while the present invention is described with respect to the preferred embodiment described below and shown in the figures , the present invention is limited only by the metes and bounds of the claims that follow . the apparatus and methods described herein enable an accurate setting of the initial coating gap in slot die coaters plus the ability for the slot die to retract in the presence of web splices , debris on , or defects in , a discrete or continuous substrate where after retraction the slot die returns with high precision to its former position . the benefits of the apparatus and methods described herein are the ability to accurately set the initial coating gap and upon retraction of the slot die to avoid damage , the ability to return with high precision to the former coating position hence maintaining the same coating gap . for a general understanding of the disclosed technology , reference is made to the drawings . in the drawings , like reference numerals have been used to designate identical elements . in describing the disclosed technology , the following term ( s ) have been used in the description . the term “ backlash ” refers herein to clearance between mating components , sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re - established . in particular , in a pair of gears , backlash is the amount of clearance between mated gear teeth . in other words it is the difference between the tooth space and the tooth thickness , as measured along the pitch circle . theoretically , the backlash should be zero , but in actual practice some backlash must be allowed to prevent jamming of the teeth due to tooth errors and thermal expansion . this gap means that when a gear - train is reversed the driving gear must be turned a short distance before all the driven gears start to rotate . backlash is an unavoidable property of nearly all reversing mechanical couplings . the term “ leadscrew ” refers herein to a screw designed to translate rotational motion into linear motion . this is accomplished by the rotation of a threaded rod that has been inserted into a leadscrew nut such that when the threaded rod is rotated the leadscrew nut is moved a specified linear distance ( depending upon the pitch of the threads in the rod ). leadscrews exhibit backlash similar to that exhibited by a pair of gears . the term “ accurate ” or “ accurately ” refers herein to a positioning or measurement relating to an absolute value . that is , an accurate measurement of a quantity will be relatively close to its actual ( true or desired ) numerical value . preferably an accurate measurement will be one that is within , at most , a few percent of its true value . for the slot die apparatus and method disclosed herein a coating gap accuracy of preferably about 50 . 00 microns ( 0 . 0019 inches ), more preferably about 30 . 00 microns ( 0 . 0011 inches ), even more preferably about 20 . 00 microns ( 0 . 00078 inches ) and most preferably about 12 . 7 microns ( 0 . 00050 inches ) is maintained . the term “ precision ” or “ precisely ” refers herein to the degree that repeated positioning or measurements under unchanged conditions show the same results . note that while the repeated measures may be numerically very close to each other , the measurements may not be close to the actual ( true or desired ) numerical value . preferably a series of precise measurements will be within , at most , a few percent of each other . for the slot die apparatus and method disclosed herein a coating gap precision of preferably about 5 . 00 microns ( 0 . 00019 inches ), more preferably about 3 . 00 microns ( 0 . 00011 inches ), even more preferably about 2 . 00 microns ( 0 . 000078 inches ) and most preferably about 1 . 27 microns ( 0 . 000050 inches ) is maintained . the term “ disturbance ” refers herein to environmental forces or effects that tend to induce change in a process . typical disturbances of interest include both web splices and web defects . the term “ feed - forward control ” refers herein to a form of control that only requires the detection of an impending process disturbance to initiate corrective action . one aspect of the invention is directed to a coating apparatus , exemplified herein as a slot die coater . the apparatus includes a support device that supports an object to be coated . the support device is exemplified as coating roller 105 and web 110 . the apparatus further includes a coating head , a first support supporting said coating head in a selected position , said first support movable along at least one axis , an adjustment mechanism positioned to move the first support relative to the support device to adjust a gap between said coating head and said object to be coated , a cam positioned to move the first support , and a cam drive for providing rotation to the cam , wherein rotation of the cam adjusts the position of said coating head relative to said object to be coated . in the embodiments described below , these features of the invention are exemplified as follows : the coating head as coating head 107 ; the first support as the combination of die mount 102 , die pivot 109 and machine tool slide 103 ; adjustment mechanism as manual gap adjustment 104 and tapered rod 301 ; cam as cam 302 ; and cam drive as servomotor 200 . the coating apparatus may include a second support supporting the first support , which is exemplified as side rails 108 , wherein the first and second supports are movable with respect to each other along the at least one axis . fig1 is a schematic plan view of the slot die assembly where the slide springs 101 provide tension for the machine tool slide 103 supporting the die pivot 109 and the die mount 102 . the coating head 107 is attached to the die mount 102 where