Program 2011/2012 - maxon motor - #39

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maxon flat motor maxon motor Multipole EC motors, such as maxon flat motors, require a greater number of commutation steps for a motor revolution (6 x number of pole pairs). Due to the wound stator teeth they have a higher terminal inductance than motors with an ironless winding. As a result at higher speed, the current cannot develop fully during the correspondingly short commutation intervals. Therefore, the apparent torque produced is lower. Current is also fed back into the controller‘s power stage. As a result, motor behaviour deviates from the ideal linear speed-torque gradient. The apparent speed-torque gradient depends on voltage and speed: The gradient is steeper at higher speeds. Mostly, flat motors are operated in the continuous operation range where the achievable speed-torque gradient at nominal voltage can be approximated by a straight line between no-load speed and nominal working point. The achievable speed-torque gradient is approximately. Acceleration In accordance with the electrical boundary conditions (power supply, control, battery), a distinction is principally made between two different starting processes: – Start at constant voltage (without current limitation) – Start at constant current (with current limitation) Start under constant current A current limit always means that the motor can only deliver a limited torque. In the speed-torque diagram, the speed increases on a vertical line with a constant torque. Acceleration is also constant, thus simplifying the calculation. Start at constant current is usually found in applications with servo amplifiers, where acceleration torques are limited by the amplifier‘s peak current. n Start with constant terminal voltage Here, the speed increases from the stall torque along the speedtorque line. The greatest torque and thus the greatest acceleration is effective at the start. The faster the motor turns, the lower the acceleration. The speed increases more slowly. This exponentially flattening increase is described by the mechanical time constant tm (line 15 of the motor data). After this time, the rotor at the free shaft end has attained 63% of the no-load speed. After roughly three mechanical time constants, the rotor has almost reached the no-load speed. n n n M M – Angular acceleration (in rad / s2) at constant current I or constant torque M with an additional load of inertia JL: – Mechanical time constant – Mechanical time constants inertia JL: m (in ms) of the unloaded motor: m ’ (in ms) with an additional load ‘ – Run-up time t (in ms) at a speed change n with an additional load inertia JL: – Maximum angular acceleration motor: max (in rad / s2) of the unloaded max (in rad / s2) with an additional max (all variables in units according to the catalog) – Maximum angular acceleration load inertia JL: max – Run-up time (in ms) at constant voltage up to the operating point (MB , nB ): May 2011 edition / subject to change Key information 39