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The computer in the numerical control of machine tools
The computer in the numerical control of machine tools I. Berenyi
SUMMER 1971
Numerical control is a field of computer applications which has so far received less than its fair share of attention in this country, either from the computer manufacturers or from manufacturing industry in goneral. As a result, Britain is already lagging behind the United States and even Germany in machine tool usage, and the gap is widening. Only about 5 ~ of machine tools sold in the United Kingdom are numerically controlled, compared with some 11 ~ in America and 8 in Germany. More important than this, however, is the fact that the five-axis machine tools which account for most new sales in the U.S.A., and which allow for the production of much more complex parts, have so far made very little impression in this country. Investing in numerical control is admittedly a costly business of course, demanding an initial investment of at least £60000 to £100000 already at the most basic level of the state of the ark It must be remembered, however, that a large proportion of this cost will be for the machine tool itself. Another factor which presents an obstacle to companies contemplating n.c. is that the right combination of circumstances is necessary to get the best return on investment. Like so many computer applications, n.c. work has a high set-up time - and cost - and economies can only be achieved on longer production runs. The ideal situation for costeffective numerical control is thus one requiring the manufacture of large batches of relatively simple parts. The more complex the workpiece, the larger, in theory, the batch should be. In practice, of course, the tendency is for this ratio to be the other way around. A further problem is the sheer complexity of numerical control itself. Even without considering computer control, there is a vast range of machine tools available, performing numerous different functions, such as boring, milling or turning with varying degrees of flexibility and complexity. The simplest type of machine tool is the co-ordinate drilling machine. With this machine, a part to be worked on is clamped to a table which is capable of moving in two directions (x and y) under a spindle moving vertically. When a different size hole is required, a tool has to be changed in this type of machine. A more complicated machine tool may have five or six spindles in the form of a turret revolving about the part; with this, there is no need to change tools for different size holes. In yet more advanced types of machine tools the part itself moves in one or more axes while in contact with a revolving cutter. This enables profiles made up of straight lines or arcs to be cut and is normally used in milling tools. In some machines, the spindle may be horizontal while the part can move from left to right as well as up and down; in others, again, the part is rotated about a vertical axis and in so-called multi-axis machines the spindle mounting is able to swivel about its axis. It is quite common for a part to require a number of machine operations to be carried out upon it. These then may be either carried out by a number of specialised machines or by the same machine in a 'machining centre', in which case the machine is normally capable itself of selecting the different tools needed for rotating the part and loading the next one. There are numerous companies manufacturing machine tools. Among the best known are Cincinnati, Herbert, Sandstran, Siemens, Bradley and Plessey, to mention but a few and the total number of manufacturers is well in
excess of 200. The number of models available is, of course, even much larger. At the LH.A. '70 International Machine Tool Exhibition in Hanover - held last September, this was the largest show of its kind to date - for example 350 different types of machine tools were exhibited, 229 of which were numerically controlled and 23 of which were machining centres. Plessey Numerical Controls Ltd. are the largest British makers of machine tools. Their range, which now includes Airmec and Ferranti systems, covers almost the complete spectrum of complexity in n.c. equipment. When it comes to the automatic control of machine tools, the bewildered factory manager finds that there are almost as many different methods as there are machine tools, hiding behind apparently indistinguishable names such as APT, IITRIAPT, 2CL and PICNIC. On closer inspection, however, it turns out that there are certain features common to most of these methods, as all but a very few numerically controlled machine tools are equipped with an electro-mechanical controller. This is driven by a punched paper tape containing instructions which the controller translates and uses to control the machine tool. These instructions indicate not only the path of the machine tool over the workpiece, but the particular tool to be selected, spindle speeds and all other operations. The control tape may be produced either manually or with the help of a computer, and it is here that methods differ significantly. Manual production of control tapes is directly parallel to programming in binary, since it uses the language of the machine. This is clearly only suitable for producing the simplest parts, and in any case the parts programmer is a skilled