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Transcript
PRECISION AIR TECHNIQUES FOR PRECISION AIR TEMPERATURE TEMPERATURE CONTROL CONTROL Hans J. J. Hansen Hans Division, Lawrence Lawrence Livermore Livermore National National Laboratory Laboratory Materials Fabrication Division, 808, LL-330, P. P. 0. 0. Box 808, -330, Livermore, Livermore, California California 94550 Abstract for minimizing High quality temperature control control can can provide provide an an excellent excellent means means for minimizing the the .thermal thermal drift drift of of quality air temperature High air in air practical. Improvements in not practical. are not means are other means when other instruments when machine tools inspection instruments and inspection tools and careful the careful one byby the to one ten to as ten much as as much by as areas by machining areas several machining in several improved in been improved has been temperature control control has theory. control theory. classical control fundamental classical some fundamental of some application of the application and the loads and heat loads identification of heat identification Introduction usually . are usually part are produce aa part can produce tool can machine tool which aa machine to which accuracy to the accuracy govern the which govern errors which of errors kinds of The kinds that reported that has reported (1.) has errors. Donaldson (1.) nonrepeatable errors. and nonrepeatable categories: repeatable and into two broken broken into two categories: result, and asas aa result, small, and very small, are very errors are nonrepeatable errors the nonrepeatable to the compared to when compared errors when repeatable errors the repeatable frequently the large large improvements improvements in in machine machine performance performance can can often often be be obtained obtained by by trying trying to to decrease decrease the the nonrepeatable nonrepeatable is changing the most common that the indicates that He also errors. also indicates common cause cause of of nonrepeatability nonrepeatability is changing temperature temperature and and the the errors. structure. machine structure. the machine of the deformation of consequent thermal thermal deformation the to the solutions to long plagued has long Thermal Thermal distortion distortion has plagued the the areas areas of of precision precision machining machining and and gaging. gaging. Past Past solutions day/night to day respect to with respect processes with of processes scheduling of careful scheduling included careful have included problem have /night ambient ambient temperature variations, variations, construction construction of of subterranean subterranean inspection inspection facilities facilities (2.) (2.) and and machine machine temperature temperature control control by by In many flooding. In liquid many cases cases the the thermal thermal distortion distortion problem problem could could have have been been minimized minimized adequately adequately if if air air liquid flooding. flood cooling applications of flood successful applications Examples of successful cooling enough. Examples well enough. controlled well been controlled have been temperature could have temperature for for temperature temperature control control have have been been proven proven by by Bryan Bryan at at LLNL LLNL on on Diamond Diamond Turning Turning Machines Machines #1 #1 and and #2 #2 (3.) (3.) and and on on nearly 1010toto 1 1 factor ofof nearly by aa factor stability by thermal stability in thermal improved in was improved which was machine which #3 measuring machine aa modified Moore #3 increased cost in production and increased cost both inconvenience in solutions, although sufficient have caused both (4.). These solutions, (4.). utilized onon-off have utilized solutions have the solutions of the required. In facilities required. the facilities and the the product and of In addition, addition, many of -off of both both the for the changes. An alternate approach provides for load changes. heat load to heat sensitive to controls controls and and have been consequently sensitive remove to remove used to is used cooling is liquid cooling closed liquid scheme, closed In this this scheme, control. In temperature control. air temperature and air use use of of both both liquid and localized localized heat heat from from the the machine, machine, while while aa light light air air shower shower is is used used to to maintain maintain the the temperature temperature of of the the slide drive spindle drive superstructure. Localized Localized heat would would include include heat heat produced produced by by the the spindle drive motor motor and and slide drive the machine on the loads on heat loads are heat there are if there that if is that desirable is sometimes desirable is sometimes this approach is that this machine motors. The reason that motors. air alone if air transfer if heat transfer necessary heat required to are required velocities are air velocities high air substantial, high which are substantial, to provide provide the the necessary alone operator. The combined the operator. for the as well be unpleasant as well as as unhealthy unhealthy for high air velocities can be The high used. The is is used. LLNL. at LLNL. machines at turning machines precision turning several precision on several implemented on approach approach is is being implemented insufficient that insufficient is that difficult is be difficult to be temperature control The main thing that makes precision air temperature control appear to control temperature control the temperature of the dynamics of the dynamics present, the sources present, heat sources the heat of the analysis of the analysis to the attention attention is is paid to static on static designed on are designed systems are control systems temperature control air temperature Most air implemented. Most control implemented. of control system system and and to to the the mode of steady or loads are loads with and cooling heating and such as criteria such criteria as maximum heating cooling loads with no no regard regard to to whether the the loads are steady or in many is ever variable. Very Very little attention attention is ever paid paid in many cases cases to to the the type type of of controller controller used used since since the the type simpleonon-off