, as indicated by axes32and33inFIG. 2, this causes the centre of the Hooke's joint35to move laterally. That in turn causes rotation of the spherical joint21, which alters the direction of the attachment22relative to the terminal link20of the surgical instrument. In this way, when an end effector is coupled to the attachment the attitude of the end effector can be altered.

The motion of the control rod relative to the tube can be driven by any suitable means, for example electric motors or hydraulic or pneumatic rams. The control rod can be elongated so that it runs from the distal end of the terminal link20to near the proximal end of the terminal link, with the result that those drive means can be located near the proximal end of the terminal link. That is convenient because it reduces the weight that is suspended near the distal end of the terminal link, making the terminal link easier to control.

A further advantage of the mechanism described above is that the spherical joint21is relatively compact, meaning that when the attachment22is deflected at a significant angle to the terminal link20the terminal end of the surgical instrument can be brought relatively close to a patient on whom the robot is operating. The compactness of the joint also allows multiple similar robot arms to work in close proximity.

The pantograph mechanism for maintaining the direction of the control rod could be replaced with another mechanism for achieving the same purpose, for example a set of interlinked rockers running between the inner wall of the tube and the control rod and terminating in slip rings in which the control rod runs. Alternatively, the control rod could be permitted to yaw relative to the tube. For example the control rod could run through a spherical joint mid-way along the tube.

FIG. 3shows an alternative design of joint for a surgical instrument. InFIG. 3the end-most part of the terminal link of the surgical instrument is shown at50. The terminal link of the surgical instrument ends in a wrist joint51which carries an attachment52to which a surgical end effector can be attached. The joint51articulates the attachment52relative to the terminal link50of the surgical instrument. A control rod53runs inside the terminal link of the surgical instrument for controlling motion of the joint51.

The joint51comprises a can54, which is shown in more detail inFIG. 4. An inner end of the can is attached to the distal end of the control rod53. The attachment52is provided at the outer end of the can. The can is mounted relative to the terminal end of the surgical instrument in a joint55. The joint55provides the can with freedom to rotate about axes orthogonal to the terminal link of the surgical instrument. In the example illustrated in the figures the spherical joint is provided by a gimbal ring, but it could be provided in other ways, for example it could be a spherical joint provided by a part-cup fast with the terminal end of the surgical instrument in which a part-ball formation of the can54is captive.

Referring toFIG. 4, the can comprises an outer shell60. At each end of the shell is a spherical joint61,62defined by a part-cup63,64that is attached to the shell and a part-ball65,66that is captive in the cup. The outer side of one part-ball65is coupled to the control rod53. The outer side of the other part-ball66is coupled to the attachment52. The inner side of each part-ball is provided with a universal joint67,68whose centre is offset from the rotation centre of the respective part-ball. The universal joints67,68are linked by a connecting rod69. The connecting rod69is equipped with a mechanism70whose purpose is to prevent the connecting rod from rotating about axes transverse to its length. In the example ofFIG. 4, that mechanism is provided by a flat slipper washer71which is attached to and extends transversely to the connecting rod69. The slipper washer can slide snugly in an annular passageway72which also runs transversely to the connecting rod. The fact that the slipper washer is located in the annular passageway prevents the connecting rod from yawing.

FIG. 5shows a similar can to that ofFIG. 4. Like parts are designated the same inFIG. 5as inFIG. 4. InFIG. 5the mechanism for preventing the connecting rod from yawing is a pantograph having two links73,74which are hinged relative to each other. One of the links,73, is also hinged relative to the interior of the can. The other of the links,74, carries a slip ring in which the connecting rod runs snugly.

As the part-balls65,66rotate relative to the can the distance between the universal joints67,68will change. To accommodate that the connecting rod could be made in two parts, one sliding snugly over the other. Alternatively, the attachment52and the control rod53could run slidably through the part-balls65,66and terminate within the can in the universal joints. Then the connecting rod could be of fixed length.

When part-ball65, which is connected to the control rod53, is rotated relative to the can about an axis other than the can's longitudinal axis, that rotation causes the connecting rod69to translate laterally within the can. That in turn causes the part-ball66to rotate relative to the can in a way that mirrors the rotation of the part-ball65.

