Basic stepper motors revolve by means of a magnetic rotor core that interacts with the pulsating electromagnetic field generated by the stator. Linear motors convert rotary motion into linear motion by combining a screw and a nut. Power screws are often perceived as being simple to operate, but making them appear easy is the result of thorough mechanical analysis and design, along with the appropriate selection of the proper components.
Classification of screw
There are two main types of power screws: ball screws, which operate on rolling contact, and lead screws, which operate on sliding contact.The ball screw assembly is typically made of carbon steel or stainless steel, with a recirculating ball bearing that rolls along helical grooves in the screw and nut. Thus, the nut can move along the screw without encountering sliding friction.Typically, sliding contact assemblies use nuts that are internally lubricated or made from bearing-grade bronze. Plastic nuts are generally mounted on stainless steel screws, while bronze nuts are mounted on carbon steel screws; stainless steel screws can also be used if the nut is a medium-grade bronze.
Which screw to choose?
Based on some common design parameters, it is possible to summarize the advantages of each screw type.A top priority is often given to load capacity. In general, ball screws are capable of achieving equal or greater loading than comparable lead screws.Lead screw load capacity is greatly affected by the choice of nut material. While bronze nuts are capable of carrying considerable weight, depending on their grade, plastic nuts are typically used for loads of 100 pounds or less, though they can be designed for loads of 300 pounds or more.A power screw's material and style may be affected by the operating environment. Carbon steel ball screws (a common choice) may be sensitive to certain corrosive environments when they are made of carbon steel.A lead screw is typically configured with a stainless steel screw and plastic nut, or with a stainless steel screw and bronze nut. Bronze nuts of medium grade (and medium capacity) can be used with stainless steel screws as well as carbon steel screws. However, the heavy grease used with bronze nut assemblies is effective against corrosion whether the screw is stainless steel or not.The stainless steel and plastic combination, which does not require lubrication, is highly corrosion resistant regardless of the conditions, withstanding clean rooms, outdoor moisture, etc. The situation is different when it comes to temperature. The plastic nut may be limited to temperatures between 30°F and 120°F.