Introduction
Endoscopic surgery has become popular in recent years because it is a minimally invasive but accurate surgical procedure that offers an expanded field of view and leaves only small scars. When performing surgery in which it is important to preserve organ functions, the affected area must be identified and the field of view expanded safely and effectively. To perform accurate surgery, it is important for the organ to be grasped and pulled in two directions, and cut when it is under sufficient tension. However, surgeons must manipulate tools with insufficient degrees of freedom (DOFs) and the effects of hand tremors need to be minimized. In addition, cooperation is required between the doctor performing the surgery and assistants using an endoscope or forceps. Many master-slave controlled manipulators [
1] have been developed to solve these issues. Well-known surgical robots in current clinical use are the ZEUS [
2] and da Vinci [
3] systems, which have three or four arms attached to a tool with 6 or 7 DOFs; they are operated remotely by a surgeon in a non-sterilized area. Such systems allow high positional accuracy because of the use of motion scaling and low-pass filtering to counteract tremors. Another master-slave controlled surgical robot in clinical use is the NeuRobot system [
4,
5], which is used for neurosurgery.
Because of the possibility of emergencies occurring, local operation must be considered safer than remote operation. For this reason, our goal is robotically assisted surgery performed by a single surgeon situated in a sterile area near the patient. A large number of locally operated surgical robots and devices have been developed. The manually controlled mechanical forceps Radius [
6] and Autonomy [
7] have 3 DOFs. The passive brake controlled stabilizer used in the intelligent armrest EXPERT [
8,
9] allows tremor elimination. The endoscope-holding robot AESOP [
10] can be operated via voice control, Naviot [
11] via forceps-mounted button control, and FreeHand [
12] via head-mounted sensor control; these systems have 2 or 3 DOFs. These endoscope-holding robots eliminate the need for cooperation with an endoscope assistant. However, there is no locally operated forceps robot that can grasp organs and provide traction.
Except for university hospitals where interns or residents are educated, there are advantages to single surgeons performing endoscopic surgery without an endoscope assistant, in that the number of operations can be increased. This is particularly true for hospitals where a large number of surgeons are endoscope specialists. Even in hospitals where few surgeons are endoscope specialists, those specialists would often prefer to change their technique from open abdominal or chest surgery to endoscopic surgery, since the latter is minimally invasive to patients. Again, this could be accomplished more efficiently if an endoscopic assistant was not required. One problem with the well-known da Vinci system is that it is difficult for a single surgeon to operate alone in the clean area, both for safety reasons and because of the need for tool changing. However, if a locally operated forceps robot was developed, a surgeon could perform safe, accurate endoscopic surgery holding mechanical forceps in the hands stabilized by intelligent armrests, while controlling an endoscope-holding robot and the new forceps robot using a choice of interfaces. Because anastomosis of arteries with diameters of less than 1 mm has been successfully performed using the EXPERT system, such procedures are also expected to be possible by robotically assisted surgery performed by a single surgeon.
To this end, we propose a manipulator that can act as a third arm for a surgeon in the sterile environment of the operating room. It uses a detachable commercial forceps, allowing the surgeon to intuitively handle internal organs. It can be operated by the surgeon’s hand or foot and can be removed from the surgical table as required. For conventional manipulation using a pivot point at the abdominal wall, 5 DOFs are required: the roll, pitch and yaw axes, the insertion/extraction axis, and the open/close axis. It is also necessary for the grasp and traction force to be greater than 5 N [
13]. We therefore developed a locally operated detachable end-effector manipulator (LODEM) based on a selective compliance assembly robot arm (SCARA) with 5 DOFs, an acting force of more than 5 N, and an accuracy of 0.5 mm, and applied it to it in vivo laparoscopic cholecystectomy [
14,
15].
The compact and simple structure of the developed device allows its easy introduction into operation rooms. Simple transportation and installation of the manipulator are important because it allows the doctor to be mobile. It is therefore necessary to use a mechanism that can be disassembled into compact parts. However, although the SCARA LODEM [
14] is compact, it uses a remote pivot point that is controlled mathematically, so that its operation is not intuitive. The parallel-link manipulator [
16] offers high accuracy and is capable of operating in narrow working spaces, but it also has the same variable pivot point. The R-guided manipulator [
17] uses a fixed mechanical pivot point, but it is difficult to disassemble into compact parts. To overcome these difficulties, we previously proposed crank-slider and cable-rod mechanisms [
18]. The crank-slider mechanism converts linear motion into rotary motion and can have an ‘L’ shape or an ‘I’ shape. The cable rod is composed of an outer stainless steel tube and an inner stainless steel cable. The cable rod is connected to the actuator that is driven by a forceps and the forceps-driving mechanism. We also developed a mobile LODEM which can be disassembled into compact parts and we applied it to a simulated surgical procedure.
