The SLO-SYN Stepping Motor

The SLO-SYN stepper motor provides continuous holding power of machine table lead screw and when rotating, it provides driving torque for a machine table lead screw in either direction of rotation.

The SLO-SYN N/C positions the machine table by precisely controlling the SLO-SYN Precision Stepping Motors that drive the lead screws. In effect the stepping motor is an electronically controlled device that replaces the manually turned lead screw crank. It represents the power pack that moves the machine table to predescribed locations with speed and accuracy.

Motor Construction

Above an image of the construction of a stepping motor. Please note that this image is actual from a synchronuous motor, but the construnction principle is exactly the same as a stepping motor, the only difference is the windings.

The parts

• Nameplate, often fixed with three small screws
• The terminal plate for the connection. In this case there are three terminals and three wires
• Rear end bell with the four mounting screws
• A shim washer, to reduce the axial play of the rotor
• The rotor with the two ball bearings
• The stator with the windings, this is one part
• The Front bell
• The four nuts for the mounting screws

Note that this motor does not contain brushes, slip rings, or any other commutating devices. Stepping action results from the magnetic attraction and repulsion of the stator and rotor members. The rotor sections are of a fixed magnetic polarity determined by a captivated permanent magnet. Drive circuit switching changes the polarity of the stator poles, energizing the motor to move one step into the new position of maximum magnetic attraction. The drive circuit then maintains this new polarized condition. The motor thus provides either continual holding power or driving torque.

The cross-section model of a stepping motor shown has stator teeth cut into the eight pole pieces at a 48 tooth pitch. The rotor has 50 teeth. The vernier relationship created between the rotor and stator members in combination with the magnetic drive circuit results in a shaft rotation of 1.8 degrees. This amount of shaft rotation is known as a step. There are 200 of these steps for each complete revolution of the shaft.

When the shaft is connected to a lead screw on a table this rotary motion is changed to linear motion. When the motor shaft turns one step or 1/200 revolution, the lead screw turns 1/200 revolution, and of course, 200 steps of the motor revolve the shaft one complete revolution. Even though several motor steps have been made to accomplish one revolution of the shaft, no error has accumulated. The accuracy at any point is +- 0.09 degrees of the desired shaft position and is non cumulative.

Most machine tables are equipped with five-pitch lead screws. Five revolutions are necessary to move the table one inch. Thus one inch of table travel is accomplished by 1000 steps of the stepping motor. Similarly, a travel of 0.001 inch is obtained with only one step of the stepping motor. The required table motion in inches, therefore, can easily be converted into the number of motor steps required to produce that motion by simply moving the decimal point. For example, a table motion of 8.750 inches requires 8750 motor steps.