Final Design
SonoHand
From Left to Right: Isometric View, Front View, Side View
SonoHand consists of four primary subassemblies: the hand mechanism, the articulated arm, the base mechanism, and the locking mechanism. Below is a flow diagram of the total assembly accompanied by detailed descriptions of our design choices for the subassemblies.
Flow Diagram of SonoHand Assembly
Part Name
Hand
Mechanism
Image of Part
Description
The hand clamp is made of injection molded plastic because it has high strength, lower cost for mass production than machined materials, smaller lead times, and easy to manufacture. There is a support material placed on the hand to provide more grip strength and an easy press fit location for the probes. In addition, the hand is attached to a spring pressure application mechanism to achieve constant skin contact for the sonogram. The pressure device is manually controlled by the operator. This is due to safety issues regarding struggle from the patient, so the pressure device must automatically move after being push with a hard enough force.
The base clamp is the only machined metal fixture of SonoHand. It is made from Aluminum 6061-T6 because the material is lightweight, strong, durable, and is relatively cheap compared to other metals. All of the moment forces that result from the other arm components affect the base, so it is extremely important that it is the sturdiest part of the device. It is in the shape of a C clamp for ease of manufacturability and versatility. There is a threaded attachment that is adjusted to fit any railing or platforms regardless of being different sizes.
The articulated arm is composed of small aluminum rods linkages and ball and socket joints. There are 3D printed slots that attach the linkages and joints through a combination of press fitting and threaded holes. Initially, the arm was going to be made of acrylic rods, but a risk reduction showed that acrylic was not viable as it deflected 10 mm. The aluminum was also risk reduced and deflected only 1 mm, so a higher strength material, such as steel was not needed. There is a static rod in the arm to provide additional support to the base, while the other joints are all motor controlled to still give 6 degrees of freedom.
The locking mechanism is primarily electrically controlled and has only one manual knob. The manual knob is on the static rod of the arm to set an initial height for the SonoHand to reach all areas of operation for a given patient. The electrical locks utilize foot pedal controlled servo motors. During operations, it is not convenient for the operator to do things manually due to sterilization and time issues, so the foot pedal is applied for ease of access.
Base
Mechanism
Articulated
Arm
Locking
Mechanism
Performance Results:
SonoHand meets all of the primary requirements that our sponsor desired, and partial progress on some of the secondary requirements.
Requirement(s)
- Keeping the arm within a sterile field (sheath for the ultrasound device) by guiding it through the wire
- Moveable arm that can hold the sonar equipment against skin with ample pressure
- Maintain contact during operation unless the patient moves with a strong enough pushing force
- Easy way to lock and unlock the arm
- Ability to have 360 motion
- Rotational freedom on probe that locks at -90 and 90 degree orientation
Video
Comments
Ultrasonic operations require sterilization of the equipment due to the chance of working on open wounds. A sheath is always placed over the probe, and in this case the arm as well. Our sponsor provided us with one of these medical sheaths that the UCSD Medical School uses. It fits snugly as long as the person placing it over does not rush it or put too much force.
SonoHand's hand was tested on the members of this project, a mannequin in the UCSD Medical School's Simulation Center, and on gel blocks. The hand holds skin contact by its sheer weight and can produce a sonogram. However, it is not optimal as the springs do not engage fully. They can be set to a position, but they will return to the equilibrium position because there is no lock. On the other hand, when struck with a large enough force, the spring system easily comes off (the force to overcome is the friction on the point of contact caused by some of the arm's weight).
The arm currently is able to lock and unlock with our locking mechanism. When the foot pedal is stepped on, the arm is in its unlocked position and can be moved freely. Once the desired position is reached, the operator just needs to get their foot off and SonoHand will automatically lock its position.
The arm must have a 360 degree range of motion in order to reach all parts of the patient's body. Our arm meets this requirement through the use of the ball and socket joints.
The hand has the ability to turn 360 degrees due to the ball and socket joint. When SonoHand is unlocked, the joint that connects to the hand can be turned. There is not currently a locked position for the 90 and -90 degree orientation, but it can be reached with precision.
Conclusion:
To conclude, it took 5 iterations to create the SonoHand. Initially, the arm was designed with hinges as our joints, but no analysis was done other than for the cantilever beams' deflection. This proceeded on for 3 iterations, which we then learned from our mistakes and did a redesign (using the same parts). This redesign featured ball and socket joints as those gave rotational freedom, so we could reduce the lengths of the arm linkages and decomplicate our hefty base. Moment calculations were done on each linkage as well. Currently, SonoHand meets all the primary requirements that were set initially, and some of the secondary requirements that came up along the way. The ones that could not are motorizing the entire arm, creating an auto sheath slider, have a holder for the needle to relieve two hands in the operation, and having the ability to rotate 90 and -90 degrees in an instant. There have been multiple design recommendations created by us, but could not be inputted in this limited resource and limited time quarter. We learned that doing the paperwork can save you time and effort, that forcing something that failed can end up in bigger failure, and that scope creep has to be checked based off of the amount of time, money, and brains that you have.