Portable laser scanning system and scanning methods

• US 4,496,831 A
• Filed: 11/16/1981
• Issued: 01/29/1985
• Est. Priority Date: 02/29/1980
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Harrison, Shelley A., Barkan, Edward, Swartz, Jerome
• Primary Examiner(s): Pitts, Harold I.
• Application Number:
  US06/321,934
• Time in Patent Office: 1,170 Days
• Field of Search: 235/472, 235/467, 350/6.6, 310/49
• US Class Current: 235/472.01
• CPC Class Codes: G06K 2207/1016 Motor control or optical moving unit control
• CPC Class Codes: G06K 7/10633 by oscillation
• CPC Class Codes: G06K 7/10881 constructional details of hand-held scanners

Abstract

An entirely field-portable laser scanning system for reading bar code symbols includes a light-weight and small-sized laser scanning head. The laser source, power supply component, optics, scanning elements, sensor circuit, and signal processing circuitry are specially designed for minimal size and weight and volume such that they can all be mounted in the head. The head can be bracket-mounted or hand-held. The housing for the head can be provided with a handle grip, or can be gun-shaped. High-speed oscillating scanning motors and/or penta-bimorph scanners are used as scanning elements. A trigger initiates repetitive scanning of each object bearing a symbol, and an indicator indicates when the scanning of that particular object has been terminated. A body harness supports the remaining scanner system circuitry. A non-bulky, freely-movable cable interconnects the head to the body harness. Methods of scanning the symbol and of operating the system are also disclosed.

Claims

1. A light-weight, high-speed, miniature scanning device for repetitively scanning light, comprising:

(a) a scanning motor having a stator, a rotor, and an elongated shaft operatively connected to the rotor for joint movement about an axis which extends along the elongation of the shaft;

(b) light-reflecting means mounted on the shaft for joint movement;

(c) means for magnetically generating a centering force which acts on the rotor to urge the shaft and light-reflecting means to a center position, said magnetically-generating means including means for establishing at the stator and the rotor respective magnetic fields which interact to cause the magnetic field of the rotor to align itself with the magnetic field of the stator; and

(d) motor control means for repetitively driving the shaft and light-reflecting means thereon in alternate circumferential directions about said axis to respective scan positions angularly spaced from said center position, said motor control means including means for electromagnetically moving the rotor against the action of the centering force in one circumferential direction about said axis over an arc length less than 360°

, and thereupon for electromagnetically moving the rotor against the action of the centering force in the opposite circumferential direction about said axis over an arc length less than 360°

.

2. The scanning device of claim 1, wherein the stator includes a pair of stator coil windings;

and wherein the rotor is constituted of a magnetizable material; and

wherein the establishing means includes means for applying a generally constant electrical signal to one of the stator windings to generate a first magnetic field, and means for magnetizing the rotor to generate a second magnetic field which interacts with said first magnetic field.

3. The scanning device of claim 2, wherein the rotor is a permanent magnet.

4. The scaning device of claim 2, wherein the motor control means includes means for applying a periodic electrical signal of time-varying amplitude to the other of the stator windings, said motor control means being operative to drive the shaft and light-reflecting means thereon to scan positions whose angular spacing from said center position is a function of the amplitude of the periodic signal, and at a speed which is a function of the rate of change of the periodic signal.

5. The scanning device of claim 4, wherein the motor control means includes feedback means electrically connected to the other stator winding for driving the shaft and light-reflecting means thereon at a uniform linear rate of speed.

6. The scanning device of claim 4, wherein the periodic signal has positive- and negative-sloped sections, and wherein the motor control means is operative to drive the shaft and light-reflecting means thereon in said one and said opposite circumferential directions in dependence on the sloped sections of the periodic signal.

7. The scanning device of claim 6, wherein the periodic signal has a triangular waveform characteristic.

8. The scanning device of claim 4, wherein the periodic-signal-applying means is operative to generate a third magnetic field of one polarity to interact with said second magnetic field of the rotor to move the same in said one circumferential direction, and of the opposite polarity to interact with said second magnetic field of the rotor to move the same in said opposite circumferential direction.