result simple as aa result and as applications and precision applications high precision for high designed for not designed are not systems are of systems majority of majority -off type suffice. will suffice. controls will controls considerations load considerations Heat load heat net heat the net affects the nothing which affects as nothing long as equilibrium as long thermal equilibrium static thermal at static be at will be tool will A machine tool not cause rate will constant rate at aa constant heat from aa machine at remove heat or remove supply or which supply Things which changes. Things will not cause it changes. transfer to it the the temperature temperature distribution distribution of of the the machine machine to to change change after after it it has has been been allowed allowed to to reach reach thermal thermal equilibrium equilibrium heat at remove heat or remove supply or hand, things the other hand, sinks. On the or sinks. sources or those sources in in the the presence presence of those things which supply at thermal resulting thermal with aa resulting time with in time vary in to vary distribution to temperature distribution the temperature cause the variable rates rates will will inevitably inevitably cause variable drift. drift. sinks beyond sources or heat sources necessary to not necessary is not it is that it is that conclusion is primary conclusion The primary The to worry worry about constant heat or sinks beyond ensuring that that the the static static heating heating or or cooling cooling capacity capacity of of the the room room is is adequate adequate to to handle handle the the net net heat heat input input or or ensuring to be is to distribution is temperature distribution if aa constant temperature that if is that conclusion is secondary conclusion The secondary room. The be the room. removal removal from the removed or sources or sinks the machine, throughout the maintained throughout maintained machine, variable variable sources sinks must must be be either either removed or their their effects effects reduced reduced distribution. temperature distribution. machine temperature in machine change in tolerable change a tolerable level which which produces a to aa level Constant Constant sources sources of of heat heat typically typically include include things things like like CNC CNC units, units, lights lights (which (which are are left left on on day day and and Variable constantly. Variable operates constantly. which operates room which the room as the space as same space night) night) and and any any other other equipment equipment within the same drive machine drive and machine temperature, and air temperature, varying air temperatures, varying wall temperatures, varying wall sources include include people, people, open open doors, doors, varying sources able to be able should be system should control system temperature control air temperature units designed air speeds. A well varying speeds. at varying well designed operate at which operate units which wall varying wall personnel, varying of personnel, effects of the effects minimize the and minimize temperature, and constant temperature, sufficiently constant provide air at sufficiently doors. open doors. and open temperatures and temperatures 84 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms A useful useful technique technique for for representing representing heat heat load load information information is is the A the generation generation of of aa heat heat load table the table for the space in question. question. It It is is aa list list of heat loads space occupied occupied by by the the machine machine in of all all of of the the heat loads present present and and an an indication indication of their their nature nature (i.e. (i.e. steady steady or or variable). variable). In In addition addition it it includes includes totals totals for for heating heating and of and cooling cooling loads loads which are useful useful for for determining determining necessary necessary system system capacity. capacity. An example which are example for for aa typical typical machining area area is is given inri Table ldu ' e 1. Table!. Table 1. Sample Heat Load Table Winter Load Type Type Latent Sensible Summer Total Total Latent Sensible BTU/HR BTU /HR Total BTU/HR BTU /HR Conduction To Inside Spaces To Inside Spaces DN ON 0 0 00 0 0 0 0 00 00 Conduction Thru Thru North Wall Wall DN ON 0 0 -15092 -15092 0 0 14063 14063 Conduction Roof Thru Roof ON ON 0 0 -31040 -31040 0 0 69134 69134 Conduction Conduction Thru Floor SS 00 00 00 0 0 00 00 6132 3000 9132 6132 6132 3000 9132 Personnel Personnel Heat Load DN Air Handler 7-1/2 7 -1/2 BHP BHP SS 00 19100 19100 19100 00 19100 19100 Infiltration S S 00 -10780 -10780 0 0 0 0 0 Make-Up Make -Up Air Air (7000 SCFM Max) Max) (7000 SCFM VV 00 -332640 -332640 00 279720 279720 0 0 Lighting sS 0 28700 28700 00 28700 28700 c ( Machine Tools Machine V 00 12804 12804 12804 12804 00 12804 12804 S 0 0 59633 59633 00 59633 59633 59633 6132 6132 -266315 -260183 6132 486154 486154 492286 6132 6132 *66325 *72i457 *72457 6132 *206434 *212566 {( TOTALS ** Includes of Separate Separate System System for Includes Effect of for Makeup Makeup Air Air The idea idea of heat load load table table of of this this kind kind is is not not uncommon The of making making aa heat however, most most uncommon to to the HVAC HVAC profession; profession; however, tables the nature nature of of the the loads. loads. Time tables do do not not present present the Time history history information information is is useful useful in in the the design design of of the the control system system for for determining determining the the kind kind of of disturbance disturbance rejection rejection which control which will will hebe necessary. necessary. In In addition addition the the results of results of the the heat heat load load table table will will indicate indicate what what modes modes of of conditioning conditioning are are required, required, whether whether heating heating or or cooling or or both. both. It It is desirable from from aa controls cooling point of view is desirable controls point view to to only only have have heating heating or or cooling cooling since since it it is is difficult for precision precision applications applications which difficult to to find find controls controls for which