technician, whose time is too valuable to waste on such low level programming. The obvious solution is to use a high-level language, in which the parts programmer need only state his axes, co-ordinates and curves, leaving the detail work to be interpolated by a compiler. This process differs somewhat from the production of a normal computer program. The parts program will be punched on tape and fed into a computer to be translated by the processor. This will probably be written in Fortran and will, of course, have to be adapted to each type of computer on which it is to run. In addition, the difference between various kinds of machine tools means that the output must then be retranslated by the appropriate post-processor for the machine tool on which it is to be used. This produces the final control tape. The choice of a programming language by the parts programmer wilt depend on the complexity of the machining the shop expects to carry out, and on the types of machine tools involved. Machining may be either point-to-point or continuous path. Point-to-point work, as the name implies, involves straight line cutting and positioning for drilling; continuous path machining, on the other hand, provides facilities for curves and complex shapes and may be carried out in two, three or five axes The most powerful, if over-complex, parts programming language is APT - the initials stand for Automatically Programmed Tools. This was developed in America in the early 1950s jointly by the Massachusetts Institute of Technology and the U.S. Air Force - and quickly adopted by a contingent of 20 firms in the American aerospace industry. APT provides all facilities from point-topoint work to five-axes continuous path machin-
41
ing, allowing tbr the production of 'sculptured' shapes. As it grew too large and thereby virtually unmanageable over the years, the International Standards Organisation supervises its development and, since 1965, the IITRI organisation in the U.S.A. maintains it. In the U.K. its use is administered by the National Engineering Laboratory, which has a special department wholly devoted to debugging and updating APT and keeping users informed of new features. The latest development in the maintenance of APT is the setting up of the Computer Aided Manufacturing International association in America. CAMI will maintain a basic version of the language for a membership fee of £2100 annually and relay new inclusions to members. The complexity of APT means that it requires a large computer - on an IBM 360 series machine, for example, it runs a 256k partition - and is thus expensive to use. It can usually only be justified for the most complex machining work, such as that required in the aerospace industry. APT is the only three-dimensional language. For two, and 2½-dimensional machining, a whole range of other languages has been developed. Some experts tend to say, that these languages become cheaper and easier to use in direct proportion to the loss of flexibility and facilities, but the point is much-mooted. Many of these simpler languages are derived from APT, as their names imply. IBM, for example, have developed their own language, ADAPT. This is one of the 2~-dimensional languages, which means that it is possible to machine 3-dimensional shapes, but they must be cut in a series of layers. Other such languages are IITRIAPT, the first derivative developed by the Illinois Institute of Technology in Chicago and maintained by the IITRIAPT organisation for an annual membership fee of £2100; IFAPT, developed in France; Honeywell Information Systems' GEAPT; Germany's EXAPT and halfa-dozen others. EXAPT is the outstandingly most popular among these languages. Developed at Aachen University's Machine Tool Institute and maintained since 1966 by the EXAPT association, the use of this language is now spreading throughout Europe and considerable use is made of it in the U.K., particularly by Baric. A particular feature of the EXAPT series is the emphasis placed on the technology of numerical control. In addition to specifying the geometry of a workpiece, EXAPT will also select the right tools and the correct sequence of operations to produce a particular result. All the parts programmer need do is specify the material he is working in. Reliance on EXAPT does, however, necessitate that the machine tool to be used is a well-equipped, advanced piece of equipment, as otherwise the capabilities of the language can not be exploited to the full. There are three separate languages in the EXAPT series. EXAPT 1, which was originally developed on Aachen University's CDC 6400 and has since been adapted to the Univac 1100 and IBM 360 series, is a drilling program; EXAPT I1, which is considerably larger almost up to APT-like size serves turning (its prime user in the U.K. is Rolls Royce]; and EXAPT III, which is about to be passed on from its developer, Aachen University, to the EXAPT association, milling. The two main languages to be developed in this country are 2CL and Profiledata. 2CL was created by the National Engineering Laboratory, assisted by sub-contractors Scicon under what was originally a Ferranti assignment, and is another 2½-dimensional language. Two specialpurpose subsets, 2C and 2PL, have been
42
