Some good progress:)
16th June – 22nd June
19th/ 20th June:
We kicked the week off with our second informal progress check with Dr Ho and the TA’s, during which we gathered many valuable feedback and suggestions on how we could improve our product design. One such suggestion involves using a belt system to power the rotation of the two supporting shafts on each end of a single strip to reduce the number of motors required in our build.
With the timely delivery of our foam sheet, our first task back in the lab was to test the reactivity of the pressure sensors beneath the foam sheet. We found that lying in the lateral position gives us a higher pressure reading compared to the supine position. These findings are rather promising as they tell us that we are able to differentiate one’s sleeping positions based on the different pressure reading ranges.
Next, we learnt how to operate the linear stepper actuators provided to us. To eventually accommodate 6 motors in our build, we decided to switch from the Arduino Uno to Arduino Mega fitted with RAMPS 1.4. The RAMPS 1.4 is a shield used in 3D printers which allows up to 5 stepper motors to be controlled independently. It also contains enough analog pins to receive input from our film pressure sensors. With the help of the TA’s, we succeeded in getting two linear actuators to move simultaneously (view video V1 here). We also managed to establish good communication between the sensors and the actuators via the Arduino Mega (e.g. moving the linear actuator up by 1 revolution when a specific pressure is read).
We concluded with a short discussion on the specifics of our pillow design, such as how the horizontal supporting strips should be mounted onto the actuators, and how the adjustment mechanism should be hidden for the user’s safety. The use of air bags was also brought up as a support mechanism for the upper head (where less resolution is needed, hence the use of a single air bag for height adjustments sufficient). With that, we proceeded with a mini shopping spree to secure additional components for our build.
Working hard in the lab!
21st/ 22nd June:
Over the weekend, we discussed the specifics of the aluminium strips that would form the foundation of the pillow’s head and neck support. We wanted the support strips to be long enough to allow space for head movement, yet not deform too much under load to first provide good support, and secondly minimise the effect of deformation on the pressure sensor readings.
To do this, we contacted a local metals supplier to obtain the catalogue containing aluminium bars of different dimensions and evaluated them using the beam deflection formula from mechanics. Eventually, we settled for 400 x 31.75 x 4.5 millimeter strips as they would deflect less than 1 centimeter under the maximum estimated load of 5 kilograms, providing good support. Recalling our TA’s advice on the rigidity of the support strips, we decided that some deflection of the strips may also be necessary to allow higher user comfort.
Calculating beam deflection