University of Waterloo Team 21
Project Design
This section provides a high-level overview of the product.
System Overview
The system design consists of 3 main components: control, display and hardware. The control system consists of the 3 micro controllers, two Arduino Unos and an Arduino Mega, which are used to control the software in the system and interface the various hardware of the system. The display system is composed of a TouchPad, which is a 4-wire resistive touch panel that will be used for input, and a LCD TouchShield, which interfaces directly with the Arduino Uno. The hardware system consists of an electromagnetic array, a haptic pen and a hall-effect sensor, all of which will work together to provide the haptic feedback desired. The Touchpad Uno is responsible for reading the touch input from the touchpad and sending the necessary information to the other micro controllers. The Display Uno is primarily responsible for displaying data on the display shield. The Mega is responsible for controlling the hardware controlling the electromagnetic array and the pen.
The system design consists of 3 main components: control, display and hardware. The control system consists of the 3 micro controllers, two Arduino Unos and an Arduino Mega, which are used to control the software in the system and interface the various hardware of the system. The display system is composed of a TouchPad, which is a 4-wire resistive touch panel that will be used for input, and a LCD TouchShield, which interfaces directly with the Arduino Uno. The hardware system consists of an electromagnetic array, a haptic pen and a hall-effect sensor, all of which will work together to provide the haptic feedback desired. The Touchpad Uno is responsible for reading the touch input from the touchpad and sending the necessary information to the other micro controllers. The Display Uno is primarily responsible for displaying data on the display shield. The Mega is responsible for controlling the hardware controlling the electromagnetic array and the pen.
Mechanical Design
The mechanical design is largely driven by the needs of the system design. The first aspect of the mechanical design to be considered is the development of the electromagnetic array. The design of the electromagnetic array in turn drives the design of the electromagnets, which once again drives the electromagnetic array to be redesigned. This process is iterated until a satisfactory array and coil design is met.
Once the electromagnetic array is designed, the other associated components can be arranged into the main assembly that fulfills the constraints of the design. These other components impose a restraint on their position, as the display module should be relatively close to the drawing surface. Furthermore, sufficient space for battery packs and electrical assemblies must be allocated to ensure a feasible design.
Once the main assembly has been designed, the haptic pen can be designed. The pen must allow for a relatively ergonomic operation and an acceptable method to balance the weight of the linear actuator. Due to the shape of the linear actuator the bulk of the actuator must be placed at the end of the pen away from the drawing point. To control the pen a rod is attached to the end of the actuator that is capable of pressing against the ball bearing.
The mechanical design is largely driven by the needs of the system design. The first aspect of the mechanical design to be considered is the development of the electromagnetic array. The design of the electromagnetic array in turn drives the design of the electromagnets, which once again drives the electromagnetic array to be redesigned. This process is iterated until a satisfactory array and coil design is met.
Once the electromagnetic array is designed, the other associated components can be arranged into the main assembly that fulfills the constraints of the design. These other components impose a restraint on their position, as the display module should be relatively close to the drawing surface. Furthermore, sufficient space for battery packs and electrical assemblies must be allocated to ensure a feasible design.
Once the main assembly has been designed, the haptic pen can be designed. The pen must allow for a relatively ergonomic operation and an acceptable method to balance the weight of the linear actuator. Due to the shape of the linear actuator the bulk of the actuator must be placed at the end of the pen away from the drawing point. To control the pen a rod is attached to the end of the actuator that is capable of pressing against the ball bearing.
Electrical Design
The electrical system is separated into three main sub systems: the Touchpad Uno, Display Uno, and Arduino Mega. They all work mostly independent of each other, and are connected to an I2C bus for sharing touch data.
Touchpad Uno is dedicated to only run the algorithm required to calculate the touch location because the A/D conversion were found to take a lot of processing time. The TouchPad is a 5.0" 4-wire resistive touch screen made by IDW/TFS.
