Lead is the axial distance the nut advances over one revolution of the screw. Throughout this catalog, lead will be the term used for the linear distance traveled over one revolution of the screw.
The larger the lead, the greater the linear distance travelled per one revolution of the screw. Lead = Pitch x number of screw starts.
Pitch is the axial distance between threads.
Pitch is equal to lead in a single start screw. There may be more than one thread “strand”on a single screw. These are called starts.
Lead screws with multiple starts are usually more stable and efficient at power transmission.
Specified as a measurement over a given length of the screw.
For example: 0.004 inch per foot.
Lead accuracy is the difference between the actual distance travelled versus the theoretical distance travelled based on the lead.
For example: A screw with a 0.5 inch lead and 0.004 inch per foot lead accuracy rotated 24 times theoretically moves the nut 12 inches.
However, with a lead accuracy of 0.004 inch per foot, actual travel could be from 11.996 to 12.004 inches.
Vertical orientation applications add the potential problem of backdriving when power to the motor is off and without an installed brake.
Vertical application also have an additional gravity factor that must be part of the load/force calculation.
The hybrid stepper motor’s resonance will be occurred when pulse is up to 200PPS.
Try starting your acceleration ramp at above these levels. Micro-stepping will also help through these ranges.
Stepper motors require some external electrical components in order to run. These components typically include a power supply, logic sequencer, switching components and a clock pulse source to determine the step rate.
Many commercially available drives have integrated these components into a complete package.
Very basic stepper drivers have various functions and it can generate high performances. DINGS' already has wide range of driving part so please consider to take and use.
A load that tends to stretch the screw is called a tension load.
A load that tends to “squeeze” or compress the screw is called a compression load.
Depending on the size of the load, designing the screw in tension utilizes the axial strength of the screw versus column loading.
A load perpendicular to the screw.
This is not recommended unless additional mechanical support such as a linear guide is used.
A load that exerted at the center line of the lead screw.
Backdriving is the result of the load pushing axially on the screw or nut to create rotary motion. Generally, a nut with an efficiency greater than 50% will have a tendency to backdrive.
Selecting a lead screw with an efficiency below 35% may prevent backdriving. The smaller the lead, the less chance for backdriving or free wheeling.
Vertical applications are more prone to backdriving due to gravity.
The required motor torque to drive just the lead screw assembly is the total of:
Standard metric or English options are available.
Custom end machining specifications are also available upon request. Please contact your local DINGS' representative.
The performance (speed and efficiency) of the screw system is affected by how the screw ends are attached and supported.
|Type of End Fixity||Relative Rigidity||Critical Speed Factor||Critical Load Factor|
Critical speed is the rotational speed of the screw at which the first harmonic of resonance is reached due to deflection of the screw. A system will vibrate and become unstable at these speeds.
Several variables affect how quickly the system will reach critical speed:
An example in the figure, it shows the screw rod with a diameter of 19.05mm (0.75inch) and a length of 1778mm (70inch) has a safety factor of K = 1.25,And under the fixed mode of FS = 0.32, the critical speed is 187rpm.
Backlash is the relative axial movement between a screw and nut at standstill. It is normal for backlash to increase with wear over time.
Backlash compensation or correction can be accomplished through the application or an anti-backlash nut.
Backlash is usually only a concern with bi-directional positioning.