U.S. patent application number 15/696680 was filed with the patent office on 2019-03-07 for stabilizing operation of a high speed variable focal length tunable acoustic gradient lens in an imaging system.
The applicant listed for this patent is Mitutoyo Corporation. Invention is credited to Isaiah Freerksen, Paul Gerard Gladnick.
Application Number | 20190075234 15/696680 |
Document ID | / |
Family ID | 63683626 |
Filed Date | 2019-03-07 |
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United States Patent
Application |
20190075234 |
Kind Code |
A1 |
Freerksen; Isaiah ; et
al. |
March 7, 2019 |
STABILIZING OPERATION OF A HIGH SPEED VARIABLE FOCAL LENGTH TUNABLE
ACOUSTIC GRADIENT LENS IN AN IMAGING SYSTEM
Abstract
A method is provided for operating an imaging system to maintain
a tunable acoustic gradient (TAG) lens at a desired operating
state. In a first step, the TAG lens operates using a standard
imaging drive control configuration (e.g., a standard drive voltage
and duration) during a plurality of imaging drive mode time
periods, to achieve a standard imaging state of the TAG lens. In a
second step, the TAG lens operates using a regulating adaptive
drive control configuration during a plurality of regulating
adaptive drive mode time periods, wherein at least one of a
different respective TAG lens drive voltage and a different
respective TAG lens drive duration is used for different respective
regulating adaptive drive mode time periods, based on a monitoring
signal that is indicative of a difference between the standard
imaging state and a current operating state of the TAG lens.
Inventors: |
Freerksen; Isaiah; (Bothell,
WA) ; Gladnick; Paul Gerard; (Seattle, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitutoyo Corporation |
Kanagawa-ken |
|
JP |
|
|
Family ID: |
63683626 |
Appl. No.: |
15/696680 |
Filed: |
September 6, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 5/2256 20130101;
G02F 2001/291 20130101; H04N 5/2353 20130101; H04N 5/23245
20130101; G02F 2203/18 20130101; H04N 5/23212 20130101; H04N 5/2352
20130101; H04N 5/2354 20130101; G02F 1/29 20130101 |
International
Class: |
H04N 5/232 20060101
H04N005/232; H04N 5/235 20060101 H04N005/235; G02F 1/29 20060101
G02F001/29 |
Claims
1. A method of operating an imaging system comprising a tunable
acoustic gradient (TAG) lens, a TAG lens controller, a camera, and
an exposure time controller, in order to establish or maintain the
TAG lens at a desired operating state for imaging, the method
comprising: controlling the TAG lens using a standard imaging drive
control configuration during a plurality of imaging drive mode time
periods, wherein each instance of the imaging drive mode time
period provides image data acquired while operating the TAG lens
according to the standard imaging drive control configuration,
wherein the standard imaging drive control configuration includes a
standard imaging drive voltage and a standard imaging drive
duration and is configured to achieve a standard imaging state of
the TAG lens; and controlling the TAG lens using a regulating
adaptive drive control configuration during a plurality of
regulating adaptive drive mode time periods that are different from
the imaging drive mode time periods, wherein the regulating
adaptive drive control configuration is configured to provide at
least one of a different respective TAG lens regulating drive
voltage and a different respective TAG lens regulating drive
duration for different respective regulating adaptive drive mode
time periods, based on a TAG lens monitoring signal that is
indicative of a difference between the standard imaging state of
the TAG lens and a current operating state of the TAG lens.
2. The method of claim 1, wherein the imaging drive mode time
periods and the regulating adaptive drive mode time periods are
interspersed in a predetermined sequence.
3. The method of claim 2, wherein the predetermined sequence
comprises alternating between the imaging drive mode time period
and the regulating adaptive drive mode time period.
4. The method of claim 1, wherein the monitoring signal monitors an
operating resonant frequency of the TAG lens.
5. The method of claim 1, wherein the monitoring signal monitors an
operating temperature of the TAG lens.
6. The method of claim 1, wherein the standard imaging state of the
TAG lens comprises an operating temperature of the TAG lens that is
greater than a maximum specified environmental operating
temperature of the TAG lens or of the imaging system.
7. The method of claim 6, wherein the TAG lens is insulated to
reduce heat dissipation to an environment.
8. The method of claim 1, wherein the regulating adaptive drive
control configuration is configured to provide a respective TAG
lens regulating drive voltage that is greater than the standard
imaging drive voltage for at least some of the respective
regulating adaptive drive mode time periods.
9. The method of claim 1, wherein the TAG lens comprises a heater
that inputs an amount of heat energy into the TAG lens, wherein the
amount of heat energy is approximately fixed for at least some of
the plurality of regulating adaptive drive mode time periods.
10. The method of claim 9, wherein the amount of heat energy is
nominally constant at all times of operation.
11. The method of claim 1, wherein the imaging system comprises
Z-height (focus distance) calibration data that relates respective
Z-heights (focus distances) to respective phase timings within a
period of a standard imaging resonant frequency of the TAG lens,
wherein the calibration data corresponds to operating the TAG lens
according to the standard imaging drive control configuration.
12. The method of claim 1, comprising: acquiring observational
images during the regulating adaptive drive mode time periods and
displaying the acquired observational images in a user interface of
the imaging system.
13. The method of claim 1, comprising: not acquiring images during
the regulating adaptive drive mode time periods, or suppressing an
output of images acquired during the regulating adaptive drive mode
time periods.
14. The method of claim 1, comprising: in response to the
difference between the standard imaging state of the TAG lens and
the current operating state of the TAG lens exceeding a threshold,
transitioning from controlling the TAG lens using the standard
imaging drive control configuration to controlling the TAG lens
using the regulating adaptive drive control configuration, and in
response to the difference not exceeding the threshold, continuing
controlling the TAG lens using the standard imaging drive control
configuration.
15. An imaging system, comprising: a camera, an exposure time
controller configured to control image data acquisition by the
camera, a tunable acoustic gradient (TAG) lens, and a TAG lens
controller which, in operation, controls the TAG lens using a
standard imaging drive control configuration during a plurality of
imaging drive mode time periods, wherein each instance of the
imaging drive mode time period provides image data while operating
the TAG lens according to the standard imaging drive control
configuration, wherein the standard imaging drive control
configuration includes a standard imaging drive voltage and a
standard imaging drive duration and is configured to achieve a
standard imaging state of the TAG lens; and controls the TAG lens
using a regulating adaptive drive control configuration during a
plurality of regulating adaptive drive mode time periods that are
different from the imaging drive mode time periods, wherein the
regulating adaptive drive control configuration is configured to
provide at least one of a different respective TAG lens regulating
drive voltage and a different respective TAG lens regulating drive
duration for different respective regulating adaptive drive mode
time periods, based on a TAG lens monitoring signal that is
indicative of a difference between the standard imaging state of
the TAG lens and a current operating state of the TAG lens.
16. The imaging system of claim 15, wherein the exposure time
controller comprises a circuit that controls a strobe light source
of the imaging system to strobe at a respective controlled
time.
17. The imaging system of claim 16, further comprising Z-height
(focus distance) calibration data that relates respective Z-heights
(focus distances) to respective phase timings within a period of a
standard imaging resonant frequency of the TAG lens, the
calibration data corresponding to operating the TAG lens according
to the standard imaging drive control configuration, wherein the
exposure time controller controls the strobe light source of the
imaging system to strobe at a respective controlled time
corresponding to a respective phase timing within the period of the
standard imaging resonant frequency.
18. The imaging system of claim 15, wherein the exposure time
controller comprises a circuit that controls a camera shutter to
acquire an image signal at a respective controlled time.
19. The imaging system of claim 15, comprising a heater arranged to
input an amount of heat energy into the TAG lens, wherein the
amount of heat energy is approximately fixed for at least some of
the plurality of regulating adaptive drive mode time periods.
20. The imaging system of claim 15, wherein, the exposure time
controller prevents image exposure during the regulating adaptive
drive mode time periods, or the imaging system suppresses an image
display of image data acquired by the camera during the regulating
adaptive drive mode time periods.