can can control control both both processes. processes. Control system system considerations considerations Control There are two two common common control control problems problems one one or or both both of There are of which which many many systems systems are are plagued plagued with. with. The first first problem is is steady steady oscillation oscillation of of air air temperature temperature with problem with respect respect to to time. time. The The most most common common cause cause of of this this is is the the on-off on -off controllers controllers frequently frequently used. used. Their very nature nature is is destabilizing destabilizing from Their very from aa controls controls point point of To of view. view. To be specific, the the on on-off be more more specific, -off action action introduces introduces aa non non linearity linearity to to the the system system which which usually usually results results in in aa limit cycle limit cycle condition. Almost all heat heat transfer transfer devices devices are are nonlinear nonlinear to to begin begin with Almost all -off with and and an an on on-off controller the whole whole system system more more so. controller just just makes makes the so. Most Most adjustments adjustments made to the the system system will will only made to only vary vary the the amplitude of the the oscillation. oscillation. The amplitude and and frequency frequency of The discussion discussion should should not not be be construed construed as as that that no no oscillation oscillation of kind is is acceptable. acceptable. McClure of any any kind (5.) demonstrated demonstrated that that machine McClure (5.) machine tools tools do demonstrate demonstrate aa thermal thermal frequency frequency response, and for ambient ambient temperature temperature variations variations above response, and that that for above some some frequency frequency characteristic characteristic ofof the the machine, machine, it's response in in terms terms of of drift drift is it's response is negligible. negligible. The appears quite quite often often in The second second problem problem which which appears /night in air air temperature temperature control control systems systems isis aa day day/night temperature variation. This This is temperature variation. is an an indication indication that that the the system system has has aa relatively relatively poor poor disturbance disturbance rejection rejection at at low frequency, obviously, that that some some low low frequency, and and more more obviously, low frequency frequency disturbance disturbance is is present. present. The The changes changes in in disturbance disturbance are are caused caused by by both both changes changes in in outside outside air air temperature temperature and and also also by by changes changes in in the the temperatures temperatures and and heating heating fluids and pressures pressures of of the the cooling cooling and fluids used used in in the the control control system. system. Both Both of of the the above above problems problems can can often often be be dealt dealt with with by by being being more more attentive attentive to to the the interaction interaction of of the the controller heating and and/or controller with with the the heating /or cooling cooling device device and and in in general general by by being being more more careful careful in in the the selection of aa controller. In controller. heating and and/or In the the case case of of the the heating /or cooling cooling devices devices it it is is desirable, desirable, whenever whenever possible possible to to consider static heat heat transfer transfer characteristics, characteristics, but consider not not only only their their static but their their dynamic dynamic characteristics characteristics asas well. well. Sometimes devices which are are inherently inherently easier Sometimes it it leads leads to to devices easier to to control. control. Controllers in most cases need need not not be be much much more more sophisticated Controllers in most cases sophisticated than than to to have have proportional proportional and and integral integral actions actions although although it it usually usually costs costs no no more more once once proportional proportional and and integral integral are are present present to to get get derivative derivative action as well. well. Proportional action as action is is linear linear in in contrast contrast to to on on-off Proportional action -off action action and and the the integral integral action action is all is all 85 85 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms that is is normally normally required required to to remove remove day day/night that /night temperature temperature variations variations given adequate system capacity. capacity. With With the the advent advent of of the the microprocessor, microprocessor, many many control control manufacturers manufacturers are are offering offering digital digital controllers controllers with with PID PID action, suitable suitable for for air air temperature temperature control control systems systems for action, for less less than than $1000. $1000. Application of the the principles principles Application of BODTM enclosure BODTM enclosure The BODTM (Baby (Baby Optics Optics Diamond Diamond Turning Turning Machine) Machine) (6.) (6.) is is aa small small tt-based The BODTM -based machine which has has shown shown the the capability of producing producing parts parts to to 20 20 microinch microinch size size and and contour contour tolerances tolerances using capability of -process gaging with using post post-process feedback. feedback. A factor contributing contributing to to the the capability capability of of the A major major factor which is is the machine is is its its high repeatability repeatability which made by minimizing minimizing thermal thermal distortion. made possible possible by distortion. Two Two efforts efforts are are made made to to control control the the distortion. distortion. One One is is the the application application of of closed closed flow flow cooling cooling to to the the spindle spindle drive drive motor motor and and the the other other is is maintaining.good maintaining good control control of of the ambient ambient air air temperature. temperature. The the was originally originally housed housed