I've drawn up two possible configurations that have focal points.  I believe something like the first design was shown in class (the Arc). The second one is another idea I had where I have fixed the probe at a specific point, forcing it to have a focal point.  Thoughts?

SCARA vs PUMA Config

So we've decided 5-DOFs is appropriate.

BUT, what about the Config?

There are two basic categories most applicable to our task:

1. SCARA - Selectively Compliant Articulated Robot Arm
2. PUMA - Programmable Universal Machine for Assembly

SCARA

• PROs
1. compliant (not rigid) in X-Y plane BUT not Z direction.
2. accurate and precise due to rigidity
3. adept at pick-and-insert operations
• CONs
1. less flexibility in potential operations
2. smaller workspace 

 PUMA (similar to 2 Wrist + Prismatic config proposed earlier)

• PROs
1. more flexibility in potential operations
2. larger workspace
• CONs
1. compliant in X, Y and Z directions. 
2. less accurate and precise due to less rigidity
3. adept at operations that do NOT require high precision, ie welding and stacking, etc.

Robot # of DOFs and Configurations

The project prompt states the following:
"In liver radiofrequency ablation, a surgeon places a needle into a lesion (e.g. cancer) located in the liver, starts radiofrequency ablation, removes that needle, after which he places another needle and repeats the procedure as many times as needed (sometimes, over 10 times).
The goal of this project is to develop a robotic device to consecutively place series of needle in a lesion and allow for surgeon to perform radio frequency ablation."

I highlighted the text to show that we need more that 2 DOF to perform the task for the following reasons.

1. 2-DOFs (of the RP & PP type shown below) allows for only a 2D work-space.  We need a 3D work-space to ensure accurate needle placement.
2. Since we are required to perform multiple ablations per lesion, Yaw and Pitch of the needle should be considered if we would like to keep the procedure as minimally invasive as possible.  Depending on the size and number of lesions in the liver, it would be ideal to be able to completely ablate these lesions from the least number of incision points. (See fig 1).

Fig 1: Yaw and pitch of ablation needle

 So, how many DOFs do we need?

I think a 5-DOF design would be the best option. This allows the needle to reach any place in the workspace at any yaw or pitch angle.

What are some configuration options?

Hoi's suggestion of 2 Wrist + Prismatic Joint configuration would work.  We may also want to consider the SCARA configuration which from some prelim research seems popular in robotic surgical systems (Figure 2 and 3).

Fig 2: SCARA + Wrist (5 DOF) Robot CAD model

Fig 3: Coordinate Frame

Robot Design: Draft ver. 1.0

Overview of the Design Requirements:
- The robot can be placed on a manually wheeled cart or in some other way we find suitable.
- Assume that the liver is a sphere with a 10 cm diameter.
- Assume that the force needed to push through the liver is 10 N.
- Orientation of the needle around its own axis is not important.

In other words, points of interest of the robot (an in no particular priority order):
i)  An interchangeable end-effector. A gripper should suffice for this condition.
ii) A proximity/distance sensor to keep track and navigate the needle inside the liver.
iii) A force sensor to puncture the liver wall.

Conditions that are of little importance to our robot:
iv)  Robot base/stand. The robot can sit on a rolling platform with brakes for all we care so we'll begin by designing it as a robot generally sitting from the ground.
v) Orientation of the needle (i.e. the roll, pitch, and yaw angles of the needle tip). Therefore, only the insertion of the needle is the necessary factor to consider for the end-effector.


The minimalist robot with the lowest degree-of-freedoms could be a planar robot that is Revolute-Prismatic (RP) or a Prismatic-Prismatic (PP) robot (I was thinking it would only be a prismatic robot but there has to be some sort of height adjustment). The last degree of freedom should be a prismatic joint, because only a prismatic joint allows the needle to insert into and out of the liver.
From the Project Guidelines in section 1:
a. What is the minimal required number of DOFs to complete the task? 2 DOFs
b. What is the required workspace? Needs to be addressed.
c. What is the estimated speed of each joint (very difficult to do, just guess something that sounds reasonable). Needs to be addressed.

Figure 1: Examples of an RP (left) and PP (right) robot. This would be the most basic robots that will meet the design requirements

The most complex robot that should be considered would be a 5 DOF (degree-of-freedom) robot. Structurally, it would consist of two wrists (a wrist is a couple R-R joint) and a prismatic joint and would work in 3-D.

Figure 2: Examples of the 5 DOF robot (Very poorly drawn, sorry, but it was the quickest way I could get a picture of it up on the blog). The bottom picture is the same as the top, but with GREEN highlights that are links, and RED highlights of the z-direction of each link.

Even though it might be redundant, if time permits we should draw everything in MATLAB using the robotics toolkit. Those figures and illustrations in MATLAB would be great for the slides in our presentation, as well as for our report.

Project Guidelines, section 2: Propose a robot kinematics for the task.
We should probably consider a robot between 2 to 5 DOFs.
What do you guys think?

Project Assignment: Radio-frequency Ablation Robot

Radio-frequency ablation is a procedure in which radio waves are generated on a tip of a needle. The radio waves cause the exposed tissue to heat up causing cell death. This method is used to destroy cancer cells in various organs. In this project, we will focus on liver cancer.

In liver radio-frequency ablation, a surgeon:
i)  places a needle into a lesion (e.g. cancer) located in the liver,
ii) starts radio-frequency ablation,
iii) removes that needle,
iv) after which he places another needle, and
v) repeats the procedure as many times as needed (sometimes, over 10 times).


The goal of this project is to develop a robotic device to consecutively place series of needles in a lesion and allow for surgeon to perform radio frequency ablation.

Design Requirements:
- The robot can be placed on a manually wheeled cart or on the patents table or in some other way we find suitable.
- Assume that the liver is a sphere with a 10 cm diameter.
- Assume that the force needed to push through the liver is 10 N.
- Orientation of the needle around its own axis is not important.