Description
BACKGROUND
Technical Field
[0001] This disclosure relates to precision metrology using a high
speed variable focal length lens (e.g., in a machine vision
inspection system) and, more particularly, to monitoring and
stabilizing operation of a high speed variable focal length lens in
an imaging system.
Description of the Related Art
[0002] Precision non-contact metrology systems such as precision
machine vision inspection systems (or "vision systems" for short)
may be utilized to obtain precise dimensional measurements of
objects and to inspect various other object characteristics, and
may include a computer, a camera and optical system, and a
precision stage that moves to allow workpiece traversal and
inspection. One exemplary prior art system is the QUICK VISION.RTM.
series of PC-based vision systems and QVPAK.RTM. software available
from Mitutoyo America Corporation (MAC), located in Aurora, Ill.
The features and operation of the QUICK VISION.RTM. series of
vision systems and the QVPAK.RTM. software are generally described,
for example, in the QVPAK 3D CNC Vision Measuring Machine User's
Guide, published January 2003, and the QVPAK 3D CNC Vision
Measuring Machine Operation Guide, published September 1996, each
of which is hereby incorporated by reference in its entirety. This
type of system uses a microscope-type optical system and moves the
stage so as to provide inspection images of either small or
relatively large workpieces.
[0003] General-purpose precision machine vision inspection systems
are generally programmable to provide automated video inspection.
Such systems typically include GUI features and predefined image
analysis "video tools" such that operation and programming can be
performed by "non-expert" operators. For example, U.S. Pat. No.
6,542,180, which is incorporated herein by reference in its
entirety, teaches a vision system that uses automated video
inspection including the use of various video tools.
[0004] Multi-lens variable focal length (VFL) optical systems may
be utilized in an imaging system for observation and precision
measurement of surface heights. The imaging system may be included
in a microscope system and/or in a precision machine vision
inspection system, for example as disclosed in U.S. Pat. No.
9,143,674, which is hereby incorporated herein by reference in its
entirety. Briefly, a VFL lens is capable of acquiring multiple
images at multiple focal lengths, respectively. As one type of VFL
lens, tunable acoustic gradient ("TAG") lenses are known. A TAG
lens is a high speed VFL lens that creates a lensing effect using
sound waves in a fluid medium. The sound waves may be created by
application of an electrical field at a resonant frequency to a
piezoelectric tube surrounding the fluid medium. The sound waves
create a time-varying density and index of refraction profile in
the lens' fluid, which modulates its optical power and focal length
or focus position. A TAG lens may periodically sweep a range of
focal lengths at a resonant frequency of up to several hundred kHz,
i.e., at a high speed. Such a lens may be understood in greater
detail by the teachings of the article, "High speed varifocal
imaging with a tunable acoustic gradient index of refraction lens"
(Optics Letters, Vol. 33, No. 18, Sep. 15, 2008), which is hereby
incorporated herein by reference in its entirety. Tunable acoustic
gradient index lenses and related controllable signal generators
are available, for example, from TAG Optics, Inc., of Princeton,
N.J. The Model TL2.B.xxx series lenses, for example, are capable of
modulation up to approximately 600 kHz.
[0005] Various embodiments of the present invention are directed to
improving operation of an imaging system that incorporates a TAG
lens as a VFL lens.
BRIEF SUMMARY
[0006] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This summary is not intended to identify
key features of the claimed subject matter, nor is it intended to
be used as an aid in determining the scope of the claimed subject
matter.
[0007] An imaging system utilizing a TAG lens may be calibrated for
its focal length or position as a function of phase timing during
its resonant cycle, using known operating conditions for the
calibration, e.g., while using a particular drive amplitude at a
particular resonant frequency. During calibration, stable
environmental conditions may be provided to ensure that the desired
operating conditions are stable and known throughout the
calibration data acquisition. After calibration, for a surface that
produces a best-focused image when exposed using a particular phase
timing, the calibration data may be used to indicate the focal
position of that surface relative to the imaging system, which
provides a measurement of its position or height. In operation,
however, the operating conditions of a TAG lens may drift due to
various factors, and may fail to precisely match the operating
conditions used for calibration. This may result in small, but
non-negligible, measurement errors. It is known that the resonant
frequency of a TAG lens will slightly vary as a function of the
lens temperature, for example. This reflects a change in the
electro-mechanical response of the lens to the drive signal. It is
also known that a change in the temperature of the lens fluid
changes its nominal refractive index. Any such change in the
electro-mechanical response of the lens and/or its fluid properties
necessarily changes the optical power (or focal length) response of
the lens to the drive signal, resulting in the aforementioned
measurement errors. A need exists for techniques that facilitate
stabilizing operation of a TAG lens (e.g., including its operating
temperature), which will stabilize the operation of an imaging
system including a TAG lens and allow the reduction or elimination
of the aforementioned measurement errors.
[0008] According to exemplary embodiments, a method is provided for
operating an imaging system including a tunable acoustic gradient
(TAG) lens, a TAG lens controller, a camera, and an exposure time
controller, in order to establish or maintain the TAG lens at a
desired (standard) operating state for imaging. The method includes
generally two steps. In a first step, the TAG lens is controlled
using a standard imaging drive control configuration during a
plurality of imaging drive mode time periods. Each instance of the
imaging drive mode time period provides image data acquired while
operating the TAG lens according to the standard imaging drive
control configuration. The standard imaging drive control
configuration includes a standard imaging drive voltage and a
standard imaging drive duration, and is configured to achieve a
standard imaging state of the TAG lens (e.g., a state that
corresponds to the conditions used as the basis for calibration
data). In a second step, the TAG lens is controlled using a
regulating adaptive drive control configuration during a plurality
of regulating adaptive drive mode time periods that are different
than the imaging drive mode time periods. The regulating adaptive
drive control configuration is configured to provide at least one
of a different respective TAG lens regulating drive voltage and a
different respective TAG lens regulating drive duration for
different respective regulating adaptive drive mode time periods,
based on a TAG lens monitoring signal that is indicative of a
difference between the standard imaging state of the TAG lens and a
current operating state of the TAG lens.
[0009] According to further implementations, an imaging system is
provided including a camera, an exposure time controller configured
to control image data acquisition by the camera, a tunable acoustic
gradient (TAG) lens, and a TAG lens controller. The TAG lens
controller is configured to control the TAG lens using a standard
imaging drive control configuration during a plurality of imaging
drive mode time periods, and to control the TAG lens using a
regulating adaptive drive control configuration during a plurality
of regulating adaptive drive mode time periods that are different
than the imaging drive mode time periods, as described above.
[0010] The method and imaging system according to various
embodiments are therefore capable of monitoring and stabilizing
operation of a TAG lens and stabilizing operation of the imaging
system that incorporates the TAG lens, during ongoing
operation.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0011] FIG. 1 is a diagram showing various typical components of a
general-purpose precision machine vision inspection system;
[0012] FIG. 2 is a block diagram of a control system portion and a
vision components portion of a machine vision inspection system
similar to that of FIG. 1 and including features disclosed
herein;
[0013] FIG. 3 is a schematic diagram of an imaging system that may
be adapted to a precision non-contact metrology system such as a
machine vision inspection system and operated according to the
principles disclosed herein;
[0014] FIG. 4 is a diagram of a graph illustrating resonant
frequencies of a VFL (TAG) lens at various operating
temperatures;
[0015] FIG. 5 is a timing chart illustrating one exemplary
operation of an imaging system including a TAG lens;
[0016] FIG. 6 is a flow diagram illustrating one exemplary
implementation of a routine for operating an imaging system
including a TAG lens; and
[0017] FIG. 7 is a flow diagram illustrating another exemplary
implementation of a routine for operating an imaging system
including a TAG lens.
DETAILED DESCRIPTION
[0018] FIG. 1 is a block diagram of one exemplary machine vision
inspection system 10 usable as an imaging system in accordance with
methods described herein. The machine vision inspection system 10
includes a vision measuring machine 12 that is operably connected
to exchange data and control signals with a controlling computer
system 14. The controlling computer system 14 is further operably
connected to exchange data and control signals with a monitor or
display 16, a printer 18, a joystick 22, a keyboard 24, and a mouse
26. The monitor or display 16 may display a user interface suitable
for controlling and/or programming the operations of the machine
vision inspection system 10. It will be appreciated that in various
implementations, a touchscreen tablet or the like may be
substituted for and/or redundantly provide the functions of any or
all of the computer system 14, the display 16, the joystick 22, the
keyboard 24, and the mouse 26.