developed for turning and point-to-point machining. Under a joint development programme between NEL and Aachen University's Machine Tool Institute a 2CL-EXAPT I program was created last year for the production of control tapes for NC milling and drilling machines and for machining centres. The program was demonstrated at the I.H.A. '70 exhibition in September 1970, using a terminal linked to a Univac 1108 computer. It can also be used on CDC 6000 series computers, although 2CL itself is limited to the 1108 and the ICL 1900 family. Profiledata was written by Ferranli, and has had considerable success in this country. Ferranti's machine tool division has since been taken over by Plessey, and the language adopted for use with the whole Plessey range, including the Airmec series of machine tools. Other languages include IBM's AUTO POL (Automatic Programming of Lathes), AUTOSPOT (for point-to-point work), FMILL and Romance; as well as Mini-APT, Uni-APT, Picnic and its interactive version, Telepicnic. Most of these are designed for use with parts which are just a little too complex for manual programming and present reduced core-demand, although AUTO POL, for example, takes up a 256k partition in the IBM 360 series of computers. With more complex languages, requiring large compilers and post-processors, the user will often not have a computer large enough to produce his own tapes, and will have to engage the services of a bureau. In theory any bureau would do, but in practice most users find it desirable, if not essential, to use one of the few specialist services which are available. One such service is. as has been already mentioned, provided by Baric, who speciatise in EXAPT for a wide range of machine tools, i.e. in EXAPT I and EXAPT 11. The work is carried out at Kidsgrove, and is at present being transferred from the KDF-9 to a System 4 computer. Another, and probably most important, n.c. centre in this country is that set up by Plessey Numerical Controls at Salfords, neat London. In addition to tape preparation, the Salfords centre provides consultancy services and a wide range of courses. It is still only recently established, and is at present concentrating on Profiledata, but will gradually offer languages as well. Plessey are also planning to set up similar centres on the Continent, to start with in the E.E.C. countries. Other sources of specialist assistance are APACE at Aldermaston; SIA in London's Victoria district; NEL and the London centre of IBM Data Centre Services and IBM-Birmingham. The next step for numerical control is clearly towards direct control of the machine tool by computer, or c.n.c, and d.n.c. These are already very much of a reality in America, Japan, and in Germany, although in the U.K. and the rest of Europe they largely remain on an experimental basis. Plessey, for example, are experimenting with a Honeywell 112 as a control computer, following up Ferranti's work using an Argus 400. One of the main advantages of direct computer control as far as the builder of control systems is concerned is that he can build a much more flexible controller, which can be interfaced then to any machine tool with only a minimum of software alterations. This could certainly help to prevent the proliferation of programming languages which is at present threatening the industry. A further development of this c.n.c, concept is the use of a single computer to control a number of machine tools. Such a system has been
COMPUTER AIDED DESIGN
developed by the largest builder of controllers in Europe, Siemens, using a 301 process control computer, which is claimed to be capable of controlling up to 60 machine tools. Germany's second electronics giant, AEG-Telefunken, is merely involved in c.n.c., on the other hand, using a 60-10 process control minicomputer for the control of single machine tools. In the U.S.A., much publicity was attracted by the efforts of Douglas Aircraft, General Motoi's and the Kerney and Trecker Corporation. Douglas use an IBM 1800 to control six machine tools simultaneously; G M ' s Allison division a 64k IBM 360/30 to control 15 machine tools via an equal number of interpolating buffer units; and Kerney and Trecker a whole battery of alphascopes to evaluate many factors such as job status and stock positions and locations at the same time as providing machining and tooling instructions. A remarkable pioneering effort in this field, which has already been realised, is Molins System 24. This is in effect an automatic factory, consisting of a number of machine tools again linked to a central controller. In this case, however, the parts to be machined are stacked up on pallets, and from there on are processed without human intervention. They are passed automatically from one machining process to the next, and finally passed out again on pallets to be taken away by the operators. The only fault with System 24 appears to have been that it arrived slightly ahead of its time. A number have already been sold, however, among others to IBM and ICL, and although for a time it seemed that System 24 would become a sad monument to the results of technology out-
Ommission
The following information was ommitted from the survey on Remote multi-access computing systems published in C.A.D., Winter, 1971.
SYSTEMSHARE 9 Atholl Crescent, Edinburgh, EH3 8HA. London Office: 4 Vigo Street, London, W1X 2AD. An interactive general purpose time-sharing service using the G.P.O. public telephone network. The service has been running since July, 1969.
