For each table series, Lintech provides a table in the catalog which reflects the Maximum Safe Table Operating Speed. These listed speeds are a mechanical limitation. The maximum speed of a positioning table depends upon the screw diameter, screw lead, screw length, and the screw end bearing support configuration. Lintech typically utilizes a fixed-simple screw end bearing support configuration in its positioning tables. The correct motor and drive system needs to be selected in order to reach the rated maximum table speeds. Below is the table for the 160 & 170 series tables.
It is possible to increase the speed limitation a little bit beyond the listed limit IF the end support configuration is modified to a rigid-rigid design. This configuration increases the screw rigidity by changing the bearing arrangements on each end and therefore enables the screw to rotate at a bit higher speed before whipping will occur.
Lintech actually chose to offer the rigid-rigid design as a “standard” on the 610 linear table series. This is a little more expensive but enables the 610 series tables to have a somewhat higher speed rating.
If you want to use a ball screw driven table and need to push the envelope a little for some reason, contact Lintech for ideas.
For designers building their own linear motion systems, the choice may be made to utilize a ball screw as the drive mechanism. There are a variety of companies offering ball screws of different diameters and leads, but many do not offer the accessories to simplify the integration of the screw into the motion system. For instance, the screw needs to be held in place, the load needs to be connected to the ball nut, etc. Lintech offers some options to assist in the integration process by offering ball screw support assemblies, brackets to enable the attachment of the load to the nut as well as many other items which will be needed in a motion system.
When selecting a ball screw from Lintech, the part number configurator leads you through the selection of components for the assembly and not just the screw and nut. Of course, if the design does not enable selection of these pre-engineered accessories, Lintech can supply the basic screw and nut only.
When initially selecting a linear guide the idea, of course, is to select a component which will last what you determine to be an acceptable “life”. That may be some number of cycles, millions of inches of travel, etc. To get the life you desire, you would initially select a catalog product with appropriate load ratings. However, In order to achieve the rated catalog load/life, you may need to dodge or lessen the impact of potential linear guide life shortening circumstances.
What are some of those circumstances? Common causes are contamination, corrosion, excessive or incorrect loading, lubrication failure, vibration, improper mounting and excessive temperatures. When one of these circumstances is present, it can often develop into other problems. For instance, a lubrication failure will lead to high temperature, as you might imagine.
Since the designer does not often have total control over the conditions to which the linear guide is subjected, the goal would be to minimize the degree of those conditions. Contamination is probably the most common cause of premature failure. You would not want to operate linear bearings in an environment as depicted below. However, if you had a degree of contamination in your application that is out of your control, maybe there is a better sealing option which would minimize contamination.
Likewise, if you had an environment which was very humid, you might select bearings which were stainless or plated. If there were “high” temperatures, possibly selecting lubrication rated for higher temperatures would be helpful and/or blowing cool air on the linear guide.
The point is that linear guides have the best potential of achieving their rated life if the common causes of premature failure are recognized and an attempt is made to minimize those causes of premature failure.
When Lintech has the opportunity to be considered for a new application, we have a worksheet which reminds us to inquire into the application environment as well as all of the standard application specifications. If you would like assistance selecting components for a new linear motion application, please contact http://www.LintechMotion.com.
When selecting a positioning table, in addition to the topics to consider from the December 15th post, each of the following items should be reviewed thoroughly by the user. Some items will not be of major importance for a specific application. However, by reviewing each and every item(explained in more detail in the Lintech Positioning Systems Catalog), a positioning table can be selected that will give the required performance over the life of the system.
