Example of Vacuum calculation

Transcription

1 > Technicl informtion bout products CATALOGUE > Relese 8.5 Exmple of Vcuum clcultion System design - the procedure In this section the design procedure is described for complete system step by step. This exercise is bsed on typicl design exmple. 7. Vcuum switch 6. Solenoid vlves 5. Vcuum genertor 4. Vcuum hose 3. Mounting elements 2. Suction pds 1. Clcultion of the forces Flowchrt for system design The clcultions in the exmple re bsed on the following dt: Workpiece Mteril: steel sheets, stcked on pllet Surfce: smooth, flt, dry Dimensions: length: mx.2500 mm width: mx.1250 mm thickness: mx.2,5 mm weight: circ 60 kg Hndling system System used: portl trnsfer unit Avilble compressed ir supply:: 8 br Control voltge: 24 V DC Trnsfer procedure: horizontl - horizontl Mx. ccelertion vlues X nd Y xes: 5 m/s 2 Z xis: 5 m/s 2 Cycle time: 30 s Plnned times: for picking up: <1s for relesing: <1s Clculting the weight of the workpiece For ll subsequent clcultions, it is importnt to know the mss of the workpiece to be hndled. This cn be clculted with the following formul: Mss m [kg ]:m = L x B x H x ρ L = lenght [m] B = width [m] H = hight [m] ρ = density [kg/m 3 ] Exmple: m = 2,5 x 1,25 x 0,0025 x 7850 m = 61,33 kg Forces - how high forces do the suction pds hve to support? In order to determine the necessry holding forces, the bove mss clcultion is needed. In ddition, the suction pds must be cpble of hndling the ccelertion forces which, in fully utomtic system, re by no mens negligible. In order to simplify the clcultion, the three most importnt nd most frequent lod cses re shown grphiclly nd described below. Importnt: In the following simplified representtions of the lod cses I, II nd III, the worst cse with the highest theoreticl holding force must lwys be used for the subsequent clcultions. /

2 CATALOGUE > Relese 8.5 > Technicl informtion bout products Lod cse I: horizontl suction pds, verticl force F TH = theoreticl holding force [N] m = mss [kg] g = ccelertion due to grvity [9,81 m/s 2 ] = system ccelertion [m/s 2 ] (remember to include the emergency off sitution!) S = sfety fctor (minimum vlue 1,5; for criticl inhomogeneous or porous mterils or rough surfces 2,0 or higher) Exmple: FTH = 61,33 x (9,81 +5)x 1,5 FTH = 1363 N The suction pds re plced on horizontl workpiece which is to be moved sidewys. Lod cse II: horizontl suction pds, horizontl force FTH = m x (g +/µ)x S The suction pds re plced on horizontl workpiece which is to be moved sidewys. FTH = theoreticl holding force [N] F = ccelertion = m m = mss [kg] g = ccelertion due to grvity [9,81 m/s 2 ] = system ccelertion [m/s 2 ] (remember to include the emergency off sitution!) µ = coeff. of friction* = 0,1 for oily surfces = 0,2...0,3 for wet surfces = 0,5 for wood, metl, glss, stones,... = 0,6 for rough surfces S = sfety fctor (minimum vlue 1,5; for criticl inhomogeneous or porous mterils or rough surfces 2,0 or higher) Exmple: FTH = 61,33 x (9,81 +5/0,5)x 1,5 FTH = 1822 N * Attention! The coefficients of friction shown bove re verge vlues. The ctul vlues for the workpiece to be hndled must be determined by testing. Lod cse III: verticl suction pds, verticl force FTH = (m/µ)x (g +)x S The suction pds re plced on verticl or horizontl workpiece which is to be moved verticlly or turned to the other orienttion. FTH = theoreticl holding force [N] m = mss [kg] g = ccelertion due to grvity [9,81 m/s 2 ] = system ccelertion [m/s 2 ] (remember to include the emergency off sitution!) µ = coeff. of friction = 0,1 for oily surfces = 0,2...0,3 for wet surfces = 0,5 for wood, metl, glss, stones,... = 0,6 for rough surfces S = sfety fctor (minimum vlue 2; higher for criticl, inhomogeneous or porous mterils or rough surfces) Exmple: FTH = 61,33 x (9,81 +5/0,5)x 1,5 FTH = 1822 N For the exmple used for this description, lod cse III cn be ignored, since the workpieces re to be hndled only in horizontl orienttion. Comprison: A comprison of the figures for lod cses I nd II results, in this exmple, in mximum vlue for FTH =1822 N in lod cse II, nd this vlue is therefore used for further design clcultions. /

