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Ball Screw Assembly Handling, Installation Tips, Mounting & Alignment

January 15, 2018

Lintech provides Service Manuals for the components and complete linear motion systems manufactured. There are some very helpful tools within the manuals. A critical process for putting a linear motion system together using individual components is the proper alignment of the screw and linear rails. If misalignment between these components is present in a linear motion, it could result in extreme overloading, high heat, increased torque/motor stalling, etc.

Attached is a segment from the Positioning Components Installation & Service Manual. There is a separate manual for the Systems which include screw driven & belt driven tables.

Ball Screw Assembly Tips and Installation

If you have questions about a particular application, please contact Lintech.

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Motion Control “Accuracy” Considerations

January 3, 2018

There are some important terms pertaining to motion control positioning which sometimes get lumped together under the term accuracy.

Accuracy versus Repeatability:

Accuracy & Repeatability

Quite often, applications require good repeatability more than accuracy.

Accuracy is described as how well a positioning system makes a true relative move in reference to an absolute 3D location. In essence, if we lived in a perfect world, when a positioning system makes a 1.0 inch (25.4 mm) move, it truly moves 1.0 inches (25.4 mm). However, there are mechanical errors associated with every positioning system. These errors will cause the positioning system to be less than perfect when making moves. Move distances that will be something different than what were truly desired.

For whatever reason, sometimes specific applications may require more emphasis on “characteristics” of the accuracy within the overall move.

Yaw, Pitch, Roll, Flatness & Straightness.jpg

Linear bearing & structure inaccuracies will cause a positioning system to move something other than what is desired. LINTECH includes these errors in the overall “Position Accuracy” value described on the website and in catalogs. LINTECH also provides flatness & straightness specifications for each table series. These values can be used as a general gauge to the overall linear bearing & structural quality of a positioning table. The better these values are, results in better accuracy & repeatability of the positioning table.

Linear bearing & structure inaccuracies include:

  • angular (roll, pitch, & yaw)
  • vertical runout (flatness)
  • horizontal runout (straightness)

Some of the sources of these errors are:

  • straightness of the linear rail
  • entry & exit of recirculating balls in the linear bearings
  • variation of the preload when moving along the rails
  • contaminants between linear bearings & rails
  • machining of the rail mounting surface on the table
  • machining of the base, carriage, and other components

Inaccuracies in the linear drive mechanism of a positioning table also contribute to its overall position accuracy. LINTECH provides acme screw, ball screw, and belt driven linear positioning tables.

Linear drive mechanism sources of errors include:

  • lead error of the screw
  • end support mounting of the screw
  • nut and screw quality & wear
  • lead error of the belt
  • belt stretch
  • end pulley quality & alignment

So, it is important to consider what move characteristics are most important to the performance of each application and maybe also to clarify what is undesirable for the application in order to consider the most suitable components.

For more information on component choices, contact Lintech.

Application Example: Matching a Motor with a 180 Series Lintech BELT DRIVE Table to Meet a Performance Requirement

December 15, 2017

Let’s say that the determination has been made that the Lintech 180 series table 18412054-CP0-1-D1-M04-C130-L04-E00-B00 is suitable to perform the mechanical task for an application.

  • 18612054 – 11,670lb dynamic horizontal capacity rating for 50km of travel life, 54” of travel capability.
  • CP0 – No top or side cover plates necessary.
  • 1 – English mount inserts in the carriage for mounting the load.
  • D1 – Drive shaft/right hand single shaft
  • M04 – NEMA 34(English interface) motor mount adapter.
  • C157 – “H” type, 3 member clamp style design coupling. Bores of .375”(table side) and .500”(motor side).
  • L04 – “Reed” End-of-travel & home switches.
  • E00 – No linear or rotary encoder mounted directly on the table.
  • B00 – No “power-off” brake mounted directly to the table.

The table selection process has been omitted for our purposes. Naturally, careful thought goes into selecting the part number such that the table will meet the accuracy, load/life, environmental, and overall performance necessary for the application.

Having determined the appropriate table for the mechanical specifications, a motor package needs to be chosen which will move the application load in the desired time frame. There are many motor sizing programs available which assist with calculations. However, they require some information about the drive mechanism (belt drive in this case), load, orientation of load, speed and start/stop times.

For the 180 series table, the belt/pulley information below is found on the website (lintechmotion.com).

Pulley Weight: 0.39lbs.

Pulley Diameter: 1.128 Inches

Number of Pulleys: 2

Belt weight for 54” Travel Unit: 15.8 Ounces

Breakaway Torque: < .75 oz.-in

Friction Coefficient: < .01

Load Weight: ?

Load Angle: ?

Motor Inertia: ?

Maximum Speed Desired: ?

Move Distance: ?

Acceleration Time: ?

Now, some information from the application is needed to answer the items with a “?” above. So, some assumptions will be created for this fictitious application.

