Automated rotation mechanism for spherically mounted retroreflector

An apparatus includes a kinematic nest that supports an element having a spherical surface, a rotation mechanism that rotates the element, and processor that activates the rotation mechanism.

BACKGROUND

The present disclosure relates to automation of three-dimensional (3D) coordinate measurements.

One set of coordinate measurement devices belongs to a class of instruments that measure the three-dimensional (3D) coordinates of a target point by sending a beam of light to the point. The beam of light may impinge directly on the point or on a retroreflector target in contact with the point. In either case, the instrument determines the coordinates of the target point by measuring a distance and two angles to the target. The distance is measured with a distance-measuring device such as an absolute distance meter or an interferometer. The angles are measured with an angle-measuring device such as an angular encoder. The beam may be steered with a gimbaled mechanism, a galvanometer mechanism, or other mechanism.

A tracker is a particular type of coordinate-measuring device that tracks the retroreflector target with one or more beams it emits, which may include light from a laser or non-laser light source. Coordinate-measuring devices closely related to the tracker include the total station. A total station is a 3D measuring device most often used in surveying applications. It may be used to measure the coordinates of a diffusely scattering target or a retroreflective target. Hereinafter, the term tracker (or laser tracker) is used in a broad sense to include trackers as well as total stations and to include dimensional measuring devices that emit laser or non-laser light.

In many cases, a tracker sends a beam of light to a retroreflector target. A common type of retroreflector target is the spherically mounted retroreflector (SMR), which comprises a cube-corner retroreflector embedded within a metal sphere. The cube-corner retroreflector comprises three mutually perpendicular mirrors. The vertex, which is the common point of intersection of the three mirrors, is located at the center of the sphere. Because of this placement of the cube corner within the sphere, the perpendicular distance from the vertex to any surface of the SMR rests remains constant, even as the SMR is rotated. Consequently, the tracker can measure the 3D coordinates of a surface by following the position of an SMR as it is moved over the surface. Stating this another way, the tracker measures only three degrees of freedom (one radial distance and two angles) to fully characterize the 3D coordinates of a surface.

One type of tracker contains only an interferometer (IFM) without an absolute distance meter (ADM). If an object blocks the path of the beam of light from one of these trackers, the IFM loses its distance reference. The operator must then track the retroreflector to a known location to reset to a reference distance before continuing the measurement. A way around this limitation is to put an ADM in the tracker. The ADM can measure distance in a point-and-shoot manner. Some trackers contain only an ADM without an interferometer.

A gimbal mechanism within the tracker may be used to direct a beam of light from the tracker to the SMR. Part of the light retroreflected by the SMR enters the tracker and passes onto a position detector. A control system within the tracker uses position of the light on the position detector to adjust the rotation angles of the mechanical axes of the tracker to keep the beam of light centered on the SMR. In this way, the tracker is able to follow (track) a moving SMR.

Angle measuring devices such as angular encoders are attached to the mechanical axes of the tracker. The one distance measurement and two angle measurements of the tracker are sufficient to specify a three-dimensional location of the SMR. In addition, several trackers are available or have been proposed for measuring six degrees-of-freedom (six-DOF), rather than the ordinary three degrees-of-freedom. Such six-DOF measuring device may include tactile probes, triangulation scanners, sensors, and projectors, for example.

Many trackers today include one or more cameras. Such cameras may be attached to outer portions of the rotatable tracker frame or may be positioned internal to the tracker. The main uses for such cameras are in determining the location of retroreflectors or in performing six-DOF measurements.

In some cases, a tracker tracks the movement of an SMR and records 3D coordinates of an object when the SMR is brought in contact with the surface of the object. In other cases, a tracker tracks the movement of a six-DOF device and measures 3D coordinates of an object with the six-DOF device. In these types of measurements it is frequently necessary to measure an object from multiple different directions. For example, it may be necessary to measure an auto body-in-white from the front, right side, rear, and back side. When the tracker is moved from location to location to obtain these different 3D measurements, a method is needed for bringing the 3D measurements obtained by the tracker in the different locations into a common frame of reference. A way of doing this in practice is to place at three or more SMRs on kinematic nests spaced around the object to be measured. At each location, the tracker measures the positions of the different SMRs. In each case, the SMR is pointed back at the tracker to allow the beam of light from the tracker to fall within the acceptance angle of the SMR. To do this, an operator walks to each SMR and rotates it to face the tracker. In the case of a fully automated measurement, for example, when a tracker is on a self-propelled mobile stand or the object being measured is on a conveyor belt, it may not be possible for the operator to manually turn each SMR.