[0019] Those skilled in the art will appreciate that the
controlling computer system 14 may generally consist of any
computing system or device. Suitable computing systems or devices
may include personal computers, server computers, minicomputers,
mainframe computers, distributed computing environments that
include any of the foregoing, and the like. Such computing systems
or devices may include one or more processors that execute software
to perform the functions described herein. Processors include
programmable general-purpose or special-purpose microprocessors,
programmable controllers, application-specific integrated circuits
(ASICs), programmable logic devices (PLDs), or the like, or a
combination of such devices. Software may be stored in memory, such
as random-access memory (RAM), read-only memory (ROM), flash
memory, or the like, or a combination of such components. Software
may also be stored in one or more storage devices, such as
optical-based disks, flash memory devices, or any other type of
non-volatile storage medium for storing data. Software may include
one or more program modules that include routines, programs,
objects, components, data structures, and so on that perform
particular tasks or implement particular abstract data types. In
distributed computing environments, the functionality of the
program modules may be combined or distributed across multiple
computing systems or devices and accessed via service calls, either
in a wired or wireless configuration.
[0020] The vision measuring machine 12 includes a moveable
workpiece stage 32 and an optical imaging system 34 that may
include a zoom lens or interchangeable lenses. The zoom lens or
interchangeable lenses generally provide various magnifications for
the images provided by the optical imaging system 34. The machine
vision inspection system 10 is also described in commonly assigned
U.S. Pat. Nos. 7,454,053; 7,324,682; 8,111,905; and 8,111,938, each
of which is hereby incorporated herein by reference in its
entirety.
[0021] FIG. 2 is a block diagram of a control system portion 120
and a vision components portion 200 of a machine vision inspection
system 100 similar to the machine vision inspection system of FIG.
1, and including features as described herein. As will be described
in more detail below, the control system portion 120 is utilized to
control the vision components portion 200. The vision components
portion 200 includes an optical assembly portion 205, light sources
220, 230, and 240, and a workpiece stage 210 having a central
transparent portion 212. The workpiece stage 210 is controllably
movable along x- and y-axes that lie in a plane that is generally
parallel to the surface of the stage where a workpiece 20 may be
positioned.
[0022] The optical assembly portion 205 includes a camera system
260, an interchangeable objective lens 250, a variable focal length
(VFL) lens 270 which is a TAG lens in various exemplary
embodiments, and may include a turret lens assembly 281 having
lenses 286 and 288. Alternatively to the turret lens assembly, a
fixed or manually interchangeable magnification-altering lens, or a
zoom lens configuration, or the like, may be included. In various
implementations, the various lenses may be included as part of a
variable magnification lens portion of the optical assembly portion
205. In various implementations, the interchangeable objective lens
250 may be selected from a set of fixed magnification objective
lenses that are included as part of the variable magnification lens
portion (e.g., a set of objective lenses corresponding to
magnifications such as 0.5.times., l.times., 2.times. or
2.5.times., 5.times., 10.times., 20.times. or 25.times., 50.times.,
100.times., etc.).
[0023] The optical assembly portion 205 is controllably movable
along a z-axis that is generally orthogonal to the x- and y-axes by
using a controllable motor 294 that drives an actuator to move the
optical assembly portion 205 along the z-axis to change the focus
of the image of the workpiece 20. The controllable motor 294 is
connected to an input/output interface 130 via a signal line 296.
As will be described in more detail below, the VFL (TAG) lens 270
may be controlled via a signal line 334' by a lens control
interface 134 to periodically modulate a focus position of the
lens. The lens control interface 134 may include a lens drive mode
manager 180 according to various principles disclosed herein, as
described in greater detail below. A workpiece 20, or a tray or
fixture holding a plurality of workpieces 20, which is to be imaged
using the machine vision inspection system 100 is placed on the
workpiece stage 210. The workpiece stage 210 may be controlled to
move relative to the optical assembly portion 205, such that the
interchangeable objective lens 250 moves between locations on a
workpiece 20, and/or among a plurality of workpieces 20.
[0024] One or more of a stage light 220, a coaxial light 230, and a
surface light 240 (e.g., a ring light) may emit source light 222,
232, and/or 242, respectively, to illuminate the workpiece or
workpieces 20. The coaxial light 230 may emit light 232 along a
path including a mirror 290. The source light is reflected or
transmitted as workpiece light 255, and the workpiece light used
for imaging passes through the interchangeable objective lens 250,
the turret lens assembly 281 and the VFL lens 270, and is gathered
by the camera system 260. The image of the workpiece(s) 20,
captured by the camera system 260, is output on a signal line 262
to the control system portion 120. The light sources 220, 230, and
240 may be connected to the control system portion 120 through
signal lines or busses 221, 231, and 241, respectively. The control
system portion 120 may rotate the turret lens assembly 281 along
axis 284 to select a turret lens through a signal line or bus 281'
to alter an image magnification.
[0025] As shown in FIG. 2, in various exemplary implementations,
the control system portion 120 includes a controller 125, the
input/output interface 130, a memory 140, a workpiece program
generator and executor 170, and a power supply portion 190. Each of
these components, as well as the additional components described
below, may be interconnected by one or more data/control busses
and/or application programming interfaces, or by direct connections
between the various elements. The input/output interface 130
includes an imaging control interface 131, a motion control
interface 132, a lighting control interface 133, and the lens
control interface 134. The lens control interface 134 may include
the lens drive mode manager 180 including a lens operating circuit
and/or routine to control the drive mode of the TAG lens 270
according to principles disclosed herein, and/or as described in
greater detail below with reference to a lens controller 334
comprising circuitry and/or routines as shown in FIG. 3. In some
embodiments, the lens control interface 134 and the lens controller
334 may be merged and/or indistinguishable. The motion control
interface 132 may include a position control element 132a, and a
speed/acceleration control element 132b, although such elements may
be merged and/or indistinguishable. The lighting control interface
133 may include lighting control elements 133a, 133n, and 133f1
that control, for example, the selection, power, on/off switch, and
strobe pulse timing, if applicable, for the various corresponding
light sources of the machine vision inspection system 100. The
lighting control element configured to control strobe pulse timing
generally corresponds to an exposure (strobe) time controller 393
as shown in FIG. 3, described in greater detail below.
[0026] The memory 140 may include an image file memory portion 141,
an edge-detection memory portion 140ed, a workpiece program memory
portion 142 that may include one or more part programs, or the
like, and a video tool portion 143. The video tool portion 143
includes video tool portion 143a and other video tool portions
(e.g., 143n) that determine the GUI, image-processing operation,
etc., for each of the corresponding video tools; and a region of
interest (ROI) generator 143roi that supports automatic,
semi-automatic, and/or manual operations that define various ROIs
that are operable in various video tools included in the video tool
portion 143. The video tool portion also includes an autofocus
video tool 143af that determines the GUI, image-processing
operation, etc., for focus height measurement operations. In
various implementations, the autofocus video tool 143af may
additionally include a high-speed focus height tool that may be
utilized to measure focus heights with high speed using hardware
described in FIG. 3, as described in more detail in U.S. Pat. No.
9,143,674, which is hereby incorporated herein by reference in its
entirety. In various implementations, the high-speed focus height
tool may be a special mode of the autofocus video tool 143af that
may otherwise operate according to conventional methods for
autofocus video tools, or the operations of the autofocus video
tool 143af may only include those of the high-speed focus height
tool.
