Elec­tric lin­ear drives are a game changer

DEMM Engineering & Manufacturing - - NEWS -

In ad­di­tion to pure en­ergy costs, the in­vest­ment and main­te­nance costs must also be in­cluded in a to­tal cost cal­cu­la­tion.

Tests have shown that al­to­gether they make up about 20 per­cent of to­tal op­er­at­ing costs. In the ex­am­ple shown here, there­fore, about 750 eu­ros ($1500) must be spent on this each year, so the to­tal op­er­at­ing costs add up to 3,750.

Man­u­fac­tur­ers of pneu­matic so­lu­tions rate the to­tal costs (af­ter en­ergy ef­fi­ciency mea­sures) to be 0.025 euro per stan­dard cu­bic me­ter of com­pressed air. For our ex­am­ple, this would re­sult in to­tal an­nual op­er­at­ing costs of 3,750 eu­ros for the amount of 150.000 Nm³ of com­pressed air re­quired for one cylin­der, which sup­ports the above cal­cu­la­tion ex­am­ple.

A lin­ear drive, in­clud­ing all re­quired com­po­nents (ca­bles, in­verter, etc.), in con­trast, does cost more than a pneu­matic drive (in­clud­ing valves, tub­ing, etc.). The sig­nif­i­cantly lower en­ergy costs, how­ever, mean that the elec­tric drive pays for it­self in less than half a year. Af­ter that point the sav­ings are sig­nif­i­cant. The en­ergy costs in our ex­am­ple ex­ceed the in­vest­ment costs for the pneu­matic cylin­der af­ter just three weeks.

Anal­y­sis of the in­vest­ment and en­ergy costs in this ap­pli­ca­tion ex­am­ple shows that the sav­ings from the use of an in­dus­trial lin­ear mo­tor, com­pared to the use of a pneu­matic cylin­der, are 2300 eu­ros and 5900 eu­ros at 12 and 24 months of ser­vice re­spec­tively.

Chang­ing to an elec­tric lin­ear drive can also dras­ti­cally re­duce CO2 emis­sions. Ac­cord­ing to ini­tial fig­ures in 2011, the CO2 emis­sions fac­tor for the power mix in Ger­many, with a high level of re­new­able en­ergy con­tent, was 559 g/kWh.

The 25,000 kWh that the pneu­matic cylin­der in the ex­am­ple cal­cu­la­tion re­quires, rel­a­tive to the 800 kWh/year for the elec­tric lin­ear drive, thus cor­re­spond to an an­nual in­crease of 13,360 kg of CO2 emis­sions.

If a Ger­man com­pany re­places one pneu­matic cylin­der with one lin­ear drive, an em­ployee can drive his Seat Ibiza SC Eco­mo­tive 1.4 TDI (98 g CO2/km) for 136,000 km, or the owner can drive his Fer­rari 612 Scagli­etti (470 g C02/km) for an­other 28,500 km at least, with­out de­grad­ing the com­pany’s CO2 foot­print.

Due to ris­ing en­ergy prices and the re­quire­ment for dras­ti­cally re­duc­ing CO2 emis­sions, var­i­ous providers have projects for in­creas­ing the ef­fi­ciency of pneu­mat­ics. Con­sid­er­ing the 30 times higher en­ergy re­quire­ment in the con­crete ap­pli­ca­tion ex­am­ple, how­ever, it will re­main dif­fi­cult to even come close to the en­ergy ef­fi­ciency of lin­ear di­rect drives.

Im­prove­ments of about 10-15 per­cent are pos­si­ble for the com­pres­sor, but then the phys­i­cal lim­its are reached. The leak­age can be op­ti­mized to be­low 10 per­cent with ap­pro­pri­ate ef­fort. And even if the task in the ap­pli­ca­tion ex­am­ple could be han­dled with a smaller 32 mm pneu­matic cylin­der, the en­ergy re­quire­ments and CO2 emis­sions would still ex­ceed those of the lin­ear mo­tor by a fac­tor of 12.5, or 1,250 per­cent.

When this is com­pared to the le­gal re­quire­ments for en­ergy ef­fi­ciency of asyn­chro­nous mo­tors that went into force in 2011 (le­gal reg­u­la­tion for sav­ing ‘only’ two to 22 per­cent), the mag­ni­tude of the dif­fer­ence in en­ergy ef­fi­ciency be­tween pneu­mat­ics and lin­ear mo­tors be­comes clear.

In ad­di­tion to the lower en­ergy re­quire­ments, the elec­tric vari­ant has the ad­van­tage of greater flex­i­bil­ity in the de­sign of pro­duc­tion se­quences and mon­i­tor­ing sys­tems. Mo­tion se­quences in elec­tric lin­ear drives can be sig­nif­i­cantly more dy­namic and have higher re­peata­bil­ity.

The mo­tion pro­file can be pro­grammed freely, so that even com­plex mo­tion se­quences can be im­ple­mented quickly with­out a prob­lem. They can also be adapted to new re­quire­ments, even dur­ing oper­a­tion.

Lin­ear drives are sig­nif­i­cantly qui­eter and more durable. They are not sen­si­tive to changes in load and can be started and stopped smoothly. Anal­y­sis of the data pro­duced in the in­verter also al­lows var­i­ous process vari­ables to be mon­i­tored with­out additional sen­sors, which can also be used for re­mote di­ag­nos­tics on the sys­tem.

Not least, fewer in­di­vid­ual com­po­nents are re­quired, and they can be ser­viced and re­placed much more eas­ily than those used for pneu­mat­ics. This is re­flected in lower costs for in­stal­la­tion, main­te­nance, and lo­gis­tics.

When more than two po­si­tions are needed, when mo­tions are to be syn­chro­nized to a mas­ter shaft, or when the dy­nam­ics or ser­vice life of a pneu­matic cylin­der are no longer suf­fi­cient, the de­signer has for years gladly turned to lin­ear di­rect drives from LinMot.

Due to high op­er­at­ing costs for pneu­mat­ics, the use of in­dus­trial lin­ear mo­tors pays off to an in­creas­ing de­gree, even for sim­ple point-to­point mo­tions with only two end po­si­tions. This is es­pe­cially true when mo­tions are per­formed reg­u­larly in cycli­cal op­er­a­tions, and pneu­matic cylin­ders need to be sized gen­er­ously due to speed and load con­di­tions. In this case, the elec­tric lin­ear drive pays for it­self within a few weeks.

Con­tact John Brooks, 0800 484950.

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