Although trackers and other 3D measuring instruments are generally suitable for their intended purpose, the need for improvement remains, particularly in enabling automation of 3D measurements by the tracker or other 3D measuring device.

SUMMARY

According to an embodiment of the present invention, an apparatus comprises: a kinematic nest operable to support a first element, the first element having a spherical surface; a rotation mechanism operable to rotate the first element on the kinematic nest while the spherical surface retains contact with the kinematic nest; and a first processor operable to activate the rotation mechanism.

According to another embodiment of the present invention, a method comprises: providing a system processor; providing a collection of at least three devices, each device having its own kinematic nest, rotation mechanism, and device processor, each device coupled to a first element having a spherical surface, the rotation mechanism operable to rotate the first element on the kinematic nest while holding the spherical surface in contact with a kinematic nest; and sending a signal from the system processor to the device processor in one of the devices and, in response, rotating the first element with the rotation mechanism.

DETAILED DESCRIPTION

An exemplary tracker10is shown inFIG. 1. As explained in the introduction, the term tracker is here in a general sense that includes total stations. The beam of light90may come from a laser, a superluminescent diode, a light emitting diode (LED), or other type of collimated light source.

The exemplary tracker10inFIG. 1sends outgoing light90through an exit aperture74to a retroreflector95, which returns the light along a parallel path as returning light92, which passes a second time through the exit aperture74. The tracker includes a base assembly30, a yoke assembly60, and a payload assembly70. An outer portion of the payload assembly70includes payload assembly covers72, a first target camera76, a second target camera78, and payload indicator lights80. The target cameras are also referred to as locator cameras. In an embodiment, the indicator lights80may emit a predetermined first color, such as green for example, to indicate found target, a second predetermined color, such as red for example, to indicate measuring, and other predetermined colors, such as blue or yellow for example, for user-definable or six-DOF indications. In an embodiment, an outer portion of the yoke assembly60includes yoke-assembly covers62and yoke indicator lights64. In an embodiment, yoke indicator lights may advantageously be seen at large distances from the tracker. An outer portion of the base assembly30includes base-assembly covers32and magnetic home-position nests34operable to hold SMRs of different diameters. In an embodiment, three magnetic home-position nests34accept SMRs having diameters of 1.5 inches, 0.875 inch, and 0.5 inch. The 1.5-inch home-position nest is labeled34A. A mandrel20may optionally be attached to a lower portion of the tracker10.

FIG. 2shows a front view of the tracker10. The base assembly30is ordinarily stationary with respect to a work area, for example, being mounted on an instrument stand or an industrial tripod. The yoke assembly60rotates about an azimuth axis12, sometimes referred to as a standing axis or a vertical axis, although it should be appreciated that the tracker10may, in general, be positioned upside down or be rotated to an arbitrary angle with respect to a floor. The payload assembly70rotates about a zenith axis14, sometimes referred to as a transit axis or a horizontal axis.

In an embodiment illustrated inFIG. 3, one or more target cameras76,78are used to locate one or more retroreflectors95in an environment. A stereo pair of target cameras, such as cameras76,78, is described in U.S. Pat. No. 8,670,114, the contents of which are incorporated by reference herein. In an embodiment, the light sources76B,78B, located close to the camera photosensitive arrays76A,78A, are periodically flashed at regular intervals. The flashing lights76B,78B illuminate the retroreflector95. Reflected beams of light77,79travel to the photosensitive arrays76A,78A, respectively. In an embodiment, the image capture rate of the photosensitive arrays76A,78A is set to half the flash rate of the lights76B,78B so that the retroreflector95appears to be brightly and dimly illuminated in alternate images. In an embodiment, the dimly illuminated retroreflector images are subtracted from the brightly illuminated retroreflector images, thereby obtaining bright a bright image spot for each illuminated retroreflector. However, the light from the light sources76B,78B is not reflected in a concentrated manner from non-retroreflective objects. Consequently, background images when subtracted appear to be relatively dim compared to the retroreflectors. This use of flashing lights76B,78B greatly simplifies the identification of retroreflectors in the environment.

In an embodiment, the light sources76B,78B are light emitting diodes (LEDs) that emit light at a near infrared wavelength such as 850 nm. In an embodiment, the beam of light92shown inFIG. 1includes a different wavelength such as 635 nm, which corresponds to red light. In an embodiment, it is desirable for the cameras76,78to accept visible wavelengths as well as the wavelengths emitted by the light sources76B,78B as this provides color images that further show bright flashing spots of light at the locations of retroreflectors such as the retroreflector95. The target cameras76,78may also be used without turning on the lights76B,78B. In this mode of operation, color images may be obtained without retroreflectors95producing bright spots in captured 2D images.

