Overview of the hardware structure of the control system: All components
use the central SPI bus that connects all sensors and the actuator. The SBC
acts as the master and collects all sensor data over the bus. The hardware watchdog
monitors the activity on the bus, and switches to the hardware P-controller as long as
the single board computer does not send commands to the pwm-amplifier, assuming
an SBC failure.
the layer where they occurred. This safety system allows experiments and application
of the exoskeleton in life-like environments.
But it has to be pointed out that a secure fallback state does not exist for an exoskeleton.
Depending on the movement in which the error occurs, the system cannot
determine a safe position on its own to avoid stumbling and to maintain a stable pose.
For example, extending or flexing the knee joint by default might unbalance the operator,
and holding the knee angle fixed can lead to stumbling over an obstacle or a step.
Nevertheless, some actions can be performed to minimize consequences of a failure.
The following subsections are arranged in order of fault-handling, explaining possible
error sources and countermeasurements.