Modeling of Laparoscopic Forceps with Sensing

Progress of minimally invasive surgery stimulates the development of sensory techniques. The present study is related with creation of a mechatronic clamping laparoscopic device (forceps) that allows transferring tactile sensations from the jaws of the clamp to the handles of the master manipulator operated by surgeon. The user presses the handles of the manipulator. The change in the angle between the handles is synchronized with the change in the angle between the jaws of the forceps (slave link) that grasps the soft tissue. The contact load is identified based on the voltage applied to the electric motor connected to the forceps and then transferred to the control unit. This control unit adjusts the operating frequency of the piezoelectric actuator in such a way as to generate a force corresponding to the measured load. This force is applied to handles of the manipulator. It creates a moment in the handle, which is felt by the user. Thus, the system provides the tactile feedback. In order to describe the dynamics of the piezoelectric actuator, a finite-dimensional empirical model is used. In order to describe the dependence of the moment, with which the soft tissue acts upon the jaws of forceps, on the span angle between the forceps, a mathematical model is proposed. This model takes into account the properties of the soft tissue (which is assumed elastic) and geometry of the surface of forceps jaws. An algorithm for identification of the moment acting from the tissue on the forceps is proposed. Numerical simulation of dynamics of the system is performed. The results of calculations confirm the efficiency of the algorithm for identifying the moment created by tissue.

Design and Analysis of a Symmetric Articulated Single-Port Laparoscopic Surgical Device

Laparoscopic surgery is a practice of minimally invasive surgery (MIS) performed in the abdominal area. Prior to surgery, instead of exposing the target region to air as in a typical conventional open surgery, “key holes” are opened for positioning ports, through which surgical tools (e.g. laparoscope, needle drivers, etc.) are inserted. MIS therefore minimizes trauma and reduces the risk of hemorrhaging and infection. MIS also generates economic benefits such as shorter hospitalization time for patients and better utilization of operating rooms and wards for hospitals. MIS procedures, however, require extra dexterity from surgeons: they must use instruments with little to none haptic feedback to remotely manipulate tissue within a limited range of motion, assisted by an indirect view from laparoscope. Such unintuitive operations not only require additional training, but also increase the risk of medical errors. Thus, the development of novel surgical devices that can provide a better operating experience will allow surgeons to deliver safer and more effective surgeries. At the advent of MIS only rigid straight laparoscopic instruments were available. Therefore, surgeons used multiple incisions to position the tools and achieve triangulation. In single port laparoscopic surgeries (SPLS), only one incision is made for positioning a port. Two rigid straight instruments inserted through one incision cannot provide sufficient triangulation for operations. Rigid bent, or articulated, instruments can achieve triangulation, but the tools must intersect at a point. The mapping to control the end-effector, therefore, must be inverted such that the right hand controls the left end-effector, and vice versa [1]. Given this inverted mapping, surgeons need to undergo extra training to intuitively control the end-effector, and greater attention is required toward operating the device, which can potentially detract from the ability of surgeons to focus on procedures. The disadvantage of an inverted mapping can be overcome by providing additional mobility with flexible tools and actuating structures [2]. For example, Transenterix has developed a flexible laparoscopic device which utilizes a cable-driven system for articulation of the end-effectors. However, using flexible elements as the driving mechanism can result in new problems such as diminished force feedback [3]. In 2015, a novel design of an articulated single port laparoscopic device was presented with 6 degrees of freedom (DOF). The system provides intuitive control, accurate force feedback, and sufficient manipulation for laparoscopic procedures. The design proposed in this paper keeps much of the functional features in the previous model, including 1:1 mapping and force feedback, while incorporating flexible hydraulic graspers. The articulated mechanism was redesigned to have a symmetrical structure, which is more intuitive to control and provides better operating angles for surgeons. Joint structures are redesigned for enhanced robustness and misalignment prevention. Kinematic analysis is presented for the proposed mechanisms, which is used to determine the manipulator workspace.