FIG. 4Ais a front view of the payload assembly70and an upper portion of the yoke assembly60.FIG. 4Bis a cross-sectional view D-D (as shown inFIG. 4A) showing optical elements within the payload assembly70. Optical elements placed mainly along a central portion of the payload assembly70are referred to as a central-optics assembly400, which includes a launch/collimator assembly410and a position-detector assembly460. Outside the central-optics assembly410are an ADM module465and an internal camera470.

The combiner assembly450is used to combine the launch/collimator assembly410with the position-detector assembly460, and it is also used to combine different beams of light from the position detector splitter454and the beam splitter456. The position-detector assembly460includes a position detector mounted on a position-detector circuit board. The position detector is a detector that converts light into electrical signals and further provides secondary electrical signals that enable determination of a position at which light strikes a surface area of the position detector478. Examples of position detectors include a lateral effect detector, a quadrant detector, a complementary metal-oxide-semiconductor (CMOS) array, and a charge-coupled detector (CCD).

The position-detector assembly460is ordinarily used to keep the outgoing beam of light90centered or nearly centered on a moving retroreflector95, thereby causing the returning beam of light92to follow the same path as the outgoing beam of light90. A control system (also referred to as a tracking system) causes the tracker motors to steer the beam to keep moving the beam toward the center of the position detector, thereby enabling tracking of the retroreflector95with the tracker10. In practice, when the outgoing beam is exactly centered on a retroreflector, the returning beam may fall a little off a center of the position detector. The position on the position detector of the return beam when the outgoing beam is centered on the retroreflector is referred to as the retrace point of the position detector.

In an embodiment, the tracker10includes an internal camera470that provides a high resolution color image over a relatively narrow FOV. In an embodiment, the beam splitter456is coated to reflect a color image into the internal camera470.

FIG. 5shows a computing system500coupled to the tracker10, either as computing components within the tracker or as external computing components coupled to the tracker computing system, possibly by a networking link such as a link544. The term computing system as used herein is taken as having the same meaning as processing system or simply processor. The term processor as used herein is taken to include all components used to support computing. Memory elements such as registers, cache, volatile memory, non-volatile memory, and remote storage are included as a part of the processor. Devices such as central processing units (CPUs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), and all support electronics that connect together computing and memory components are also included. Input/output devices through which the computing and memory elements receive information, possibly from a user, are also included as a part of the processor. Some typical computing functions510found in a laser tracker10are shown inFIG. 5. In an embodiment, these include position detector processing512, azimuth encoder processing514, zenith encoder processing516, indicator lights processing518, absolute distance meter (ADM) processing520, target camera processing522, and gestures pre-processing526. This is only a partial list of processing functions included within the tracker. The processing elements within the tracker are connected to one another and to external computers570through a bus530. Communication with external computers, including networked computers, may be carried out through wired or wireless communication channels.

The optical axis of the tracker is the axis through which the beam of light92leaves the tracker and returns to the tracker. The position of the retroreflector in the first images indicates the direction the position of the retroreflector95in space in relation to the tracker. Positions on the photosensitive arrays76A,78A of the target cameras74,76are indicative of angles of objects in relation to a perspective center of the camera lens systems. Hence the positions of a retroreflector95on first images of the cameras76,78may be used to determine the angles to points on an object of interest in relation to the cameras76,78.

A common situation is for an object to be measured by a tracker placed at multiple different locations relative to an object to be measured. It may be that the object is stationary while the tracker is moved to the multiple different objects, or it may be that the tracker is held fixed in location, while the object is moved to multiple different locations. Regardless, the changing the relative pose of the tracker and the object allows the tracker to make 3D measurements on multiple portions of an object or on multiple sides of an object. As further described herein, the object is taken as stationary while the tracker is taken as moving. However, in an embodiment the reverse may also be true—for example, when an object is moving on a conveyor while the tracker is held still. This embodiment is illustrated inFIGS. 12A, 12B, 12Cand discussed herein. To simplify the discussion herein, the tracker is generally illustrated and described as moving to different locations while the object is held fixed. However, it should be understood that the relative motion may likewise result from movement of the object.

