Final Design

System

Figure 1 shows the process flow of the orthosis. The device takes inputs from the user, who bends their wrist to cause resistance changes in the bend sensors. These inputs go to an Arduino Nano, which controls a linear actuator and changes the angle of the arm.

                    Figure 1: System breakdown

Brace

Figure 2 shows the system developed to allow user-controlled elbow rotation for the left arm. Support cuffs (Figure 3) were fabricated with a positive mold taken of Max's arm. This process shown in Figure 4 was completed with the help of professional Orthotists at ABI Prosthetics, an organization specializing in custom-fit orthotic devices. A mechanical joint pictured in Figure 5 with hard stops circled in green was designed to attach to these cuffs. This joint contained attachment points for a linear servo which changes the angle of rotation of the joint. Hard stops were implemented to prevent the actuator from hyper-extending the arm while opening or closing the joint. This added safety feature proved crucial in testing as it reduced the possibility of injury to the user.

   Figure 1: Actuation system for left arm                                  Figure 2: Support cuff for lower arm                                      Figure 3: Fabrication process of arm cuff around mold of Max's arm              Figure 4: Mechanical joint with hard stops to prevent over-rotation

Electronics

A Printed Circuit Board shown below in Figure 5 was chosen to house the electronics to reduce wiring clutter and make connections as neat as possible. An Arduino Nano was selected as the device's microcontroller and was soldered into the PCB. Green DigiKey connectors were soldered into the board to make screw-in connections possible for wiring. A battery terminal was created to make connecting a power supply as easy as possible. Figure 6 shows the PCB schematic, which was drawn in and ordered from PCBExpress. Three through-board holes were added to connect the board to a housing.

                                            Figure 5: PCB with electronic components                                    

                                                      Figure 6: PCBExpress schematic

Sensors

Adafruit bend sensors pictured in Figure 7 were chosen to take user inputs. It was decided that bending of the wrist in the desired direction of the arm's actuation would be the most intuitive method for Max to use to control the device. Shown below is a custom-sewn glove for Max, which houses the bend sensors inside a pocket sleeve. These bend sensors pick up inputs every time he flexes his wrist. Figure 8 shows the data collected by Max wearing the device - the red curve represents the upward-bending resistor while the black curve represents the downward-bending resistor. Note that each resistor changes oppositely in resistance. Flexing of a resistor in one direction causes an instantaneous opposite reaction for the resistor attached to its backside. This data reassures that the sensors can accurately determine when Max is flexing his wrist up, down, or not at all. Pressure sensors as shown in Figure 7 were also considered for this device to control actuation, but they were not as easy for Max to reach and were frustrating for him to press.

                    Figure 7: Flex Sensor Data

                    Figure 8: Flex Sensor Data