Conveyor system

1. A conveyor system comprising:

an elongated guide defining a closed transport path extending through a plurality of treatment stations;

a plurality of carriers movable on the guide along the path and each capable of holding a respective workpiece;

at least one magnet on each carrier;

an annular row of individually energizeable electromagnets extending along the path and capable of exerting force on the magnets of the carriers so as to displace the respective carriers along the path; and

means including a plurality of sensors spaced along the path for detecting the carriers and generating outputs indicating positions and movement of the carriers along the path, at least some of the electromagnets at least intermittently forming some of the sensors.

2. The conveyor system defined in claim 1 wherein the row of electromagnets is subdivided into groups of electromagnets forming respective sections of the path, the system further comprising

control means for energizing each of the groups independently of the other groups to form a respective linear actuator.

3. The conveyor system defined in claim 2 wherein the electromagnets are equispaced along the path at a spacing that is a small fraction of a length measured parallel to the path of each of the carriers.

4. A method of operating a conveyor system having:

an elongated guide defining a closed transport path extending through a plurality of treatment stations;

a plurality of like carriers of predetermined length movable on the guide along the path and each capable of holding a respective workpiece;

at least one magnet on each carrier; and

an annular row of individually energizeable electromagnets extending along the path and capable of exerting force on the magnets of the carriers so as to displace the respective carriers along the path,

the method comprising the steps of:

subdividing the row of electromagnets into a succession of sections each having a plurality of the magnets, each section being substantially longer than the predetermined length;

using at least some of the electromagnets at least intermittently as sensors;

detecting positions and movements of the carriers along the path in the sections with the sensors; and

in accordance with the detected positions and movements, energizing the electromagnets of each section individually so as to move a one of the carriers in the section in a displacement mode that can be different from a displacement mode of other carriers in other sections.

5. The method defined in claim 4 wherein the magnets on the carriers are permanent magnets.

6. The method defined in claim 4 wherein the electromagnets are operated individually.

7. The method defined in claim 4 wherein the electromagnets can be operated in a synchronous displacement mode for displacing all the carriers synchronously around the path at generally the same speed, or in a section mode group-wise with carriers in different sections being operated with different displacement modes.

8. The method defined in claim 7 wherein when the electromagnets are operated group-wise at least one carrier is moved in steps through the respective section.

9. The method defined in claim 7 wherein the electromagnets are operated individually in the section mode.

10. The method defined in claim 7 wherein the two modes are overlain.