tailieunhanh - Industrial Brushless Servomotors Episode 9

Tham khảo tài liệu 'industrial brushless servomotors episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Motor rating and selection 155 motor case of the motor and so the winding must heat up before the stator core. The winding heats quickly particularly at the start of the torque pulse and also cools quickly at the start of the pulse gap. This means that the average time constants of the rising and falling waveforms of winding temperature in Figure are lower than the value of Tth quoted for the motor as a whole 9 . The ripple on the winding temperature becomes more pronounced as t is increased. The ripple also increases as Zp is reduced assuming the average losses are kept the same by increasing the torque. The extreme case would be if the motor produced four times its continuous rated torque over a pulse width of tp t 16. As a rule of thumb the ripple in the steady-state winding temperature will normally be confined to a band of 10 C when 7th loot where Tth 25 minutes and the maximum average temperature rise is 100 C. When Tth 100 the ripple may still fall within the 10 C band at the higher end of the tp t range. Such cases should be considered individually. Calculations are relatively easy when the period of the intermittent operation is less than 1 of the thermal time constant of the motor. The maximum ripple is 10 C. The designed maximum rise in the winding temperature is 110 C and so the maximum average losses are those which lead to an average winding temperature of 110 - 10 or 100 C above ambient. The losses are found by adding the i2R loss to the speed-sensitive loss as estimated from the Soac diagram. Example The sinusoidal motor of Example is to provide the intermittent torque shown in Figure at a speed of 2500 rpm. What is the maximum height Tmax of the torque pulse 156 Industrial Brushless Servomoters assuming that the peak temperature rise of the winding is limited to 110 C The motor constants are as follows Rll Q Kt Nm A Tfh 35 minutes R h C W The current at Tmax is I A. Ay The effective stator resistance for the