Introduction: Prosthesis With Temperature Sensitivity
Our project is an actualization to the old mechanical prosthesis that exists now a day. There is a lot of prosthesis in the market that helps to recover the mechanical part of your hand but there is no prosthesis capable of getting your sense of touch and sensitivity to temperature back. For this reason, we work in to develop a system to get back all this senses. After a long thought, we decide to publish this project so we can contribute with our part to the world. The idea is that with this we can help the people that lost this sense.
The way we manage to recover the temperature sensibility was placing temperature sensors to the hand (or Claw in the case of the prototype) and some RGB LEDs that light up in different colors. By averaging the total temperatures we assign a specific color to each temperature. In this way when the object taken was between 0 to 10 degrees Celsius the hand its going to light up in a blue color, then when the temperature rises in 10 degrees the hand will become green, then pink, then purple and so on till it gets red in 100 degrees Celsius.
Our gripper was made from a budget of 130 dollars approx and was made from recycled materials, mainly aluminum and steel. The gripper was poured of resin and hand machined with a Dremel to give the final finish.
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Step 1: Lets Build Something! (Mechanics)
The first step in building the robotic hand was the mechanical parts. The basic idea was to make the transparent grippers and light them up with leds. We first thought to make the parts in acrylic but we don't have any type of machine to making them. (laser cutter or a cnc) so we choose resin like the other alternative material. The next thing was to build the resin molds. We make first the gripper in wood that we use the thermoformer machine of the school and make the molds with transparent plastic.
then we work the pieces by hand with a dremel to make them lighter and give them a more modern look in the end. Working with resin was really hard and time consuming.
Step 2: Electronics 1 (Installing the RGB Leds)
Installing the RGB leds!
RGB leds are a kind of special leds that light up in red, green and blue light. Also you can make combinations of colors by light up two or more colors at the same time. We use the leds in digital mode so we only have 10 combinations of colors. We make this on purpose so the changes in temperature its going to be more noticeable for the user.
When we get the leds they came with a small datasheet like the one below. It was wrong!!! Actually we end up burning a lot of leds by connecting them wrong like in the datasheet. The real pins are: The longer lead is Ground and the others are the colors, NOT like the datasheet says.
Step 3: Electronics 2 (Temperature Sensors)
The next step was to place the temperature sensors. As we realized that the temperature sensor where not really accurate we have the idea to place three of them, in that way we can reduce the error and make a avarage temperature. Also in that way we can know the temperature of all the object that the gripper is taking and not only the temperature in one spot. The temperature sensors where protected by aluminum foil and heat resistant silicon in the terminals so they never touch to prevent a shortcut.
Te temperature sensors we use where the TMP-36, which came in a SO-16 package that is the same a small transistor came. This sensor works by sending a voltage corresponding to the temperature they measure. Depending of the temperature they are measuring is the voltage we obtain in the base of the sensor.
This sensor have a solid state technique to determine the temperature. This means that doesn't use mercury (like other devices), bimetallic plates or thermistors. Like in a diode that we know that the voltage resistance rises with the temperature as we amplify precisely the voltage in the sensor its really easy to generate a analog signal that is directly proportional to the temperature. This is basically how temperature is measure.
The characteristics of this sensor are this:
Size: TO-92 package (more or less 0.2” x 0.2” x 0.2”) with three pins
Temperature Range: 0.1V(-40°C) to 2.0V(150°C) But efficiency decreases after 125°C
Power Supply: 2.7V to 5.5V, and only consume 0.05mA of current.
The way we can know the temperature is this:
Temp in °C= [(Vout in mV)-500]/10
For example if we have a voltage in the base of 1V that means the temperature is:
Temp in °C= [(1000mV)-500]/10=50 °C
Step 4: Control
Because we need to control the prosthesis in some way we decide to use a button control because we don't have the resources to buy electrodes. We are planing to get some of those in the future.
We make the control in some way that you can control all with only one arduino analog pin.
Our control looks like this:
Step 5: Getting All Parts Together
All the parts get together in an Arduino PCB, we can take the temperature measures in an analog pin, control de RGB LEDs colors, and control de servos to move the gripper. All with a control made by us. The circuit in the photo is the 2.1 PCB, we already have the 4.0 PCB please enter to my blog
to download the files. The PCB in the image is the 3.5.
In the fritzing image, the ones in the upper left are voltage regulators for each servo, the ones in the upper right are MOSFETs to control the RGB LEDs, the one in the bottom left is a voltage regulator for Arduino and the temp sensors, and finally in the bottom right two potentiometers to control temperature sensibility and two connectors, one for the temp36 sensors and one for the control.
Step 6: The Last Step, Attach to the Arm!
The material we use in here was completely recycled. We get the back part from a PC keyboard and the upper part from a dump site. The small pieces we get them from a meccano game that was about to get in the trash, we also use the meccano gears to give the motor more strength.
The arm attachment was made to fit my arm, having in mind that this part is just to demonstrate the principle of having the gripper mount in a real arm. We have to get someone without a hand and make a real attachment to his or her measures.
Step 7: Working!!!
Here are two little videos of the Gripper/prosthesis already working.
Step 8: The Future!
We have great plans for the future to add more senses to the prosthesis, giving back to the people all those senses they loose in the past. We are working in the next model to give the person the capability to feel how hard he/she is taking and object, and also the capacity to feel textures and shapes. Also we are thinking in add this senses to industry robots, kitchen gloves and pans in a way of making them safer and help people to make them lives a little easier.
We are really interested in develop technologies to help people and make her lives a little better.
The next step is to build a more human hand and add some electrodes to control the prosthesis like a real hand. But as you know is all about getting sponsorship to continue working. :P
Step 9: Some Media We Appeared
This are some media that we appeared with the prosthesis
Step 10: Special Thanks :)
We want to thank all the people that help us with this proyect, and all the people that does't think we are crazy by making a robot from scratch and without any money. We hope this project will be useful for someone, even one person in the world, that would be a great success for us already. For any information please write us, and we hope if you have any question or comment, ask us. Thank to all :)
Step 11: If You Like This Project!
If you like this project, please come to our page and comment!