In the last several postings we saw how a ball screw changed the rotary motion of the stepper motor to linear motion. We calculated the rotational equivalent of a 200 pound linear load that was effectively reduced by the inverse square of the pitch or more accurately: J load = (W/P2)* 0.0253 where the J […]
Calculating Reflected Inertia for Linear Systems (cont.) Read More »
Review from last time In the last several postings we talked about ball screws and acme screws along with the advantages and disadvantages of both of them. In this posting we’ll get to calculate the inertia that this type of rotary-to-linear converter reflects back to the motor. Setting up the assumptions for the calculation We’re going to assume
Calculating Reflected Inertia for Linear Systems Read More »
Revisiting last time In our last posting we discussed the pros and cons of an acme screw. The self-locking characteristic was an important feature that prevented the load from being dropped when the servo amplifier tripped out from an over current condition. The good news was that the system didn’t need to run the test’s
An ACME screw story In our last posting we talked about the advantages and disadvantages of ball screws and ACME (lead) screws. In the next two postings I’ll share two stories, one about the Road Runner and the other about Wile E Coyote…If you’re just joining us and this makes little sense to you, you
In our last posting, we talked about the positional accuracy of a point of the moveable plate or work surface of our ball screw table with the terms roll, pitch, and yaw. The application that you’re trying to solve should be with the most cost-effective positioning solution.
ACME screws – a cost effective alternative to ball screws Read More »
Let’s start this discussion with the bearing supports for the ball screw. Let’s assume we have a ball screw that is 18” long and it provides 12” of travel. We have 3” on both ends that have been machined down past the root of the thread to form a smooth surface to install bearings that will support the screw. Let’s place the screw so it’s oriented left to right and our stepper motor and its coupling is on the left. We could install a number of bearing combinations on both ends of the ball screw that’s easier to define with a table:
In our last posting, we introduced leadscrews, ball screws and linear slides. We’re going to continue with that discussion by considering how accurately the threads are cut into the screw. Using the five-pitch screw as an example, we understand that five revolutions are supposed to move the plate one inch, but what happens if the thread is cut too long or too short. Five revolutions might move the plate 0.990” or 1.010”.
Linear Systems: Thread precision and mechanical backlash Read More »
With this posting, we’ll begin a discussion about leadscrew/ball screw/linear slide systems. Picture a screw with a nut on it. No, no not a Walnut. Sighhhh. OK then, picture a right-hand threaded 1/4-20 screw with a 1/4-20 nut threaded on to the screw. A 1/4-20 screw has an outside diameter or major diameter of 0.25” and the thread of the screw has 20 turns per inch.
Linear Systems: Lead screws, Ball screws and Linear Slides Read More »