Items to review:
- Bearing Designs – Linear (ball, cross roller, round rail, square rail, and air) bearings, along with rotary bearings. Different linear bearing types offer advantages and/or disadvantages(See pages A-10 to A-12 of the Positioning Systems catalog)
- Drive Mechanisms (acme screws, ball screws, belt, and worm gears). See pages (A-13 to A-15 of the Positioning Systems catalog)
- How to Select a Positioning Table which includes safety factors and travel life. (See page A-16 of the Positioning Systems catalog)
- Load Capacities of all the critical elements of a positioning table need to be thoroughly reviewed in order to select the proper table for a given application. This includes capacities for bearings, drive mechanisms, and table structures. (See pages A-17 to A-27 of the Positioning Systems catalog)
- Maximum Speed of a positioning table sometimes depends on the bearing components and sometimes depends on the drive mechanism. (See page A-28 of the Positioning Systems catalog)
- Acceleration & Thrust Forces are parameters that can put extra stresses on positioning table components in certain situations. (See page A-29 of the Positioning Systems catalog)
- Accuracy & Repeatability are two of the most misunderstood parameters when selecting a positioning table. By determining what it is you really need, will help you select a cost effective positioning system. (See pages A-30 to A-33 of the Positioning Systems catalog)
- Table Physical Size (See page A-34 of the Positioning Systems catalog)
- Lubrication (See page A-35 of the Positioning Systems catalog)
- Mounting Considerations (See page A-36 of the Positioning Systems catalog)
- Motor Couplings (See page A-37 of the Positioning Systems catalog)
- EOT (end of travel) & Home Switches (See page A-38 of the Positioning Systems catalog)
- Encoders (See page A-39 of the Positioning Systems catalog)
- Power-off Brakes (See page A-40 of the Positioning Systems catalog)
- Multi-Axis Systems (See page A-41 of the Positioning Systems catalog)
- Environments (See page A-42 of the Positioning Systems catalog)
- Testing (See page A-43 of the Positioning Systems catalog)
- Custom Systems (See page A-44 of the Positioning Systems catalog)
- Application Guide (See page A-45 of the Positioning Systems catalog)
- Motor Sizing (See pages A-46 to A-49 of the Positioning Systems catalog)
What kind of Positioning System do I need?
There are several different mechanical devices that can be chosen for a given motion control positioning application. These devices can have differences in the load carrying components, drive mechanisms, support structures, physical construction, along with numerous other options. All these parameters lead into a mechanical device that has certain performance specifications. Before selecting a mechanical device, one needs to understand these performance specifications, along with the pro’s & con’s of each mechanical device & its options.
Linear Positioning Systems consist of many different types of mechanical positioning devices. We are limiting our discussion here to electromechanical devices. Some of these devices are more suited to generate thrust forces, while other devices are more suited to position a load accurately & repeatedly.
Actuators (electric cylinders) are mainly thrust producing devices. These devices use either an acme or ball screw as the driving mechanism with the screw mounted in a rigid-free arrangement. Any moment or side load needs to be properly supported by a separate mechanical structure. From a positioning standpoint these actuators are neither highly accurate, nor repeatable.
Rodless Actuators are also mainly thrust producing devices. However, because of their design, they can be used in some positioning applications. These devices use either an acme screw, ball screw, or a belt as the driving mechanism. These devices have both ends of the driving mechanism supported, therefore longer travels and higher speeds are attainable. The carriage for the user load is mounted to some kind of linear bearing system, thus allowing for small side loads. Nylon bushings, plastic bearings, rollers, wheels, round or square rails are typically used for the linear bearing system. From a positioning standpoint these devices are not highly accurate, however they can be very repeatable.
Screw Driven Positioning Tables are typically used in applications where accuracy & repeatability are more important than axial thrust forces. The base, carriage, and all critical components are precision machined which contribute to the accuracy and repeatability of the system. These positioning tables use either an acme or ball screw as the driving mechanism. Ball & rod, cross roller, round rail, or square rail linear bearings are used to carry the user load. These linear bearing designs allow the user load to be positioned very accurately & repeatedly.
Belt Driven Positioning Tables are typically used in high speed (and/or long travel) positioning applications where a screw driven table is not applicable. The belt & pulley drive mechanism, along with either round rail or square rail linear bearings, provide a repeatable, high speed positioning table. These tables provide the same speed capability independent of travel length. Using a high quality belt, pulley, and linear bearing mechanism provides a fairly accurate & repeatable positioning table.
