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. 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
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.
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.
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.