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Precision power transmission
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........
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Precision Power Transmission J. C. Moore discusses the hardware of a new concept in power transmission which promises to give greater precision The sprocket chains and pulley belts described in this article (Fig 1) are designed for electro-mechanical instrumentation, servo-systems, or other miniature motion or powertransmission applications. They are made from steel-cored polyurethane and provide design advantages not now available with existing chain and belt drives. (Sprockets and geared pulleys are supplied for use with the chains and belts.) The new transmission systems are being investigated and used by many organizations, including Union Carbide, Hewlett-Packard in their high-speed printers, GTE Sylvania, Borg-Warner, du Pont and numerous
government agencies. Since the sprocket chain was the first to be introduced, and since it is more universally applicable, it is most widely used. IBM, for example, employs many thousands of feet in its recently introduced Series III copier. The chains and belts consist of 1/32in (0.8mm) diameter stainlesssteel cables jacketed with polyurethane which is integrally moulded to perpendicular polyurethane cogs that engage sprocket and pulley teeth. These sprocket chains resemble conventional sprocket or roller chains, capacity curves for both single and dual types are given in Figs 2 and 3. Pulley belts have a single central cable
% Fig 1 New "M/n-E-Pitch" steel-cored-polyurethane sprocket chains (left) and pulley belts offered by Winfred It#. Berg, Inc. A fifth belt is similar to the upper belt shown but of different pitch ~t) ,eeEh
~
f,.-
+,o
)~o teeth +
60 t e e l h
with perpendicular side cogs which engage teeth in pulley flanges as the cable rides in the pulley groove. Fig 4 gives pulley-belt capacity curves. Both chains and belts provide a high degree of position control, minimum backlash, and minimum lost motion, even under reversedirection operation. These conditions cannot be met in existing link, ladder, bead or conventional timing chain. Chain and pulley systems provide greater accuracy than precision-gear trains; eliminate costly multiple-gear shaft assemblies; and can be used in long spans. Chains and belts have a pitch-to-pitch accuracy of 0.0002 in (5/~m) and a non-adjacent pitch accuracy of 0.0006 in (15/~m). Chain-and-sprocket systems operate with extremely high accuracy even if shafts are not truly parallel, and even if sprockets are misaligned, due to chain flexibility. Belt-andpulley systems enable use of nonparallel shafts; since the belts have but one cable, they accommodate a certain amount of twist, and pulley shafts need not be parallel but can be at angles with one another. Cogs of the chains and belts mesh snugly with teeth of the sprokets and pulleys. Up to half the teeth (an average of 180 o per sprocket or pulley) are continually in contact with the sprocket or pulley. The sprocket or pulley, when rotated, causes instant chain or belt response which mean zero backlash, and motion is transmitted from one sprocket or pulley to another with 100 % accuracy. Even with slack in the chain or belt, response is instant. There is no play between teeth and cogs. If desired, however, spring-loaded idlers can be used to control slack. Cables are spliced endless with a stainless-steel bushing at a cog location. Bushings are positioned and applied by tooling to give precise pitch spacing. Splices can be overmoulded and chain splices can be connected with a cog. Sprockets and pulleys are shaped and formed to offer easy entrance and exit on each side and to support engaged cogs under load. Table 1 indicates maximum load
411 t e e l h
t~) teetl,
so t e e l h
I
.... 25
6O teeth
t! f / l
...... v ) teet h
,,+ r
]
~
J4 i#e h Ul t e e l h
0
o
iP,o o
2{H~)
Fig 2 Capacity curves for singlesprocket chains
30(~)
4~
5OO0
,oeed rpm
,peed. +,~,n
I00o
2000
3000 speed, r p m
4q~0
50@j
Fig 3 Capacity curves for dual-
sprocket chains
Fig 4 Capacity curves for pulley belts
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: .:.:. :":':':':':":':':':":':':":"~:':':':':':":":':":':':':":":':':':':':~':":'.'::~'~:~:~~::::::'!~'i::~~:'~:"::':~:~.~:::::::::::::::::::::::::::::::::::':~::-':'-:~':'-:':':':':':':"::~.~:':'~:::::":':,:~":':':":':":':":':':':-:":",:::.:::::::::::::::::::::::::::::::::::::::::::::':':":';":':":+:':
Table 1. Details on the components maxioperating cable mum tensile tensile load per strength, strength, strands cog, Ib Ib Ib single double tri pie
10
60
100
20 30
120 180
200 300
per cog, operating tensile and cable tensile for single, double and triple strand belt and chain. Large sprockets and pulleys minimize cable and splice fatigue. Ten to fourteen-tooth sprockets and pulleys should be used as idlers only. Their small diameters would reduce cable life.