in in an an inspection inspection laboratory laboratory with The machine machine was with ++_ .20° .20° FF temperature control. When programmatic needs temperature control. needs demanded demanded that that the When programmatic the machine machine be be moved to to a with ^2.0° +-2.0° FF air air a shop shop with temperature temperature control, control, the the problem problem of of how how to to provide provide adequate adequate air air temperature temperature control control materialized. materialized In response, small temporary In response, aa small temporary enclosure enclosure was was constructed constructed to to house house the the machine machine which which would would be be capable capable of of providing air air temperature temperature control control commensurate commensurate with what existed existed in providing in the the machine's prior habitat. habitat. The The control scheme scheme involved drawing drawing air from the shop control 2.0° FF variations variations and heating shop which had had ++ 2.0° heating it it at variable variable rates the necessary necessary control rates in in order to provide the control accuracy. accuracy. TFe resulting conditioned conditioned air air was was blown blown over over the the The resulting machine and and then then returned returned to to the the surrounding surrounding shop. machine shop. Figure 11 shows of the the enclosure. shows the the configuration of enclosure. Blowers Air Air Proportional controller Clear plastic curtains Figure 1. BODTM BODTM enclosure Figure 1. enclosure design design The air air temperature temperature was heated by by arrays of standard standard 100 The was heated arrays of 100 WW light light bulbs bulbs which which received varying amounts amounts of of received varying power depending depending upon upon the the output output signal signal of of the the temperature temperature controller. power controller. The latter was was aa basic basic commercial commercial The latter proportional control it's input proportional control which which had had as as it's input aa thermistor thermistor type type temperature temperature probe probe located located within within the the enclosure near near the the slides slides of of the the machine. machine. Light enclosure bulbs were were chosen chosen for for their their fast fast thermal thermal response response as Light bulbs as well well as availability. availability. as Several efforts in order to Several efforts were were made in to attempt to to reduce reduce the the effects effects of of the the surroundings surroundings on on the the temperature the enclosure. temperature within the enclosure. The first thing thing that that was was done done was was to to equip equip the The first the enclosure enclosure with with transparent transparent plastic curtains curtains to to contain contain the the conditioned conditioned air air and and minimize minimize the the infiltration plastic infiltration of of outside outside air. air. The net The net positive pressure pressure provided provided inside inside by by the the blowers blowers also also helped helped to positive to inhibit inhibit the the entry entry of of outside outside air. air. The The second to design design the the enclosure enclosure to to limit limit the second thing thing which which was was done done was was to the entry entry of of the the operator operator to to the the minimum minimum requirement hands, and and hence hence reduce reduce the the amount of of variable variable heat heat contribution requirement of of arms arms and and hands, contribution by by the the operator. operator. 86 86 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms 0.3° FF while to +_+ 0.3° inside to air temperature the air of maintaining capable of is capable The crude, is maintaining the temperature inside while although crude, enclosure, although The enclosure, from recording from temperature recording sample temperature F. A sample 2.0° F. as ++_ 2.0° much as as much varies as shop varies surrounding shop the surrounding the the temperature temperature in in the can enclosure can the enclosure since the that since is that the design design is The main caveat of the 2. The Figure 2. in Figure given in is given enclosure is the enclosure within the within The only provide provide heating, heating, the the temperature temperature inside inside can can only only be be held held higher higher than than the the outside outside shop shop temperature. temperature. The only different with aa different area with an area in an inspected in are inspected parts are the parts if the that if is that first is The first twofold. The are twofold. consequences consequences of of this this are be generally be can generally problem can this problem However, this present. However, be present. doubt be no doubt will no discrepancies will temperature, size size discrepancies temperature, accommodated by by simply simply taking taking into into account account the the coefficient coefficient of of thermal thermal expansion expansion of of the the part part material material and and the the accommodated that is that consequence is second consequence environments. The second inspection environments. and inspection machine and the machine between the temperature difference temperature difference between since the enclosure enclosure temperature temperature is is linked linked to to the the outside outside shop shop temperature, temperature, if if the the latter latter should should depart depart since the widely from from the the set set point point temperature temperature within within the the enclosure, enclosure, control control will will be be either either lost lost or or severely severely widely (under low cost rapid, low for aa rapid, design provided the design of the simplicity of note, the simplicity On aa more more positive note, provided for cost (under degraded. On degraded. the of the downtime of reliability, downtime In terms terms of of reliability, BODTM. In on BODTM. problem on control problem temperature control the temperature for the solution for $5000) $5000) solution completion. enclosure has has been been less less than than one one week week in in the the one one year year of of continuous continuous operation operation since since it's its completion. enclosure 15 min hH -I - 1-F temperature Sample temperature 2. Sample