Lab 2:Arduino Intro + Actuator Basics

lab partner: Salma Kashani.



Smart haptic panel using multiprobe surface scanner with tunable turning disc.

Chances are so high, that we have seen or at least have heard about a mechanical recording and reproducing device,it's called phonograph or later known as gramophone. A song can be recorded by engraving or etching grooves and incisions on a rotating disc. As the  result when the probe is tracing for any groove and incisions, while the disc is rotating, it will be vibrated and creates the recorded sound.

Being made by Edison at 1890s, gramophone is still fascinating enough to inspire us to use it in our next variation in lab2. We exploited this mechanism to generate different local vibration patterns on an smart haptic panel. The haptic panel can provide users with different experiences, when they are trying to press or drag their finger in it. Our system consists of 3 main parts,

• Tunable turning disc
• Multiprobe surface scanner
• Smart haptic panel

The rest of this post will continue as follow. First, I will explain each part in more details and it's functionality, principle mechanism and science behind it. Then, I will explain the the iteration and improvement for each section. Later, I will describe the system as whole and how these parts work together, and finally I will come with some problems and future plan.

1. Tunable turning disc

In first step, we needed to make a rotating disc with premade vibration patterns. We have used a DC motor to produce our rotational movement. In order to reduce the speed and enhancing the torque, we mounted two stages of 3:1 gear train between motor and disc. A stepper motor is also tried, but due to vibration and lower speed we prefered to use a DC motor.

To control the rotational speed of the motor we changed the driving voltage of motors by means of pulse width modulation method. Each time Arduino  will read the voltage of variable resistor (Potentiometer) using AnalogRead with 10 bit resolution and  accordingly, will map it to 1 to 255 ratio of duty cycle. Arduino will generate pulses with different duty cycles and switch the voltage across the motor using a Mosfet so that by changing the potentiometer we can control the speed of rotation.

Fig 1) Arduino kit and motor driving circuit (photo courtesy Salma Kashani)

Fig 2) Rotational speed control using potentiometer (photo courtesy Salma Kashani)

To create the vibration pattern we tested different cavity and bump structures and got into the conclusion that for our purpose a simple ramp which is cut through the disc will work just fine.

We observed that our probes will got stuck in some ramp edges so we covered the disc with a layer of plastic sheet. By having different ramp heights we can control the magnitude of vibration.

Fig 3) Cutting ramps through the rotating disc to generate vibration (photo courtesy Salma Kashani)

          2-Multiprobe surface scanner

As described in previous post a multiprobes surface scanner (MSS) can detect the roughness and surface properties including concave and convex areas. As depicted in Fig 4, we mounted the MSS system over the turning table so it can scan the surface of the rotating disc.Fig 5 shows how the rotational movement of the disc is transformed in linear vibration of probes.  

Fig 4) Multiprobe surface scanner is mounted on turning bench.  (photo courtesy Salma Kashani)

Fig 5) Transformation of rotational movement to linear displacement of probes is generating vibration on each probe.  (photo courtesy Salma Kashani)

(photo courtesy Salma Kashani)

           3-Smart Haptic panel

The mystery behind our smart haptic panel is a non-Newtonian fluid called Oobleck; These group of materials  has properties of both liquids and solids at the same time. You can slowly dip your hand into it like a liquid, but you will feel it solid if you squeeze or punch it.  We have experienced that just by vibrating this material it can create different feeling of pressing or friction when you are dragging your finger into it. In another word, the viscosity of this material will change based on frequency and amplitude of vibration which is analogous to  change of damping ratio or friction. Basicly you will feel the dragging force while pressing or moving your finger on the panel. Higher frequency ==> higher viscosity==> feels like moving your finger in a honey jar, Lower frequency==> lower viscosity==> feels like moving your finger into glass of water. Bellow you can see a movie of the effect of vibration on changing the viscosity of Oobleck. The trace behind the finger is relative to the viscosity of liquid.

         Results:

Now assume that you have a liquid panel of Oobleck  with a number of local vibrators. At each segment you can control the stiffness/viscosity by changing the vibration's frequency. The magnitude of vibration also controls the size of each segment and it's range. To generate many vibrations with just one motor, we have used the MSS which is connected to the rotating disc. by controlling the speed of rotation and size of the ramps we can control the frequency and magnitude of vibration. 

Future plan:

More flexible material is required instead of the plastic plate that can transform the vibration to the Oobleck (maybe ziploc!). The coupling between rotational and linear motion needs further improvements.