Programs available Vehicle Routing (STEERS); Storm sewer design (HYGRAF) ; Time-series forecasting ; coordinate geometrysystem (COGO) ; project network analysis with resource aggregation and negative float; analog simulation package; simulation package (GASP); BSRA shipbuilding library; local authority civil engineering library; actuarial calculations package (PACT); electronic circuit analysis program - a.c., d.c., transient (ECAP); torsional vibration program; discounted cash flow; stepwise regression program; mechanical engineering library of Weir Pumps Ltd. ; logic design (LOGIC). SUMMER 1971
stripping the requirements of industry, the manufacturer now confidently claims a bright future for its system, There are, clearly, many areas of potential improvement in n.c. One recent development, for example, has been that of the LECTRA automatic trace reading system by the Societe CERCI in Paris. This, consisting of a reading head, two control motors, a logic computer and a t.v. screen-like control panel, can follow any trace or continuous profile, however complex, to insure the advance control of milling-cutting machines along two axes. Apart from the importance of n.c. for domestic industry, its advancement is also clearly in the national interest from the viewpoint of its export potential. For one, the Russians are interested in large-scale imports, and British and French co-operation projects are under way simultaneously as a prelude to a decision by Russia between the two nations' digital control technologies. At the moment, France appears to be nearer to capturing this immense market due to the efforts of Alcatel in the joint manufacturing of cutting tools and regular courses run by the French manufacturer for Russian parts programmers. In the rest of east Europe, the scales are tipping towards Germany's Krupp Works due to its generosity in granting manufacturing iicences. The limited success of Molins System 24 - up to now at least - is the apotheosis of what is happening throughout the field of numerical control in Britain. The high cost of investment rather than ludditism may be the cause of this sluggishness, but whatever the reason, there is little doubt that the potential of n.c. is hardly tapped here.
Languages BASIC, FORTRAN IV.
Computer G E 430.
Remote terminal equipment ASR 33; Olivetti TE318; Tektronix; other teletype compatible terminals and V.D.U.s. Charges Connect time Compute time Prog. storage unit (180 characters)
£5.00 per hour £0.05 per second
£0"05 per unit per month. No minimum monthly charge, no installation charge. Scales available for use of central site peripherals, microfilm plotters and flatbed plotter.
Service hours 09.00-21.00 Monday, Wednesday, Thursday. 09.00-17.30 Tuesday, Friday. 43
SUMMER 1971
Numerical control is a field of computer applications which has so far received less than its fair share of attention in this country, either from the computer manufacturers or from manufacturing industry in goneral. As a result, Britain is already lagging behind the United States and even Germany in machine tool usage, and the gap is widening. Only about 5 ~ of machine tools sold in the United Kingdom are numerically controlled, compared with some 11 ~ in America and 8 in Germany. More important than this, however, is the fact that the five-axis machine tools which account for most new sales in the U.S.A., and which allow for the production of much more complex parts, have so far made very little impression in this country. Investing in numerical control is admittedly a costly business of course, demanding an initial investment of at least £60000 to £100000 already at the most basic level of the state of the ark It must be remembered, however, that a large proportion of this cost will be for the machine tool itself. Another factor which presents an obstacle to companies contemplating n.c. is that the right combination of circumstances is necessary to get the best return on investment. Like so many computer applications, n.c. work has a high set-up time - and cost - and economies can only be achieved on longer production runs. The ideal situation for costeffective numerical control is thus one requiring the manufacture of large batches of relatively simple parts. The more complex the workpiece, the larger, in theory, the batch should be. In practice, of course, the tendency is for this ratio to be the other way around. A further problem is the sheer complexity of numerical control itself. Even without considering computer control, there is a vast range of machine tools available, performing numerous different functions, such as boring, milling or turning with varying degrees of flexibility and complexity. The simplest type of machine tool is the co-ordinate drilling machine. With this machine, a part to be worked on is clamped to a table which is capable of moving in two directions (x and y) under a spindle moving vertically. When a different size hole is required, a tool has to be changed in this type of machine. A more complicated machine tool may have five or six spindles in the form of a turret revolving about the part; with this, there is no need to change tools for different size holes. In yet more advanced types of machine tools the part itself moves in one or more axes while in contact with a revolving cutter. This enables profiles made up of straight lines or arcs to