Referring again toFIG. 3, the can is mounted in a spherical joint55relative to the terminal link of the surgical instrument. The control rod runs through a guide tube75that is mounted in a spherical joint76in the mid-part of the terminal link of the surgical instrument. That arrangement permits the control rod to rotate about that spherical joint and also to slide along its axis relative to that joint. When the control rod is moved so that its distal end moves transverse to the terminal link of the surgical instrument, that motion is transmitted to the inner part-ball65of the can. The can reacts against the spherical joint55, resulting in rotation of the inner part-ball65relative to the can about an axis transverse to the terminal link of the instrument and also in rotation of the can relative to the instrument about an axis transverse to the terminal link of the instrument. The action of the connecting rod69means that the rotation of the inner part-ball is transmitted to the outer part-ball66, causing it also to rotate relative to the can about an axis transverse to the terminal link of the instrument.

The terminal link of the surgical instrument ofFIG. 3is a rigid shaft, defined by a stiff outer tube53. At the distal end of the tube is a spherical joint21. Spherical joint21comprises a part-ball24which is captive in a part-cup25. The part-cup is fast with the terminal link20of the surgical instrument. The part-ball is fast with the attachment22. The spherical joint allows the attachment to move with three degrees of rotational freedom, but no translational freedom, relative to the terminal link of the surgical instrument.

As can be seen inFIG. 3, this arrangement allows the attachment52for the end effector to be deflected to relatively large angles relative to the terminal link of the surgical instrument. In a typical embodiment it may be expected that the attachment can be deflected through a cone approaching 180°.

It can also be seen fromFIG. 3that the joint51at the terminal end of the surgical instrument is relatively compact. This is illustrated at70. The compactness of the joint also allows multiple similar surgical instruments to work in close proximity.

A further advantage of the joint ofFIGS. 3 to 5is that rotation of the control rod53about its longitudinal axis can be conveyed to the end effector with constant velocity. This may be useful if, for example, the end effector is a drill. It may also simplify the strategy needed to manage the motion of the control rod. To permit this behaviour it is preferable that the joint55in which the can54is mounted relative to the terminal link of the surgical instrument does not permit rotation of the can about the longitudinal axis of the terminal link of the surgical instrument. The joint55could be a gimbal joint.

The motion of the control rod53relative to the tube can be driven by any suitable means, for example electric motors71or hydraulic or pneumatic rams. The control rod can be elongated so that it runs from the distal end of the terminal link50to near the proximal end of the terminal link, with the result that those drive means can be located near the proximal end of the terminal link. That is convenient because it reduces the weight that is suspended near the distal end of the terminal link, making the terminal link easier to control.

The joints described above can be used in other applications. For example, the joints could be used for joints in robots other than surgical robots; and for joints other than wrist joints, whether in surgical robots or for other purposes. The joints could be used in non-robotic applications, for example in vehicles (e.g. in drive shafts or steering columns) or in other machinery.

The end effector could be engaged in the attachment22,52by any suitable mechanism, for example by a screw, bayonet or snap fitting.

The can54need not enclose the connecting rod69.

FIG. 6shows a further way in which the can54could be controlled. In this mechanism three push rods80,81,82are attached to the inner end of the can, at locations spaced around the can. The push rods can be moved axially relative to the terminal link of the surgical instrument, e.g. by screw drives, to cause the can to adopt a desired location. The control rod53is mounted to a universal joint83within the terminal link of the surgical instrument, and is made in two parts, with one surrounding and being splined to the other in order to accommodate changes of distance between the universal joint83and its point of attachment to the inner part-ball65. This arrangement is convenient in that the control rod53can readily be rotated by way of the universal joint83independently of the mechanism for setting the attitude of the end effector.

FIGS. 3 to 6illustrate using a spherical joint to couple the control rod to the can and another spherical joint to couple the attachment to the can. Other joints may be used in these instances instead of a spherical joint. For example, a gimble joint may be used. As another example, a universal joint may be used.FIG. 7illustrates an example in which two universal joints90and91are used to couple control rod53to attachment52via intermediate shaft96. Control rod53terminates in U-joint92which rotates about axes A1and A2. Intermediate shaft96comprises U-joint93which is arranged perpendicular to U-joint92and is coupled to U-joint92via cross-piece97. U-joint93rotates about axes A1and A2. Attachment52terminates in U-joint94which rotates about axes A3and A4. Intermediate shaft96comprises U-joint95which is arranged perpendicular to U-joint94and perpendicular to U-joint92and is coupled to U-joint94via cross-piece98. U-joint95rotates about axes A3and A4.

