DirectLOGIC Motion Control: Position of a Part on a Conveyor (Part 3 of 8) from AutomationDirect

In the following video I will cover some of the typical Motion Control applications that are used with stepping systems, and then explain the hardware for the linear slide application I am using for the video series demonstration. One of the most popular applications using a stepping system for Motion Control involves converting a stepping motor’s rotary motion into linear motion. This is accomplished with the use of a leadscrew. As the leadscrew rotates, a matched threaded nut, that is mechanically adapted to a slide mechanism, moves the slide along guides. The slide usually rides on two rods with rotating ball bearings attached to the slide. This arrangement provides the mechanical translation from rotary to linear motion. The slide is moved from position to position, as needed, to perform the work or sequences the process requires. The number of threads per inch, or pitch, determines the distance the slide mechanism will travel. For example, if we use a lead screw with 10 threads per inch, then one revolution of the attached stepping motor will cause the lead screw to produce 0.100 inches of travel. Let’s call it a tenth of an inch of travel. Using a stepper motor to drive a conveyor belt is another typical application. In this type of application we would be able to precisely control the position of a part on the conveyor, stop the part at various positions, back the belt up if the process required a second look be taken, such as a visual inspection, and then either move the part to an acceptance area, or possibly stop it a short distance from the inspection point, and then eject it into a rejection bin. The part’s position on the conveyor could be altered on the fly to suit changing conditions. Complex movements can also be handled with a stepping motor driving a conveyor. Different speed rates can be programmed, along with various acceleration and deceleration times, synchronizing with other devices in the process. A stepper motor coupled to a rotary table provides a simple method for indexing a table into precise locations. This type of application is ideal for assembly machines that may have multiple locations where various steps or operations are preformed. The use of a stepper motor can provide excellent repeatability between the various stations on an assembly machine. The same locations can be accurately returned to with each move. Another great benefit of using a stepper motor for this type of applications, and others, is the stepper motor cannot be damaged by mechanical overload. I chose a linear leadscrew slide driven with a SureStep stepper motor as my demonstration for this video series. The linear slide has a total travel distance of 300 millimeters, or approximately 11 and 3/4 inches if you prefer. The linear slide includes a mounting adapter that can accept a NEMA 23 frame size. The slide also includes a shaft coupler that matches the lead screw’s shaft diameter to the stepper motor's shaft diameter. The leadscrew on the slide has eight threads per inch. This means the slide will move a total of one inch for eight full revolutions of the leadscrew. In general practice, inch based leadscrews are defined in terms of Threads per Inch, abbreviated as TPI. Metric leadscrew threads are generally defined by ‘Pitch’. Without trying to be too confusing, I could say my slide leadscrew has a ‘Pitch’ of 1/8 inch or 0.125 inches. What does this mean? The slide can move a distance of 0.125 inches for every revolution of the stepping motor. Based on the 2,000 micro stepping steps per revolution I will use from the SureStep drive, my slide will move 0.0000625 inches per step! In Part Four, I will cover the wiring of the Motion Control demonstration, show how to configure the CTRIO module’s jumpers, and then show how to set the STP-DRV-4035 drive’s DIP switch parameters to match my application selections. Motion Control – VID: L-PC-DL-STP-001-3 Part 3 of 8 – Typical Stepping System Applications & Demo Linear Slide Hardware 0 2