3 > Technicl informtion bout products CATALOGUE > Relese 8.5 How to select the suction pds The suction pds re normlly selected on the bsis of the following criteri: Operting conditions: the operting conditions (single or multiple shift opertion, expected lifetime, ggressive surroundings, temperture etc.) t the point of use re decisive for the selection of the suction pds. Surfce: depending on the surfce of the hndled workpieces, certin suction-pd versions my be more suitble. The product rnge includes flt nd bellows suction pds. For the selection of the vcuum pd mteril in reltion to the type of work piece to hndle, see the tble shown in the end of the vcuum pd section. Exmple: In this exmple, where steel sheets re to be hndled, we will use the flt suction pds, Mod. VTCF in NBR. This is the best nd most efficient solution for the hndling of smooth, flt workpieces. Clcultion of the suction force FS [N] FS = FTH /n FS = suction force FTH = theoreticl force n = number of suction pds Exmple: For medium sized (2500 x 1250 mm) steel sheets, normlly 6 to 8 suction pds would be used. The most importnt criterion for deciding the number of suction pds in this exmple, is the flexing of the steel sheet during trnsport. Clcultion of the suction force FS [N] FS = 1822/6 FS = 304 N According to the Technicl Dt s shown on section /3.07_01 for Series VTCF, 6 pcs. of suction pds Mod. VTCF-0950N re needed with suction force of 340 N ech. Clcultion of the suction force FS [N] FS = 1822/8 FS = 228 N According to the Technicl Dt s shown on section /3.07_01 for Series VTCF, 8 pcs. of suction pds Mod. VTCF-800N re needed with suction force of 260 N ech. In this exmple we decide to use 6 pcs. of suction pds Mod. VTCF-950N since this number is sufficient nd helps to keep the costs down. Importnt: - The lod which ech suction pd cn crry is shown in the tble Technicl Dt. - The lod-crrying cpcity of the suction pd must lwys be greter thn the clculted vlue. Selection of the mounting elements Normlly, the mnner in which the suction pds re mounted is defined to meet the customer s needs. However, there my be specil resons which mke specific mounting element mndtory in certin cses: Uneven or sloping surfces The suction pd must be ble to dpt itself to the slope:» flexible nipple NPF Different heights or thicknesses The suction pds must be spring-mounted in order to compenste for vrying heights:» spring plunger NPM-NPR Exmple: In this exmple the steel sheets re stcked on pllet. If the sheets re lrger thn the pllet, they my hng down t the ends. This mens tht the suction pds must be ble to compenste for considerble height differences nd slope ngles. We decide to use: Spring plunger NPM-FM-1/4-75 We need the lrgest possible stroke to cope with the hnging ends of the steel sheets. The 1/4 thred is needed for connection to the flexible nipple. Flexible nipple Mod. NPF Optimum flexibility for inclined workpiece surfces. Check vlves Mod. VNV These re used on vcuum gripper systems contining multiple suction pds in order to shut off indivul suction pds which re not covered by the workpiece, (when hndling work pieces of different sizes). Note: When selecting the mounting elements, plese mke sure tht these cn be screwed onto the suction pds, i.e. tht they hve threds of the sme size. Also note the lod-crrying cpcities of the mounting elements. Selection of vcuum hoses The size of the vcuum hose should mtch the suction pds which re used. For the selection of the suitble tube dimensions, see recommendtions under Technicl Dt. Exmple: For exmpe, from the tble with Technicl Dt we choose TRN 8/6 hose in polymmide. /