Design advantages Cable-cored-chain and belt systems eliminate or minimize a riumber of critical design considerations inherent to precision-gear systems, heretofore the only way to control backlash when
increasing or decreasing speed in precise electro-serve systems. These include close-tolerance shaft centres, drive torque, material selection, lubrication, noise, and operating speed. Close shaft centre-distance tolerances are not required with chain and cable systems since the contact of many cogs assures immediate precise response. Even sprocket or
pulley eccentricity would be absorbed by the chain or belt slack. Precisiongear systems require shaft centredistance precision of 0.0002 in to
0.0005 in (5.08 to 12.7/~m). Torque required to drive precision gearing can be of extreme importance, but is not a factor with chain and belt systems, since the sprocket and pulley centres do not have to be loaded. Plastic chains and belts meshing with metal sprockets and pulleys are exceptionally quiet, even at high speeds. In addition, multiplecog contacts automatically dampen noise-producing vibration and shock. Gear systems must sometimes employ non-metallic gears to avoid noise. Due to material characteristics and component design, there is virtually no wear between polyurethane of the chain or belt and metal of the sprockets or pulleys. Material selection of precision gears is an important consideration in minimizing wear of these components: aluminium gears are usually meshed with steel to minimize wear. Lubrication is not required when meshing plastic cogs and metal teeth; it must be considered for mating gears. There is no static build up on plastic chains or belts, an important consideration in paper processing equipment. Chain-and-sprocket and pulleybelt systems readily operate at speeds up to 15000 rev/min due to light
Fig 5 "3-D" belt designed f o r use with shafts at right angles to one another
weight and low inertia. Precision gears are limited in speed by gear accuracy: top quality precision gears can operate at up to 10000 rev/min for a limited time. Commercial gears operate only to 400 rev/min. Certain high-quality, and therefore high-cost, factors required of precision gears are not required of sprockets and pulleys. These include jig-bored centres, precise tooth profile and tooth finish, and close-tolerance pitch diameter. Although even mouldedplastic sprockets and pulleys have proven successful in service, these units can be cut with the same precision as gears if ultimate precision is desired. Further information can be obtained from Joseph C. Moore, Publicist, 20t Judson Avenue, Dobbs Ferry, NY10522, USA, or from the manufacturers Winfred M; Berg Inc., 449 Ocean Avenue, East Rockaway, NY 11518, USA
Engin ring education Manufacturing technology has undergone significant changes over the last 25 years and all the indications are that it will continue to change as new technologies are introduced. These changes, and the proper utilisation of new technologies, require new knowledge and training for manufacturing engineers. The Society of Manufacturing Engineers have announced two contributions to this growing educational need: the completion of a study that "redefines the manufacturing engineer in the context of a rapidly changing industrial environment" and the establishment of the SME Manufacturing Engineering Education Foundation.
The maH~turing en~eer Prepared by Battelle/Columbus Laboratories, 'The Manufacturing Engineer: Past, Present and Future'
170
presents a profile of the manufacturing engineer, forecasts the future of ~nanufacturing engineering and discusses educational needs. Of particular interest are the forecasts of the future of manufacturing engineering. The Battelle Report notes that modern industry is rapidly evolving in response to technological advance and social pressures. Areas of special concern noted are the energy shortage, social changes of the past decade, lagging industrial productivity, and the computer-oriented accomplishments of the past 15 years. In the area of technology, the computer is predominant.
a reality within the next ten to fifteen years, say the Battelle researchers. Already in use, and on the increase, flexible manufacturing systems use numerically controlled machine tools that are fed by automatic material handling systems, although actual loading of the parts into the machine is still manual. Parts to be machined are classified by coding techniques into families of parts for automatic processing.
