Datasheets

08/22 Our policy is one of continued research and development. We therefore reserve the right to amend, without notice, the specifications given in this document. (2019-9261a) © 2020 IMI International S.R.O. en 1.6.300.010 Sizing Rules and Formulas 1. Definition of the load cycle The load cycle includes all movements of the actuator. For every step, the following values must be defined: • Direction of the movement • End position of the movement • External load mass • Friction coefficient of a possible external guiding • Acceleration and deceleration • Maximum velocity • Constant external forces • Possible pause times at the end of the movement Due to the high positioning accuracy of the Norgren ELION actua- tors, the number of steps in one cycle is not limited. 2. Calculation of the forces acting on the actuator For a basic selection of the actuator, the knowledge of the acting forces during the load cycle is essential. For each movement of the load, the total force must be calculated. The total force F tot can be calculated as the sum the inertial force F I , external friction forces F fr , the gradient force F gr caused by moving a mass against gravity and possible constant external forces F const. The forces can be calculated as follows: a Acceleration/deceleration m/s² m mov,act Moving mass of the actuator kg m load Load mass applied on actuator kg Δx Stroke of each movement m j Direction of the movement ° μ Friction coefficient - g Gravitational acceleration m/s 2 3. Selection of the actuator 3.1 Safety stroke Disregarding the initial set up, the actuator must not touch its mechanical end stops. A safety stroke should be considered, respecting the application boundaries and environments. We generally recommend a safety stroke of 20 mm per side for electric actuators. The order stroke = working stroke + safety stroke of 2 x 20 mm. 3.2 Spindle pitch The pitch of the driving spindle can be defined by the maximum velocity of the load cycle. The correlation between the maximum stroke length and the max- imum velocity of the actuator must be considered as well as the different spindle pitch values defining the maximum velocity. Using the values for stroke length and velocity, the maximum force necessary during the load cycle can be compared to the maximum force applicable to the actuator. Here, the direction of movement has to be considered to prevent buckling of the cylinder rod and spindle. In general, side loads on the actuator should be avoided. If lateral forces appear, an external guiding system must be applied! 4. Selection of a motor For each actuator, two motor sizes are available. The selection of the motor is based on the driving torque T and rotational speed rpm which have to be calculated for each step of the load cycle. All values calculated must be below the intermittent torque the motor can deliver (diagr. p. 35 to 38). T Torque Nm rpm Rotational speed min -1 v max,step Maximum velocity of each step m/s P spindle Spindle pitch mm To avoid overheating of the motor, the mean torque T rms of the load cycle must be lower than the continuous torque (diagr. p. 35 to 38). 5. Estimation of expected life time The estimated life time of the ball screw drive can be calculated according to DIN ISO 3408-5. Therefore, the mean velocity v m and the mean force F m must be calculated. Then, the life time in revolutions is calculated from the dynamic force C of the ball screw nut and the mean force. The life time L km in km is then calculated with the spindle pitch P. For more information please visit: https://www.norgren.com/us/en/list/electric-actuators

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