Finger Attachment Workpiece mg μF μF F F Selection Procedure Step 1 Step 1 Check the gripping force. Check the gripping force. Check the gripping point and overhang. Check the external force on fingers. Workpiece mass: 0.1 kg Pushing force: 70% Pushing force is one of the values of step data that is input into the controller. Example Guidelines for the selection of the gripper with respect to workpiece mass �� Although conditions differ according to the workpiece shape and the coefficient of friction between the attachments and the workpiece, select a model that can provide a gripping force of 10 to 20 times Note) the workpiece weight, or more. Note) For details, refer to the calculation of required gripping force. �� If high acceleration or impact forces are encountered during motion, a further margin of safety should be considered. Example) When it is desired to set the gripping force at 20 times or more above the workpiece weight. Required gripping force = 0.1 kg x 20 x 9.8 m/s2 . 19.6 N or more LEHZ20 When the LEHZ20 is selected. �� A gripping force of 27 N is obtained from the intersection point of gripping point distance L = 30 mm and pushing force of 70%. �� Gripping force is 27.6 times greater than the workpiece weight, and therefore satisfies a gripping force setting value of 20 times or more. Step 2 Step 3 Gripping force F [N] Gripping point L [mm] 50 40 30 20 10 0 27 0 20 30 40 60 80 100 120 140 70% 40% LEHZ20 �� Pushing speed is satisfied at the point where 70% of the pushing force and 30 mm/sec of the pushing speed cross. Pushing force/Trigger level [%] Pushing speed [mm/sec] 110 100 90 80 70 60 50 40 30 0 10 20 30 40 50 60 Pushing force and trigger level range “Gripping force at least 10 to 20 times the workpiece weight” . The “10 to 20 times or more of the workpiece weight” recommended by SMC is calculated with a margin of “a” = 4, which allows for impacts that occur during normal transportation, etc. Calculation of required gripping force Coefficient of friction μ (depends on the operating environment, contact pressure, etc.) Coefficient of friction μ 0.1 0.2 0.2 or more Attachment . Material of workpieces (guideline) Metal (surface roughness Rz3.2 or less) Metal Rubber, Resin, etc. Note) . Even in cases where the coefficient of friction is greater than μ = 0.2, for reasons of safety, select a gripping force which is at least 10 to 20 times greater than the workpiece weight, as recommended by SMC. . If high acceleration or impact forces are encountered during motion, a further margin should be considered. Electric Gripper 2-Finger Type Series LEHZ Model Selection Step Motor (Servo/24 VDC) Check the conditions. Select the pushing speed. Calculate the required gripping force. Select the model from gripping force graph. Pushing force 100% Gripping point distance: 30 mm Pushing speed: 30 mm/sec When gripping a workpiece as in the figure to the left, and with the following definitions, F : Gripping force (N) μ : Coefficient of friction between the attachments and the workpiece m : Workpiece mass (kg) g : Gravitational acceleration (= 9.8 m/s2) mg : Workpiece weight (N) the conditions under which the workpiece will not drop are 2 x μF > mg and therefore, F > With “a” representing the margin, “F” is determined by the following formula: Number of fingers mg 2 x μ mg 2 x μ F = x a When μ = 0.2 When μ = 0.1 F = x 4 = 10 x mg mg 2 x 0.2 F = x 4 = 20 x mg mg 2 x 0.1 10 x Workpiece weight 20 x Workpiece weight Note) Confirm the pushing speed range from the determined pushing force [%]. 324