Intermediate shaft96may house the components interior to the can shown inFIGS. 3 to 6. In this case the attachment52is mechanically slaved to the control rod53via the mechanisms described with respect toFIGS. 3 to 6except that the universal joints90and91provide the articulation provided by the spherical joints inFIGS. 3 to 6. In other words, the rotation of universal joint90about axes A1and A2mirrors the rotation of universal joint91about axes A3and A4. In an alternative implementation, the rotation of universal joint90about axes A1and A2is asymmetric to the rotation of universal joint91about axes A3and A4. For example, the double universal joint may be constructed such that universal joint90has ˜±90° of travel about axis A1and ˜±30° of travel about axis A2, and universal joint91has ˜±30° of travel about axis A4and ˜±90° of travel about axis A3.

In this alternative implementation, the slaving may be accomplished mechanically by driving both joints from a common drive but with different gear ratios in the joint mechanisms. In the example given, a common drive input causes universal joint90to rotate around axis A1and universal joint91to rotate around axis A4. However different gear ratios are used in the joint mechanisms, such that when driven, universal joint90rotates three times as far as universal joint91. This would lead to both joints reaching the limit of their range at the same time. Another common drive input causes universal joint90to rotate about axis A2and universal joint91to rotate about axis A3. Different gear ratios are used in the joint mechanisms, such that when driven, universal joint91rotates three times as far as universal joint90. This would lead to both joints reaching the limit of their range at the same time. Alternatively the joints may be slaved electronically. In this case, each axis is independently controlled and software implemented to ensure the correct relationship between all the joint movements.

The attachment52and control rod53may be mechanically slaved together as illustrated inFIGS. 3 to 6. Alternatively, the attachment52and control rod53may be partially or fully electronically slaved to one another in order to provide the same range of motion described with respect toFIGS. 3 to 6.

FIG. 8illustrates some exemplary slaving arrangements for a first joint J1which is the terminal joint of control rod53and a second joint J2which is the terminal joint of attachment52. Joints J1and J2may be spherical joints, universal joints, gimble joints or any other joints which enable the same articulation between the control rod53and the intermediate shaft96/can54and the intermediate shaft96/can54and the attachment52as described above.

In one implementation ofFIG. 8(a), J1and J2are wholly electronically slaved together. In this case, control shaft101driven by motor103controls part of the motion of J1and J2. The other part of the motion of J1and J2is controlled by control shaft102driven by motor104. Control shaft101is coupled to J1and terminates at J2. Control shaft102is coupled to J1and terminates at J2. Motor103is located either in control rod53or further towards the base of the surgical instrument or robot arm. Motor104is located either in control rod53or further towards the base of the surgical instrument or robot arm. In the case of a double universal joint as shown inFIG. 7, rotation of the universal joint90about axis A1is controlled by motor103via control shaft101. Similarly, rotation of the universal joint91about axis A4is controlled by motor103via control shaft101. Rotation of the universal joint90about axis A2is controlled by motor104via control shaft102. Rotation of the universal joint91about axis A3is controlled by motor104via control shaft102. Motors103and104drive their respective control shafts to cause J1and J2to articulate in the same manner as if J1and J2were mechanically slaved together as described above.

In an alternative implementation ofFIG. 8(a), J1and J2are mechanically slaved together by intermediate shaft96/can54, for example as discussed above with reference toFIGS. 3 to 7. Control shaft101driven by motor103terminates at J2. Motor103is located either in control rod53or further towards the base of the surgical instrument or robot arm. Control shaft102driven by motor104also terminates at J2. Motor104is located either in control rod53or further towards the base of the surgical instrument or robot arm. In the case of a double universal joint as shown inFIG. 7, rotation of the universal joint91about one axis A3or A4is controlled by motor103via control shaft101. Similarly, rotation of the universal joint91about the other axis A3or A4is controlled by motor104via control shaft102. J1is mechanically slaved to J2, thus when J2is driven by motors103and104, J1also moves in a manner determined by the manner in which J1and J2are mechanically slaved. InFIG. 8(a)the joint J2which is the most distal of joints J1and J2from the control rod53is driven by motors103and104. Alternatively, the control shafts101and102may be attached to and drive joint J1, and joint J2moves in a manner determined by the mechanical slaving between J1and J2.

