LEADSCREWS AND LINEAR RAILS 2 Leadscrews & Linear Rails Introduction Huco has chosen to offer Kerk Leadscrews because they are designed specifically for precision motion control applications. The screw thread form is unique to Kerk and has been created for maximum life, quiet operation and repeatable accuracy. Positional bi-directional repeatability is achieved within 0.0013 mm (0.0005î) and standard lead accuracy is better than 0.0006 mm/mm. Lead accuracies are available to 0.0001 mm/mm with individual screw mapping (laser interferometer verification) optional. A number of unique, patented, anti-backlash nut options are available to suit a variety of load conditions. Kerk nuts are characterised by low drag torque, low wear and high axial stiffness. Kerk ScrewRailsTM are a patented innovation in linear motion, combining both drive and support / guidance functions in a single, compact, coaxial component. The ScrewRail’s unique design eliminates the need for any external rail to screw alignment, giving savings in space as well as cost over typical two-rail systems. Where external rail support is required Kerk Linear Rails are designed to provide low cost, low friction and long life in a variety of motion control applications. Linear rails are available in burnished or TFE coated stainless steel. The Kerk Spline Shaft system has been designed for light load applications, again where low cost, low friction and long life are needed. These assemblies consist of light weight, aluminium splined shafts treated with Kerkís proprietary low friction TFE coating, mated with graphite and PTFE filled thermoplastic bushings. The bushings are supplied with integral brass collars to enable various mounting options without distorting the nut. Tel: +44 (0) 1992 501900 Leadscrews 3 Axial take-up mechanism The standard method for taking up backlash is to ∆ 1 LOAD bias two nut halves axially using some type of compliant spring. Wavy washer, compression spring, (L) NUT HALF NUT HALF rubber washer, etc.) The unit is very stiff in the direction in which the nut half is loaded against the flank of the screw thread. However, in the direction away from the screw thread, the nut is only as axially stiff as the amount This gap (∆1 + ∆2) is now the amount of backlash of preload which the spring exerts. which has developed in the unit. This backlash can be removed by replacing the stiff spacer with a SPRING PRELOAD new spacer equal to (L+∆1 + ∆2). This process, although effective, would be extremely costly and NUT HALF NUT HALF difficult to implement on a continuous basis. What is needed then, is a stiff spacer which will For example, if the the maximum axial load to which SPRING FORCE the system is subjected is 20kg., the amount of NUT HALF LOAD AGAINST spring preload must be equal to, or greater than, SCREW FLANK 20kg. in order to maintain intimate screw/nut contact. The problems arising from preloading in this manner are increased torque and nut wear. Obviously, the higher the load at the screw/nut continually expand to accommodate the wear interface, the higher the required torque to drive the which occurs during use. This is done by creating nut on the screw and the more susceptible the unit a spacer threaded at one end with a is to nut wear. complimentary nut torsionally biased to advance when a gap develops. The thread at the end of the spacer is a fine helix such that an axial load will not back drive the nut STIFF SPACER once spacer growth has occurred. (L) The amount of preload on the unit is only that NUT HALF NUT HALF necessary to turn the spacer nut on the spacer rod and is independent of the external system loadings. We thus have a self-wear compensating unit which has extremely low frictional drag torque yet high axial stiffness. An alternate method replaces the spring with a stiff spacer sized to fit exactly between the two nut halves. There is no excessive preload force at the interface and the unit is capable of carrying high axial loads in either direction with no backlash. This is fine initially. However, as use time increases, wear begins on the nut threads causing a gap to develop between the spacer (L) and the nut halves. www.huco.com 4 Leadscrews Available Standard Metric Leads The following table shows the range of standard metric leads available, non-standard leads can be manufactured subject to tooling charge. Lead (mm) Diameter Series (mm) 0.5 1.0 1.4 1.5 2.0 2.5 3 4 5 6 7 8 10 12 14 15 16 19 20 24 25 50 03 4.76 G 04 6.35 G G G G G 06 9.53 G G G G G G 07 11.11 G G G G G G 08 12.7 G G G G G G 10 