the coating gap 106 between the coating head 107 and the coating roller 105 is initially adjusted using the manual gap adjustment 104 . the machine tool slide 103 , the die pivot 109 , the die mount 102 and the coating head 107 all move as an integral unit in the side rail 108 . fig2 is a schematic side view of the slot die assembly showing the unit configuration of the machine tool slide 103 , the die mount 102 , the die pivot 109 , the coating head 107 as a single unit 201 and the side rail 108 . the directional arrow k shows the axis of movement of the single unit 201 . it also shows the position of the servo motor 200 and the manual gap adjustment 104 . fig3 is a schematic bottom view of the slot die assembly where the servo motor 200 has been removed to allow a view of the tapered rod 301 and cam 302 which when used in combination with the manual gap adjustment 104 enables setting of the initial coating gap 106 . fig4 is a schematic diagram of a slot die position control system based upon feed - forward control where a coating roller 105 rotating in a clockwise manner supports a moving substrate 110 . at multiple positions on the coating roller in advance of the application of the coating at the coating gap 106 , substrate splices are sensed using a sensor 411 and substrate coating defects are sensed with a sensor 412 . signals indicative of such splices or defects are sent to a retract logic circuit 413 which determines what action should be taken . the appropriate action via a resultant signal is then sent to the feed - forward controller 414 . the feed - forward controller 414 using a model of the coating process , essentially a transport delay , then sends a signal to a positioner ( not shown ) which retracts the coating head 107 , part of the single unit 201 , subsequently changing the coating gap 106 during the time that the splice or defect is in the coating gap 106 . the directional arrow k indicates the axis of movement of the single unit 201 . fig5 is a graph of the feed - forward controller 414 operation depicting the relationship between the cam 302 rotation position and the associated coating gap 106 . in the diagram above the graph , the wedge - shaped member 600 is shown abutting the cam 302 at the 12 : 00 or 0 ° position . the x - axis represents the degree of rotation of the cam as dictated by the feed - forward controller 414 output and the y - axis represents the resulting coating gap 106 . for coating bead pick up , the feed - forward controller rotates the cam 302 to the 12 : 00 or 0 ° position which has a fixed gap of y 1 . once coating is established , the controller rotates the cam 302 to the nominal 3 : 00 or 90 ° position which has an adjustable coating gap as indicated by y 2 . upon the detection of a splice in the web being coated , the feed - forward controller rotates the cam 302 , during the appropriate interval , to the 6 : 00 or 180 ° position which increases the coating gap as indicated by y 3 which is also adjustable . upon the detection of a web defect , the feed - forward controller rotates the cam 302 , during the appropriate interval , to the 9 : 00 or 270 ° position further increasing the coating gap to y 4 . fig6 is a view of internal components featuring the details of the cam 302 and its relationship to the wedge - shaped adjustment member 600 . fig7 a and 7b are three - dimensional views of the details of a representative wedge - shaped adjustment member , the solid figure bounded by the points abcdefgh , and a representative tapered rod adjustment member , the solid frustum of a right cone x bounded by the circles y and z . the wedge - shaped adjustment member is supported by mounts ( indicated , but not shown in fig6 ) abutting the aceg plane . the tapered rod adjustment member is supported by a shaft aligned with the central axis of the frustum connected to both sides of the machine tool slide 103 ( as shown in fig2 ). referring now to fig1 in more detail , in the preferred embodiment of the herein described slot die coater , the plan view shows the coating head 107 is attached to the die mount 102 . the die mount 102 in turn is positioned on the top of the die pivot 109 which is in turn placed upon the machine tool slide 103 . the machine tool slide 103 is mounted into the side rail 108 which enables movement of the entire single unit 201 transversely either toward or away from the coating roller 105 . the machine tool slide 103 is tensioned by springs 101 which provide a force that tends to move the machine tool slide 103 toward the coating roller 105 . the coating gap 106 is maintained by the adjustment of the manual gap adjustment 104 . in fig2 , the side view shows the servomotor 200 mounted perpendicular to the axis of movement of the machine tool slide 103 and single unit 201 as indicted by the arrow k . in fig3 , the bottom view ( where the servomotor 200 has been removed ) shows the manual adjust 104 connected to a tapered rod 301 which is supported on both ends by the machine tool slide 103 . while a tapered rod is shown and described , any wedge shape element that is able to manually positioned perpendicular to the axis of movement of the machine tool slide 103 and single unit 201 may be used . the tapered rod 301 impinges upon a cam 302 mounted on the shaft 202 of the servomotor 200 . the cam 302 is held in tension against the tapered rod 301 by springs 101 . this set up maintains the machine tool slide 103 under spring tension at a particular position . rotation of the manual gap adjustment 104 causes the tapered rod 301 to move perpendicular to the axis of movement of the machine tool slide 103 and single unit 201 such that when the cam 302 is in a fixed position this rotation causes the coating gap 106 to increase or