WO2001033303A1

WO2001033303A1 - Galvanometer having incorporated date memory

Info

Publication number: WO2001033303A1
Application number: PCT/US2000/016385
Authority: WO
Inventors: Michael B. Nussbaum
Original assignee: General Scanning Inc
Current assignee: General Scanning Inc
Priority date: 1999-10-29
Filing date: 2000-06-14
Publication date: 2001-05-10
Anticipated expiration: 2002-04-29

Abstract

A self-tuning galvanometer scanner is shown, which incorporates an electronically programmable read-only memory chip (EPROM) (32) programmed with an on board personality chart such that when a servo amplifier is connected to the scanner it has access to the information stored in the ROM, and uses this information to tune itself automatically without the need for manual adjustment.

Description

GALVANOMETER HAVING INCORPORATED DATE MEMORY

BACKGROUND OF THE INVENTION

This invention relates to limited-rotation oscillatory motors or galvanometers. A common use of these devices is to drive optical elements such as mirrors for the purpose of guiding light beams. An assembly of this type is often called a "scanner." Common types of galvanometers include the moving coil or so-called D'Arsonval galvanometer, the moving iron galvanometer and the moving magnet galvanometer. The invention relates primarily to the moving-magnet type galvanometer; however, it may be employed with the other types of galvanometers.

A typical moving-magnet galvanometer includes a cylindrical magnetic rotor and a stator. The rotor is mounted for rotary oscillation about a central axis, and is normally polarized into two essentially semi-cylindrical poles on opposite sides of the axis. The stator is mounted concentric with the rotor, and generally has two poles that are disposed on opposite sides of the rotor, with coils wound on neck portions of the poles. Additionally, a servo amplifier controls the angular position of the rotor by means of drive currents applied to the stator coils.

Often the accuracy of the angular position of the rotor is critical to the proper operation of the galvanometer. Some examples of these types uses include; electronic manufacturing and repair operations in which a laser beam is directed to perform tasks such as the profiling, marking, cutting, drilling, and trimming of silicon and other semiconducting materials, the trimming and cutting of thick and thin films on semiconductors, the drilling of via holes in printed circuit boards, and the inspection of solder paste and component placement on printed circuit boards, among many others. Unfortunately, galvanometers display variability in characteristics over a small range as a result of manufacturing tolerances, variability in materials, etc. These varieties adversely affect operation of the servo controller especially if accurate measurement of the rotor position at high speed is desired. It has therefore been possible to obtain the highest levels of performance only by manually tuning the servo loop to compensate for the individual characteristics of the particular scanner to be controlled by the servo. This process, in general, requires access to the scanner to comprehensively adopt the servo to its characteristics. This is difficult if not impossible to per- form at the location of the use of the scanner.

As a result, if a servo amplifier fails in the field, it has been necessary to dismount the scanner it controlled and send that particular scanner back to the factory so that a new amplifier could be adjusted to the scanner. Of course, when the scanner was reinstalled in the machine from which it came, complex alignment was required.

SUMMARY OF THE INVENTION

In general, the invention features a non- volatile memory resident within a scanner. The memory is loaded with the operating characteristics of the scanner. These characteristics include, but are not limited to, information describing the scanner dy- namics, position detector gain and linearization and system temperature coefficients. In addition, the memory may also contain information not limited to the servo system.

The servo system to which the scanner is later connected in use has access to the information stored in the memory and uses this information to "tune" itself to the characteristics. As a result, any scanner can be connected to any amplifier, and the memory describing the scanner characteristics can be read to obtain optimum performance without the need for manual adjustment. This allows servo electronics and scanners to be replaced in the field without the need for laborious adjustment and tuning.

BRIEF DESCRIPTION OF THE DRAWINGS The invention description below refers to the accompanying drawings, of which:

Fig. 1 shows a cross section of a typical prior art closed loop servo optical scanner with its major components; Fig. 2 shows an electrically programmable read-only memory chip (EPROM) incorporated into the closed loop servo optical scanner of FIG. 1.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE

EMBODIMENT FIG. 2 shows the elements of a moving magnet scanner, or galvanometer: a limited-rotation motor 10 comprising a rotor 12, a stator 14, a position detector 16, and an electronic servo control unit 18.

The servo control unit 18 applies power to the motor 10 and the position detector 16 and receives position signals from the detector 16. The control unit includes a microprocessor 30 that operates in accordance with instructions contained in a memory 32 and command inputs from an input terminal 34. The scanner also includes a nonvolatile memory 36 containing the characteristics of the motor 10, a load rotated by the motor (not shown), and the position detector 16.

In accordance with the instructions in memory 32, the processor executes a digital servo loop program for control of the motor 10, accessing the memory 36 for various parameters to incorporated into the digital servo loop. The memory 36 is packaged within and identified specifically with motor 10. The latter unit is thus automatically "tuned" to the characteristics of the motor 10 and its load. The simplified drawing does not show various components, such as digital-analog and analog-digital convert- ers, common to digital servo controllers.

The art will recognize other variations and modifications of the details of construction described here, while taking advantage of the principles of the invention.

What is claimed is:

Claims

1. A galvanometer comprising: (a) a motor; (b) a load reciprocally rotated by the motor; (c) a servo controller to control the motor; and (d) a non-volatile memory residing in the motor containing characteristics of the motor, position detector and the load, the servo controller having access to the contents of the memory for use in setting parameters of the controller.

2. A galvanometer comprising: (a) a rotor including a permanent-magnet armature concentric with the rota- tional axis of said rotor said armature being polarized with diametrically opposed poles; (b) a stator, concentric with said rotor, said stator including a drive coil for generating a magnetic field that interacts with flux from said armature; (c) a servo controller operatively connected with said coil for driving said motor in a closed-loop configuration; (d) a load reciprocally rotated by the motor; (e) a non- volatile memory containing characteristics of the motor, the load, and a position detector; (f) the controller accessing the non- volatile memory for use in setting pa- rameters of the controller.