Patent GB-942171-A (GB)
Title: Rotor excited stepper motor
Inventor: WELCH ELVIN CARL
IPC: H02K37/00
Filed: 1961-10-27
Abstract: 942,171. Electric motors. AUTOMATION DEVELOPMENT CORPORATION. Oct. 27, 1961, No. 38555/61. Heading H2A. A stepper motor comprises stator windings for establishing a stator magnetic field in one direction, control means switching between first and second conditions in response to electrical pulses, a rotor having rotor windings connected to the control means for establishing a rotor magnetic field in response to the first condition of the control means and in a reverse direction in response to the second condition of the control means, motion initiating means responsive to the pulses and input means for passing the electrical pulses to the control means and the motion initiating means. In a 180 degrees stepper motor pulse input terminals 10, 11 are connected through a selecting circuit 22 to a bi-stable circuit 24, the two sides of which, A, B, are connected respectively through two slip rings 27, 28, mounted for rotation on and with the motor shaft S, to a split rotor coil having sides A<SP>1</SP>, B<SP>1</SP> and including a centre tap lead 31 connected to a third slip ring 32 engaged by brush 33 providing voltage from a battery 34. The stator windings 36, 37 are connected in series with battery 34 and at right angles to motion initiating windings 18, 19 connected to the input terminals 10, 11 by conductors 16, 17 respectively. At time T 1 , Fig. 2, the bi-stable circuit 24 is in its first state, i.e. side A conducting and side B non-conducting, so that the rotor winding A<SP>1</SP> is energized and the rotor aligns itself in the direction of the stator winding field 36, 37 as shown. When a pulse is applied to terminal 10 at time T 2  the bi-stable circuit 24 is switched to its second state so that the curront in the rotor winding now flows through the part B<SP>1</SP> and the rotor field is reversed. Simultaneously coil 18 is energized by the pulse so that its field is established at right angles to the steady magnetic field of the stator windings 36, 37; the resultant magnetic field from these two stator fields initiating motion of the rotor in an anti-clockwise direction. After the pulse has finished the rotor will come to rest in the position as shown at time T 3  and remains there until the next pulse is applied at T 4  when the winding 18 is again energized for the duration of the pulse and the bi-stable circuit is switched back to the original state at time T 1  so that the rotor winding field is again reversed. The resultant stator magnetic field will again cause the rotor to commence rotating until it is in the position of T 1  again. The rotor can be caused to rotate in a clockwise direction by applying the pulses to terminal 11 instead of terminal 10. In a modification, the rotor can be made to step in alternate steps of 45 degrees and 135 degrees, Fig. 3 (not shown), by applying square wave pulses to lines 16 or 17; the operation being similar to that of Fig. 2 except that as a consequence of the square pulses the coil 18 will be energized for a finite length of time to establish a resultant stator field at 225 degrees. In consequence, the rotor will assume this position until cessation of the square wave at which time it will then step through the remaining 45 degrees or 135 degrees and the case may be, to align vertically with the field established by windings 36, 37.