4 CATALOGUE > Relese 8.5 > Technicl informtion bout products Clcultion vcuum genertors Bsed upon our experience nd upon the vlues mesured during the system design, we recommend to choose the vcuum genertor depending on the dimeter of the suction pd, ccording to the tble below: Clcultion of the required suction rte V [M 3 /H, L/MIN] V = n x VS n = number of suction pds VS = required suction rte for single suction pd [m 3 /h, l/min] The suction rte vlues of the different vcuum genertors cn be found in the tble Technicl Dt. Exmple: V = 6 x 16,6 V = 99,6 l/min Required suction rte s function of the suction pd dimeter Suction pd Ø Required suction rte Vs up to 20 mm 0,17 m 3 /h 2,83 l/min up to 40 mm 0,35 m 3 /h 5,83 l/min up to 60 mm 0,5 m 3 /h 8,3 l/min up to 90 mm 0,75 m 3 /h 12,7 l/min up to 120 mm 1 m 3 /h 16,6 l/min Note: The indicted vlues pply to ll types of vcuum genertors. The recommended suction rte is for single suction pd nd is vlid only for smooth, ir-tight surfces. For porous surfces we recommend the execution of suitble test before the selection of the vcuum genertor. We choose compct ejector Mod. VEC-20 with suction rte of 116 l/min. Selection of vcuum switches Vcuum switches nd pressure guges re normlly selected on the bsis of the functions required in the ppliction nd on the switching frequency. The following functions re vilble: - djustble switching point - fixed or djustble hysteresis - digitl nd/or nlog output signls - sttus LED - disply with keypd - connection with M5 Femle thred, G1/8 Mle flnge or plug-in tube Exmple: - vcuum switch SWD-V00-PA with digitl disply, djustble switching point nd djustble hysteresis (lredy integrted in the compct ejector) - pressure guge. Selection of the vcuum switches nd pressure guges Even if you re confident tht the results of the system-design work re correct, you should still crry out tests with originl workpieces to be on the sfe side. However, the theoreticl system design will give you good ide of the generl prmeters for the intended ppliction. /

5 > Technicl informtion bout products CATALOGUE > Relese 8.5 Technicl informtion bout suction pds When designing vcuum circuit nd selecting suitble suction pds it is necessry to follow certin clcultions to select ech individul component in correct wy. Listed below is summry of the most common dt to tke into considertion. Technicl informtion Lterl force The mesured vlue in N t vcuum of -0,6 br on dry or oily, flt nd smooth workpiece surfce. These vlues do not include sfety fctor. Minimum workpiece curvture rdius This specifies the minimum rdius t which the workpiece cn be gripped securely by the suction pd. Theoreticl suction force Theoreticl force (N) t -0,6 br mesured t se level. Since this is theoreticl vlue, it is necessry to reduce this vlue by dding sfety fctor to compenste for friction or loss of vcuum, depending on the ppliction (from rough workpiece surfce or porous mteril etc.) Internl volume This is used to clculte the totl volume of the gripper system. With this vlue, it is lso possible to clculte the evcution time. Suction pd stroke This is the lifting effect which occurs during evcution of bellows type suction pd. Suction pd stroke Suction pd mteril selection Applictions NBR SI Food Oily prts Slight mrking of workpieces For high tempertures For low tempertures Very smooth surfces (glss) Very rough surfces (wood, stone) /

6 CATALOGUE > Relese 8.5 > Technicl informtion bout products Selection nd configurtion Plnning check-list for selection of suction pds Wht re the workpiece dimensions nd weight? How is the workpiece surfce (rough, structured, smooth)? Could the workpiece be dirty? If so, wht kind of dirt? Wht is the highest workpiece temperture? Is n ccurte gripping/plcing/positionining, required? Wht is the cycle time? Wht is the mximum ccelertion during hndling? Which kind of hndling is needed (moving, slewing, turning over)? This is importnt dt for the suction force clcultion nd to estblish the required suction force nd number of suction pds (see technicl informtion). It determines the kind of suction pd (mteril, shpe, dimensions). This is importnt informtion to select the suction pd dimensioning (see technicl informtion) nd lso for the design of the dust filter. Temperture is importnt to select the suction pd mteril. At tempertures bove 70 C the use of silicone versions should be considered. Determines the structure, the type nd the version of the suction pd. This dt is importnt for the dimensioning nd plys prt in the clcultions (for instnce the vcuum genertor suction cpcity clcultion); (see the technicl informtion). This is importnt for the dimensioning nd design of the suction force, together with the relted clcultions (for instnce the suction cpcity nd the moment of inerti); (see the techn. inf.). This dt is importnt to estblish the dimension nd the suction force clcultion. Mterils summry Chemicl designtion Nitrile rubber Silicone Abbrevition NBR SI Wer resistnce Resistnce to permnent deformtions Generl wether resistnce Resistnce to ozone Resistnce to oil Resistnce to fuels Resistnce to lcohol, ethnol 96 % Resistnce to solvents Generl resistnce to cids Resistnce to stem Tensile strength Abrsion vlue in mm 3 s. DIN (pprox.) t 60 Sh. t 55 Sh. Specific resistnce [ohm * cm] - - Short-term temperture resistnce in C from -30 to +120 from -60 to +250 Long-term temperture resistnce in C from -10 to +70 from -30 to +200 Shore hrdness to DIN from 40 to 90 from 30 to 85* Colour/Coding blck white * After-bke of silicone 10 h/160 C = Shore A excellent very good good poor to stisfctory /