FIG. 6illustrates an arrangement that enables 3D measurements made by a tracker in multiple locations relative to an object frame of reference. The object frame of reference as here defined is a frame of reference fixed with respect to the object. In an embodiment illustrated inFIG. 6, a tracker10in a first location C is denoted as tracker10C. The same tracker10at a different location D is denoted as tracker10D. The tracker10at location C and at location D measure 3D coordinates of different sides of the object620. In an embodiment, the tracker10at either location C or location D has an internal tracker frame of reference with tracker axes XT, YT, ZTtied to the geometry of the tracker10. In an embodiment, the internal tracker frame of reference has an origin at 3D coordinates (0, 0, 0) at the tracker gimbal point, which is the ideal center of mechanical rotation of the tracker. In an embodiment, the XTaxis is pointed forward (toward the SMR95inFIG. 1), the YTaxis is pointed to the tracker's left (to the right inFIG. 2), and the ZTaxis is pointed upward (along the direction12inFIG. 2). The corresponding tracker10at location D has the same axes XT, YT, ZTin its internal tracker frame of reference.

The 3D measurements obtained by the tracker10at the location C and the 3D measurements obtained by the tracker10at the location D are transformed into an object frame of reference630-O, which has three mutually perpendicular coordinate axes x, y, z. The tracker at the location C has a first frame of reference630-1with axes X1, Y1, Z1. In general, each of the axes X1, Y1, Z1are translated and rotated relative to the axes x, y, z of the object frame of reference. The tracker at the location D has a second frame of reference630-2with axes X2, Y2, Z2. In general, each of the axes X2, Y2, Z2are translated and rotated relative to the axes x, y, z of the object frame of reference.

To consistently combine 3D coordinates measured by the tracker at the location C with the 3D coordinates of the tracker at the location D, a method is used to transform the 3D coordinates of the object620measured by the tracker10in the first frame of reference630-1at the location C and by the tracker10in the second frame of reference630-2at the location D into 3D coordinates in the object frame of reference630-O. Such a transformation may be made by performing a mathematical transformation procedure. Many types of mathematical transformation procedures are equivalent and may be used. In an embodiment, a rotation matrix and a translation matrix are applied in turn to each of the measured 3D coordinates. In an embodiment, this mathematical transformation procedure is applied to the 3D coordinates measured at locations C and D, with the values of the rotation matrix and the translation matrix differing for the locations C and D. The result is to place all the 3D coordinates measured at locations C and D into the single object frame of reference630-O.

A way to collect the information needed to transform 3D coordinates from the tracker frame of reference to the global frame of reference is now described. The retroreflectors95A,95B,95C are all fixed in the object frame of reference630-O, which means that they are fixed with respect to the object620. The retroreflectors95A,95B,95C have central reflection points96A,96B,96C, also referred to herein as the first point, the second point, and the third point, respectively. For the case of an SMR that contains a cube-corner retroreflector, the central reflection point is at the vertex of the cube-corner, which is located at the center of the SMR sphere.

In an embodiment, the tracker10at location C measures the central reflection points96A,96B, and96C, and the tracker10at location D also measures the central reflection points96A,96B,96C. These measured points are used to transform the measured 3D coordinates at the locations C and D into the object frame of reference630-O. In a simple exemplary case, the first frame of reference630-1of the tracker at location C is also taken as the object frame of reference630-O. Since the second frame of reference630-2is different than the first frame of reference630-1, the second frame of reference630-2may not in this instance coincide with the object frame of reference630-O. Other tracker measurements, for example, of features on the object620from the tracker at location C or D, could be used to determine transformations fixing the global frame of reference to some features of the object. However, in the illustrated embodiment, the three measurements of the central reflection points96A,96B,96C from the tracker10at locations C and D provide the information to place 3D coordinates of points measured on the object620into the object frame of reference630-O.

In an embodiment, the reflection points96A,96B,96C are the vertexes of cube-corner retroreflectors centered in SMRs. In an embodiment, the SMRs95A,95B,95C are placed on kinematic nests610A,610B,610C. In an embodiment, each kinematic nest includes three spherical contact points611in contact with the spherical surface of the SMRs95A,95B,95C. Other types of kinematic mounts are possible, and kinematic nests610A,610B,610C are not limited to having spherical contact points. In an embodiment, a kinematic nest includes a magnet that securely holds a ferromagnetic SMR in place. Note that the SMRs95A,95B,95C may be rotated on the kinematic nests610A,610B,610C, respectively, without changing the location of the sphere center or vertex. This property of the kinematic nests when used with the SMR enables the SMRs to retain constant 3D coordinate values for the reflection points96A,96B,96C as the SMRs is pointed to a beam of light from each tracker10at locations C and D or other locations in space.