be cut and is normally used in milling tools. In some machines, the spindle may be horizontal while the part can move from left to right as well as up and down; in others, again, the part is rotated about a vertical axis and in so-called multi-axis machines the spindle mounting is able to swivel about its axis. It is quite common for a part to require a number of machine operations to be carried out upon it. These then may be either carried out by a number of specialised machines or by the same machine in a 'machining centre', in which case the machine is normally capable itself of selecting the different tools needed for rotating the part and loading the next one. There are numerous companies manufacturing machine tools. Among the best known are Cincinnati, Herbert, Sandstran, Siemens, Bradley and Plessey, to mention but a few and the total number of manufacturers is well in
excess of 200. The number of models available is, of course, even much larger. At the LH.A. '70 International Machine Tool Exhibition in Hanover - held last September, this was the largest show of its kind to date - for example 350 different types of machine tools were exhibited, 229 of which were numerically controlled and 23 of which were machining centres. Plessey Numerical Controls Ltd. are the largest British makers of machine tools. Their range, which now includes Airmec and Ferranti systems, covers almost the complete spectrum of complexity in n.c. equipment. When it comes to the automatic control of machine tools, the bewildered factory manager finds that there are almost as many different methods as there are machine tools, hiding behind apparently indistinguishable names such as APT, IITRIAPT, 2CL and PICNIC. On closer inspection, however, it turns out that there are certain features common to most of these methods, as all but a very few numerically controlled machine tools are equipped with an electro-mechanical controller. This is driven by a punched paper tape containing instructions which the controller translates and uses to control the machine tool. These instructions indicate not only the path of the machine tool over the workpiece, but the particular tool to be selected, spindle speeds and all other operations. The control tape may be produced either manually or with the help of a computer, and it is here that methods differ significantly. Manual production of control tapes is directly parallel to programming in binary, since it uses the language of the machine. This is clearly only suitable for producing the simplest parts, and in any case the parts programmer is a skilled technician, whose time is too valuable to waste on such low level programming. The obvious solution is to use a high-level language, in which the parts programmer need only state his axes, co-ordinates and curves, leaving the detail work to be interpolated by a compiler. This process differs somewhat from the production of a normal computer program. The parts program will be punched on tape and fed into a computer to be translated by the processor. This will probably be written in Fortran and will, of course, have to be adapted to each type of computer on which it is to run. In addition, the difference between various kinds of machine tools means that the output must then be retranslated by the appropriate post-processor for the machine tool on which it is to be used. This produces the final control tape. The choice of a programming language by the parts programmer wilt depend on the complexity of the machining the shop expects to carry out, and on the types of machine tools involved. Machining may be either point-to-point or continuous path. Point-to-point work, as the name implies, involves straight line cutting and positioning for drilling; continuous path machining, on the other hand, provides facilities for curves and complex shapes and may be carried out in two, three or five axes The most powerful, if over-complex, parts programming language is APT - the initials stand for Automatically Programmed Tools. This was developed in America in the early 1950s jointly by the Massachusetts Institute of Technology and the U.S. Air Force - and quickly adopted by a contingent of 20 firms in the American aerospace industry. APT provides all facilities from point-topoint work to five-axes continuous path machin-
41
ing, allowing tbr the production of 'sculptured' shapes. As it grew too large and thereby virtually unmanageable over the years, the International Standards Organisation supervises its development and, since 1965, the IITRI organisation in the U.S.A. maintains it. In the U.K. its use is administered by the National Engineering Laboratory, which has a special department wholly devoted to debugging and updating APT and keeping users informed of new features. The latest development in the maintenance of APT is the setting up of the Computer Aided Manufacturing International association in America. CAMI will maintain a basic version of the language for a membership fee of £2100 annually and relay new inclusions to members. The complexity of APT means that it requires a large computer - on an IBM 360 series machine, for example, it runs a 256k partition - and is thus expensive to use. It can usually only be justified for the most complex machining work, such as that required in the aerospace industry. APT is the only three-dimensional language. For