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Has NC made tracers obsolete
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Has NC made tracers obsolete C. Glover discusses the relative merits of NC and tracer control and, in this context, outlines development and application experience with a hydraulic positioning system New technology is being offered, with increasing frequency, as the panacea for the problems industry faces: and all too often numerical control is sold for applications which could be handled by lower cost tracer-controlled machinery. Is too much emphasis being placed on magic boxes? Is too little attention payed to the practicalities of an engineered system which can duplicate the advantages without the heinous capital expenditure? During the late 1960's all the market's innovators in the field were keeping a close watch on the rapid development of NC. As interpolative circuitry advanced and contouring NC became well suited to lathes, machine axis drives appeared to be a limiting factor, not only in the cost of the motor/ball screw package, but in speed, response, stiffness, and even accu racy. With a generation of hydraulic experience behind them, Mimik set out to apply their expertise to this problem. They developed Datadrive, which uses a stepping or DC motor, depending on whether an open or closed loop NC package is used, to position the spool of a hydraulic servo valve. The valve body attaches to the moving machine member, and as the spool is displaced, hydraulic oil is passed to a cylinder which positions the machine member to create a null position in the valve. Heat generation, which might at first sight appear to be a problem, is balanced by convective losses: experience shows that an equilibrium, low, temperature is rapidly established with extremely low variation and with no effect on positioning accuracy.
formance. And, because there is no lead screw, there is no wind up deflection due to load. The drive is in a loop with the moving machine member and will correct for deflections which are not even felt by the drive motor. Because of the direct mechanical link between moving and stationary members, normal lost motion due to thermal expansion, thrust bearing play and backlash are not experienced.
Applications The first applications of the Datadrive were made on two milling machines in Mimik's own workshop. Productivity gains were remarkable, 500 to
......
1 some cases, and Mimik gained nd experience in the use of ",al control. : was evident that hydraulic rs are best suited to applicvhere high-speed positioning over istances is required: for proprietary machine tool packages, it was decided that chucking machines would be the most logical application. The Hardinge HC chucker was selected for its quality and simplicity as a first venture. It followed naturally that Mimik, having developed the universal tracer attachment, would pursue a similar course in NC. And so the Series 2000 was introduced as a second product. The guiding philosophy here was to apply the Datadrive technology to two essential problems. Firstly, almost every machine shop has engine lathes in good operating condition, though, regardless of their ability to remove metal, they are hopelessly unproductive compared to NC. Secondly, attempts to retrofit NC to conventional lathes have generally been unsuccessful because of the extensive rework necessary to fit ball screws and the refitting needed to the sliding machine members. In short, the machines were not designed for high performance.
System characteristics System response is extremely short. The motor has virtually 'no load' acceleration and deceleration per44
The first commercial application of Datadrive
P R E C I S I O N ENGII',,IEERING
The Datadrive Series 2000 provides independent two-axis sliding ways for attachment to the machine bed, so that only the spindle and tailstock of the basic machine were used. When fitted with a tape--directed indexing toolpost, the result was a low-cost full contouring NC lathe with full retention of the basic machine for conventional use. S m a l l p a rt s m a r k e t
Surveys show that there is a substantial market in the US, UK and Europe for an NC lathe aimed at the small parts market. Surprisingly, at the outset customers did not show much preference for specific control systems, as had been expected, but readily accepted the system with the shortest delivery time. Another interesting discovery was that customers argue little about the price of a machine once they have decided upon it, somewhat in contrast to conventional machine tool buying practices. There is a tendency as well, to order the most sophisticated versions with all the options available. In certain instances, customers wilt order controls with storage and edit capability which they rarely, if ever, use. With several such systems on the floor, the total premium paid for this option amounts to more investment than a general-purpose computer from which all systems could be run via a DNC link. During 1976, there was a tremendous increase in the preference for CNC. This, combined with advances in microprocessor technology, has effected sweeping changes in the industry. Prices for control systems now vary widely, depending on the technology, It is apparent, however, that a basic CNC control with more capability than a conventional hardwired model can be bought for much less and NC machine manufacturers will be offering more stripped-down versions with plug-in options to suit the customer's requirements. The field of NC is becoming more and more an offshoot of the computer industry and DNC is again being looked at as a practical venture, even by relatively small companies. The entire situation is highly transient today and great pattern changes can be expected within the next 12 months. Two major NC builders have left the field in the past year or so and others are watching the situation most carefully as the technology/price solution continues in flux.