Group technology, also in use and rapidly proliferating, involves the organising and planning of the production of parts into batches that exhibit some similarity of geometry or processing Computer integrated manufactursequence. This is a small-batch teching is the higtlest level of automation, nique, but 75% of all machined parts are the plateau at which computers are used produced in small batches. Group techto co-ordinate the optimise all phases of nology, which is discussed in detail in manufacturing. When fully implemented, the Battelle Report, brings a vastly increased efficiency and productivity to it will give us the automatic factory, a the productionprocess. It also forces currently visionary concept that will be
PRECISION ENGINEERING
........
ii
ii
Precision Power Transmission J. C. Moore discusses the hardware of a new concept in power transmission which promises to give greater precision The sprocket chains and pulley belts described in this article (Fig 1) are designed for electro-mechanical instrumentation, servo-systems, or other miniature motion or powertransmission applications. They are made from steel-cored polyurethane and provide design advantages not now available with existing chain and belt drives. (Sprockets and geared pulleys are supplied for use with the chains and belts.) The new transmission systems are being investigated and used by many organizations, including Union Carbide, Hewlett-Packard in their high-speed printers, GTE Sylvania, Borg-Warner, du Pont and numerous
government agencies. Since the sprocket chain was the first to be introduced, and since it is more universally applicable, it is most widely used. IBM, for example, employs many thousands of feet in its recently introduced Series III copier. The chains and belts consist of 1/32in (0.8mm) diameter stainlesssteel cables jacketed with polyurethane which is integrally moulded to perpendicular polyurethane cogs that engage sprocket and pulley teeth. These sprocket chains resemble conventional sprocket or roller chains, capacity curves for both single and dual types are given in Figs 2 and 3. Pulley belts have a single central cable
% Fig 1 New "M/n-E-Pitch" steel-cored-polyurethane sprocket chains (left) and pulley belts offered by Winfred It#. Berg, Inc. A fifth belt is similar to the upper belt shown but of different pitch ~t) ,eeEh
~
f,.-
+,o
)~o teeth +
60 t e e l h
with perpendicular side cogs which engage teeth in pulley flanges as the cable rides in the pulley groove. Fig 4 gives pulley-belt capacity curves. Both chains and belts provide a high degree of position control, minimum backlash, and minimum lost motion, even under reversedirection operation. These conditions cannot be met in existing link, ladder, bead or conventional timing chain. Chain and pulley systems provide greater accuracy than precision-gear trains; eliminate costly multiple-gear shaft assemblies; and can be used in long spans. Chains and belts have a pitch-to-pitch accuracy of 0.0002 in (5/~m) and a non-adjacent pitch accuracy of 0.0006 in (15/~m). Chain-and-sprocket systems operate with extremely high accuracy even if shafts are not truly parallel, and even if sprockets are misaligned, due to chain flexibility. Belt-andpulley systems enable use of nonparallel shafts; since the belts have but one cable, they accommodate a certain amount of twist, and pulley shafts need not be parallel but can be at angles with one another. Cogs of the chains and belts mesh snugly with teeth of the sprokets and pulleys. Up to half the teeth (an average of 180 o per sprocket or pulley) are continually in contact with the sprocket or pulley. The sprocket or pulley, when rotated, causes instant chain or belt response which mean zero backlash, and motion is transmitted from one sprocket or pulley to another with 100 % accuracy. Even with slack in the chain or belt, response is instant. There is no play between teeth and cogs. If desired, however, spring-loaded idlers can be used to control slack. Cables are spliced endless with a stainless-steel bushing at a cog location. Bushings are positioned and applied by tooling to give precise pitch spacing. Splices can be overmoulded and chain splices can be connected with a cog. Sprockets and pulleys are shaped and formed to offer easy entrance and exit on each side and to support engaged cogs under load. Table 1 indicates maximum load
411 t e e l h
t~) teetl,
so t e e l h
I
.... 25
6O teeth
t! f / l
...... v ) teet h
,,+ r
]
~
J4 i#e h Ul t e e l h
0
o
iP,o o
2{H~)
Fig 2 Capacity curves for singlesprocket chains
30(~)
4~
5OO0
,oeed rpm
,peed. +,~,n
I00o
2000
3000 speed, r p m
4q~0
50@j
Fig 3 Capacity curves for dual-
sprocket chains
Fig 4 Capacity curves for pulley belts
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: .:.:. :":':':':':":':':':":':':":"~:':':':':':":":':":':':':":":':':':':':~':":'.'::~'~:~:~~::::::'!~'i::~~:'~:"::':~:~.~:::::::::::::::::::::::::::::::::::':~::-':'-:~':'-:':':':':':':"::~.~:':'~:::::":':,:~":':':":':":':":':':':-:":",:::.:::::::::::::::::::::::::::::::::::::::::::::':':":';":':":+:':
Table 1. Details on the components maxioperating cable mum tensile tensile load per strength, strength, strands cog, Ib Ib Ib single double tri pie
10
60
100
20 30
120 180
200 300
per cog, operating tensile and cable tensile for single, double and triple strand belt and chain. Large sprockets and pulleys minimize cable and splice fatigue. Ten to fourteen-tooth sprockets and pulleys should be used as idlers only. Their small diameters would reduce cable life.