Figure Figure 2. enclosure BODTM enclosure from BODTM recording from recording enclosure PERL enclosure PERL turning small turning is aa small LLNL is at LLNL under construction at now under The (PERL) now Research Lathe (PERL) Precision Engineering Research The Precision between the differences between the major of the machine. One BODTM machine. One of major differences the aforementioned BODTM the aforementioned to the ways to many ways machine in many similar in machine similar is it is When it BODTM 1 s. When than BODTM's. higher than magnitude higher of magnitude order of an order accuracy an design accuracy has aa design two machines machines is is that the PERL has two shop as finished it is is slated slated to to operate in in the the same same shop as the the BODTM BODTM and and therefore therefore some some means means will will be be required required to to finished it for variation for temperature variation air temperature design air The design temperature. The constant temperature. at constant it at around it temperature around the air temperature maintain the F. 0.25° F. as ++_ 0.25° specified as is specified the machine the machine is and the considered and pitfalls of the pitfalls of the all of During the design design of the of the the BODTM BODTM enclosure enclosure were were considered the the enclosure all During design: subsequent design: the subsequent improve the to improve made to were made decisions were following following decisions 1. 1. decreased. be decreased. temperature would air temperature shop air outside shop on outside would be enclosure on the enclosure The dependence of the and curtains and through curtains to work have to not have 2. would not work through so that the operator would be configured so 2. The enclosure would be face. her face. or her his or past his air past enclosure air escaping enclosure of escaping flow of the flow to the would exposed to be exposed not be would not by acceptance by improve acceptance to improve enclosure to the enclosure of the aesthetics of 3. the aesthetics upon the placed upon be placed 3. More emphasis would be operators. operators. inside stand inside can stand the operator that the so that designed so is designed and is flow and air flow operator can closed air features closed resulting enclosure features The resulting covered formica covered and formica members and structural members aluminum structural extruded aluminum features extruded machine. Construction features the machine. to the next to next attenuation noise attenuation and noise insulation and thermal insulation it's thermal for it's design for the design in the used in panels. Some wood was used panels. finds commonly finds one commonly what one to what similar to curtains similar plastic curtains of plastic made of are made enclosure are the enclosure of the walls of The walls characteristics. The characteristics. the inhibiting the access while for ease provide for ease of of operator operator access while inhibiting supermarkets. They provide in supermarkets. cases in refrigeration cases on on refrigeration 3. Figure 3. in Figure depicted in is depicted enclosure is the enclosure of the design of The design air. The outside air. infiltration of infiltration of loosely loosely controlled controlled outside as almost as areas almost face areas plenums with large plenums by two the machine by of the top of the top Air two large with face over the distributed evenly over is distributed Air is U-shaped through aa Ureturned through is returned air is shaped return return duct duct which which exists exists itself. The air enclosure itself. the enclosure large large as as the the area area of of the of about rate of back. AA 1/2 it's back. across it's and across along both both sides sides of the machine and 1/2 HP HP blower blower draws draws the the air air at at the the rate about along 700 700 CFM CFM and and forces forces it it through through aa conventional conventional furnace furnace filter filter and and through through aa small small water water to to air air heat heat exchanger exchanger plenums. supply plenums. the supply before before the the air air arrives arrives at at the 87 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms machine Perl Perl ntachine 9'0" 7'-6" 7' -6' 90.00 - Water Water to to air air heat exchanger 9'-0' "(108.00) -- 1108.00) - Supply ductwork II ___ JL-JL-I 1 6'-9" 6' -9' (81.00) `TE -- -1 i`-; J jdM Blower *i,1I plenums air plenums -Return air J plastic Clear Clear p astic curtains cu tains 3. Figure Figure 3. Return air plenumsplenums design enclosure design PERL enclosure PERL slides. The the machine near the located near sensor located type sensor thermistor type by aa thermistor sensed by is sensed air is the air temperature of The The temperature of the machine slides. controller. The PID controller. digital PID available digital comrnercially available to aa commercially sent to is sent conditioning, is after conditioning, signal signal from from the the sensor, sensor, after turn modulate in turn solenoid valves controller controller has has aa time time proportioning proportioning output output and and operates operates solenoid valves which which in modulate the the flow flow of of the showing the diagram showing schematic diagram water-to-air the water through the water through 50° 50° FF chilled chilled water -to -air heat heat exchanger. exchanger. A schematic interconnections interconnections of of the the sensor, sensor, conditioner, conditioner, controller, controller, valves valves and and the the heat heat exchanger exchanger is is shown shown in in Figure the at the right available always is water cold fresh that ensure first to used are valves solenoid Two 4. Two solenoid valves are used to first ensure that fresh cold water is always available right at 4. hammer. water hammer. of water effect of the effect minimize the to minimize second to and second exchanger and exchanger Digital PID Digital PID control control with time Thermtstor time proportioning proportioning output output Thermistor signal conditioner signal conditioner } r Thermistor Solenoid valve control Solenoid valves 0.6 sec rWater to air heat exchanger Solenoid valves - Flowmeter £ 50- chilled Chilled water supply water 4. Figure 4. Figure |+ 15 15 min return 0.1 0.1 system control system PERL PERL enclosure enclosure control FF -- temperature Sample Sample temperature enclosure PERL enclosure the PERL from the recording from recording 5. Figure 5. Figure Proportional Proportional and and integral integral actions actions have have been been used used on on the the control control to to provide provide +_+ 0.08° 0.08° FF air air temperature temperature 5. The Figure 5. in Figure given in is given recording is temperature recording sample temperature variation. A sample day/night visible day no visible with no control with control /night variation. variation variation in in temperature temperature has has an an oscillatory oscillatory nature nature which which appears appears at at this this time time to to be be as as aa result result of of the the find a low cost means are now under way to find action. Efforts are valve action. solenoid valve means of of the solenoid by the introduced by nonlinearity nonlinearity introduced nonlinearity. of nonlinearity. introduction of less introduction with less flow with the flow modulating the modulating 88 88 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms CBN room CBN room The Cubic Cubic Boron Boron Nitride Nitride (CBN) (CBN) machine machine is is aa tt-based The -based precision precision turning turning and and boring boring machine currently currently under under construction at at LLNL. LLNL. It construction It has has aa design design disc disc check check accuracy accuracy on on the the same same order order as as LLNL's LLNL's existing existing diamond diamond turning turning machines machines but but is is designed designed to to be be stiffer stiffer and and hence hence more more suitable suitable for for use use with with cubic cubic boron boron nitride nitride cutting tools. tools. The The machine is built built around around the the base base of of aa 920 920 EXCELLO EXCELLO for for an an indication indication of cutting machine is of the the size size of overall size. overall machine machine size. Due to to the involved, close close air air temperature temperature control Due the accuracies accuracies involved, control was was deemed deemed necessary. necessary. The design design control control level 0.1° F. F. Since the machine level was was 68 68 4+ 0.1° Since the machine was was fairly fairly large large it it was was more more reasonable reasonable to to put put it it in in aa room with room with good temperature temperature control good control as as opposed opposed to to constructing constructing an an enclosure enclosure around around it it as as in in the the cases cases of of BODTM BODTM and and PERL. No room room with the necessary necessary temperature PERL. temperature control existed within No with the control existed within MFD's MFD's machining complex, was complex, so one was specially designed. specially designed. The room was the objective objective of of providing providing close The room was designed designed with with the close air temperature control control by minimizing the by minimizing the effects variable heat heat sources. sources. Since Since the the variable variable heat effects of of variable heat sources sources on on the the machine all all have closed flow flow liquid cooling, heat remaining radiation from liquid cooling, the the primary primary sources sources of of variable variable heat remaining are are conduction conduction and and radiation walls, from the walls, heat and infiltration infiltration of of air air by heat generation generation by by the the operator operator and by leaks leaks and and the the makeup makeup air air system. system. In order In order to to minimize minimize the the contribution contribution from from the the walls walls supply supply and and return return registers registers were were constructed constructed around around the the perimeter perimeter of of the the room room and and adjusted adjusted to to provide provide aa relatively relatively high high velocity velocity curtain curtain of of air air around around the the perimeter. Velocities are on on the the order order of of 100 100-150 FPM along along the the walls. walls. Air is perimeter. Velocities are -150 FPM is also also distributed distributed over over the top top of of the the machine machine by by two two large large plenums plenums with with exit exit areas areas slightly slightly larger larger than than the the projected projected area area of of the the machine. Air Air velocities velocities out out of of the the plenums plenums averages averagesbetween machine. -40 FPM. between3030-40 FPM. This This air air returns returns along along with the the high high velocity velocity perimeter perimeter air air through the perimeter perimeter registers. registers. The The air air distribution distribution scheme scheme is is shown shown in in Figure 6. 6. -High High velocity velocity supply supply registers registers - Laminar flow plenums. 18" ,) 138" J Raised computer Return grills 1 III I 18" 248" Figure Figure 6. 6. CBN scheme CBNroom roomair airdistribution distribution scheme AA unique unique feature design is is the feature of of the the design the configuration of the the return return ducting. ducting. The height of the machine The height of the machine spindle spindle centerline centerline made made it it necessary necessary to to construct construct aa raised raised floor floor around around the the machine machine to to facilitate facilitate operator operator access. The floor is access. is actually floor and and provides The floor actually aa computer computer floor provides for for about 18 inches inches of clearance between between the the bottom of the raised raised floor floor and and the the floor floor on bottom of the on which which the the machine machine rests. rests. The The clearance clearance space space serves serves as as the the return duct, some cost cost savings savings in in sheet sheet metal return duct, providing providing some metal work. work. The same as The control control scheme scheme implemented implemented is is the the same as that implemented on the the PERL PERL enclosure enclosure with with the the exception exception implemented on that that the the air air flow is is increased increased to to 10,000 10,000 CFM. CFM. Only Only cooling cooling is is required required since since there there are are enough enough heat heat sources sources present the year to maintain maintain 68° 