Load: 80lbs.

Load Angle: Horizontal motion – “0” angle

Maximum Speed: 20”/second

Move Distance 49”

Acceleration Time: .5 seconds adequate time to get to 20”/second

At this point, the belt specifics and application requirements can be plugged into any sizing software program to determine the basic torque requirement and motor speed. However, before searching for a motor having the required torque at that motor speed, it may be a good time to step back and consider “potential” application variables. For instance, should there be a safety factor built in so the motor is not required to perform at its highest torque capability? Is there a chance that at some point down the road, the load, speed, or some other application change could occur? By the same token, having too much of a safety factor might mean that the resulting motor selection is too large and/or expensive. The safety factor chosen should be somewhat application driven. Typically, Lintech would suggest a safety factor between 25% – 100%. A 50% safety factor will be used for this fictitious application.

So, by using a 50% safety margin in the software being used in this example, the torque total maximum to move the load horizontally at 20”/second is calculated to be 237.47 oz.-in.(different software programs will calculate slightly different results). The program also calculates that the motor needs to be able to have this minimum torque available at 338.62 rpm to achieve the application linear speed. Now that the torque and motor speed have been determined while considering a safety margin, the search for a capable motor begins.

When sizing a motor to an application load and speed, it is generally assumed that an inertia ratio of less than 10:1(load:motor) is needed to perform properly. However, obtaining the 10:1 ratio often requires belt driven applications to utilize a gearhead in order to meet the ratio between the load and the motor. If a gearhead is necessary, it is best to utilize the lowest ratio which will comply with the inertia ratio target of within 10:1. The reason is that a higher gearhead ratio equals a higher motor speed to achieve the application requirement. If the motor speed requirement gets too high, motor “options” may become reduced.

It is assumed for these purposes that the choice of servo or stepper has been made along with the desired feedback, control capabilities, budget, physical size available, etc. So, the focus here is to find a motor with a suitable torque curve.

So, an inertia ratio of 10:1 will be used for the load:motor in addition to the motor having a torque curve which obviously reflects the power to move the load at the desired speed.

34HC-1 Torque Curve

Working through the sizing program, the motor above was selected. In order to meet the inertia goal, a 3:1 gearhead was incorporated with a NEMA 34 frame motor having a rotor inertia of 7.8 oz-in squared. The 3:1 gearhead reduced the torque required to 93.35 oz-in but it also tripled the motor speed necessary to reach 20 linear inches per second. Therefore, the selection required a motor to have at least 93.35 oz-in of torque at 1015.88 rpm. The red line in the graph represents about 1015.88 rpm. The different dotted lines in the graph also indicate that any of the acceptable voltages of 12, 24, 36 or 48v would offer the necessary torque at the target speed. The sizing program indicates that the inertia ratio of the load to the motor chosen is 5.92:1 which is within the 10:1 goal.

If you have more questions regarding motor sizing or would like assistance, please contact Lintech.

Application Example: Matching a Motor with a 170 Series Lintech Table to Meet a Performance Requirement

December 1, 2017

Let’s say that the determination has been made that the Lintech 170 series table 174624-CP0-1-S115-M02-C435-L01-E00-B00 is suitable to perform the mechanical task for an application.

  • 174624 – 7,7800lb dynamic horizontal capacity rating for 50km of travel life, 24” of travel capability.
  • CP0 – No top or side cover plates necessary.
  • 1 – English mount inserts in the carriage for mounting the load.
  • S115 – Precision ball screw .625” diameter x .20” lead with preloaded nut for zero backlash.
  • M02 – NEMA 23(English interface) motor mount adapter.
  • C435 – “G” type, low wind up, high torque, clamp style bellows coupling. Bores of .375”(table side) and .250”(motor side).
  • L01 – Mechanical End-of-travel & home switches.
  • E00 – No linear or rotary encoder mounted directly on the table.
  • B00 – No “power-off” brake mounted directly to the table.

The table selection process has been omitted for our purposes. Naturally, careful thought goes into selecting the part number such that the table will meet the accuracy, load/life, environmental, and overall performance necessary for the application.

Having determined the appropriate table for the mechanical specifications, a motor package needs to be selected which will move the application load in the desired time frame. There are many motor sizing programs available which assist with calculations. However, they require some information about the drive mechanism (ball screw in this case), load, orientation of load, speed and start/stop times.

For the 170 series table, the screw information below is found on the website (lintechmotion.com).

Screw Lead: 0.2”

Screw Diameter: 0.625”

Screw Overall Length: 34”

Screw Efficiency: 90%

Breakaway Torque: 20 oz.-in

Friction Coefficient: .01

Load Weight: ?

Load Angle: ?

Motor Inertia: ?

Maximum Speed Desired: ?

Move Distance: ?

Acceleration Time: ?