[0027] In the context of this disclosure, and as is known by one of
ordinary skill in the art, the term "video tool" generally refers
to a relatively complex set of automatic or programmed operations
that a machine vision user can implement through a relatively
simple user interface (e.g., a graphical user interface, editable
parameter windows, menus, and the like), without creating the
step-by-step sequence of operations included in the video tool or
resorting to a generalized text-based programming language, or the
like. For example, a video tool may include a complex
pre-programmed set of image-processing operations and computations
that are applied and customized in a particular instance by
adjusting a few variables or parameters that govern the operations
and computations. In addition to the underlying operations and
computations, the video tool comprises the user interface that
allows the user to adjust those parameters for a particular
instance of the video tool. For example, many machine vision video
tools allow a user to configure a graphical region of interest
(ROI) indicator through simple "handle dragging" operations using a
mouse, in order to define the location parameters of a subset of an
image that is to be analyzed by the image-processing operations of
a particular instance of a video tool. It should be noted that the
visible user interface features are sometimes referred to as the
video tool, with the underlying operations being included
implicitly.
[0028] One or more display devices 136 (e.g., the display 16 of
FIG. 1) and one or more input devices 138 (e.g., the joystick 22,
keyboard 24, and mouse 26 of FIG. 1) may be connected to the
input/output interface 130. The display devices 136 and input
devices 138 may be used to display a user interface that may
include various graphical user interface (GUI) features that are
usable to perform inspection operations, and/or to create and/or
modify part programs, to view the images captured by the camera
system 260, and/or to directly control the vision system components
portion 200. The display devices 136 may display user interface
features (e.g., as associated with the autofocus video tool 143af,
etc.).
[0029] In various exemplary implementations, when a user utilizes
the machine vision inspection system 100 to create a part program
for the workpiece 20, the user generates part program instructions
by operating the machine vision inspection system 100 in a learn
mode to provide a desired image-acquisition training sequence. For
example, a training sequence may comprise positioning a particular
workpiece feature of a representative workpiece in the field of
view (FOV), setting light levels, focusing or autofocusing,
acquiring an image, and providing an inspection training sequence
applied to the image (e.g., using an instance of one of the video
tools on that workpiece feature). The learn mode operates such that
the sequence(s) are captured or recorded and converted to
corresponding part program instructions. These instructions, when
the part program is executed, will cause the machine vision
inspection system to reproduce the trained image acquisition and
cause inspection operations to automatically inspect that
particular workpiece feature (that is the corresponding feature in
the corresponding location) on a run mode workpiece, or workpieces,
which matches the representative workpiece used when creating the
part program.
[0030] FIG. 3 is a schematic diagram of a VFL lens system 300 (also
referred to as imaging system 300) that includes a TAG lens 370 and
may be adapted to a vision system and operated according to the
principles disclosed herein. It will be appreciated that certain
numbered components 3XX of FIG. 3 may correspond to and/or have
similar operations as similarly numbered components 2XX of FIG. 2,
except as otherwise described below. As shown in FIG. 3, the VFL
lens system 300 includes a light source 330, an objective lens 350,
a tube lens 351, a relay lens 352, a VFL (TAG) lens 370, a relay
lens 356, a lens controller 334, a camera/detector 360, a Z-height
(focus distance) calibration portion 373, a focus signal processing
portion 375 (optional), and an optical focus monitoring portion 376
(optional). In various implementations, the various components may
be interconnected by direct connections or one or more data/control
busses (e.g., a system signal and control bus 395) and/or
application programming interfaces.
[0031] In operation, in the implementation shown in FIG. 3, the
light source 330 may be a "coaxial" or other light source
configured to emit source light 332 (e.g., with strobed or
continuous illumination) along a path including a partial mirror
390 and through the objective lens 350 to a surface of a workpiece
320, wherein the objective lens 350 receives workpiece light 355
that is focused at a focus position FP proximate to the workpiece
320, and outputs the workpiece light 355 to the tube lens 351. The
tube lens 351 receives the workpiece light 355 and outputs it to
the relay lens 352. In other implementations, analogous light
sources may illuminate the field of view in a non-coaxial manner;
for example a ring light source may illuminate the field of view.
In various implementations, the objective lens 350 may be an
interchangeable objective lens and the tube lens 351 may be
included as part of a turret lens assembly (e.g., similar to the
interchangeable objective lens 250 and the turret lens assembly 281
of FIG. 2). In various implementations, any of the other lenses
referenced herein may be formed from or operate in conjunction with
individual lenses, compound lenses, etc.
[0032] The relay lens 352 receives the workpiece light 355 and
outputs it to the VFL (TAG) lens 370. The VFL (TAG) lens 370
receives the workpiece light 355 and outputs it to the relay lens
356. The relay lens 356 receives the workpiece light 355 and
outputs it to the camera/detector 360. In various implementations,
the camera/detector 360 may capture an image of the workpiece 320
during an image exposure period, and may provide the image data to
a control system portion.
[0033] In the example of FIG. 3, the relay lenses 352 and 356 and
the VFL (TAG) lens 370 are designated as being included in a 4f
optical configuration, while the relay lens 352 and the tube lens
351 are designated as being included in a Keplerian telescope
configuration, and the tube lens 351 and the objective lens 350 are
designated as being included in a microscope configuration. All of
the illustrated configurations will be understood to be exemplary
only, and not limiting with respect to the present disclosure. In
various implementations, the illustrated 4f optical configuration
permits placing the VFL (TAG) lens 370 (e.g., which may be a low
numerical aperture (NA) device) at the Fourier plane of the
objective lens 350. This configuration may maintain the
telecentricity at the workpiece 320 and may minimize scale change
and image distortion (e.g., including providing constant
magnification for each Z-height of the workpiece 320 and/or focus
position FP). The Keplerian telescope configuration (e.g.,
including the tube lens 351 and the relay lens 352) may be included
between the microscope configuration and the 4f optical
configuration, and may be configured to provide a desired size of
the projection of the objective lens clear aperture at the location
of the VFL (TAG) lens 370, so as to minimize image aberrations,
etc.
[0034] In various implementations, the lens controller 334 may
include a drive signal generator portion 335. The drive signal
generator portion 335 may operate (e.g., in conjunction with a
timing clock 335') to provide a periodic drive signal to the high
speed VFL (TAG) lens 370 via a signal line 334'. In various
implementations, the drive signal generator may include a known
type of circuit that automatically seeks or follows any changes in
the peak resonant frequency. In such an implementation, a known
type of circuit (e.g., a clock counting circuit gated by the
periodic drive signal zero crossings) may output an indication of
the actual resonant frequency of the TAG lens in near real time,
which may be used as a TAG lens monitoring signal in some
implementations, as outlined in greater detail below.
[0035] In various implementations, the lens controller 334 may
monitor an operating state of the TAG lens 370 and stabilize
operation of the TAG lens 370 based on a monitoring signal. As
previously described in the summary section, an imaging system
incorporating a TAG lens is typically calibrated under stable
conditions, with lens' operational parameters remaining constant,
at desired standard operating conditions. It is therefore desirable
to stabilize operation of the TAG lens by establishing and
maintaining these parameters at the same desired (standard) values
during normal operation, in order to minimize measurement errors
that may otherwise arise at non-standard operating conditions. More
specifically, in some implementations it is desirable to stabilize
the lens' operational parameters, such as a resonant frequency
and/or an operational temperature of the lens during ongoing
operation of the lens. By monitoring and stabilizing any of these
operational parameters of the TAG lens, various embodiments of the
invention ensure proper operation of the imaging system
incorporating the TAG lens in accordance with its initial
calibration.
[0036] The operational parameters of a TAG lens to be monitored and
stabilized may be, for example, a resonant frequency of the TAG
lens 370, a temperature associated with the TAG lens 370 such as
the operational temperature of the TAG lens 370 itself or a
temperature of a component proximate to the TAG lens 370, or any
other meaningful operational attribute of the TAG lens 370. Of the
operational parameters, a resonant frequency of a TAG lens is
generally correlated with, and a sensitive indicator of, an
operating temperature of the TAG lens, as shown in FIG. 4. FIG. 4
is a diagram of a graph 400 illustrating resonant frequencies of a
TAG lens at various operating temperatures. The graph 400 shows a
set of measured resonant frequencies 410 of a TAG lens (in kHz) as
a function of temperature (in degrees C.), expressed as a linear
fit 420. The linear fit 420 has a slope of approximately -130
Hz/degree C. Thus, monitoring and stabilizing an operational
temperature of a TAG lens facilitates correspondingly stabilizing
the resonant frequency of the TAG lens, and vice versa.
