ML Servomotor - Mavilor

TYPICAL SERVOMOTOR APPLICATIONby Enric SolsonaThis article offers an indepth explanation of theadvantages of servomotors for high dynamic duty cycleas beverage labels.START STOP PROCESSSTART requires an accelerationfrom 0 rpm until a speed (S)regime is achieved.STOP requires a decelerationfrom the nominal speed to 0 rpm.PROCESS can be for example:- filling and packing- cut-to-length- plastic bag production- insertion- pick & placeCYCLE TIME =TRANSFER TIME+ PROCESS TIMEFrom the servo system it is notpossible to reduce the processtime. However it is possible toreduce the transfer time for theapplications where the cycle timeis a premium.The Transfer Time Reduction ispossible if:- acceleration time isshorter- running speed is higher- deceleration time isshorter- all the above occurs.To achieve short acceleration anddeceleration times it is necessaryto consider the transmissionmechanism. In ideal conditions,the inertia of the motor, this isthe difficulty to change from onedetermined speed to anotherone, must match the inertia of theload.Note: as inertia of the motor wemust consider the rotor and otherelements mounted on the motor'sshaft such brake or feedbackdevice, although for quickestimations only the rotor's inertiais considered.In order to highlight the dynamicresponse of the motor, we willherein consider that the motorsare applied in ideal inertiaconditions.The typical pattern of the speedtimecurve in a cut-to-lengthapplication is:rpmA(fig.1)Fig. 2 describes in advance thecase described below:trpm(fig.2)The area A equals to space,distance. This can be achievedfollowing both patterns, althoughin high demanding dynamicresponse applications (fig.2) is themost commonly used.When we apply this to a specificcase, like cut-to-length of labelsfor beverages, we come to someinteresting conclusions.tExample:The Marketing Department at abeverage company requireslabels are in the range of 35mm,and the sheets containing thelabels to be cut to length, looklike in the following sketch:In these conditions, 1 revolutionof the wheel driven by theservomotor equalsL = 157,08 mm.DATA: Requested productionoutput: 50.000 bottles / h.Paper length run per hour:50.000 * 0,035 m = 1.750meters / hour à approx. 0,5m/s.Cycle time: 0,035 / 0,5 = 70miliseconds.Out of this cycle time, we willconsider 60 miliseconds for thecutting operation, and theremaining 10 miliseconds are6