PRECISTION ENGINEERING
made for its use, particularly as a retrofit package. Vertical boring machines It was a commonly-held belief that the and vertical turret lathes, where one increased use of NC would render the cut may take several hours to comtracer control obsolete; and no company plete, are particularly good examples had greater opportunity to see the effects of both these conditions. The longer than Mimik. A careful watch over several the job run, the more justification for years saw the versatile tool-path control a tracer because the customer is not market, as opposed to cam machines, paying for the versatility of NC which which had at one time been almost the he is not using. exclusive domain of tracing, giving way The benefits of NC are well to a great extent to NC. Paradoxically, documented. There is no question the largest manufacturers of NC systems about its ability to perform work continued to be good tracer customers, involving various operations in astoniand remain so to this day. shingly short times. Most limitations Determining why this is so of modern NC are imposed by the requires an understanding of the role inability of the users to get the best of each, its relationship to the machine out of them. As a rule of thumb, tool, and to the individual application therefore, if one tool will complete for which the customer intends it. a part, give serious consideration to Generally, a tracer equipped machine tracing. If more than one tool is tool can remove metal over a contour required, or if a wide range of different as rapidly as can an NC machine, once parts is encountered, take a very close the tool has been positioned for the look at NC. cut. If the 'time spend removing metal' portion of work is substantial, then a Further information can be obtained from tracer will probably yield a higher the author's company, Heathway Engineering Company, Mimik Division, Uxbridge return than NC, based on its lower Road, Hillingdon, Uxbridge, Middlesex UBIO cost. Also, if the cost of adding a tracer OPA, UK, or from Datadrive Division, Mimik is small, relative to the cost of the of CanadaLtd, Gait Avenue, Cambridge, machine, then a strong case can be Ontario, Canada, USA Tracers versus N C
The future of assembly... In 1977 the Society of Manufacturing Engineers and the University of Michigan initiated a series of forecasts on the future of various aspects of manufacturing. Their forecast on assembly has recently been published. One of the often quoted benefits of increased precision in manufacturing is to enable 'fitting' to be replaced by assembly. This Delphi forecast, a consensus of opinion from a panel of experts, on the future of assembly should, for this reason alone, be of at least passing interest to precision engineers. Further interest could be generated not by the predictions themselves but by the implied innovative precision engineering that will be needed if some of the prophecies are to be fulfilled. In particular, considerable advances in robotics, sensing, and inspection devices are predicted.
and manufacturing technology In May 1978, SME issued a 'position paper' calling for increased US government support for advanced manufacturing technology programs to improve productivity. SME describe official response to date as "excellent": both US House and Senate committees on science and technology have endorsed
.he paper, as have the Deputy Director of Science and Technology and senators from Illinois and Michigan. The paper notes that manufacturing costs have increased more rapidly than productivity and suggests that "manufacturing costs must be reduced through increased application of advanced manufacturing technology". A 'national commitment' to advanced manufacturing techology, including strengthening existing federal programs, funding research, and assisting in "transfer of such technology to industry" is recommended. According to SME, the alternative to a co-operative effort by industry, academics, governmept, and technical societies is "the rapid decay of American industry and the degeneration of America itself into a small and unimportant industrial backwater. More information from SME, One SME Drive, P.O. Box 930, Dearborn, Michigan 48128, USA Editor's note This section o f PRECISION ENGINEERING will report on, and provide a platform for discussion of, the many factors affecting the implementation o f precision engineering in industry or affecting the future or development o ~the technology. Potential contributors are urged to contact the Editor.