[0037] Referring back to FIG. 3, in various implementations, the
lens controller 334 may include a lens drive mode manager 380
comprising circuitry and/or routine(s) and operable according to
principles disclosed herein. In some embodiments, the lens
controller 334 and the lens drive mode manager 380 may be merged
and/or indistinguishable. In various implementations, the VFL lens
system (or imaging system) 300 may comprise a control system (e.g.,
the control system portion 120 of FIG. 2) that is configurable to
operate in conjunction with the lens controller 334 to control the
VFL (TAG) lens 370 via the signal line 334', by driving the VFL
(TAG) lens 370 to periodically modulate its focus position. In
various implementations, the lens controller 334 may operate to
drive the VFL (TAG) lens 370 in two modes: in a standard imaging
drive mode (or "imaging drive mode") in which the lens controller
334 drives the VFL (TAG) lens 370 using a standard imaging drive
control configuration including a standard imaging drive voltage
and a standard imaging drive duration; and in a regulating adaptive
drive mode in which the lens controller 334 uses a regulating
adaptive drive control configuration configured to provide at least
one of a different (adjusted) TAG lens regulating drive voltage and
a different (adjusted) TAG lens regulating drive duration to drive
the VFL (TAG) lens 370, for reasons described in greater detail
below.
[0038] The standard imaging drive control configuration is used
during a plurality of imaging drive mode time periods. Each
instance of the imaging drive mode time period provides image data
acquired while operating the TAG lens 370 according to the standard
imaging drive control configuration, which is defined to achieve a
standard imaging state of the TAG lens (e.g., the same as the
imaging drive control configuration used during calibration.) On
the other hand, the regulating adaptive drive control configuration
is used during a plurality of regulating adaptive drive mode time
periods that are different from the imaging drive mode time
periods. The regulating adaptive drive control configuration
provides at least one of a different respective TAG lens regulating
drive voltage and a different respective TAG lens regulating drive
duration for different respective regulating adaptive drive mode
time periods, which results in different respective rates of power
dissipation or heating within the TAG lens for different respective
regulating adaptive drive mode time periods.
[0039] The regulating adaptive drive control configuration is based
on a TAG lens monitoring signal that is indicative of a difference
between the standard imaging state of the TAG lens 370 and a
current operating state of the TAG lens 370. For example, the TAG
lens monitoring signal may be provided by a temperature sensor 336
associated with the TAG lens 370 to monitor an operating
temperature of the TAG lens 370. As another example, the TAG lens
monitoring signal may be provided by the drive signal generator
portion 335 or any suitable sensing circuit that monitors an
operating resonant frequency of the TAG lens 370 (e.g., as outlined
previously.) In various implementations, the regulating adaptive
drive control configuration is configured to compensate or reduce
or eliminate the difference between the standard imaging state and
the current operating state of the TAG lens 370 as indicated by the
monitoring signal.
[0040] For example, when a TAG lens monitoring signal indicates an
operating temperature of the TAG lens 370 lower than a defined
(standard) temperature value, the regulating adaptive drive control
configuration may be configured to provide a respective TAG lens
regulating drive voltage that is greater than the standard imaging
drive voltage for at least some of the respective regulating
adaptive drive mode time periods. Alternatively, or additionally,
the regulating adaptive drive control configuration may be
configured to provide a respective TAG lens regulating drive
duration that is longer than the standard imaging drive duration
for at least some of the respective regulating adaptive drive mode
time periods. Referring to FIG. 4, when a TAG lens monitoring
signal indicates an operating resonant frequency of the TAG lens
370 higher than a defined (standard) resonant frequency, the
regulating adaptive drive control configuration may be configured
to increase the operating temperature of the TAG lens 370, which
correspondingly lowers the operating resonant frequency of the TAG
lens 370 to be closer to the defined (standard) resonant frequency
of the TAG lens 370. For example, the regulating adaptive drive
control configuration may provide a respective TAG lens regulating
drive voltage that is greater than the standard imaging drive
voltage and or a respective TAG lens regulating drive duration that
is longer than the standard imaging drive duration for at least
some of the respective regulating adaptive drive mode time periods
in order to increase heating in the lens and raise its temperature
and lower the operating resonant frequency of the TAG lens 370.
[0041] It will be appreciated that in the absence of a cooling
system, the temperature of the TAG lens 370 will generally
fluctuate with the ambient temperature, and will not be lower than
the ambient temperature after a period of operation. Therefore, if
a single standard operating temperature is to be chosen for use
under all specified conditions, it must be chosen to be above the
maximum allowed or specified environmental temperature range.
Accordingly, in various implementations, a standard operating
temperature of the TAG lens 370 is set greater than a maximum
specified environmental (ambient) operating temperature of the TAG
lens 370 or the imaging system 300. In order to achieve that
standard temperature, when the ambient temperature is relatively
low, relatively more heat must be generated in or around the lens.
Conversely, when the ambient temperature is relatively high, less
heat must be generated in or around the lens.
[0042] For example, when a specified environmental operating
temperature of the TAG lens 370 or the imaging system 300 is in the
range of 15 to 30 degrees C., by setting the standard operating
temperature of the TAG lens 370 at an elevated temperature (e.g.,
35 degrees C.) greater than the maximum specified environmental
operating temperature (e.g., 30 degrees C.), more or less heat
energy added by the regulating adaptive drive control configuration
can always be used to correct (increase) the lens' operating
temperature to meet its standard operating temperature.
[0043] According to various implementations, the TAG lens 370 may
be insulated to reduce heat transfer between the TAG lens 370 and
its environment. For example, a container of the fluid medium
forming the TAG lens 370 may be made of or covered with a suitable
heat-insulating material to reduce heat dissipation from the TAG
lens 370 into the environment.
[0044] As shown in FIG. 3, the imaging system 300 may optionally
include a lens heater 337 associated with the TAG lens 370. The
lens heater 337 is configured to input an amount of heat energy
into the TAG lens 370 to facilitate heating of the TAG lens 370
according to some implementations and/or operating conditions. The
amount of heat energy provided by the heater 337 may be
approximately fixed, at least for extended periods of lower ambient
temperatures and/or lens temperatures. For example, it may be
turned on below a temperature threshold value (e.g., below the
middle of the specified ambient temperature range), and off above
that value. In some implementations, the heat energy provided by
the heater 337 may be nominally constant at all times of operation.
The purpose of such a heater is simply to reduce the amount of heat
energy that must be supplied and dissipated in the lens during the
regulating adaptive drive mode time periods. The heater effect need
not have a fast response time, or closed loop control, in various
implementations. A simple, lost cost heating arrangements is
possible in such cases. In some implementations, an ambient
temperature may be sensed and the heater 337 may be driven
according to a linear control profile that is a function of the
ambient temperature so as to nominally make up for any reduction in
the ambient temperature below the maximum specified ambient
temperature. This allows for the regulating adaptive drive control
configuration to essentially work within a constant compensation
range (with regard to the energy it is required to dissipate into
the TAG lens 370) regardless of the ambient temperature.
[0045] As previously indicated, in various implementations, a
standard operating temperature of the TAG lens 370 is set greater
than a maximum specified environmental (ambient) operating
temperature of the TAG lens 370 or the imaging system 300. It will
be understood that when the temperature of TAG lens 370 is
relatively low compared to that standard temperature (and/or an
operating resonant frequency of the TAG lens 370 is relatively
higher than a standard frequency), in order to provide the desired
stabilization, relatively more heat must be generated in the lens
during corresponding regulating adaptive drive mode time periods.
