stepper motor control

Posted on Feb 6, 2014

The 3D printer requires separate control for three independent axis. Each of the controlled axis must have a high precision electronic driver. Mechanical part of the each axis is based on a precise bipolar stepper motor connected to a drive shaft via claw coupling. An additional driver and mechanics are used for the extruder. The stepper motor con

stepper motor control
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trol is based on a TI DRV8818. The DRV8818 is an improved version of the TI DRV8811. Main difference between these two devices is in the value of the ON-resistance of the DRV8818 output MOSFET. A direct dependence of total power dissipation (TPD) over the device and ON-resistance is a critical parameter when running motors at higher levels of currents. Roughly calculated, difference of the ON-resistance between the two before mentioned devices is 0. 6 ©. At the peak current value, TPD of the DRV8818 is 1. 46 W and is lower by 2. 37 W then it would be if the DRV8811 was selected. Both DRV8811 and DRV8818 are fully functional stand alone stepper motor drivers. The integration of various functions in single IC package decreases the requirements on the processor unit. The processor unit controls only three signals per driver. This allows minimal MSP430 processor pin usage per driver device and that was one of the important parameters for a project design. Furthermore, the stepping sequence for the motor is realized by the DRV8818 internal step indexer logic which also reduces the computational burden on the processor unit. The DRV8818 supports advanced current routing for motor windings realized by an integrated H-bridge. Integration of the H-bridge inside the DRV8818 package reduce the number of external discrete elements and improves matching and thermal equilibrium between the transistors. The transistor switches used in the...

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