High Accuracy Positioning Tables are typically used in applications where high accuracy and repeatability are very important. All components are machined to very tight tolerances in order to achieve the required accuracy and repeatability. Precision ground acme screws, precision ground ball screws, or brushless linear motors are typically used as the driving mechanisms. Precision ground cross roller, ultra-high accuracy square rail, or air bearings are mainly used for the linear bearings. The combination of these precision components produces a very smooth operating table. Granite or a precision machined steel plate is typically used for the table mounting surface. Temperature controlled environment, machine shock absorbers, and high resolution linear encoders are also usually required in order to obtain the system accuracy and repeatability. All this comes at an increase to the overall positioning system cost.
Rotary Positioning Systems consist of mainly three different major designs to choose from. These are mechanical tables, direct drive tables, and rotary positioning tables.
Mechanical (air actuated) rotary tables are inexpensive devices that rotate to a finite number of locations. You typically cannot change their resolution and over time the repeatability can, and usually will change. Load capacities are typically large and these tables are very durable. However, an air source is required to operate the tables.
Direct Driven Rotary Devices have a built in brushless motor that turns the table top. Key benefits include high accuracy and torque in a package that does not have a gear reducer. Thus, there is little concern over mechanical wear of a gear reducer. The key disadvantages include high system cost, a tall table package, and the requirement of using a specific motor control system, one designed for that rotary table device.
Rotary Positioning Tables use a precision machined worm gear assembly and either ball, cross roller, or angular contact bearings to support the table top load. Different gear ratios allow for either high resolution or high speed in a low profile package. The use of any step motor, or servo motor system to drive this rotary table is a key advantage. This allows the use of a preferred motion control system.
Linear Bearings and Ball Screws:
Lintech manufactures a wide range of linear and rotary mechanical positioning motion control products, from profile rail linear guides to round rail linear bearings. We offer linear components to completely pre-engineered positioning actuators, slides, stages and tables. We also have rolled, precision rolled, and precision ground ball screw assemblies available in any length required for an application.
Motorized Linear Slides, Rotary Stages and Custom Motion Systems:
Two different rotary positioning stages are available with several different worm gear ratios. One has a load capacity of 100 pounds, while the other has a 1,000 pound load capacity with a large through hole that can accommodate user electrical or pneumatic cabling. Our standard linear positioning slides come with numerous ball screw options for different leads, diameters, and lengths. We also offer with these linear slides many different motor adapter plates, end of travel switches, home switches, rotary encoders, linear encoders, and cover plate options. If a standard positioning table is not available to meet the application requirements, Lintech has the experience and engineering staff to design a custom mechanical positioning system to meet the expectations for the application.
Catalogs pertaining to the categories above can be downloaded by clicking catalog download.
Lower capacity – Lintech offers a large selection of belt driven linear positioning actuators, slides, stages and tables. The 140 series is our smallest linear belt slide at only 2.875 inches wide with a height of 2.375 inches but is available in travel lengths out to 120 inches. This linear stage, just like all of our systems, has numerous options available for the customer to choose from in order to make a particular linear actuator fit a set of specific requirements. The 140 series has top and side cover plate options, motor or gear head adapter plate options, 11 different end of travel and home switch options, rotary encoder options, brake options, and can be supplied with either English or metric load mounting inserts. The 120 series linear actuator has all of the same options available as the 140 series, but has a larger load capacity and thus a longer potential life when moving a user load in an application.
Higher capacity – The 180 series is the most versatile and most popular linear belt table from Lintech as it can handle large load capacities and has either a 6 or 12 inch carriage length option, is available with a top cover plate, side cover plates, or waycovers to choose from. The 550 series linear belt tables have several different high load capacity carriages that can move a load up to a distance of 360 inches or 30 feet. Below is an overview of the belt drives and some basic differences.