Display Uno is dedicated to power and manage the display. The display is a 2.8" TFT TouchShield made by Adafruit. It features a built in microSD card reader/writer used to store or load drawings.
Lastly, the Arduino Mega runs the tactile feedback components of the project. It sends outputs to the Linear Actuator Controller, which in turn controls the extension and speed of the Linear Actuator used to push against the roller ball found in the stylus. Protection diodes were used to protect the microcontroller from the potential spike of current caused by the electromagnets. The diodes are connected to the electromagent array, and allows the magnets to output their fields in both polarities.
The electrical system is separated into three main sub systems: the Touchpad Uno, Display Uno, and Arduino Mega. They all work mostly independent of each other, and are connected to an I2C bus for sharing touch data.
Touchpad Uno is dedicated to only run the algorithm required to calculate the touch location because the A/D conversion were found to take a lot of processing time. The TouchPad is a 5.0" 4-wire resistive touch screen made by IDW/TFS.
Display Uno is dedicated to power and manage the display. The display is a 2.8" TFT TouchShield made by Adafruit. It features a built in microSD card reader/writer used to store or load drawings.
Lastly, the Arduino Mega runs the tactile feedback components of the project. It sends outputs to the Linear Actuator Controller, which in turn controls the extension and speed of the Linear Actuator used to push against the roller ball found in the stylus. Protection diodes were used to protect the microcontroller from the potential spike of current caused by the electromagnets. The diodes are connected to the electromagent array, and allows the magnets to output their fields in both polarities.
Software Design
The haptic feedback tablet requires several operations to run concurrently. To make this design work, three processors are used to perform all necessary tasks. The Touchpad Uno is used to sample the touchpad and determine the position where the touchpad was touched. This Uno continuously sends the position and pressure information to the other two micro controllers via a Serial bus using I2C protocol. The Display Uno is always waiting for the delivery of data from Touchpad Uno. Once it receives the data, it either sets global configurations related to the drawing settings, or it outputs the image being drawn to the the screen. The Mega works in a similar manner. However, instead of settings related to drawing, the Mega sets different hardware settings. It also controls the hardware by outputting signals to actuate the linear actuator and electromagnets.
The haptic feedback tablet requires several operations to run concurrently. To make this design work, three processors are used to perform all necessary tasks. The Touchpad Uno is used to sample the touchpad and determine the position where the touchpad was touched. This Uno continuously sends the position and pressure information to the other two micro controllers via a Serial bus using I2C protocol. The Display Uno is always waiting for the delivery of data from Touchpad Uno. Once it receives the data, it either sets global configurations related to the drawing settings, or it outputs the image being drawn to the the screen. The Mega works in a similar manner. However, instead of settings related to drawing, the Mega sets different hardware settings. It also controls the hardware by outputting signals to actuate the linear actuator and electromagnets.
Permanent magnets are mounted at the end of the haptic stylus to increase the strength of the electromagnetic response. Lastly, the enclosure is designed in a landscape orientation to maximize user comfort. By having the enclosure in a landscape view, users can rest their hands on the sides like a real desk.
Based on the direction and location of where the user is drawing, the system will determine which electromagnets to activate. As a user moves in one direction, the magnets closest to the direction of movement will activate to the appropriate level to give the user, making it harder and easier to move.
The Haptic stylus works by applying force on the end of the ball caster. This restricts the movement of the ball, making it more and less difficult for the user to draw. This helps simulate the effect of different resistances to movement.
These motions and interactions were simulated on Solidworks to ensure that the desired effect was produced
Based on the direction and location of where the user is drawing, the system will determine which electromagnets to activate. As a user moves in one direction, the magnets closest to the direction of movement will activate to the appropriate level to give the user, making it harder and easier to move.
The Haptic stylus works by applying force on the end of the ball caster. This restricts the movement of the ball, making it more and less difficult for the user to draw. This helps simulate the effect of different resistances to movement.
These motions and interactions were simulated on Solidworks to ensure that the desired effect was produced