45
]
j
\
. . . . . J_. . . . . . . . . . _ /
Has NC made tracers obsolete C. Glover discusses the relative merits of NC and tracer control and, in this context, outlines development and application experience with a hydraulic positioning system New technology is being offered, with increasing frequency, as the panacea for the problems industry faces: and all too often numerical control is sold for applications which could be handled by lower cost tracer-controlled machinery. Is too much emphasis being placed on magic boxes? Is too little attention payed to the practicalities of an engineered system which can duplicate the advantages without the heinous capital expenditure? During the late 1960's all the market's innovators in the field were keeping a close watch on the rapid development of NC. As interpolative circuitry advanced and contouring NC became well suited to lathes, machine axis drives appeared to be a limiting factor, not only in the cost of the motor/ball screw package, but in speed, response, stiffness, and even accu racy. With a generation of hydraulic experience behind them, Mimik set out to apply their expertise to this problem. They developed Datadrive, which uses a stepping or DC motor, depending on whether an open or closed loop NC package is used, to position the spool of a hydraulic servo valve. The valve body attaches to the moving machine member, and as the spool is displaced, hydraulic oil is passed to a cylinder which positions the machine member to create a null position in the valve. Heat generation, which might at first sight appear to be a problem, is balanced by convective losses: experience shows that an equilibrium, low, temperature is rapidly established with extremely low variation and with no effect on positioning accuracy.
formance. And, because there is no lead screw, there is no wind up deflection due to load. The drive is in a loop with the moving machine member and will correct for deflections which are not even felt by the drive motor. Because of the direct mechanical link between moving and stationary members, normal lost motion due to thermal expansion, thrust bearing play and backlash are not experienced.
Applications The first applications of the Datadrive were made on two milling machines in Mimik's own workshop. Productivity gains were remarkable, 500 to
......
1 some cases, and Mimik gained nd experience in the use of ",al control. : was evident that hydraulic rs are best suited to applicvhere high-speed positioning over istances is required: for proprietary machine tool packages, it was decided that chucking machines would be the most logical application. The Hardinge HC chucker was selected for its quality and simplicity as a first venture. It followed naturally that Mimik, having developed the universal tracer attachment, would pursue a similar course in NC. And so the Series 2000 was introduced as a second product. The guiding philosophy here was to apply the Datadrive technology to two essential problems. Firstly, almost every machine shop has engine lathes in good operating condition, though, regardless of their ability to remove metal, they are hopelessly unproductive compared to NC. Secondly, attempts to retrofit NC to conventional lathes have generally been unsuccessful because of the extensive rework necessary to fit ball screws and the refitting needed to the sliding machine members. In short, the machines were not designed for high performance.
System characteristics System response is extremely short. The motor has virtually 'no load' acceleration and deceleration per44
The first commercial application of Datadrive
P R E C I S I O N ENGII',,IEERING
The Datadrive Series 2000 provides independent two-axis sliding ways for attachment to the machine bed, so that only the spindle and tailstock of the basic machine were used. When fitted with a tape--directed indexing toolpost, the result was a low-cost full contouring NC lathe with full retention of the basic machine for conventional use. S m a l l p a rt s m a r k e t
Surveys show that there is a substantial market in the US, UK and Europe for an NC lathe aimed at the small parts market. Surprisingly, at the outset customers did not show much preference for specific control systems, as had been expected, but readily accepted the system with the shortest delivery time. Another interesting discovery was that customers argue little about the price of a machine once they have decided upon it, somewhat in contrast to conventional machine tool buying practices. There is a tendency as well, to order the most sophisticated versions with all the options available. In certain instances, customers wilt order controls with storage and edit capability which they rarely, if ever, use. With several such systems on the floor, the total premium paid for this option amounts to more investment than a general-purpose computer from which all systems could be run via a DNC link. During 1976, there was a tremendous increase in the preference for CNC. This, combined with advances in microprocessor technology, has effected sweeping changes in the industry. Prices for control systems now vary widely, depending on the technology, It is apparent, however, that a basic CNC control with more capability than a conventional hardwired model can be bought for much less and NC machine manufacturers will be offering more stripped-down versions with plug-in options to suit the customer's requirements. The field of NC is becoming more and more an offshoot of the computer industry and DNC is again being looked at as a practical venture, even by relatively small companies. The entire situation is highly transient today and great pattern changes can be expected within the next 12 months. Two major NC builders have left the field in the past year or so and others are watching the situation most carefully as the technology/price solution continues in flux.
