Output Devices

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Hand Splinting Orthotic Considerations

As a Designer I didn#t have the medical expertise, nevertheless I tried to understand the process of designing a orthotic , and I found some references with give me an idea of the analysis and implementation of an Orthotic I find this book: Hand Splinting / Orthotic Intervention: Principles of design and fabrication. You can find more Information in the following Link.

Movemets of the fingers

As you can See here I thought in the Design of a Splint for a Hand enable the mobilization, using the nitinol wire as actuator for generation this movement.

Forces and design of the phalanges

As you can See here I thought in then Design of a Splint ofr a Hand emnable the movilization in the using the nithinol wire as actutor for generation this movement.

Angles of the Movements of the fingers

Smart Memory Alloy

Due the space restrictions I wanted to implement the nitinol wire to implement a semi Invisible actuator helping the mobilization of the finger in a fine construction. for this reason before to starting work with work with the this material I look a little bit around the datasheet In the following pictures of the datasheet you can see some abstract of the Nitinol wire as a part

As you can See here I thought in then Design of a Splint ofr a Hand emnable the movilization in the using the nithinol wire as actutor for generation this movement.

Inmobilization of the arm through the splint

allowing the movemet of the hand

Movemets of the fingers

Experiments Smart Memory Alloy

I did some experiments with Shape memory alloy's from the company Dynalloys. you can consult the data sheet here. in the test I could confirm that it is not enough strong to move such as a paper but in textiles has a better reaction I test the Shape memory alloys with the Lab power Supply In order to now a bit empirical of the material. with 320 mm and 100 cm for 320 mm you have a resistance around 7 Ohms and you can use around 3.7 V and 0.5 A. for testing the level of reaction,. more details of cooling you and explore in the datasheet . As you can see in the small Video the small piece of nitinol is attached to the paper with tape, in a big area of paper , nevertheless with this amount of paper , the nitinol is not able to move the area . therefore I use the smaller one.

Advantages: The nitinol use permits the natural movement of the muscles, and is an ideal application for a body device, due to its flexibility. The SMA as wire, can be embedded onto textiles, In addition I can integrate the actuators in the shape of the orthotic.

Disadvantages: Less Force: depending of the diameter of the wire the force is directly proportional to the needed current.(force) Retraction: for the simulation of the muscles, the capacity of reaction should react in milliseconds, that the commercial SMA does not have. (time/speed) (gravity can improve the results of retraction) Current needed for the hold function of the hand, could be a risk for this are that has a lot of contact with different surfaces and materials.

Servo Motors

Motor Considerations

About the Servo motor, pneumatic motor, stepper motor?

This application required More strength in the mobilization of the fingers but at the same time a motor wich is alight and simple to use for tis application. that someone can wear and provide enough torque to move minimal 3 fingers (900 grams)

Servo motor: is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration.[1] It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors. Servomotors are not a specific class of motor although the term servomotor is often used to refer to a motor suitable for use in a closed-loop control system. Servomotors are used in applications such as robotics, CNC machinery or automated manufacturing. You can find more information under the following Link

For Index and thumb Finger there is a servomotor for each one, it is responsible for the flexion and extension, The Index which is the most important finger in which I based the implementation of the phalanges design. The thumb has two phalanges, stead to create a circumduction movement (circular movement of the finger) it has a linear movement that is synchronized to the Index finger for grasping objects. The middle Finger motor is attached to the two others finger to achieve the hold movement of the hand.

http://www.hobbyking.com/hobbyking/store/__31633__HobbyKing_8482_HKSCM9_6_Singlechip_Digital_Micro_Servo_1_6kg_0_07sec_10g_EU_Warehouse_.html HKSCM9-6/31633 HobbyKing™ HKSCM9-6 Singlechip Digital Micro Servo 1.6kg / 0.07sec / 10g

Description: Spec. Torque: 1.4kg @ 4.8v, 1.6kg @ 6v Weight: 10g Speed: 0.09/60deg @ 4.8v, 0.07/60deg @ 6v Voltage: 4.8v~6v Plug: JR

Wiring: Servo motors have three wires: power, ground, and signal. The power wire is typically red, and should be connected to Vcc. The ground wire is typically black or brown and should be connected to ground on the GYRO SK . The signal pin is typically yellow, orange or white and should be connected to a digital pin in this case I used one of PWM (9, 6, 5 pins). With the servos that I used i didn#t require more power than the 5V. You can find the description in the following link:

For one motor, I have enough strength to control the movement of flexion and reflexion of the Thumb and the Index. For the middle Finger and the other two fingers I use other reference of motor, in order to have a little bit more strength. It means i don't want to break he frank finger. DS238MG/51892 Corona DS238MG Digital Metal Gear Servo 4.6kg / 0.14sec / 22g

Trials:

In the second week I did some for finger for prosthetics, working with the design of the joints, And I printed it in an Ultimaker Also al I printed a part of the the raptor hand from enabling future community,(http://enablingthefuture.org/upper-limb-prosthetics/the-raptor-hand/ ) looking for the for of movement in this case they elastic bands and threads. Also I did some trials making simulating the movement of the fingers and three servomotors with a piece of fabric.

Experimenting with the force of the motor and the torque of the motor. In this cases I didn’t achieve only the reflection of the fingers , but not the flexion. In this case I had to look for a stable option. But in this case I needed a strong structure for supporting the hold hand movements, in fact design a structure simulating a exosquelette, I did the design of the phalanges in the first part as a joints in 3d Printing (you can se more information in the 3D Printing assignment.)

Afterwards I implement the design of the movement of with making the exosquelette in laser cutter parts, in order to accelerate this process , and also to do a more stable function for the motor. In the first Arduino sketch I used the servo library, afterwards, I used the Library “Var Speed”, in that sense to control the speed and the angle of the servos better. In the following video you can see the calibration and function of the motor for Frank inger. After the calibration of the sensor I have also to calibrate the direction of the motors:

IMPORTANT: the library Var Speed doesn’t accept negative values it means you have to calculate the value in 360 degrees. From the begin of the torque.

AC 2016:

Is the microcontroller board based on the Satsha kit that's Included a socket for the 3 servos (thumb, Index and middle finger) and the 3 MYOs (I decided afterwards to have only 2 MYOs and programming with this two function the hold movements of the fingers. ) It really takes a sohr time to develop this boar , on basis of the experience from the Gyro asacha it was really easy to conclude this board. Iyuo can see in the job and the milling process was really easy :) TIPPS : If you have a roland and you past normally double side tape , use the mos thinner one to level as flat as possible your copper board. Soldering: Using the the offset path 5 make a huge difference in terms of soldering , it take relative short time to solder the board , I was sorted the components before making this process really comfortable . After a successful test I could proceed to assembly the hold components in the MyOrthotics.

Disadvantage:

I will prefera a small boar in order to package better the electronics, nevertheless I was really happy , that I the end was easily to produce a board .

FUTURE WORK . My idea is to implement a new board using the satsha micro, in order to reduce the size of the boar , but also to make this work possible for other patients with similar situations.