15.88 G G 12 19.05 G G G G G G G G G 14 22.23 G G G G G Note: Imperial leads available to order. Tel: +44 (0) 1992 501900 Leadscrews 5 ZBX Series - anti-backlash leadscrew assemblies The patented Kerk ZBX Series anti-backlash assembly offers an effective linear actuator for design operations requiring precise positional accuracy and repeatability, with minimum cost. The standard ZBX unit utilises a patented self-lubricating polyacetal nut radially preloaded on a 303 stainless steel screw. The ZBX assembly, through its unique transfer of loads, offers exceptional torque consistency and repeatability when traversing in either direction. The inherent damping qualities of the ZBX design make it ideally suited for vertical applications requiring noise or vibration control. End machining to customer specifications and TFE screw coating are optional, as are designs for special operating configurations or environments. ZBX Series - Flange Mount ZBX Series - Thread Mount C C N D DIA. D E E 120º F DIA. -3 HOLES TYP. ON G DIA. B.C. A B A DIA. B DIA. M ZBX Series - Flange Mount Screw Diameter Nut Diameter Nut Length Flange Diameter Flange Thickness Mounting Hole Dia Bolt Circle Diameter Dynamic Load Drag Torque Series A B C D E F G kg Ncm mm mm mm mm mm mm mm ZBX.F.04M 6.35 12.7 25.4 25.4 4.6 3.6 19.1 2.3 0.4 - 1.0 ZBX.F.06M 9.52 17.8 48 38.1 4.6 5.08 28.6 5 1.0 - 2.0 ZBX.F.07M 11.11 20.3 48 38.1 4.6 5.08 28.6 7 1.5 - 3.0 ZBX.F.08M 12.70 22.6 50.8 41.2 6.6 5.08 31.8 11 1.5 - 3.0 ZBX.F.10M 15.88 26.9 50.8 44.5 6.6 5.08 34.9 16 2.0 - 5.0 ZBX Series - Thread Mount Screw Diameter Nut Diameter Nut Length Flange Diameter Flange Thickness Thread Thread Length Dynamic Load Drag Torque Series A B C D E M N kg Ncm mm mm mm mm mm in -tpi* mm ZBX.Y.04M 6.35 12.7 33 20.3 5.6 5/8 - 18 4.1 2.3 0.4 - 1.0 ZBX.Y.06M 9.52 17.8 56 25.4 4.3 5/8 - 18 9.7 5 1.0 - 2.0 ZBX.Y.07M 11.11 20.3 59 25.4 3.1 15/16 - 16 9.7 7 1.5 - 3.0 ZBX.Y.08M 12.70 22.6 59 25.9 3.1 15/16 - 16 9.7 11 1.5 - 3.0 ZBX.Y.10M 15.88 26.9 61 26.9 3.8 15/16 - 16 12.7 16 2.0 - 5.0 * Metric threads available as required To order specify Series required + Lead in mm + Overall Leadscrew Length in mm www.huco.com 6 Leadscrews ZBA Series - anti-backlash leadscrew assemblies The patented ZBA Series offers a can also be set at the factory to cost effective anti-backlash meet individual customer assembly for applications requiring specifications. The inherent precise positional accuracy and damping qualities of the ZBA repeatability. The ZBA has been design make it ideally suited for developed specifically for those applications requiring noise or applications that require very vibration control. smooth and consistent motion The standard ZBA unit utilises a such as printing, scanning, and co- self-lubricating polyacetal nut ordinate measurement systems. radially preloaded on a 303 An added benefit of the ZBA stainless steel crew. End design is the ability to manually machining to customer adjust the drag torque setting to specifications and TFE screw match the specific requirements of coating are optional. the application. This drag torque ZBA Series - Flange Mount ZBA Series - Thread Mount C C N E D DIA. F DIA. 3-HOLES D ON G DIA. B.C. E A DIA. B DIA. A B M ZBA Series - Flange Mount Screw Diameter Nut Diameter Nut Length Flange Diameter Flange Thickness Mounting Hole Dia Bolt Circle Diameter Dynamic Load Drag Torque Series A B C D E F G kg Ncm mm mm mm mm mm mm mm ZBA.F.04M 6.35 13.5 25.4 25.4 4.6 3.6 19.1 2.3 0.4 - 1.0 ZBA.F.06M 9.52 18.8 48 38.1 4.6 5.08 28.6 5 1.0 - 2.0 ZBA.F.07M 11.11 20.3 48 38.1 4.6 5.08 28.6 7 1.5 - 3.0 ZBA.F.08M 12.70 22.6 50.8 41.2 6.6 5.08 31.8 11 1.5 - 3.0 ZBA.F.10M 15.88 26.9 50.8 44.5 6.6 5.08 34.9 16 2.0 - 5.0 ZBA Series - Thread Mount Screw Diameter Nut Diameter Nut Length Flange Diameter Flange Thickness Thread Thread Length Dynamic Load Drag Torque Series A B C D E F N kg Ncm mm mm mm mm mm in -tpi* mm ZBA.Y.04M 6.35 13.5 33 20.3 3.1 5/8 - 18 4.1 2.3 0.4 - 1.0 ZBA.Y.06M 9.52 18.8 56 25.4 3.8 5/8 - 18 9.7 5 1.0 - 2.0 ZBA.Y.07M 11.11 20.3 59 25.4 2.5 15/16 - 16 9.7 7 1.5 - 3.0 ZBA.Y.08M 12.70 22.6 59 25.9 2.5 15/16 - 16 9.7 11 1.5 - 3.0 ZBA.Y.10M 15.88 26.9 61 26.9 3.1 15/16 - 16 12.7 16 2.0 - 5.0 * Metric threads available as required To order specify Series required + Lead in mm + Overall Leadscrew Length in mm Tel: +44 (0) 1992 501900 Leadscrews 7 KHD Series - anti-backlash leadscrew assemblies The Kerk KHD Series anti-backlash assembly makes use of Kerk’s patented AXIAL TAKE-UP MECHANISM (see page 3) to provide backlash compensation.