9. The scanning device of claim 1, wherein the motor control means reciprocally oscillates the shaft and light-reflecting means thereon to scan positions, each being angularly offset from the center position on the order of 5°

.

10. The scanning device of claim 1, wherein the motor control means reciprocally oscillates the shaft and light-reflecting means thereon at a rate of speed which is on the order of one hundred oscillations per second.

11. The scanning device of claim 1, wherein the establishing means includes means for adjusting the strength of the magnetic field of the stator.

12. The scanning device of claim 11, wherein the stator includes a stator coil winding, and wherein the establishing means includes means for applying a generally constant electrical signal to the stator coil winding, said adjusting means being operative to change the amplitude of the generally constant signal applied to the stator coil winding.

13. The scanning device of claim 1, wherein the motor control means is operative to drive the shaft and light-reflecting means thereon to scan positions angularly spaced apart to sweep the light to be scanned over an enlarged field of view which is larger than the field of view required to be scanned so that the shaft and light-reflecting means are driven in a generally linear manner over said field of view required to be scanned.

14. A method of repetitively scanning light, comprising the steps of:

(a) mounting a light-reflecting means on an elongated shaft operatively connected to a rotor for joint movement relative to a stator about an axis which extends along the elongation of the shaft;

(b) magnetically generating a centering force which acts on the rotor to urge the shaft and light-reflecting means to a center position by establishing at the stator and the rotor respective magnetic fields which interact to cause the magnetic field of the rotor to align itself with the magnetic field of the stator;

(c) electromagnetically moving the rotor against the action of the centering force in one circumferential direction about said axis over an arc length less than 360°

;

(d) electromagnetically moving the rotor against the action of the centering force in the opposite circumferential direction about said axis over an arc length less than 360°

; and

(e) alternately repeating steps (c) and (d) in a repetitive, rapid manner to drive the shaft and light-reflecting means thereon in alternate circumferential directions about said axis to respective scan positions angularly spaced from said center position.

15. The scanning method of claim 14, wherein said establishing step includes the step of applying a generally constant electrical signal to a stator coil winding of the stator to generate a first magnetic field, and the step of magnetizing the rotor to generate a second magnetic field which interacts with said first magnetic field.

16. The scanning method of claim 15, wherein said steps (c) and (d) include the step of applying a periodic electrical signal of time-varying amplitude to another stator coil winding to drive the shaft and light-reflecting means thereon to scan positions whose angular spacing from said center position is a function of the amplitude of the periodic signal, and at a speed which is a function of the rate of change of the periodic signal.

17. The scanning method of claim 16, wherein the periodic signal has positive- and negative-slope sections, and wherein steps (c) and (d) are performed to drive the shaft and light-reflecting means thereon in said one and said opposite circumferential directions in dependence on the sloped sections of the periodic signal.

18. The scanning method of claim 16, wherein steps (c) and (d) are performed by generating a third magnetic field of one polarity to interact with said second magnetic field of the rotor to move the same in said one circumferential direction, and of the opposite polarity to interact with said second magnetic field of the rotor to move the same in said opposite circumferential direction.

19. The scanning method of claim 14, wherein steps (c) and (d) are performed by reciprocally oscillating the shaft and light-reflecting means thereon to scan positions, each being angularly offset from the center position on the order of 5°

.

20. The scanning method of claim 14, wherein steps (c) and (d) are performed by reciprocally oscillating the shaft and light-reflecting means thereon at a rate of speed which is on the order of one hundred oscillations per second.

21. The scanning method of claim 14, wherein the establishing step includes the step of adjusting the strength of the magnetic field of the stator.

22. The scanning method of claim 21, wherein the adjusting step includes changing the amplitude of a generally constant electrical signal applied to a stator coil winding of the stator.

23. The scanning method of claim 14, wherein steps (c) and (d) are performed by moving the rotor at a uniform linear rate of speed.

24. The scanning method of claim 14, wherein step (e) is performed by driving the shaft and light-reflecting means thereon to scan positions angularly spaced apart to sweep the light to be scanned over an enlarged field of view which is larger than the field of view required to be scanned so that the shaft and light-reflecting means are driven in a generally linear manner over said field of view required to be scanned.