Now, some information from the application is needed to answer the items with a “?” above. So, some assumptions will be created for this fictitious application.

Load: 80lbs.

Load Angle: Horizontal motion – “0” angle

Maximum Speed: 5”/second

Move Distance 20”

Acceleration Time: .5 seconds adequate time to get to 5”/second

At this point the screw specifics and application requirements can be plugged into any sizing software program to obtain the basic torque requirement and motor speed. However, before searching for a motor having the required torque at that motor speed, it may be a good time to step back and consider “potential” application variables. For instance, should there be a safety factor built in so the motor is not required to perform at its highest torque capability? Is there a chance that at some point down the road, the load, speed, or some other application change could occur? By the same token, having too much of a safety factor might mean that the resulting motor selection is too large and/or expensive. The safety factor chosen should be somewhat application driven. Typically, Lintech would suggest a safety factor between 25% – 100%. A 50% safety factor will be used for this fictitious application.

So, by using a 50% safety margin in the software being used in this example, the torque total maximum to move the load horizontally at 5”/second is calculated to be 35.22 oz.-in. The program also calculates that the motor needs to be able to have this minimum torque available at 1500rpm to achieve the application linear speed. Now that the torque and motor speed have been determined while considering a safety margin, the search for a capable motor begins.

It is assumed for these purposes that the choice of servo or stepper has been made along with the desired feedback, control capabilities, budget, physical size available, etc. So, the focus here is to find a motor with a suitable torque curve.

X23C-1 Torque Curve

The torque curve above represents a specific motor that has at least 35 oz.-in of torque at 1500rpm as long as there is a minimum of 24 volts of input power. The motor in this case also has a rotor inertia value of 0.82 oz.-in squared (found in specifications). Typically, an inertia ratio between the rotor and load net (includes the effect of rotating parts and screw lead) is less than 10:1. This means that generally, the net load should not be more than 10X heavier than the rotor weight to get acceptable operational performance.

In the example above, if there was only 12v of power available the motor would not have enough power to move the load adequately or achieve the desired speed requirement.

If you have more questions regarding motor sizing or would like assistance, please contact Lintech at Lintechmotion.com.

Rotary Positioning Stages

November 15, 2017

Lintech’s Rotary Positioning Actuator Products:

Lintech has available two different high precision worm gear driven rotary positioning stages. One works well for light load applications, while the other positioning table is ideal for heavy load requirements.

300-blue-100Rotary Table - 400

 

 

 

 

 

 

Mechanical Rotary Table Configurations:

The 300 series rotary stage has a load capacity of 200 pounds, less than 150 arc-seconds of accuracy, and with worm gear ratios of 45:1, 90:1, and 180:1. This low cost rotary table is ideal for those applications requiring precise positioning using a servo or step motor system and is available with a 6, 8, 10, or 12 inch table top. Lintech has motor adapter brackets which can be used to connect any inch or metric motor to this rotary actuator. The 400 series rotary table is a heavy duty rotary positioning stage that has a load capacity of 1,000 pounds. It has a similar worm gear drive system with gear ratios of 30:1, 90:1, 180:1, 270:1 and 360:1. The large 225 ft-lbs of moment load capacity also makes this rotary positioning actuator ideal candidate for those applications that require both precise 360 degree positioning by a motor drive system along with the need to move a very heavy, off balance load. The motor mount for this 400 series rotary actuator is unique in that it can be rotated anywhere in a 360 degree plane, thus allowing the motor to be positioned in a place out of the way from other machine components. The large 4.5 inch through hole allows electrical cabling, pneumatic tubing, or other critical machine components to run directly through the stage.

170 Series Loading Capabilities

October 30, 2017

Some of the linear tables manufactured by Lintech have, as a standard option, the ability to choose the carriage length. The carriage is the portion of the linear table that moves on the linear guides as the screw or belt is driven. Having a longer carriage enables the bearing blocks to be spaced further apart and the ability to add more bearings under the carriage. This kind of flexibility results in a linear table that is capable of more demanding operating conditions. To see all of the standard options on Lintech tables, go to LintechMotion.com.Carriage Length

Precision Linear Shafting & Bushings

October 16, 2017

Lintech offers precision shafting used for linear motion. There are many variations offered to meet requirements such as metric, pre-drilled, custom machining, stainless or plated.

Precision Linear ShaftingRound Rail Pillow BlocksP_BearingsP_TRSA

Lintech has been providing linear shafting for decades and is also well suited to configure these components into a fully operational motion system complete with motors, controls, and programming. Of course, the precision shafting works in conjunction with ball bushings which are available in many configurations as well.

Precision shafting/bushings are great for applications requiring low torque, free rolling, and smooth motion. This type of linear motion product is also less complicated to align and therefore, less likely to “bind” during a move.

Lintech maintains significant stock levels on shafting and bushing types. All machining is done in southern California. In addition, the prices offered are extremely competitive.

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