DESIGN PROCESS
ROTATION SYSTEM
The rotation system is the sub-system which rotates the camera about the yaw, pitch and roll axes. Detailed designs were conceptualized for a camera rotation system that would provide the desired 3-axis control. 3D models were created of the initial concept designs in SolidWorks for geometry refinement, comparison, and prototyping purposes.
Load and stress calculations were performed on the camera rotation system design to verify the design would work with the materials used to manufacture it.
A prototype of the initial rotation system design was created using laser-cut plywood.
The design of the camera rotation system prototype was tested using brushless DC motors and a microcontroller.
Using the results of the prototype tests, a final camera rotation system design was created using servo motors and machined from aluminum.
LIFT SYSTEM
The lift system includes the column that the camera rotation system mounts to and provides vertical motion for the camera. Designs for the various viable lift technologies were created which included forming drawings and 3D models. Detailed stress and load analysis was performed on each design.
Using the chosen best design, a telescoping lift system was sourced that would be used in the final product.
A 3D model of the cart and the lift system was created so a way to connect each system together could be modelled. An attachment method was designed for the baseplate of the camera module to the cart. Clamps were sourced that would attach the baseplate and camera module together. Several attachment parts for the lift system were machined for the final product.
AUTONOMOUS FOLLOWING
The autonomous following control system is driven with incoming data from the RGB camera and depth camera from the Kinect. OpenCV, an open source computer vision library, was used to perform analysis on the RGB image from the Kinect providing the U-Kart with an estimation of the wheelchair's location with respect to the camera. A movement controller was used to plan the motion of the U-Kart based on the positional information provided by the vision systems. Combined, the two systems work towards following the wheelchair and maintaining a specified distance.
The Xbox Kinect which is outfitted with an RGB Camera, an IR Projector, and an IR Sensor. The depth information is calculated by using the information from the projected and received IR light. The depth data ranges from as short as 45cm to as far as 8m away.
EMBEDDED CONTROLLER
The embedded control system is powered by an ARM Cortex M4 microprocessor. The M4 responds to commands given to it by the NUC onboard computer via a ROS framework and controls the lift and rotation system.
To control the lift height, the M4 sends a digital logic signal to the lift motor controller that controls the lift direction and a pulse width modulation (PWM) signal that controls the lift speed. The M4 reads the values on two hall effect sensors monitoring the brushed DC motor that powers the lift to monitor how many revolutions it has taken. The M4 converts a desired height from the NUC to a number of rotations to achieve precise vertical distances within 1mm of the target.
To control the rotation system, the M4 sends serial commands to the Dynamixel servo motors. Between the M4 and Dynamixel motors is a transceiver that converts the UART serial communication protocol of the M4 to the RS485 protocol used by the motors. The M4 sends desired angles and a rotation speeds to each individual motor to control them. When dynamic stability mode is activated, the M4 receives euler angle measurements from an IMU mounted underneath the camera to automatically adjust the motor’s angles when the platform moves to keep the camera pointing in the same direction.
POWER DISTRIBUTION
Current battery technologies were researched and one was chosen that would provide the necessary current and battery life requirements. Each component requiring power was examined to find their specific voltage and current requirements. An electrical design was created to convert the battery voltage to each of the required voltages in the project, with consideration given to future component additions.
Electrical schematics for the design were created in MultiSIM and a printed circuit board was designed in Ultiboard. The designed PCB was outsourced to Turnkey PCB Assembly for fabrication and populated with components purchased from digikey.ca. The final power distribution system was tested to ensure it worked as designed.