PRECISTION ENGINEERING
made for its use, particularly as a retrofit package. Vertical boring machines It was a commonly-held belief that the and vertical turret lathes, where one increased use of NC would render the cut may take several hours to comtracer control obsolete; and no company plete, are particularly good examples had greater opportunity to see the effects of both these conditions. The longer than Mimik. A careful watch over several the job run, the more justification for years saw the versatile tool-path control a tracer because the customer is not market, as opposed to cam machines, paying for the versatility of NC which which had at one time been almost the he is not using. exclusive domain of tracing, giving way The benefits of NC are well to a great extent to NC. Paradoxically, documented. There is no question the largest manufacturers of NC systems about its ability to perform work continued to be good tracer customers, involving various operations in astoniand remain so to this day. shingly short times. Most limitations Determining why this is so of modern NC are imposed by the requires an understanding of the role inability of the users to get the best of each, its relationship to the machine out of them. As a rule of thumb, tool, and to the individual application therefore, if one tool will complete for which the customer intends it. a part, give serious consideration to Generally, a tracer equipped machine tracing. If more than one tool is tool can remove metal over a contour required, or if a wide range of different as rapidly as can an NC machine, once parts is encountered, take a very close the tool has been positioned for the look at NC. cut. If the 'time spend removing metal' portion of work is substantial, then a Further information can be obtained from tracer will probably yield a higher the author's company, Heathway Engineering Company, Mimik Division, Uxbridge return than NC, based on its lower Road, Hillingdon, Uxbridge, Middlesex UBIO cost. Also, if the cost of adding a tracer OPA, UK, or from Datadrive Division, Mimik is small, relative to the cost of the of CanadaLtd, Gait Avenue, Cambridge, machine, then a strong case can be Ontario, Canada, USA Tracers versus N C
The future of assembly... In 1977 the Society of Manufacturing Engineers and the University of Michigan initiated a series of forecasts on the future of various aspects of manufacturing. Their forecast on assembly has recently been published. One of the often quoted benefits of increased precision in manufacturing is to enable 'fitting' to be replaced by assembly. This Delphi forecast, a consensus of opinion from a panel of experts, on the future of assembly should, for this reason alone, be of at least passing interest to precision engineers. Further interest could be generated not by the predictions themselves but by the implied innovative precision engineering that will be needed if some of the prophecies are to be fulfilled. In particular, considerable advances in robotics, sensing, and inspection devices are predicted.
and manufacturing technology In May 1978, SME issued a 'position paper' calling for increased US government support for advanced manufacturing technology programs to improve productivity. SME describe official response to date as "excellent": both US House and Senate committees on science and technology have endorsed
.he paper, as have the Deputy Director of Science and Technology and senators from Illinois and Michigan. The paper notes that manufacturing costs have increased more rapidly than productivity and suggests that "manufacturing costs must be reduced through increased application of advanced manufacturing technology". A 'national commitment' to advanced manufacturing techology, including strengthening existing federal programs, funding research, and assisting in "transfer of such technology to industry" is recommended. According to SME, the alternative to a co-operative effort by industry, academics, governmept, and technical societies is "the rapid decay of American industry and the degeneration of America itself into a small and unimportant industrial backwater. More information from SME, One SME Drive, P.O. Box 930, Dearborn, Michigan 48128, USA Editor's note This section o f PRECISION ENGINEERING will report on, and provide a platform for discussion of, the many factors affecting the implementation o f precision engineering in industry or affecting the future or development o ~the technology. Potential contributors are urged to contact the Editor.
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