maxon

maxon flat motorMultipole EC motors, such as maxon flat motors, require a greater numberof commutation steps for a motor revolution (6 x number of pole pairs). Dueto the wound stator teeth they have a higher terminal inductance than motorswith an ironless winding. As a result at higher speed, the current cannotdevelop fully during the correspondingly short commutation intervals.Therefore, the apparent torque produced is lower. Current is also fed backinto the controller‘s power stage.As a result, motor behaviour deviates from the ideal linear speed-torquegradient. The apparent speed-torque gradient depends on voltage andspeed: The gradient is steeper at higher speeds.Mostly, flat motors are operated in the continuous operation range wherethe achievable speed-torque gradient at nominal voltage can be approximatedby a straight line between no-load speed and nominal working point.The achievable speed-torque gradient is approximately.maxon motor 0 N NAccelerationIn accordance with the electrical boundary conditions (power supply,control, battery), a distinction is principally made between two differentstarting processes:– Start at constant voltage (without current limitation)– Start at constant current (with current limitation)Start under constant currentA current limit always means that the motor can only deliver a limitedtorque. In the speed-torque diagram, the speed increases on a vertical linewith a constant torque. Acceleration is also constant, thus simplifying thecalculation. Start at constant current is usually found in applications withservo amplifiers, where acceleration torques are limited by the amplifier‘speak current.Start with constant terminal voltageHere, the speed increases from the stall torque along the speedtorqueline. The greatest torque and thus the greatest acceleration iseffective at the start. The faster the motor turns, the lower the acceleration.The speed increases more slowly. This exponentially flatteningincrease is described by the mechanical time constant m (line 15 ofthe motor data). After this time, the rotor at the free shaft end has attained63% of the no-load speed. After roughly three mechanical timeconstants, the rotor has almost reached the no-load speed.nnnnM– Angular acceleration (in rad / s 2 ) at constant current I or constanttorque M with an additional load of inertia J L :k M· I M = 10 4 · = 10J R+ J 4 ·LJ R+ J L– Run-up time t (in ms) at a speed change n with an additional loadinertia J L : J R+ J L = · ·300 k M· I(all variables in units according to the catalog)M– Mechanical time constant m (in ms) of the unloaded motor:J R+ R m= 100 ·k 2 M– Mechanical time constants m ’ (in ms) with an additional loadinertia J L :J R+ R J m' = 100 · 1 +Lk 2 JMR– Maximum angular acceleration max (in rad / s 2 ) of the unloadedmotor:M H max= 10 4 ·J R– Maximum angular acceleration max (in rad / s 2 ) with an additionalload inertia J L :M H max= 10 4 ·J R+ J L– Run-up time (in ms) at constant voltage up to the operating point(M L , n L ): m· InM L R1 nM 0H1 M L RM Hn 0n LMay 2012 edition / subject to changeKey information39