A stepping motor has a cylindrical case that houses a motor stator and a sensor stator. The motor stator and the sensor stator are located at the opposing ends of the case. A motor rotor and a sensor rotor are mounted on a shaft and face the motor stator and the sensor stator, respectively. The sensor rotor and the sensor stator together form a rotational position sensor. The incorporation of the rotational position sensor in the case reduces demand for installation space. The gap of approximately 40 to 50 microns between a motor stator core and motor rotor cores is achieved by accurately locating the motor stator and the motor rotor. The case is sealed by the front flange and the rear cover, thereby, unfailingly preventing the invasion of contaminating foreign matter such as dust particles, oil, moisture etc.
1. A stepping motor comprising:
a case having a first end and a second end;
a motor stator located at the first end of the case;
a motor rotor facing the motor stator;
a stage formed in the case;
a protrusion formed in the case, the protrusion and the stage together accurately locating the motor stator with respect to the motor rotor;
a sensor stator located at the second end of the case;
a sensor rotor facing the sensor stator;
a shaft rotatably mounted in the case, the shaft having the motor rotor and sensor rotor mounted on it;
a first cover mounted on the first end; and
a second cover mounted on the second end.
2. The stepping motor of claim 1 , further comprising:
a first spigot, the first spigot being integral with the first cover;
a second spigot located between the motor stator and the sensor stator;
a first bearing mounted in the first spigot; and
a second bearing mounted in the second spigot; wherein
the shaft is supported in the first bearing and the second bearing, and wherein the internal perimeter of the motor stator contacts the first spigot and the second spigot, and the internal perimeter of the sensor stator contacts the second spigot.
3. The stepping motor of claim 1 , further comprising:
a connector mounted on a side of the case, the connector being connected to at lest one of the motor stator and the sensor stator.
4. The stepping motor of claim 1 , wherein the gap between the motor stator and the motor rotor is in the range of 40 to 50 microns.
5. The stepping motor of claim 1 , wherein the gap between the sensor stator and the sensor rotor is in the range of 100 to 150 microns.
6. The stepping motor of claim 1 , further comprising:
a first seal formed between the first cover and the case; and
a second seal formed between the second cover and the case.
7. The stepping motor of claim 6 wherein the first seal and the second seal are formed by o-rings.
8. A stepping motor comprising:
a case having a first end and a second end;
a motor stator located at the first end of the case;
a sensor stator located at the second end of the case;
a motor rotor facing the motor stator;
a sensor rotor facing the sensor stator;
a shaft rotatably mounted in the case, the shaft having the motor rotor and sensor rotor mounted on it;
a first cover mounted on the first end; and
a second cover mounted on the second end.
9. The stepping motor of claim 8 , further comprising:
a first spigot, the first spigot being integral with the first cover;
a second spigot located between the motor stator and the sensor stator;
a first bearing mounted in the first spigot; and
a second bearing mounted in the second spigot; wherein
the shaft is supported in the first bearing and the second bearing, and wherein the internal perimeter of the motor stator contacts the first spigot and the second spigot, and the internal perimeter of the sensor stator contacts the second spigot.
10. The stepping motor of claim 8 , further comprising:
a connector mounted on a side of the case, the connector being connected to at lest one of the motor stator and the sensor stator.
11. The stepping motor of claim 8 , wherein the gap between the motor stator and the motor rotor is in the range of 40 to 50 microns.
12. The stepping motor of claim 8 , wherein the gap between the sensor stator and the sensor rotor is in the range of 100 to 150 microns.
13. The stepping motor of claim 8 , further comprising:
a first seal formed between the first cover and the case; and
a second seal formed between the second cover and the case.
14. The stepping motor of claim 13 wherein the first seal and the second seal are formed by o-rings.