Patent Application
20130053866
1. Field of the Invention
This present invention relates to surgical robots and particularly to control methods for operating such robots.
2. Description of the Prior Art
Robotic systems have been used in clinical practice for over twenty years, during which time much progress has been made in the theory, technique and clinical applications of surgical robotics. While the robots initially used for surgical applications were industrial robots, dedicated robots have since been developed that are specifically designed to meet the specialized needs of surgery.
Industrial robots are designed for use in a structured environment, i.e., one in which every element is fixed. Such robots thus perform pre-programmed tasks repeatedly, without allowing for human intervention. The environment in a surgical operation, by contrast, is totally unstructured because body sizes differ among different patients, and because different operations tend to involve different and complex procedures. A surgical robot must be adaptable to these differences, and surgeons and their medical staffs must be able to intervene with and work closely with the robot. To adapt to the unique requirements of surgical operations, a surgical robot should thus be adaptable to different patients and different procedures and should be able to complement human abilities and trained skills. A surgical robot must also consume as small a space in an operating room as possible in order to minimize interference with the medical staff.
Medical Robotics of Stockholm, Sweden (http://www.medicalrobotics.se), supplies a surgical robot under the name “PinTrace” for use in orthopaedic surgery. This robot has an anthropomorphic structure with six revolute joints to provide a big workspace. Mazor Robotics Ltd. of Israel (http://www.mazorrobotics.com) supplies a surgical robot called “SpineAssist” for use in minimally invasive spine surgery. This is a miniature parallel robot with six degrees of freedom which is mounted on the spine during the surgery.
Control of a surgical robot is important in providing the robot with both utility and safety. Typical robotic systems have one of three control modes. The first is a passive control in which the robot is operated manually. The second is an active control in which the robot can move autonomously according to a pre-programmed trajectory. The third one is a tele-operation mode, in which the robot is controlled in real-time in response to on-line direct orders from the operator.
The TIMC Laboratory (France) (http://www-timc.imag.fr) offers a robot arm named “PADyC” for Cardiac Surgery Applications. This robot operates as a passive guide with dynamic constraints which limit the instrument motions according to a pre-defined surgical plan. Curexo Technology (Fremont, Calif., USA) offers the “ROBODOC” system for joint replacement surgery. This system can cut bone automatically, but the interaction between cutting tools and patient is controlled only by computer. Intuitive Surgical, Inc. (Sunnyvale, Calif., USA) (http://www.intuitivesurgical.com), offers a surgical robot for endoscopic surgery under the name “Da Vinci.” This robot has three to four robot arms, and the surgeon can control these robot arms through tele-operation controllers.
The present invention resides in a surgical robot in which a tool holder is mounted to a base through linking members arranged in series, with joints connecting the linking members. The joints, which include an arc-shaped sliding joint that provides a suitable work space for surgical applications in an operating room, provide at least seven degrees of freedom. The invention also resides in a method for controlling the surgical robot by a hybrid control that includes both active and passive control modes, to provide enhanced control over the precision, utility, and safety of the surgical tool held in the tool holder.
Many surgical procedures involve movement in a linear direction, such as drilling or manipulating an instrument within the human body structure. Such procedures require only five degrees of freedom. The present invention provides two additional degrees of freedom and thereby presents a greater ability to avoid obstacles. One of the degrees of freedom is provided by a prismatic joint, which fulfills the function of motion through a linear path. Another degree of freedom is provided by an arc-shaped sliding joint, which provides motion along a fixed curve, similar to that of a revolute joint with a remote axis. The remaining degrees of freedom are supplied by revolute joints which revolve around fixed axes.
The term “prismatic joint” is used herein to denote a sliding joint that has only one degree of translation, typically in a linear direction, without allowing rotation of one part relative to another. The term “arc-shaped sliding joint” is used herein to denote a sliding joint in which the movement of one part follows an arc or a fixed curve, rather than a straight line. The typical arc-shaped sliding joint is one with a curved beam and a mating member that engages the beam such that the beam can slide within or along the mating member. The arc-shaped sliding joint is thus a form of prismatic joint since it does not allow rotation of the curved beam around an axis that is tangential to the curve of the beam. The term “revolute joint” is used herein to denote a joint with rotational motion around a single axis and no sliding motion. Each of the joints cited in this paragraph have but a single degree of freedom, although two or more joints together can provide multiple degrees of freedom.
In certain embodiments of the invention, the motion path of the prismatic joint is vertical, i.e., perpendicular to the ground, and the motion plane of the arc-shaped sliding joint is parallel with the motion path of the prismatic joint. The joints other than the prismatic and arc-shaped joints are revolute joints. The first revolute joint has an axis perpendicular to the motion plane of the second joint, and the second and third revolute joints have axes that are parallel to each other and perpendicular to the axis of the first revolute joint. The axis of the fourth revolute joint is perpendicular to the axis of the third revolute joint, and the axis of the fifth revolute joint is perpendicular to the axis of the fourth. And the fourth and fifth revolute joints have the same center of rotation, thereby collectively providing orientation adjustment around the center of a sphere.
The structure can be divided into two parts: a base with two degrees of freedom and a robot arm with five degrees of freedom. The first two joints form the base, and the prismatic joint can be used to adjust the height of the robot arm to accommodate operation tables of different heights. The arc-shaped sliding joint can then be used to adjust the position of the robot arm around the axis of the patient's body. The five revolute joints supply the five degrees of freedom to the robot arm, thereby providing sufficient dexterity for most surgical procedures.
