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Technical ReferenceService Life and MomentOne of the main factors related to an actuator's service life is the "load rating".There are two types of load rating: A static load is the weight of a load that leaves a small amount of indentation when the load is applied. A dynamic load is the weight of a load that maintains a constant survival probably of the guide when the load is applied while moving a constant distant.Guide manufacturers rate dynamic load values to maintain a 90% survival rate at a travel distance of 50km. However, when taking account the speed of movement and work rate, the actual travel distance needs to be 5000 to 10000km. While the life of a guide is sufficiently long for radial loads, it is actually the moment load that is offset from the guide center that is most problematic to its service life.The service life for IAI actuators as documented in this catalog shows the allowable dynamic moment based on a 5000 or 10000km service life.IAI uses the following equation calculate the service life:(for 10000km service life)CIA 3 L10=( P )L10 : Service life (90% Survival Probability)CIA : Allowable Dynamic Moment in IAI Catalog P : Moment usedAllowable Dynamic MomentOverhang load lengthThe allowable dynamic moment is the maximum offset load exerted on the slider, calculated from the guide service life. The direction in which force is exerted on the guide is categorized into 3 directions - Ma (pitch), Mb (yaw), Mc (roll) - the tolerance for each of which are set for each actuator. Applying a moment exceeding the allowable value will reduce the service life of the actuator. Use an auxiliary guide when working within or in excess of these tolerances.An overhang load length is specified for a slider-type actuator to indicate the length of overhang (offset) from the actuator.When the length of an object mounted to the slider actuator exceeds this length, it will generate vibration and increase the settling time. So, pay attention to the allowable overhang length as well as the allowable dynamic moment.LLLForces Acting on the Guide in 3 Directions (Ma, Mb, Mc)PitchingRollingYawingRated Moment (value in catalog) = Force computed fromguide's service lifeThe service life of the actuator shortens proportionally to the moment cubed.A static (i.e. actuator at rest) moment is acceptable within three times the moment for the running life span of 10000km, which is the documented value in the catalog.M2 (N m) = W (kg) × L (mm) × a (G) × 9.8/1000W: LoadL : Distance from work point to the center ofgravity of payload (L=T+H)T : Distance from top surface of slider to thecenter of gravity of payloadH : Distance from guide work point to the topLoad:WPattern CThe allowable overhang load length is determined by the slider length.An overhang that exceeds the allowable overhang length will generate vibration and increase settling time.L/ =5orless* Between 3 to 4 for a camera- equipped measuring machine.For example:L/ =1.2 Mechanical machine L/ = 3 Measuring machine L/ = 5 RobotThe allowable dynamic moment is calculated from the service life of the guide.How to calculate allowable dynamic momentGuide work pointMaLoad:WTLHPattern APattern BMb Load:WLMbLoad:WMaPattern DHT LPattern ELLoad:WMb Load:WLLoad:W Ma TLoad:WGuide work point Hsurface of slider Specified accelerationLa :Appendix: - 5 Technical Reference/InformationVertical HorizontalGuide work point