68° F. F. present throughout throughout the year to 89 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms has been it has that it the 66 months for the 68 ++ 0.05° providing 68 0.05° FF control control for months that been of providing has been capable of the system has Thus far the variation temperature variation later temperature 7. The giveninin~Tigure The later recording isis given A sample -Figure 7. temperature recording sample temperature produces 2.0 nicroinch microinch thermal thermal drift drift between between the the two two slides slides of of the the machine machine measured measured at at tool tool height, height, even even produces aa +_+ 2.0 base the base around the cooling around liquid cooling flow liquid room. Closed the room. Closed flow leaving the and leaving entering and when two 0E-three are entering or three machinists are when further. even further. drift even the drift reduce the to reduce expected to is expected the machine is of the in operation. operation. 15 min T H h-- 0.1°F --{ 0.1°F temperature Sample temperature 7. Sample Figure 7. room CBN room from CBN recording from recording upgrade shop upgrade Numerical control control shop Numerical needs, the programmatic needs, to meet in order Long range planners within MFD have order to to continue continue to meet programmatic the have projected that in range planners Long temperature control control in in the the shops shops which which house house it's it's precision precision turning turning and and boring boring machines machines will will have have to to be be air temperature best way the best determine the to determine order to in order study was F. A study was conducted conducted in way 0.25° F. to +^ 0.25° improved from its 2.0° FF to its current ++_ 2.0° improved load heat load preparing aa heat included preparing study included The study requirement. The improvement requirement. magnitude improvement of magnitude to meet the order of the almost order to table for for the the shops, shops, identification identification of of the the current current control control scheme, scheme, reviewing reviewing present present air air temperature temperature control control table system. current system. the current with the experiments with some experiments technology and conducting some technology was temperature was Air temperature follows: Air as follows: operated as system operated the system that the revealed that A brief system revealed review of the existing system brief review located. The The sensed by by aa thermistor thermistor type type sensor sensor located located about about 20 20 feet feet above above where where the the turning turning machines machines are are located. sensed solenoid switched aa solenoid deadband. The of deadband. The controller controller switched 0.3° FF of about 0.3° signal -off controller controller with with about on-off an on into an fed into signal was fed water chilled water The chilled valve which which modulated modulated the the flow of of air air to to aa pneumatically pneumatically operated operated chilled chilled water water valve. valve. The valve in located in exchanger located water-to-air througha awater waterthrough chilled water valve was used to -to -air heat heat exchanger flow ofof chilled the flow modulate the to modulate valve shop the shop of the temperature of air temperature the air to modulate used to was used modulate the heat exchanger was shop. The heat ductwork on on the roof the shop. of the roof of ductwork below. below. digital with aa digital it with replace it and replace the onon-off replace the to replace was to A simple -off control control and conducted was was conducted which was experiment which simple experiment other any other Without any room. Without CBN room. the CBN in the and in enclosure and PERL enclosure the PERL in the PID control control the same as used in those used as those PID of cost of total cost F. The 0.5° F. to ++_ 0.5° 2.0° FF to from _++ 2.0° The total shop went the shop in the modification, went from fluctuation in temperature fluctuation modification, the air temperature $1000. under $1000. the change was under the the between the delay between transport delay second transport 60 second was aa 60 there was that there was that Another discovery resulting from study was the study from the in that in which meant effect which is aa destabilizing sensor. This This is destabilizing effect meant that feedback sensor. temperature feedback the temperature heat exchanger and the heat that was that result was The result decreased. The be decreased. had to system had the system of the gain of loop gain the loop order to to be stability, the to obtain system stability, disturbance rejection rejection had had to to be be compromised compromised and and therefore therefore the the quality quality of of the the temperature temperature control control was was limited limited disturbance F. 0.5° F. to to ++ 0.5° system is In order to to meet meet the the temperature temperature control control requirement requirement of of +_ + 0.25° 0.25° FF aa control control system is being being built built for for In order few only aa few located only be located probe will first feedback probes. The first feedback probe will be feedback probes. temperature feedback the shop shop which which has two two temperature the The feet downstream downstream from from the the heat heat exchanger exchanger and and the the second second will will be be located located down down near near the the turning turning machines. machines. The feet loop its loop and its sensor and first sensor the first of the purpose of 8. The Figure 8. in Figure form in diagram form control The purpose block diagram in block shown in is shown control scheme is exchanger. heat exchanger. the heat from the temperature from air temperature immediate outlet the immediate over the will outlet air control over tight control fairly tight to provide fairly be to will be travels it travels as it air as the air of the temperature of the temperature in the detect changes to detect is to loop is and loop The purpose of the the second sensor changes in sensor and purpose of occur changes occur temperature changes latter temperature the latter that the shown that have shown made have Measurements made second. Measurements from the the first first sensor to the second. to the from fairly