decrease by moving the machine slide 103 and single unit 201 backwards or forward . in fig4 , a feed - forward control system is shown to maintain the coating gap 106 between the coating roller 105 and the coating head 107 plus implement slot die retraction when a substrate splice or defect is encountered . a substrate splice sensor 411 or alternatively a substrate defect sensor 412 monitors the substrate in advance of the substrate being located at the coating gap 106 . such sensors are well known in the art and may be either optical or electromechanical . the substrate height sensor ( s ) are preferably located at a position far enough in advance of the coating gap 106 such that there is adequate time for the control system to respond . when a splice or defect is sensed , a representative signal is sent to the retract logic circuit 413 which determines if a full retract is required ( often the case for defects , but this action frequently breaks the coating bead ) or if only a partial retract is required ( which usually does not break the coating bead , allowing coating to continue uninterrupted ). the appropriate signal is then sent to the feed - forward controller 414 which using the distance between the appropriate sensor ( 411 or 412 ) and the coating gap 106 coupled with the rotational speed of the coating roller 105 determines the transport lag of the substrate . the feed - forward controller 414 then times a signal to the servomotor 200 which results in the rotation of the servomotor shaft and attached cam 302 thereby increasing the coating gap 106 and safely moving the coating head 107 out of the way of the splice or defect during the time that the splice or defect is in the coating gap 106 . in essence , the retract logic circuit 413 determines how far to retract the coating head 107 and the feed - forward controller 414 determines when to retract and when to return the coating head 107 . an accurate transport lag model allows for the minimization of the amount of off - specification coated product which would be unsuitable for sale . the apparatus achieves an accurate setup for the coating gap 106 by having the tapered rod 301 mounted into the spring 101 tensioned machine tool slide 103 upon which the die pivot 109 , the die mount 102 and the coating head 107 are attached . the cam 302 mounted on the servomotor 200 shaft is placed such that the tapered rod 301 abuts the cam 302 . when the cam 302 is in a fixed position , the rotation of the manual gap adjustment 104 causes the tapered rod 301 to move in a direction perpendicular to the axis of the tapered rod 301 subsequently increasing or decreasing the coating gap 106 . in this preferred embodiment , a one degree rotation of the manual gap adjustment 104 moves the coating gap 106 about ten microns or ten - millionths of a meter ( about 500 millionths of an inch ). while subject to backlash , accurate setup of the coating gap 106 is obtained by simultaneous measurement of the coating gap while rotating the manual gap adjustment 104 . this is a much more accurate means of obtaining the initial desired coating gap 106 than any practical leadscrew configuration . the apparatus achieves web splice retraction coupled with a highly precise return of the machine tool slide 103 and single unit 201 to the prior coating gap 106 by using the servomotor to rotate the shaft holding the cam 302 . under spring 101 tension , the machine tool slide 103 ( to which is attached the die pivot 109 , die mount 102 and the coating head 107 ) moves very quickly in response to a rotation of the cam 302 . upon the sensing of the arrival of a web splice or defect or any other process disturbance requiring retraction of the machine tool slide 103 and single unit 201 , the servomotor is engaged at the appropriate time to rotate the cam 302 to a predetermined position per the table in fig5 thereby increasing the coating gap 106 . once a splice or defect is sensed , the feed - forward controller uses a model of the transport lag incorporating the rotational speed of the coating roller 105 and the position of the appropriate sensor , 411 or 412 , to determine the timing as to when to retract and return the coating head 107 . this increased coating gap 106 is maintained until the substrate splice or defect passes and then the servomotor rotates in the opposite direction returning the coating head 107 to its former coating position thus re - establishing the appropriate coating gap 106 . note that this retraction and repositioning is accomplished without backlash and , hence , can be accomplished with high precision . furthermore , the splice retract position , as indicated by y 3 in fig5 , is adjustable depending upon the specifics of an individual coating to help minimize the breakage of the coating bead . a retract logic circuit 413 operates on the signals from the substrate splice sensor 411 and the substrate defect sensor 412 to create an appropriate signal enabling the feed - forward controller 414 to partially retract the coating head 107 when a splice is encountered or fully retract the coating head 107 when a defect is encountered . partial retraction is preferred as this action is less likely to upset the coating process and break the coating bead . it will be apparent to those skilled in the art that various modifications and variations can be made to the methods and processes of this invention . thus , it is intended that the present invention cover such modifications and variations , provided they come within the scope of the appended claims and their equivalents . the disclosure of all publications cited above is expressly incorporated herein by reference in their entireties to the same extent as if each were incorporated by reference individually .