PSI - Issue 37

Pedro J. Sousa et al. / Procedia Structural Integrity 37 (2022) 730–737 Sousa et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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powering down the machine. In the case of the endstops, the system is only sensitive to transitions and not current state, which allows the machine to resume operation after being triggered. The PC status output is performed by a DT9816 DAQ from Measurement Computing, which is also responsible for acquiring the position data from a wire sensor and acquiring the force data from a load cell, which is amplified by a RW-GT01A strain gauge amplifier from Brightwin Electronics. 3.1. Control loop For this machine, the main control loop is implemented inside a Windows-based computer, where the timing of the loop is controlled by a high precision timer. A schematic representation of the implemented logic is presented in Fig. 6. It starts by reading the force and position values using the DAQ, then the motor parameters, such as torque and motor position.

Fig. 6. Main control loop logic.

When the system is in force control mode, this control loop implements the PID logic itself, while in other control types, it uses the logic embedded in the BLDC driver. Afterwards it performs a check of the user-defined virtual boundaries, which are independent of the physical endstops, stopping the motor in case of fail. In the end of each cycle, it will record the obtained data, if enabled, and trigger a GUI update if necessary.

3.2. User interface

The graphical user interface uses one main window, shown in Fig. 7, which presents three charts, one for the measured force, other for the motor torque and the last one for the relative, zero-able, position. A list of the current values of force, torque and absolute, relative and motor positions is shown to the right.