This may be achieved by using relatively higher drive voltages
and/or a relatively longer drive duration, for example. Conversely,
when the temperature of TAG lens 370 is relatively high compared to
the standard temperature (and/or an operating resonant frequency of
the TAG lens 370 is relatively lower than a standard frequency), in
order to provide the desired stabilization, relatively less heat
must be generated in the lens during corresponding regulating
adaptive drive mode time periods. This may be achieved by using
relatively lower drive voltages and/or relatively shorter drive
duration. For example, under some conditions the regulating
adaptive drive control configuration may provide a respective TAG
lens regulating drive voltage that is lower than the standard
imaging drive voltage and/or a respective TAG lens regulating drive
duration that is shorter than the standard imaging drive duration
for at least some of the respective regulating adaptive drive mode
time periods. Under other conditions, for example when the
temperature of TAG lens 370 sufficiently approaches or exceeds the
standard temperature (and/or the operating resonant frequency of
the TAG lens 370 approaches or falls below a standard frequency),
the voltage and/or drive duration used during the regulating
adaptive drive mode time periods may be set to zero (that is, no
energy dissipation is provided under such conditions.)
[0046] The lens drive mode manager 380, which is responsible for
driving the TAG lens 370 in the imaging drive mode and in the
regulating adaptive drive mode, includes standard imaging drive
mode circuits/routines 382 configured to control generation and
transmission of the TAG lens drive signal via the signal line 334'
to the TAG lens 370 during the imaging drive mode, and regulating
adaptive drive mode circuits/routines 383 configured to control
generation and transmission of the TAG lens drive signal via the
signal line 334' to the TAG lens 370 during the regulating adaptive
drive mode. In various exemplary embodiments, the lens controller
334 switches between the image mode and the regulating adaptive
drive mode according to a defined schedule or in a predetermined
sequence. For example, the imaging drive mode time periods and the
regulating adaptive drive mode time periods may be interspersed in
a predetermined sequence, as illustrated in FIG. 5 to be described
in detail below. In one specific example, the predetermined
sequence comprises alternating between the imaging drive mode time
period and the regulating adaptive drive mode time period, as also
shown in FIG. 5.
[0047] The regulating adaptive drive mode circuits/routines 383 may
include a regulating adjustment circuit/routine 384 and a
regulating monitor circuit/routine 385. In some implementations,
the regulating adjustment circuit/routine 384 is configured to
control generation and transmission of the TAG lens drive signal
via the signal line 334' to the TAG lens 370 during the regulating
adaptive drive mode time periods according to a predetermined
sequence or schedule, as described above. In these implementations,
the lens drive mode manager 380 may control switching between
triggering the standard imaging drive mode circuits/routines 382 to
enter the imaging drive mode and triggering the regulating
adjustment circuit/routine 384 to enter the regulating adaptive
drive mode according a predetermined sequence or schedule.
[0048] FIG. 6 is a flow diagram illustrating one exemplary
implementation of a routine 600 for operating the imaging system
300 to switch between the imaging drive mode and the regulating
adaptive drive mode according to a predefined sequence or schedule.
In step 610, the routine 600 controls the TAG lens 370, in the
imaging drive mode, using a standard imaging drive control
configuration during a plurality of imaging drive mode time
periods. Each instance of the imaging drive mode time period
provides image data acquired while operating the TAG lens 370
according to the standard imaging drive control configuration. The
standard imaging drive control configuration includes a standard
imaging drive voltage and a standard imaging drive duration and is
configured to achieve a standard imaging state (e.g., a standard
imaging resonant frequency and amplitude) of the TAG lens 370. In
step 620, the routine 600 controls the TAG lens 370, in the
regulating adaptive drive mode, using a regulating adaptive drive
control configuration during a plurality of regulating adaptive
drive mode time periods that are different than the imaging drive
mode time periods. The regulating adaptive drive control
configuration is configured to provide at least one of a different
respective TAG lens regulating drive voltage and a different
respective TAG lens regulating drive duration for different
respective regulating adaptive drive mode time periods, based on a
TAG lens monitoring signal that is indicative of a difference
between the standard imaging state of the TAG lens 370 and a
current operating state of the TAG lens 370. Note that, in step
620, the TAG lens monitoring signal is used to define the
regulating adaptive drive control configuration (comprising a
different regulating drive voltage and/or a different regulating
drive duration) to drive the TAG lens 370, but the TAG lens
monitoring signal is used as a basis for entering or not entering
into the regulating adaptive drive mode. Rather, the routine 600
switches between entering the imaging drive mode (step 610) and
entering the regulating adaptive drive mode (step 620) according to
a predefined sequence or schedule.
[0049] FIG. 7 shows an alternative implementation, wherein the lens
drive mode manager 380 controls switching between the imaging drive
mode and the regulating adaptive drive mode based on a TAG lens
monitoring signal meeting or exceeding a threshold value. For
example, the lens drive mode manager 380 continues to drive the TAG
lens 370 in the standard imaging drive mode as long as a difference
between the standard imaging state of the TAG lens 370 and a
current operating state of the TAG lens 370 (e.g., a
deviation/drifting of the lens' operating temperature or operating
resonant frequency) is below a threshold or within a threshold
range (e.g., as indicated by a TAG lens monitoring signal value.)
In response to the difference meeting or exceeding the threshold or
threshold range, however, the lens drive mode manager 380 triggers
the regulating monitor circuit/routine 385 to enter the regulating
adaptive drive mode that uses a regulating adaptive drive control
configuration including at least one of a different TAG lens
regulating drive voltage and a different TAG lens regulating drive
duration for a regulating adaptive drive mode time period.
[0050] For example, in FIG. 7, in step 710, a routine 700
determines the difference between a current TAG lens monitoring
signal value (e.g., the TAG lens' operating resonant frequency) and
the value corresponding to the standard or desired imaging state of
the TAG lens (e.g., the lens' standard resonant frequency). If, in
step 720, the routine 700 determines the difference to be not
significant (e.g., not exceeding a threshold), then in step 740,
the routine 700 remains in the standard imaging drive mode and
controls the TAG lens 370 using a standard imaging drive control
configuration during an imaging drive mode time period to provide
image data acquired while operating the TAG lens 370 according to
the standard imaging drive control configuration. If there are more
images to be acquired (step 750), the routine 700 returns to steps
710 and 720 to again determine if the difference between a current
TAG lens monitoring signal value and the value corresponding to the
standard imaging state of the TAG lens 370 is significant.
[0051] If the routine 700 determines the different to be
significant (e.g., exceeding a threshold), then in step 730, the
routine 700 enters the regulating adaptive drive mode and controls
the TAG lens using a regulating adaptive drive control
configuration during a regulating adaptive drive mode time period.
The regulating adaptive drive control configuration is configured
to provide at least one of a different TAG lens regulating drive
voltage and a different TAG lens regulating drive duration for the
regulating adaptive drive mode time period based on the difference
between the current TAG lens monitoring signal value and the value
corresponding to the standard or desired imaging state of the TAG
lens 370. Thus, in the routine 700 of FIG. 7, the difference is
used twice; first in step 720 to determine whether to remain in the
imaging drive mode (step 740) or transition to the regulating
adaptive drive mode (step 730), and second in step 730 to define
the regulating adaptive drive control configuration (comprising a
TAG lens regulating drive voltage and a TAG lens regulating drive
duration) to compensate or correct for the difference.
[0052] From step 730, the routine 700 returns to steps 710 and 720
to again determine if the difference between a current TAG lens
monitoring signal value and the value corresponding to the standard
imaging state of the TAG lens 370 is significant, and continues as
described above. In some cases, when the TAG lens operating state
is relatively stabilized sufficiently close to the desired standard
imaging state, the operations of step 740 may be performed several
times without interruption by the operations of step 730. It will
be appreciated that in some implementations, the imaging drive mode
time periods may be further governed by a timing signal that
ensures that they are timed to occur at a rate within a desired
image acquisition rate range (e.g., 16 to 70 times per second, for
example).
[0053] Returning to FIG. 3, in various implementations as described
above, the TAG lens 370 may rapidly adjust or modulate the focus
position periodically, to achieve a high-speed VFL lens capable of
a periodic modulation (i.e., at a TAG lens resonant frequency) of
250 kHz, or 70 kHz, or 30 kHz, or the like. As shown in FIG. 3, by
using the periodic modulation of a signal to drive the TAG lens
370, the focus position FP of the imaging system 300 may be
(rapidly) moved within a range R (e.g., an autofocus search range)
bound by a focus position FP1 and a focus position FP2.