two, and 2½-dimensional machining, a whole range of other languages has been developed. Some experts tend to say, that these languages become cheaper and easier to use in direct proportion to the loss of flexibility and facilities, but the point is much-mooted. Many of these simpler languages are derived from APT, as their names imply. IBM, for example, have developed their own language, ADAPT. This is one of the 2~-dimensional languages, which means that it is possible to machine 3-dimensional shapes, but they must be cut in a series of layers. Other such languages are IITRIAPT, the first derivative developed by the Illinois Institute of Technology in Chicago and maintained by the IITRIAPT organisation for an annual membership fee of £2100; IFAPT, developed in France; Honeywell Information Systems' GEAPT; Germany's EXAPT and halfa-dozen others. EXAPT is the outstandingly most popular among these languages. Developed at Aachen University's Machine Tool Institute and maintained since 1966 by the EXAPT association, the use of this language is now spreading throughout Europe and considerable use is made of it in the U.K., particularly by Baric. A particular feature of the EXAPT series is the emphasis placed on the technology of numerical control. In addition to specifying the geometry of a workpiece, EXAPT will also select the right tools and the correct sequence of operations to produce a particular result. All the parts programmer need do is specify the material he is working in. Reliance on EXAPT does, however, necessitate that the machine tool to be used is a well-equipped, advanced piece of equipment, as otherwise the capabilities of the language can not be exploited to the full. There are three separate languages in the EXAPT series. EXAPT 1, which was originally developed on Aachen University's CDC 6400 and has since been adapted to the Univac 1100 and IBM 360 series, is a drilling program; EXAPT I1, which is considerably larger almost up to APT-like size serves turning (its prime user in the U.K. is Rolls Royce]; and EXAPT III, which is about to be passed on from its developer, Aachen University, to the EXAPT association, milling. The two main languages to be developed in this country are 2CL and Profiledata. 2CL was created by the National Engineering Laboratory, assisted by sub-contractors Scicon under what was originally a Ferranti assignment, and is another 2½-dimensional language. Two specialpurpose subsets, 2C and 2PL, have been
42
developed for turning and point-to-point machining. Under a joint development programme between NEL and Aachen University's Machine Tool Institute a 2CL-EXAPT I program was created last year for the production of control tapes for NC milling and drilling machines and for machining centres. The program was demonstrated at the I.H.A. '70 exhibition in September 1970, using a terminal linked to a Univac 1108 computer. It can also be used on CDC 6000 series computers, although 2CL itself is limited to the 1108 and the ICL 1900 family. Profiledata was written by Ferranli, and has had considerable success in this country. Ferranti's machine tool division has since been taken over by Plessey, and the language adopted for use with the whole Plessey range, including the Airmec series of machine tools. Other languages include IBM's AUTO POL (Automatic Programming of Lathes), AUTOSPOT (for point-to-point work), FMILL and Romance; as well as Mini-APT, Uni-APT, Picnic and its interactive version, Telepicnic. Most of these are designed for use with parts which are just a little too complex for manual programming and present reduced core-demand, although AUTO POL, for example, takes up a 256k partition in the IBM 360 series of computers. With more complex languages, requiring large compilers and post-processors, the user will often not have a computer large enough to produce his own tapes, and will have to engage the services of a bureau. In theory any bureau would do, but in practice most users find it desirable, if not essential, to use one of the few specialist services which are available. One such service is. as has been already mentioned, provided by Baric, who speciatise in EXAPT for a wide range of machine tools, i.e. in EXAPT I and EXAPT 11. The work is carried out at Kidsgrove, and is at present being transferred from the KDF-9 to a System 4 computer. Another, and probably most important, n.c. centre in this country is that set up by Plessey Numerical Controls at Salfords, neat London. In addition to tape preparation, the Salfords centre provides consultancy services and a wide range of courses. It is still only recently established, and is at present concentrating on Profiledata, but will gradually offer languages as well. Plessey are also planning to set up similar centres on the Continent, to start with in the E.E.C. countries. Other sources of specialist assistance are APACE at Aldermaston; SIA in London's Victoria district; NEL and the London centre of IBM Data Centre Services and IBM-Birmingham. The next step for numerical control is clearly towards direct control of the machine tool by computer, or c.n.c, and d.n.c. These are already very much of a reality in America, Japan, and in Germany, although in the U.K. and the rest of Europe they largely remain on an experimental basis. Plessey, for example, are experimenting with a Honeywell 112 as a control computer, following up Ferranti's work using an Argus 400. One of the main advantages of direct computer control as far as the builder of control systems is concerned is that he can build a much more flexible controller, which can be interfaced then to any machine tool with only a minimum of software alterations. This could certainly help to prevent the proliferation of programming languages which is at present threatening the industry. A further development of this c.n.c, concept is the use of a single computer to control a number of machine tools. Such a system has been