slowly slowly and and hence hence will will not not be be that that difficult difficult for for the the second second sensor sensor loop loop to to correct correct for. for. fairly Second temperature temperature probe Second machines near machines is down near is 7 First First temperature probe isis near nearcooling coolingcoil coil-- r/-Temperature Temperature setpoint Valve /coil Delay +t Disturbance --1K21 K2 8. Figure 8. Figure upgrade shop upgrade NC shop for NC Control scheme scheme for Control 90 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/28/2013 Terms of Use: http://spiedl.org/terms The The control control system system is is being being configured configured around around aa small small personal personal computer, computer, not not because because the the control control scheme scheme requires requires significant significant computing computing power, power, but but because because it it will will also also be be used used to to log log temperatures temperatures at at various various locations in in the the shop shop simultaneously. simultaneously. The latter function function will be performed so that the The latter will be performed so the performance of of the the locations air temperature temperature control control system system can can be be continually continually and and conveniently conveniently observed observed by by shop shop supervisors. supervisors. The The system system air will will be be capable capable of of displaying displaying temperature temperature time time histories histories graphically graphically on on its its monitor monitor at at the the discretion discretion of of whoever is operating the keyboard. keyboard. It It will will also also be be able able to to store store several several days days worth worth of of temperature temperature data data on on whoever is operating the disk. AA layout system is layout of of the the system is shown shown in in Figure Figure 9. disk. Plotter printer Multiple temperature Data storage disk Temperature setpoint (68" F I Room temp I i-+r sensors P+l I Signal averaging r Control signal I to cooling P+l -J Scanner Duct air temp I valve J Computer Figure 9. 9. Computer Computer based based temperature temperature control control and and data data logging logging system system Conclusions Conclusions Precision Precision air air temperature temperature control control can can be be an an excellent excellent way way of of improving improving the the accuracy accuracy capability capability of of machines by removing removing one one of of the the largest largest sources sources of of nonrepeatability. nonrepeatability. Work Work at at LLNL LLNL has has demonstrated demonstrated that that machines by achievement of achievement of close close temperature temperature control control can can be be obtained obtained by by careful careful identification identification of of heat heat sources sources and and the the application classical control control theory. theory. The The work work has has also also demonstrated demonstrated that that large large application of of some some fundamental fundamental classical improvements improvements in in the the performance performance of of temperature temperature control control systems systems do do not not necessarily necessarily have have to to be be complicated complicated or or expensive. expensive. Acknowledgments Acknowledgments The author author wishes Fairley and The wishes to to thank thank D. D. C. C. Thompson, Thompson, C. C. R. R. Fairley and J. J. W. W. Roblee Roblee for their support support in the in the development in this this paper. paper. development of of the the systems systems discussed discussed in "Work the auspices auspices of of the the U.S. U.S. Department Department of "Work performed performed under under the of Energy Energy by by Lawrence Lawrence Livermore Livermore National National Laboratory underContract ContractW-W-7405-ENG-48." Laboratory under 7405- ENG -48." References 1. Donaldson, R. R., "Repeatability, "Repeatability, aa Key R. R., ", American -59 Key to to Accuracy Accuracy", American Machinist, Machinist, January 1. January 8, 8, 1983, 1983, 5757-59 2. Moore, W. R., R., Foundations Foundations of 2. Moore, W. Mechanical Accuracy, Accuracy, Moore Tool Company, Bridgeport, Connecticut of Mechanical Moore Special Special Tool Company, Bridgeport, Connecticut Bryan, J. 3. Bryan, J. B., Donaldson, R. 3. B., Donaldson, McClure, E. W., A Practical Practical Solution Solution to to the Thermal R. R., R., McClure, E. R., R., Clouser, Clouser, R. R. W., the Thermal Stability in Machine Tools, Lawrence Lawrence Livermore Livermore National National Laboratory, Stability Problem Problem in Machine Tools, 73577, Laboratory, Report Report Number Number UCRLUCRL-73577, Revision 1, 1, Livermore, Livermore, California Revision 4. 4. Bryan, Bryan, J. J. B., B., Carter, Carter, D. D. L., L., Clouser, Clouser, R. R. W., W., Hamilton, Hamilton, J. J. H., H., An An Order Order of of Magnitude Magnitude Improvement Improvement in in Thermal Stability Stability with Use of of Liquid Liquid Shower on on aa General Purpose Measuring Thermal with Use General Purpose Measuring Machine, Machine, S.M.E. S.M.E. Precision Precision Machining Workshop, Workshop, June June 66-10, Machining -10, 1982, 1982, St. St. Paul, Paul, Minnesota, Minnesota, Society Society of of Manufacturing Manufacturing Engineers paper no. no. IQ82-936. IQ82 -936. 5. 5. McClure, E. E. R., R., Manufacturing Manufacturing Through Through the the Control McClure, Thesis, Lawrence Livermore Control of of Thermal Thermal Effect, Effect, PhD PhD Thesis, National Report Number Number UCRLUCRL-50636, Livermore, California National Laboratory, Laboratory, Report 50636, Livermore, California 6. Thompson, 6. Thompson, D. D. C., C., Chrislock, Chrislock, J. J. L., L., Newton, Newton, L. L. E., E., "Development "Development of of an an Inexpensive, Inexpensive, High High Accuracy Accuracy Diamond Diamond Turning Machine Machine", Turning ", Precision Precision Engineering, -77 Engineering, 1982, 1982, Vol. Vol. 1,1, Number Number4,4,7373-77 DISCLAIMER document vas was prepared prepared as as an an account account of work work sponsored sponsored by an agency This document by an agency of of the States Government. United the United l; sited States Government. 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