[0054] In one implementation, the optional focus signal processing
portion 375 (optional) may input data from the camera/detector 360
and may provide data or signals (focus monitoring signals, or FMSs)
that are utilized to determine when an imaged surface region (e.g.,
of the workpiece 320) is at a focus position. For example, in an
implementation where the camera/detector 360 includes a camera, one
or more images acquired by the camera (e.g., an image stack), may
be analyzed using a known "maximum contrast" analysis to determine
when an imaged surface region of the workpiece 320 is at a focus
position. In another implementation, the optical focus monitoring
portion 376 (optional) may provide a focus monitoring signal (FMS),
for example a signal from a photodetector, derived for image light
345 that passes through the VFL (TAG) lens 370 and is deflected
from a beamsplitter 346' to the optical focus monitoring portion
376. In one embodiment, the optical focus monitoring portion 376
may comprise a confocal optical detector configuration. However,
more generally any other suitable known focus detection
configuration may be used.
[0055] In any case, the focus signal processing portion 375 or the
optical focus monitoring portion 376 may input image light during
the periodic modulation of the focus position (sweeping of multiple
focus positions) of the VFL (TAG) lens 370 and output a
corresponding focus monitoring signal (FMS) to the Z-height (focus
distance) calibration portion 373. The Z-height calibration portion
373 may provide a Z-height (focus distance) versus FMS value
characterization that relates respective Z-heights (focus
distances) to respective FMS values indicative of images in focus.
The Z-height calibration portion 373 may further provide Z-height
(focus distance) calibration data that relates respective Z-heights
(focus distances) to respective phase timings within a period of a
standard imaging resonant frequency of the TAG lens 370, wherein
the calibration data corresponds to operating the TAG lens 370
according to the standard imaging drive control configuration.
Because the phase timings within a period of the TAG lens' standard
imaging resonant frequency can be correlated to the FMS values or
timings, the Z-height calibration data that relates respective
Z-heights to respective phase timings can be derived from the
Z-height versus FMS value characterization received from the focus
signal processing portion 375 or the optical focus monitoring
portion 376. Alternatively, the Z-height calibration data may be
otherwise defined and stored in the Z-height calibration portion
373. Generally speaking, the Z-height calibration portion 373
comprises recorded Z-height calibration data. As such, its
representation in FIG. 3 as a separate element is only schematic,
and not limiting. The associated recorded Z-height calibration data
could be merged with and/or indistinguishable from the lens
controller 334, or the focus signal processing portion 375 or the
optical focus monitoring portion 376, or a host computer system
connected to the system signal and control bus 395, in various
implementations.
[0056] The exposure (strobe) time controller 393 controls an image
exposure time of the imaging system 300 (e.g., relative to a phase
timing of the periodically modulated focus position) and may be
merged with or indistinguishable from the camera/detector 360.
Specifically, the exposure (strobe) time controller 393, using the
Z-height calibration data available in the Z-height calibration
portion 373, may control the light source 330 including a strobe
light source to strobe at a respective controlled time. For
example, the exposure (strobe) time controller 393 may control the
strobe light source to strobe at a respective phase timing within a
period of a standard imaging resonant frequency of the TAG lens
370, so as to acquire an image in best focus within the sweeping
(periodic modulation) range of the TAG lens 370. In other
implementations, the exposure time controller 393 may control a
fast electronic camera shutter of the camera/detector 360 to
acquire an image signal at a respective controlled time. For
example, the exposure time controller 393 may control the camera
shutter at a respective phase timing within the period of the
standard imaging resonant frequency of the TAG lens 370 so as to
acquire an image in best focus within the sweeping (periodic
modulation) range of the TAG lens 370.
[0057] Generally, the exposure time controller 393 controls
acquisition of image data by controlling an image exposure period
during which the camera/detector 360 may capture an image of the
workpiece 320. Thus, the exposure time controller 393 may control
image acquisition so as to acquire image data only during the
imaging drive mode, in which accurate inspection images of the
workpiece 320 are expected, and not during the regulating adaptive
drive mode, in which some deterioration of the image quality is
expected due to an adjustment made to the drive signal of the TAG
lens 370. That is, the exposure time controller 393 may prevent
image exposure during the regulating adaptive drive mode to thereby
prevent image acquisition during the regulating adaptive drive
mode. For example, during the imaging drive mode, image data of the
workpiece 320 may be acquired and displayed in a user interface of
the imaging system 300 (see FIG. 2, display devices 136), while
during the regulating adaptive drive mode image data is not
acquired. In some implementations, image data may be acquired by
the camera/detector 360 during the regulating adaptive drive mode
but is not outputted by the imaging system 300.
[0058] In other implementations, image data may be acquired during
the regulating adaptive drive mode. For example, image data
acquired during the regulating adaptive drive mode, though the
associated image quality and or measurement accuracy may be
substandard, may still serve to provide "observational images" that
are sufficient for an operator to continuously observe the
workpiece 320 between the imaging drive mode and the regulating
adaptive drive mode. In such a case the image data acquired during
the regulating adaptive drive mode may be displayed also in the
user interface of the imaging system 300.
[0059] FIG. 5 is a timing chart illustrating one exemplary
operation of an imaging system including a TAG lens. FIG. 5
illustrates the relationship between the "Camera Exposure Timing"
500 during which image data may be acquired by the camera/detector
360, "Image Lighting" timing 502 used by the exposure (strobe) time
controller 393 to turn on or off the lighting used for image
exposure, "Difference in Monitored Signal" 503 indicative of a
difference between the standard imaging state and a current
operating state of the TAG lens 370, and "Drive Mode (Vpzt)"
configuration 504 used to drive the TAG lens 370. With a high speed
TAG lens having a rapid response time (<50 .rho.s), switching or
modulating between the two modes of operation (imaging drive mode
and regulating adaptive drive mode) may be possible within the
frame time of a typical camera/detector 360 (e.g., 16-32 frames/s),
for example per half the frame time (e.g., 32-64 times per
second).
[0060] FIG. 5 is a timing chart example of switching between the
two modes according to a predetermined sequence, as described in
the flow chart of FIG. 6. In the illustrated example, a plurality
of imaging drive mode time periods 504A and a plurality of adaptive
drive mode time periods 504B are interspersed in an alternative
manner along the time axis. Before each of the imaging drive mode
time periods 504A, a warm-up period (t1-t2, t6-t7, t12-t13, and
t15-t16) may be provided. The warm-up period is provided to allow
time for the TAG lens 370 to establish and re-establish stable
optical operation (i.e., achieving a standard imaging state) before
acquiring image data. For example, the warm-up period may
correspond to 3 TAG lens cycles operating at a resonant frequency
of 70 kHz.
[0061] In the imaging drive mode time periods 504A, a standard
imaging drive control configuration is used, such that each
instance of the imaging drive mode time period 504A provides image
data acquired while operating the TAG lens 370 according to the
standard imaging drive control configuration. In the illustrated
example, the standard imaging drive control configuration includes
a standard imaging drive voltage (e.g., 30 V or 30 Vpzt) and a
standard imaging drive duration (e.g., t2-t3, t7(t2)-t8(t3),
t13(t2)-t14(t3), and t16(t2)-t17(t3)) and is configured to achieve
a standard imaging state of the TAG lens 370. The standard imaging
drive duration may occur periodically at a rate of 16-70 times per
second, in some implementations (although, this range of rates is
exemplary only, and not limiting.) The exposure (strobe) time
controller 393 turns on the image-exposure lighting (e.g., strobe
lighting) of the imaging system 300 during a plurality of lighting
exposure periods 502A that are synchronized with the imaging drive
mode time periods 504A. Image data are acquired and integrated by
the camera/detector 360 during a plurality of image integration
periods 500A that are synchronized with the lighting exposure
periods 502A and with the imaging drive mode time periods 504A. In
various implementations, the acquired image data is displayed in a
user interface of the imaging system 300.