In one implementation ofFIG. 8(b), J1and J2are wholly electronically slaved together. In this case, control shaft105driven by motor106controls part of the motion of J1and J2. The other part of the motion of J1and J2is controlled by control shaft107driven by motor108. Control shaft105is coupled to J1and terminates at J2. Control shaft107driven by motor108terminates at one end at J1and at the other end at J2. Motor108is located in intermediate shaft96between J1and J2. Motor106is located either in control rod53or further towards the base of the surgical instrument or robot arm. In the case of a double universal joint as shown inFIG. 7, rotation of the universal joint90about axis A1is controlled by motor106via control shaft105. Similarly, rotation of the universal joint91about axis A4is controlled by motor106via control shaft105. Rotation of the universal joint90about axis A2is controlled by motor108via control shaft107. Rotation of the universal joint91about axis A3is controlled by motor108via control shaft107. Motors103and104drive their respective control shafts to cause J1and J2to articulate in the same manner as if J1and J2were mechanically slaved together as described above.

In one implementation ofFIG. 8(d), J1and J2are wholly electronically slaved together. In this case, control shaft117driven by motor118controls part of the motion of J1and J2. Control shaft117is coupled to J1and terminates at J2. The other part of the motion of J1is controlled by control shaft119driven by motor120. The other part of the motion of J2is controlled by control shaft121driven by motor122. Motor122is located in intermediate shaft96between J1and J2. Motor118is located either in control rod53or further towards the base of the surgical instrument or robot arm. Motor120is located either in control rod53or further towards the base of the surgical instrument or robot arm. In the case of a double universal joint as shown inFIG. 7, rotation of the universal joint90about axis A1is controlled by motor118via control shaft117. Similarly, rotation of the universal joint91about axis A4is controlled by motor118via control shaft117. Rotation of the universal joint90about axis A2is controlled by motor120via control shaft119. Rotation of the universal joint91about axis A3is controlled by motor122via control shaft121. Motors118,120and122drive their respective control shafts to cause J1and J2to articulate in the same manner as if J1and J2were mechanically slaved together as described above.

FIG. 8(c)illustrates an arrangement in which J1and J2are wholly electronically slaved together. Control shaft109driven by motor110terminates at J1. Motor110is located either in control rod53or further towards the base of the surgical instrument or robot arm. Control shaft111driven by motor112terminates at J1. Motor112is located either in control rod53or further towards the base of the surgical instrument or robot arm. Control shaft113driven by motor114terminates at one end in intermediate shaft96between J1and J2and at the other end at J2. Motor114is located in intermediate shaft96between J1and J2. Control shaft115driven by motor116terminates at one end in intermediate shaft96between J1and J2and at the other end at J2. Motor116is located in intermediate shaft96. Motor110drives J1to articulate about one of its axes. Motor112drives J1to articulate about the other of its axes. Motor114drives J2to articulate about one of its axes. Motor116drives J2to articulate about the other of its axes. Motors110,112,114and116drive their respective control shafts to cause J1and J2to articulate in the same manner as if J1and J2were mechanically slaved together as described above.

FIG. 8(e)illustrates an arrangement in which J1and J2are wholly electronically slaved together. Control shaft123driven by motor124terminates at J1. Motor124is located either in control rod53or further towards the base of the surgical instrument or robot arm. Control shaft125driven by motor126terminates at J1. Motor126is located either in control rod53or further towards the base of the surgical instrument or robot arm. Control shaft127driven by motor128terminates at one end in attachment52and at the other end at J2. Motor128is located in attachment52. Control shaft129driven by motor130terminates at one end in attachment52at the other end at J2. Motor130is located in attachment52. Motor124drives J1to articulate about one of its axes. Motor126drives J1to articulate about the other of its axes. Motor128drives J2to articulate about one of its axes. Motor130drives J2to articulate about the other of its axes. Motors128,130,124and126drive their respective control shafts to cause J1and J2to articulate in the same manner as if J1and J2were mechanically slaved together as described above.

The control shafts ofFIG. 8may drive the respective joints about their axes using, for example, a worm and spur gear or a worm and face gear. The control shafts may be coaxial. For example, control shafts117and119inFIG. 8(d)may be coaxial shafts where the inner shaft117drives J2and the outer shaft119drives J1. Alternatively, the joints may be driven from an off-axis control shaft which drives the joints via a bevel gear, worm gear or offset hypoid gear. Suitably, the control shafts are hollow in order to allow for control cables to pass through them.

Suitably, the motors and drive elements are located towards the base of the robot arm. This reduces the weight suspended near the distal end of the attachment, making the attachment easier to control. It also reduces the required strength of the other arm joints and surgical instrument joints, enabling the arm and surgical instrument to be lighter and hence easier to control.