Design advantages Cable-cored-chain and belt systems eliminate or minimize a riumber of critical design considerations inherent to precision-gear systems, heretofore the only way to control backlash when
increasing or decreasing speed in precise electro-serve systems. These include close-tolerance shaft centres, drive torque, material selection, lubrication, noise, and operating speed. Close shaft centre-distance tolerances are not required with chain and cable systems since the contact of many cogs assures immediate precise response. Even sprocket or
pulley eccentricity would be absorbed by the chain or belt slack. Precisiongear systems require shaft centredistance precision of 0.0002 in to
0.0005 in (5.08 to 12.7/~m). Torque required to drive precision gearing can be of extreme importance, but is not a factor with chain and belt systems, since the sprocket and pulley centres do not have to be loaded. Plastic chains and belts meshing with metal sprockets and pulleys are exceptionally quiet, even at high speeds. In addition, multiplecog contacts automatically dampen noise-producing vibration and shock. Gear systems must sometimes employ non-metallic gears to avoid noise. Due to material characteristics and component design, there is virtually no wear between polyurethane of the chain or belt and metal of the sprockets or pulleys. Material selection of precision gears is an important consideration in minimizing wear of these components: aluminium gears are usually meshed with steel to minimize wear. Lubrication is not required when meshing plastic cogs and metal teeth; it must be considered for mating gears. There is no static build up on plastic chains or belts, an important consideration in paper processing equipment. Chain-and-sprocket and pulleybelt systems readily operate at speeds up to 15000 rev/min due to light
Fig 5 "3-D" belt designed f o r use with shafts at right angles to one another
weight and low inertia. Precision gears are limited in speed by gear accuracy: top quality precision gears can operate at up to 10000 rev/min for a limited time. Commercial gears operate only to 400 rev/min. Certain high-quality, and therefore high-cost, factors required of precision gears are not required of sprockets and pulleys. These include jig-bored centres, precise tooth profile and tooth finish, and close-tolerance pitch diameter. Although even mouldedplastic sprockets and pulleys have proven successful in service, these units can be cut with the same precision as gears if ultimate precision is desired. Further information can be obtained from Joseph C. Moore, Publicist, 20t Judson Avenue, Dobbs Ferry, NY10522, USA, or from the manufacturers Winfred M; Berg Inc., 449 Ocean Avenue, East Rockaway, NY 11518, USA
Engin ring education Manufacturing technology has undergone significant changes over the last 25 years and all the indications are that it will continue to change as new technologies are introduced. These changes, and the proper utilisation of new technologies, require new knowledge and training for manufacturing engineers. The Society of Manufacturing Engineers have announced two contributions to this growing educational need: the completion of a study that "redefines the manufacturing engineer in the context of a rapidly changing industrial environment" and the establishment of the SME Manufacturing Engineering Education Foundation.
The maH~turing en~eer Prepared by Battelle/Columbus Laboratories, 'The Manufacturing Engineer: Past, Present and Future'
170
presents a profile of the manufacturing engineer, forecasts the future of ~nanufacturing engineering and discusses educational needs. Of particular interest are the forecasts of the future of manufacturing engineering. The Battelle Report notes that modern industry is rapidly evolving in response to technological advance and social pressures. Areas of special concern noted are the energy shortage, social changes of the past decade, lagging industrial productivity, and the computer-oriented accomplishments of the past 15 years. In the area of technology, the computer is predominant.
a reality within the next ten to fifteen years, say the Battelle researchers. Already in use, and on the increase, flexible manufacturing systems use numerically controlled machine tools that are fed by automatic material handling systems, although actual loading of the parts into the machine is still manual. Parts to be machined are classified by coding techniques into families of parts for automatic processing.
Group technology, also in use and rapidly proliferating, involves the organising and planning of the production of parts into batches that exhibit some similarity of geometry or processing Computer integrated manufactursequence. This is a small-batch teching is the higtlest level of automation, nique, but 75% of all machined parts are the plateau at which computers are used produced in small batches. Group techto co-ordinate the optimise all phases of nology, which is discussed in detail in manufacturing. When fully implemented, the Battelle Report, brings a vastly increased efficiency and productivity to it will give us the automatic factory, a the productionprocess. It also forces currently visionary concept that will be
PRECISION ENGINEERING