[0062] In the regulating adaptive drive mode time periods 504B, a
regulating adaptive drive control configuration is used which
provides at least one of a different respective TAG lens regulating
drive voltage and a different respective TAG lens regulating drive
duration for different respective regulating adaptive drive mode
time periods 504B, based on a TAG lens monitoring signal that is
indicative of a difference between the standard imaging state and a
current operating state of the TAG lens 370. For example, the lens
controller 334 uses a TAG lens monitoring signal that monitors an
operating resonant frequency and/or an operating temperature of the
TAG lens 370. The TAG lens monitoring signal is indicative of a
current operating state of the TAG lens 370 and, thus, may be
obtained prior to, or in correspondence with, the current
regulating adaptive drive mode time period 504B. For example, a
regulating adaptive drive control configuration applied in the
regulating adaptive drive mode time period 504B between t3 and t6
may be based on the TAG lens monitoring signal obtained prior to
t3, such as between t2 and t3, between t1 and t2, etc.
[0063] In the illustrated example, during the first regulating
adaptive drive mode time period 504B between t3 and t6, TAG lens
regulating drive voltage dA1 (e.g., 40 V) is used between t3 and
t4, TAG lens regulating drive voltage dA2 (e.g., 30 V) lower than
dA1 is used between t4 and t5, and TAG lens regulating drive
voltage dA3 (e.g., 20V) lower than dA2 is used between t5 and t6.
Periods between t3 and t4, between t4 and t5, and between t5 and t6
may be considered as respectively constituting regulating adaptive
drive mode time periods or as collectively constituting the
regulating adaptive drive mode time period 504B between t3 and t6.
The regulating adaptive drive control configuration applied in the
first regulating adaptive drive mode time period 504B between t3
and t6 has an energy dissipation level "A" as graphically
illustrated in FIG. 5. The regulating adaptive drive control
configuration is based on a TAG lens monitoring signal that is
obtained prior to, or in correspondence with, the current
regulating adaptive drive mode time period 504B between t3 and t6,
and that indicates the difference 503 between the standard imaging
state and a current operating state of the TAG lens 370.
[0064] During the "second" regulating adaptive drive mode time
period 504B between t8(t3) and t12(t6), TAG lens regulating drive
voltage dB1 (e.g., 40 V) is used between t8(t3) and t9, TAG lens
regulating drive voltage dB2 (e.g., 30 V) lower than dB1 is used
between t9 and t10, and TAG lens regulating drive voltage dB3
(e.g., 20V) lower than dB2 is used between t10 and t11. No voltage
(V=0) is applied between t11 and t12(t6). Periods between t8(t3)
and t9, between t9 and t10, between t10 and t11, and between t11
and t12(t6) may be considered as respectively constituting
regulating adaptive drive mode time periods or as collectively
constituting the regulating adaptive drive mode time period 504B
between t8(t3) and t12(t6). The regulating adaptive drive control
configuration applied in the second regulating adaptive drive mode
time period 504B between t8(t3) and t12(t6) has an energy
dissipation level "B" as graphically illustrated in FIG. 5. The
regulating adaptive drive control configuration is based on a TAG
lens monitoring signal that is obtained prior to, or in
correspondence with, the current regulating adaptive drive mode
time period 504B between t8(t3) and t12(t6) and that indicates the
difference 503 between the standard imaging state and a current
operating state of the TAG lens 370. In the illustrated embodiment,
the energy dissipation level "B" of the current regulating adaptive
drive mode time period 504B between t8(t3) and t12(t6) is different
from, or adjusted from, the energy dissipation level "A" of the
previous (first) regulating adaptive drive mode time period 504B
between t3 and t6.
[0065] During the "third" regulating adaptive drive mode time
period 504B between t14(t3) and t15(t6), TAG lens regulating drive
voltage dC1 (e.g., 40 V) is applied, which is the highest voltage
usable to drive the TAG lens 370 in the illustrated example. The
regulating adaptive drive control configuration has an energy
dissipation level "C" during the current regulating adaptive drive
mode time period 504B between t14(t3) and t15(t6) as illustrated in
FIG. 5. The regulating adaptive drive control configuration is
based on a TAG lens monitoring signal that is obtained prior to, or
in correspondence with, the current regulating adaptive drive mode
time period 504B between t14(t3) and t15(t6) and that indicates the
difference 503 between the standard imaging state and a current
operating state of the TAG lens 370. In the illustrated example,
the difference 503 indicates a sudden increase in the operating
resonant frequency of the TAG lens 370 or a corresponding sudden
decrease in the operating temperature and/or the environmental
(ambient) temperature of the TAG lens 370, as designated by 503'.
Thus, the energy dissipation level "C" of the regulating adaptive
drive control configuration to be applied between t14(t3) and
t15(t6) is configured to input more heat energy to the TAG lens
370, compared to the energy dissipation levels "A" and "B" applied
in the previous regulating adaptive drive mode time periods 504B
between t3 and t6 and between t8(t3) and t12(t6), to compensate for
the sudden change.
[0066] During the "fourth" regulating adaptive drive mode time
period 504B between t17(t3) and t18(t6) (not shown), no voltage dD1
(=0 V) is applied. The regulating adaptive drive control
configuration has an energy dissipation level "D" during the
current regulating adaptive drive mode time period 504B between
t17(t3) and t18(t6) as illustrated in FIG. 5. The regulating
adaptive drive control configuration is based on a TAG lens
monitoring signal that is obtained prior to, or in correspondence
with, the current regulating adaptive drive mode time period 504B
between t17(t3) and t18(t6) and that indicates the difference 503
between the standard imaging state and a current operating state of
the TAG lens 370. In the illustrated example, the regulating
adaptive drive control configuration applied in the previous
regulating adaptive drive mode time period 504B between t14(t3) and
t15(t6) was effective in lowering/decreasing the difference 503 (by
increasing the operating temperature of the TAG lens 370), as also
illustrated in FIG. 5. Thus, the energy dissipation level "D" of
the regulating adaptive drive control configuration to be applied
between t17(t3) and t18(t6) is configured to input "no" additional
heat energy to the TAG lens 370, which is different from any of the
energy dissipation levels "A," "B" and "C" applied in the previous
regulating adaptive drive mode time periods 504B between t3 and t6,
between t8(t3) and t12(t6), and between t14(t3) and t15(t6).
[0067] The regulating adaptive drive control configuration provides
at least one of a different respective TAG lens regulating drive
voltage and a different respective TAG lens regulating drive
duration for different respective regulating adaptive drive mode
time periods 504B so as to establish or maintain the TAG lens 370
at its standard imaging state (e.g., a standard operating resonant
frequency or a standard operating temperature). In various
implementations, the exposure (strobe) time controller 393 may turn
off the image-exposure lighting (e.g., strobe lighting) of the
imaging system 300 during a plurality of lighting exposure periods
502B that are synchronized with the regulating adaptive drive mode
time periods 504B. In some implementations, image data may be
acquired and integrated by the camera/detector 360 during a
plurality of image integration periods 500B that are synchronized
with the lighting exposure periods 502B and with the regulating
adaptive drive mode time periods 504B. The acquired data may be
presented as observational images in a user interface of the
imaging system 300. In other implementations, image data are not
acquired and integrated during the plurality of image integration
periods 500B, or an output of acquired images may be prevented
during the plurality of image integration periods 500B.
[0068] While preferred implementations of the present disclosure
have been illustrated and described, numerous variations in the
illustrated and described arrangements of features and sequences of
operations will be apparent to one skilled in the art based on this
disclosure. Various alternative forms may be used to implement the
principles disclosed herein. In addition, the various
implementations described above can be combined to provide further
implementations. All of the U.S. patents and U.S. patent
applications referred to in this specification are incorporated
herein by reference, in their entirety. Aspects of the
implementations can be modified, if necessary to employ concepts of
the various patents and applications to provide yet further
implementations.
[0069] These and other changes can be made to the implementations
in light of the above-detailed description. In general, in the
following claims, the terms used should not be construed to limit
the claims to the specific implementations disclosed in the
specification and the claims, but should be construed to include
all possible implementations along with the full scope of
equivalents to which such claims are entitled.
* * * * *