Minimally invasive surgical robotic systems are being developed to increase surgeon's dexterity when working within an internal surgical location. Such minimally invasive procedures are conducted by inserting surgical instruments through small incisions on the skin of the patient. The use of dexterous surgical instruments to manipulate tissues and suture would facilitate the performance of an endoscopic surgical procedure. A manually or robotically actuated surgical device that can articulate as well as actuate reliably would minimize patient risk and operating time.
Current minimally invasive surgical tools have many drawbacks. Most endoscopic tools have rigid shafts and are constrained to approach the workspace from the direction of a small incision. In addition, many robotic devices often have their motors or actuators mounted on the adjacent links. When these motors are mounted on moving links, their weight often reduces the performance of the device. Sometimes the volume that motors occupy near the end-effector can interfere with the access to a workspace. Furthermore, the construction and length of many endoscopic instruments reduces the surgeon's ability to feel the force exerted by tissues and organs on the end-effector. The limited dexterity and sensitivity provided by endoscopic tools is a major obstacle to the improvement and expansion of minimally invasive surgery.
Surgical tools that increase the surgeons' dexterity are needed to improve minimally invasive surgery procedures. It is desirable to provide surgical instruments having a wrist with two or tree degrees-of-freedom. It is further desirable to provide a wrist mechanism that has low friction in order to provide the surgeon with sensitivity feedback of the contact forces exerted by the surgical tools. Furthermore, it is desirable to minimize the stretch in a cable operatively coupling a portion of the tool that is inserted through the incision with power and control mechanisms that remain outside the incision.
The present invention provides a wrist in which the transmission of motion, force and/or torque around a revolute joint can be accomplished without coupling. The motion of its adjacent link does not affect the relative motion of the decoupled element. This construction allows mounting the actuators on other elements of a mechanism, so that only linkage elements move the end-effector. Thus reducing inertia of the moving elements and increasing performance of the device. The decoupled motion of the end-effector or links is achieved by routing their transmission cables around idler pulleys placed parallel to the joint rotation axis on an optimal position such that any stretch on the transmission cable is minimized. This construction may be use for robotic surgical tools that have two independently driven jaws, decoupled and orthogonal from its articulating wrist. This surgical device may also be used in grasping, cutting, suturing or alike operations.
The wrist includes a base that may be mounted to an arm or other structure that locates the wrist away from a drive mechanism. The wrist also includes a link having an end-effector portion that may be pivotally attached to an end-effector to allow the end-effector to pivot about a link axis, and a base portion that is pivotally attached to the base and operable to pivot about a wrist axis of the base. The wrist also includes an idler having a diameter and rotatably attached to the base such that the idler is operable to rotate about an idler axis that is offset from the wrist axis. A cable operatively couples the end-effector to a drive mechanism to allow a user to operate the end-effector. The offset of the idler axis is calculated to minimize stretch in the cable as the link pivots about the wrist axis. Thus, the cable is less likely to develop a permanent stretch over multiple uses, which can cause backlash and adversely affect the sensitivity or “feel” a user often requires while operating the end-effector. Furthermore, when a user pivots the end-effector relative to the link and pivots the end-effector relative to the wrist, one of the motions does not affect the other motion, i.e., the motions are independent of each other.
The offset that provides the minimal stretch in the cable over a desired range of motion, such as pivoting the link 180°, or 120° depends on the desired range of motion, the idler diameter and the ratio of the idler diameter to the distance between the link axis and the wrist axis. For example, the offset that provides the minimal stretch in the cable over a 180° range of motion with an idler pulley diameter of 5 millimeters (mm) and a 12.5 mm distance between the link axis and the wrist axis is 1.48 mm. For the same range of motion but other idler diameters and other distances between the link axis and the wrist axis the offset can be calculated from the following ratios
Where Dw is twice the distance between the link axis and the wrist axis (diameter); Di is the diameter of the idler and Cs is the offset distance. So for a given ratio of the distance between the link and wrist axes to the diameter of the idler pulley, the offset can be calculated by multiplying the diameter of the idler by the number provided in the chart.
In one embodiment of the wrist, the idler axis is parallel or substantially parallel to the wrist axis and the link axis is perpendicular or substantially perpendicular to the wrist axis. In addition, the wrist may include at least two idlers. For example, the wrist may include eight idlers in four groups of two, with the two idlers in each group concentric with each other and each idler is operable to pivot about one of four respective idler axes that are each offset from the wrist axis.
Each jaw 40.1 and 40.2 can rotate independently around the shoulder screw 41, α axis. When the two jaws rotate on the same direction, one wrist articulation motion is accomplished. And when the jaws rotate on opposite direction, the jaws will open or closed. The jaws motions are driven through their cables 50.1 and 50.2. These cable are routed through guiding idler pulleys 22 from their distal drive mechanism.
The link 30 mounts to its pulley 33 with two pins 32. The setscrew 34 couples rigidly the jaw base 30 and pulley 33 with its cable 50.3 (not shown in
There are four pairs of idler pulleys 22, two pairs per jaw; they mount between the two lateral slots of the wrist base 20 with pins 21. These idlers guide the jaw cables 50.1 and 50.2 from the jaw pulleys 42.1 and 42.2 to the drive mechanism. Note that there are four pins 21 for the idlers, two pins per side. Pins 21 cannot go through the whole wrist base 20 because they would interfere with the link 30 and it pulley 33.
AO=BO=CO
But sharp or small round edges would wear the transmission element (cable, belt, etc.) fast and increase friction. Also transmission elements required a minimum turning radius to increase their useful life. Therefore idler pulleys are required to guide the cable.
AO=0.5(Øw+Øi(π−1))
BO=0.5(Øw+Øi)
The difference is:
BO−AO=Øi(1−π/4)=0.2146 Øi
AO≈BO≈CO
The cable length remains approximately constant for any angle of β between −90° and +90°. The optimal offset Cs is sensitive to the Øi/Øw ratio. The optimal Cs to minimize cable stretch for a very large Øi/Øw ratio is 0.2854Øi. For a Øi/Øw=100 ratio, the optimal offset Cs=0.2859Øi; for Øi/Øw=50 the optimal Cs=0.2863Øi; for Øi/Øw=10 the optional Cs=0.2903Øi; for Øi/Øw=5 the optimal Cs=0.2959Øi; and for Øi/Øw=3 optimal Cs=0.3049Øi.
In particular, the embodiment shown in
But if the wrist is mounted in embodiments as the ones shown in
In general, this invention presents a method for guiding transmission cables around joints while minimizing the stretch in cable. Any mechanism with its particular Øi/Øw ratio, and range of motion β, can be designed using this method for minimizing cable stretch. For example: if the wrist shown in
This application claims priority from commonly owned U.S. Provisional Patent Application No. 60/376,964, filed May 1, 2002 titled Articulated Wrist And Tool With Decoupled Motion Transmission, presently pending, which is hereby incorporated by reference in its entirety.
Number | Name | Date | Kind |
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6394998 | Wallace et al. | May 2002 | B1 |
Number | Date | Country | |
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20030208186 A1 | Nov 2003 | US |
Number | Date | Country | |
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60376964 | May 2002 | US |