COMPUTER AIDED DESIGN
developed by the largest builder of controllers in Europe, Siemens, using a 301 process control computer, which is claimed to be capable of controlling up to 60 machine tools. Germany's second electronics giant, AEG-Telefunken, is merely involved in c.n.c., on the other hand, using a 60-10 process control minicomputer for the control of single machine tools. In the U.S.A., much publicity was attracted by the efforts of Douglas Aircraft, General Motoi's and the Kerney and Trecker Corporation. Douglas use an IBM 1800 to control six machine tools simultaneously; G M ' s Allison division a 64k IBM 360/30 to control 15 machine tools via an equal number of interpolating buffer units; and Kerney and Trecker a whole battery of alphascopes to evaluate many factors such as job status and stock positions and locations at the same time as providing machining and tooling instructions. A remarkable pioneering effort in this field, which has already been realised, is Molins System 24. This is in effect an automatic factory, consisting of a number of machine tools again linked to a central controller. In this case, however, the parts to be machined are stacked up on pallets, and from there on are processed without human intervention. They are passed automatically from one machining process to the next, and finally passed out again on pallets to be taken away by the operators. The only fault with System 24 appears to have been that it arrived slightly ahead of its time. A number have already been sold, however, among others to IBM and ICL, and although for a time it seemed that System 24 would become a sad monument to the results of technology out-
Ommission
The following information was ommitted from the survey on Remote multi-access computing systems published in C.A.D., Winter, 1971.
SYSTEMSHARE 9 Atholl Crescent, Edinburgh, EH3 8HA. London Office: 4 Vigo Street, London, W1X 2AD. An interactive general purpose time-sharing service using the G.P.O. public telephone network. The service has been running since July, 1969.
Programs available Vehicle Routing (STEERS); Storm sewer design (HYGRAF) ; Time-series forecasting ; coordinate geometrysystem (COGO) ; project network analysis with resource aggregation and negative float; analog simulation package; simulation package (GASP); BSRA shipbuilding library; local authority civil engineering library; actuarial calculations package (PACT); electronic circuit analysis program - a.c., d.c., transient (ECAP); torsional vibration program; discounted cash flow; stepwise regression program; mechanical engineering library of Weir Pumps Ltd. ; logic design (LOGIC). SUMMER 1971
stripping the requirements of industry, the manufacturer now confidently claims a bright future for its system, There are, clearly, many areas of potential improvement in n.c. One recent development, for example, has been that of the LECTRA automatic trace reading system by the Societe CERCI in Paris. This, consisting of a reading head, two control motors, a logic computer and a t.v. screen-like control panel, can follow any trace or continuous profile, however complex, to insure the advance control of milling-cutting machines along two axes. Apart from the importance of n.c. for domestic industry, its advancement is also clearly in the national interest from the viewpoint of its export potential. For one, the Russians are interested in large-scale imports, and British and French co-operation projects are under way simultaneously as a prelude to a decision by Russia between the two nations' digital control technologies. At the moment, France appears to be nearer to capturing this immense market due to the efforts of Alcatel in the joint manufacturing of cutting tools and regular courses run by the French manufacturer for Russian parts programmers. In the rest of east Europe, the scales are tipping towards Germany's Krupp Works due to its generosity in granting manufacturing iicences. The limited success of Molins System 24 - up to now at least - is the apotheosis of what is happening throughout the field of numerical control in Britain. The high cost of investment rather than ludditism may be the cause of this sluggishness, but whatever the reason, there is little doubt that the potential of n.c. is hardly tapped here.
Languages BASIC, FORTRAN IV.
Computer G E 430.
Remote terminal equipment ASR 33; Olivetti TE318; Tektronix; other teletype compatible terminals and V.D.U.s. Charges Connect time Compute time Prog. storage unit (180 characters)
£5.00 per hour £0.05 per second
£0"05 per unit per month. No minimum monthly charge, no installation charge. Scales available for use of central site peripherals, microfilm plotters and flatbed plotter.
Service hours 09.00-21.00 Monday, Wednesday, Thursday. 09.00-17.30 Tuesday, Friday. 43