In the present study, the design details of the proposed mobile LODEM are introduced. In addition, the accuracy and speed of the prototype device are evaluated while performing simulated in vivo surgery.
Discussion
The positional accuracy was 0.5 mm for the previous SCARA LODEM, which was sufficient to use it as a third arm for grasping and manipulating organs [
19]. The accuracy of the present mobile LODEM was 0.4 mm, which again is sufficient for handling organs. Since when suturing a vessel, an accuracy of 10 % of its diameter is required, both LODEMs can be used to grasp and pull organs with diameters of 4–5 mm or greater. This makes them suitable for grasping and manipulating the main abdominal organs. For the task shown in Fig.
4, the completion time for endoscope specialists was 80 s using the SCARA LODEM, but only 45 s using the mobile LODEM. In the SCARA LODEM, control of forceps motion in the horizontal and insertion directions is carried out kinematically. In contrast, each axis of the mobile LODEM can be independently mechanically controlled, leading to easier operability. The reason that the specialists were faster than the students was because the students were not used to the endoscopic view. Also, the learning curves for the endoscope specialists became constant from the third trial using the mobile LODEM, but from the forth trial using the SCARA LODEM. These results indicate that the improved mechanism and control in the mobile LODEM led to easier operability. The manipulator could be assembled and disassembled in less than 10 min, making it highly mobile, although the SCARA LODEM could not be disassembled easily. Thus, the mobile LODEM could be assembled and disassembled by medical staff rather than specialist engineers. In both the simulated and in vivo surgical procedures, the manipulator could successfully handle the target organs with the required level of dexterity. Although the size of the gall bladder and colon was only a few tens of millimeters, a surgeon can perform safe endoscopic surgery. The mobile LODEM will allow many types of endoscopic surgery to be carried out safely.
Based on these results, further improvements are being planned so that the mobile LODEM can be put to actual clinical use. First, the positional accuracy for the insertion/extraction axis is worse than the actual resolution of the motor. This is because of buckling of the cable rod and the lack of mechanical stability. Because the fixed actuator had a cantilever shape, vibration was transmitted from the motor to the tip of the forceps. To improve the accuracy so that it matches the resolution of the motor, the actuator is located on the tripod along the slider of the yaw axis. Another problem is that the transmission efficiency of the cable rod in the insertion direction is lower than that in the extraction direction. This is because of bending of the cable rod. The efficiency can be improved by changing the drive direction from push/pull to pull/pull. Finally, it was found that the trocar through the pivot point on the abdominal wall was covered by the manipulator. This leads to a risk of collision with the manipulator if the patient moves. To avoid this, the manipulator should be suitably designed so that there is a separation between it and the patient.
For use in actual surgery, the mobile LODEM must be clean and sterile. After assembling the main arm, actuators, cable rods and tripod, the manipulator can be draped with a sterile cover to keep it clean. The connection between the number of axes and the ability to keep the LODEM clean is three axes: roll, insertion/extraction and open/close. Using separate sterilized attachments made of stainless steel, the sterilized forceps can be attached to the draped manipulator. However, connecting the forceps requires the use of screws and tools. The procedure takes a few minutes and is likely to be annoying for the medical staff. To avoid this, a more ergonomic attachment method has been developed. This uses a bevel gear coupling between a gear inserted in the long axis of the forceps and a gear with a wired pulley for the roll axis, built-in screw clamps in the forceps handle for the insertion/extraction axis, and a gripping chuck inside the finger hole in the forceps handle for the open/close axis. To reduce the setup time, it is likely to be better to assemble the entire mechanical system in the operation room and not use a sterile cover. To improve the usability for sterilization of LODEM, a mechanism to be separated easily into a mechanical drive part following autoclave and an electric drive part that sterilization does not be performed is also under development.
In large city hospitals, doctors can often perform the latest surgical procedures because of the high population density in a city. However, when patients who live in the provinces require such surgery, they must either travel to a city or wait to be operated on in a rural hospital by a visiting doctor. One possible application of endoscopic surgery is carrying out procedures remotely. In this situation, a doctor in a city hospital could operate on a patient in the provinces using a master-slave control manipulator. Although such robotically assisted remote operation is technically possible [
20‐
22], it raises issues of patient safety in the event of emergencies. The local operation using the mobile LODEM is one of the solutions. To improve the safety and effectiveness of LODEM based surgery, a method for measuring the elasticity of an organ using the step-out phenomenon of a stepper motor is currently under development [
23].