Considering the human body as a cylinder, the arc-shaped sliding joint can bring the robot arm around the axis of the body, and thereby provide the most suitable work space for surgical procedures in the operating room. The arc-shaped sliding joint has the dexterity of a revolute joint plus a slide rail which provides it with the rigidity of the prismatic joint. The five revolute joints are motor-driven, for example by DC servo motors, and each one can also contain an optical encoder, a harmonic reducer, and an electromagnetic brake. Each joint therefore offers active-passive hybrid control, which means that the revolute joints can be driven both by electric power and manually.
The control mode change between the active mode and passive mode of any individual motor can be achieved by changing the power status of the motor. When the motor is powered, the holding torque of the motor will lock the joint, and the joint can operate under an active control mode driven by electric power. When power is no longer supplied to the motor, the joint can be operated manually under the passive control mode. In both the active and passive control modes, the movement of the joint can be monitored by an optical encoder, and the joint can be freely changed from active mode to passive mode and vice versa. An electromagnetic brake that is engaged when overload of the robotic system is detected provides extra holding torque to ensure the safety of the robot system.
In a surgical operation, a surgeon can move the robot arm to place the tool in a rough or approximate position, i.e., one that is near to, but not precisely at, the desired position, by operation of the robotic system in the passive control mode. The surgeon can then switch the robot to operate under active control in which fine adjustment can be performed to place the tool in its final position. This active-passive hybrid control method can shorten the operation time, minimize the range of automated motion, increase safety, and also ensure the precision and accuracy of the surgical operation.
Alternatively, the robot can be placed in an initial pose that is pre-programmed in accordance with a specific surgical operation and a specified workstation or operating room layout. It is known in the art that different surgical procedures will receive optimal performance when the surgical tool is positioned in a particular location, including position and orientation relative to the patient. Likewise, a given workspace will present certain issues such as accessibility to the patient and the need to accommodate supporting materials, equipment, or personnel. All of these factors can be included in determining the optimal initial pose for a procedure, and for any such procedure the optimal pose can be programmed into a surgical navigation system such that the robot can be automatically placed in or guided into such a position prior to the start of the operation. Fine-tuning can then be achieved by further automated movement or under visual guidance or position feedback.
Surgical navigation systems for use in the preceding paragraph are known in the art. Such systems utilize optical tracking, electromagnetic tracking, or other tracking methodologies. Tracking can entail either two-dimensional or three-dimensional image viewing from tracking devices located at the tool holder. Examples of tracking devices are light emitting diodes, ultrasonic emitters, and electromagnetic field emitters. Position feedback from a tracking device can be achieved by a computer display showing an image of the tool overlying an image of the patient or the surgical region on the patient.
The efficiency of a surgical robot is also a concern for surgeons. Robotic surgeries of the prior art tend to entail high costs in teens of time and personnel in placing the robotic system in a suitable position before surgery. With robotic systems of the present invention, the initial positions for different surgeries are planned pre-operatively. The robot can therefore be automatically placed in or guided into certain positions and orientations which are specific to the needs of different surgeries. The result is a significant decrease in setup time.
While the invention is susceptible to a wide range of implementations and embodiments, a full understanding of the novel features will be gained from an examination of a particular example. Such an example is shown in the attached drawings and described below.
The first revolute joint 21 is coupled to the rotary joint 18. The axis 22 of this first revolute joint (shown in
With the arc-shaped sliding joint formed by the block 16 and the arc-shaped beam 17, the robot arm, which term denotes all components from the first revolute joint 21 to the tool holder 35, can move around the axis of the patient's body, and thereby provide the most suitable work space for surgical procedure in the operating room.
When the DC servo motor 52 is powered, the holding torque of the motor will lock the joint 51, and the joint can operate in the active control mode driven by electric power. When the DC servo motor is not powered, the joint 51 can be moved manually in the passive control mode. During both active and passive control modes, the movement of the joint 51 is monitored by the optical encoder 53, and the operator can switch freely between the active and passive modes.
Manipulation of the surgical robot in this example is governed by a surgical navigation system that includes two tracking devices that emit or reflect infrared signals. One tracking device 58 is mounted to the shoulder of the robot arm, i.e., at the location of the first revolute joint 21. This device tracks the position of the portion of the robot arm near the shoulder. A second tracking device 59 is mounted to the tool holder 35 to track the position of the surgical tool held in the holder. Together, these two tracking devices determine the position of the robot arm and operate in conjunction with navigation control to perform a fine adjustment of the position of the surgical tool.
Initial positions of the surgical robot for different surgeries can be planned or pre-programmed before the operation begins. The robot will then automatically move to certain positions and orientations which are specialized to different surgery needs. This significantly decreases the setup time for the robot.
In the claims appended hereto, the term “a” or “an” is intended to mean “one or more.” The term “comprise” and variations thereof such as “comprises” and “comprising,” when preceding the recitation of a step or an element, are intended to mean that the addition of further steps or elements is optional and not excluded. All patents, patent applications, and other published reference materials cited in this specification are hereby incorporated herein by reference in their entirety. Any discrepancy between any reference material cited herein or any prior art in general and an explicit teaching of this specification is intended to be resolved in favor of the teaching in this specification. This includes any discrepancy between an art-understood definition of a word or phrase and a definition explicitly provided in this specification of the same word or phrase.
