Parallel robots are increasingly widely used in the medical field due to their high precision, high stiffness, excellent dynamic performance, and fast response characteristics. Various parallel robot systems have been developed and put into use. These robotic systems cover a wide range of applications from surgical assistance to rehabilitation therapy.

Surgical robot: The application of parallel robots in surgical operations is one of its most significant uses. They can perform extremely precise operations such as implantation, cutting, or suturing, especially in minimally invasive surgeries that require extremely high precision. For example, in fields such as minimally invasive ophthalmic surgery, spinal surgery, joint replacement surgery, and cardiac surgery, robots can perform precise operations under the control of doctors, reducing surgical trauma and recovery time.

Take minimally invasive ophthalmic surgery as an example, it requires a robot to drive surgical instruments to perform three rotational degrees of freedom around the iris puncture point and one degree of freedom of movement through the iris puncture point. The center should be away from the robot body to avoid interference. This type of motion around a fixed point far away from the robot body is called Remote center of motion (RCM), as shown in Figure 1. It is a new type of RCM parallel mechanism that includes a 4R parallelogram closed loop sub chain in a branch. The closed loop sub chain inside the branch gives the mechanism good stiffness. In addition, KUO et al. proposed a four degree of freedom motion decoupled parallel RCM mechanism and conducted kinematic and workspace analysis. ZOPPI et al. proposed a type of four branch parallel RCM mechanism and analyzed the workspace of minimally invasive surgery. YE et al. proposed an RCM mechanism driven by a fixed moving pair.

Figure 1. Three dimensional schematic diagram of the far center parallel mechanism

Rehabilitation robots: Parallel robots are also widely used in rehabilitation medicine to assist patients in physical function recovery training. A common type of ankle rehabilitation robot is used to treat pathological phenomena such as foot tapping, toe dragging, foot drop, and poor gait stability in patients, playing an important role in reducing disability rates. Rehabilitation therapy is a lengthy process that often requires a lot of repetitive training. With the help of rehabilitation therapists, patients can be guided to complete it one-on-one by hand or using assistive devices. Ankle rehabilitation robots can compensate for the shortcomings of traditional rehabilitation therapy methods and reduce the pressure on rehabilitation therapists. The parallel self-aligned ankle rehabilitation robot researched by Yanshan University has solved a common problem of parallel ankle rehabilitation robots, which is the difficulty of aligning the rotation center of the rehabilitation robot with the rotation center of the human ankle joint in real time, resulting in incompatible human-machine motion and causing secondary injury to patients. They introduced the conditions of "decoupling" and "few branches", proposed the self alignment principle of parallel ankle rehabilitation robots, and obtained a total of 93 parallel self aligned ankle rehabilitation robot mechanism branch motion chain structures, as shown in Figure 2.

Figure 2. Parallel self-aligned ankle rehabilitation robot

Remote healthcare: The high precision and excellent control performance of parallel robots make them an ideal choice for remote healthcare, especially in remote areas or during pandemic isolation. Doctors can perform diagnosis and surgical operations through remote operation of parallel robots, thus overcoming geographical limitations and providing timely medical services to patients. And through the remote operation mechanism, the motion control of the linear actuator can be amplified to a certain extent, making it easier for human hands to operate the robot.

Figure 3. Schematic diagram of teleoperation of parallel robot motion

Laboratory automation: In the field of laboratory automation, such as drug development and clinical testing, a large number of repetitive and precise experimental operations are required. Parallel robots can automate tasks such as sample analysis and liquid processing, improving experimental efficiency and accuracy. For example, in the automatic sorting of drug packages, the drug packages are output by the conveyor belt from the previous process and enter the visual inspection range for photo positioning. The parallel robot adjusts the suction cup direction based on the data detected by the visual system and grabs the drug packages. The parallel robot then places the grabbed products into the product chain bin of the packaging machine and transports them to the packaging line, completing a complete set of automatic sorting processes for drug packages.

Figure 4. Delta parallel robot used for automatic sorting of drug packages

The application of parallel robots in the medical field is becoming increasingly diverse, and their unique mechanical structure and control system make them show great potential in medical tasks that require high precision and reliability. In the future, with the further development of technology, the application scope of these robots will be further expanded, which will have a positive impact on improving the quality of medical services, reducing medical costs, and enhancing patient safety.