Although hidden away with no direct visibility to the eye, the electronics for every product at Mechatech goes through extensive testing and design iterations before it makes it to the final product. Every lower-level component from the sensors to the connectors are chosen very carefully with the higher-level bigger picture in mind. Primarily focused on the functionality of the components, all of the properties are weighed against each other before a component is picked. The power consumption, communication protocol, speed, reliability and even the physical dimensions of the component are compared and contrasted.
Angular position sensor, torque sensor, and inertial measurement units (IMU) are some of the integral parts of the sensor chain of the exoskeleton at Mechatech. Depending on the type of exoskeleton and the corresponding application a choice is made between a microprocessor (MCU) based system or an FPGA based system.
Breadboarding is the initial step to the sensor testing process. A sensor is breadboarded in order to establish a connection with the MCU and verify the hardware connections. The use of a breadboard, jumper wires and pluggable passives (resistors, capacitors) allows for easy modification of the hardware. No investigation into the quality of data is done at this point as the crude nature of the connections is highly likely to compromise the quality of the data.
Next would be to set up the sensor system on a Veroboard to provide more robust connections with components soldered into the board rather than plugged in. Additionally, the use of wires trimmed to the necessary length, are soldered to form the connection rather than standard length jumper wires that are only plugged in. This ensures a reliable connection and eliminates the possibility of a long jumper wire acting as a potential antenna that can corrupt the data. Each sensor is put in its own custom designed test rig to try and match the sensor arrangement in the final product. The sensor is put under different conditions and data is collected and stored for analysis. A significant amount of time is spent in analysing the data and fixing any mismatches between the collected and expected data. Modifications are made to the hardware and the software in fine tuning the data. Surprisingly, sensors do not perform to their respective datasheet specification on a consistent basis. Although, they perform as expected 99% of the time, most sensors lack consistency as they try to keep up with the expected data rate.
“A 100% performance rate is expected from a sensor for it to be able to get into a Mechatech product.”
A 100% performance rate is expected from a sensor for it to be able to get into a Mechatech product. This is primarily due to the uncompromising nature of the control system that would allow for smooth movements in the exoskeleton. Any glitches in the data would lead to jitters and unexpected movements.
Once individual sensors have passed their data tests and have been finalised, they are brought together onto a custom designed PCB. Considerations when designing a PCB for exoskeletons are mainly data integrity, safety, size and EMC compliance. A lot of pre-planning goes into arranging the components in separate domains depending on their type. The shape and size of the board dictates how the components are placed. More often than not, components are placed on both sides of the board to maintain a small form factor.
The other main aspect of the PCB is the integration of the board within the mechanical frame. The mechanical frame of the exoskeleton always tries to maintain an ergonomic shape throughout. This leads to different types of exotic shapes for the PCB. A considerate amount of time is spent in collaboration with the mechanical department in fleshing out the size and shape of the PCB so as to maintain the necessary shape while not compromising on the functionality. Accordingly, the electromechanical components are selected to allow for a smooth integration into the exoskeleton.
This is a brief description of the design processes that go on behind the scenes of every PCB in a Mechatech product. As explained throughout the post, there is a significant amount of work done in getting the exoskeleton functioning as well as it looks.