Control of Magnetic Microrobots

ASTRACT:

Robotics has offered wide field of research in using microrobots in body and for few industrial applications. The major attention is on developing systems including microrobots for biomedical applications. The fabrication, power supply and control methods needs to be selected properly for accuracy of application. This report consists of basic introduction to magnetic microrobots and controlling methods of magnetic microrobots. The most widely used method for controlling microrobots is electromagnetic actuation system. There are vast applications of electromagnetically actuated microrobots in minimally invasive surgeries, micro manipulation, cardiological treatments, cancer therapy, etc.

INTRODUCTION:

As nano and micro scale manufacturing technology has matured, the realm of small scale robotics is beginning to become a reality as many researchers have turned their attention towards developing microrobots. A microrobot is a miniaturized, sophisticated machine designed to perform a specific task or tasks repeatedly and with precision. Microrobots typically have dimensions ranging from a fraction of micrometers up to several millimetres. As a result, various microrobots have been proposed in terms of material, motion design and control method.  

Recently vascular diseases in people have been on rise owing to fatty food consumption and lack of exercise. Mortality rate due to such diseases has been increasing. Earlier the treatments used for such diseases were highly invasive. But microrobots are boon as they offer minimally invasive treatments. As microrobots have very small size they can easily enter blood vessels, arteries, etc. Magnetic microrobots designed for biomedical applications are of prolific research area. They are used for minimally invasive surgeries, targeted drug delivery, micro manipulation, medical imaging, dead cell removal, in vivo, in vitro applications. Medical microrobots have many possible advantages in various treatments. Most of these microrobots have free locomotion and precise controllability.

Various methods are used for controlling these magnetic microrobots. Research in this field is being carried out and various actuation methods such as shape memory alloy actuator, electrostatic actuator, electromagnetic actuator and piezoelectric actuator are being used. Electromagnetic actuation method is widely used for controlling motion of microrobots in biomedical applications. Recently many electromagnetically actuated wirelessly driven microrobots are being proposed and they find a way in many applications. Apart from biomedical applications single magnetic microrobot or group of magnetic microrobots can also be used in industrial applications for load carrying purpose, moving objects from one place to another. This area of application is under research.

 Control of multiple magnetic microrobots is somewhat difficult. A major challenge for manipulating multiple magnets at micro scale is that applied field affects the entire workspace, making it difficult to address individual magnets. Providing power for microrobots is challenging as traditional power sources do not come in such small packages. Several methods for powering microrobots have been explored including using propulsion of bacteria attached to structures as well as using bacterial suspensions. Though these challenges stand but microrobots have provided mankind excellent results and proved to be a boon.

MAGNETIC MICROROBOTS

What Are Magnetic Microrobots?

A magnetic microrobot is microscopic magnet that is controlled by a system of electromagnetic coils that generate a magnetic field to manipulate the magnetic robot. The magnetic microrobots are little robots which can perform delicate surgeries, diagnosis tests, and could even cure cancer. They can simulate the injection of medicine into the body. It can move in virtually any direction and has no joints. They are multifunctional. These robots can fit mostly anywhere in human body and can be used to avoid the cutting of one’s body.

Need For Magnetic Microrobots

Medical microrobots have many possible advantages in various treatments. The main advantage of these microrobots is high accessibility that they enable especially in areas that are difficult to reach by traditional surgical methods or that require highly invasive methods. Due to their small scale dimension they have accessibility to tiny and complex environments. Most of microrobotic applications are related to biomedical field. The magnetic microrobots are widely used for heart surgeries, vitrectomy, removing blockages in blood vessels, biopsy etc. It is difficult for many devices to reach small parts of body such as veins, arteries but microrobots can easily reach these parts and carry out the required treatments. With the use of magnetic microrobots the minimally invasive surgeries of delicate parts can be carried out which would otherwise take long time for the part to recover back to original form. These microrobots are of immense use in cancer treatment. Magnetic microrobots in earlier stages were developed in form of pill which had embedded camera and could be swallowed and it took images of gastrointestinal tract in human body.  Magnetic microrobots are also useful in cell manipulation.

Fabrication Methods Of Magnetic Microrobots

The methods used for fabricating magnetic miccrorobots are:-

• 3D printing
• Micro electromechanical technology
• Micro moulding
• Laser machining systems
• Photolithography

CONTROLLING METHODS FOR MAGNETIC MICROROBOTS

Open Loop And Closed Loop Control System

In open loop control system the output has no effect or influence on control action of input. The output is not fed back or compared with the input. It follows its input command regardless of final result. It cannot self correct errors and is poorly equipped to handle disturbances or change in conditions which may reduce its ability to complete desired task. The open loop controlling method consists of two types pre programmed control and teleoperation. The pre programmed control method is used to characterize microrobots, which does not require high precision control. However for many operations correction of path or position error is required due to presence of environmental noises. The teleoperation method can be applied to transportation tasks without high number of repetitions, for example targeted drug delivery, or manipulation which requires interaction with manipulators, for example selection of micro objects. In this method microrobots are controlled from distance with remote control.