It should be noted that other types of retroreflectors besides cube-corner retroreflectors or SMRs may be used. For example, one or more of the retroreflectors may be cateye retroreflectors. Such cateye retroreflectors may be made in a variety of ways. In one embodiment, the cateye retroreflector is made of two hemispherical glass elements joined at their flat surfaces and arranged so as to focus the light to a point at a rear surface of one of the two hemispheres. Such cateye retroreflectors may have an acceptance angle of +/−60 degrees, which is approximately twice the acceptance angle of a typical SMR. In embodiments of the present invention, a variety of retroreflector types may be used.

The description given above is for a single tracker10moved to two different locations C and D to measure 3D coordinates of an object620from different directions before combining the measured 3D coordinates into a common object frame of reference. Although this is a common approach in practice, it is also possible to mount two different trackers at the locations C and D and to measure 3D coordinates of points on the object620with both trackers.

In practice, when moving a tracker to a multiplicity of different locations such as the locations C and D inFIG. 6, it is often necessary to rotate the SMRs95A,95B,95C to place the angle of acceptance along a line that connects the SMR to the tracker. In an open-air cube-corner retroreflector, the angle of acceptance is approximately +/−25 degrees. Consequently, it is often the case that the SMRs such as the SMRs95A,95B,95C have to be rotated several times during completion of a measurement tasks such as measuring all four sides of an object. For measurements performed manually by an operator, it would be convenient to have the SMRs automatically rotate to face the tracker whenever the tracker was moved to a new location. For measurements performed automatically, for example, using a tracker mounted on a robotic mobile stand, automatic rotation of SMRs is desired. There are other embodiment in which the tracker is left in a single location but nests are mounted on a moveable object. An example of this situation is one in which a 3D measuring device is mounted on a cart and moved from place to place to measure 3D coordinates. A way to accurately register the 3D coordinates measured in each location is to measure with a tracker three or more SMRs placed on the cart at each location. By measuring the positions of the SMRs after each move, the tracker obtains enough information to enable registration of the multiple 3D data sets. In this case also, automatic rotation of SMRs is either convenient or essential, depending on the application.

FIG. 7A,FIG. 7B,FIG. 8,FIG. 9andFIG. 10show an embodiment of a SMR rotator700that automatically rotates SMRs95to face a laser tracker. In an embodiment, an SMR95is made to rotate on three points of a kinematic mount while the kinematic mount is held fixed in space. In an embodiment, the kinematic mount is the 1.5-inch magnetic home-position nest34A shown inFIG. 1. InFIG. 7A,FIG. 7B,FIG. 9andFIG. 10, this same nest is labeled710. Elements of this nest are shown inFIG. 7B. In an embodiment, the nest has three kinematic contact points712. These contact points serve the same function as the contact points provided by the spheres611inFIG. 6. The contact points712are configured such that the vertex99of the retroreflector98in the SMR95, which is coincident with the center of the spherical surface94, is at the same position within the magnetic nest710. Hence, the vertex99and center94of the SMR95will have the same 3D coordinates before the SMR95is removed from the nest710and after it is placed back on the nest710. As used herein, a nest having this property is referred to as a kinematic nest. In most embodiments, the change in 3D coordinates of the SMR before and after replacement will not differ by more than one micrometer for the nest710. As shown inFIG. 7B, the kinematic nest710also includes cutouts716and attachment holes717placed in a nest surface712.

The SMR95is held against the kinematic nest710by the magnet714with an SMR base718. The SMR95and it is locked in its orientation by the collar attachment assembly720shown inFIG. 9. The collar attachment assembly720includes an attachment base721, attachment bracket722, wing nut723, screw724, dowel pin725, and rubber band729. The attachment bracket722is attached on one side of the attachment base721with the wing nut723and screw725through the hole726. The attachment bracket722is attached on the other side of the attachment base721with the dowel pin725. The attachment bracket722is adjusted to a desired position and then locked in place with the wing nut723. As shown inFIGS. 7A, 8, 9, the rubber band729goes around the SMR collar97and a lip of the attachment bracket722, thereby holding the SMR95secure against the attachment bracket722. The SMR95rotates smoothly on the fixed kinematic nest710.

As shown inFIG. 9, the nest710is glued or otherwise attached to an SMR stem733. A bearing732is coupled on the inside of the bearing732to the SMR stem733. The bearing732is coupled on the outside of the bearing732to the secondary gear731. The bearing provides low friction to the secondary gear731in rotating about the SMR stem733. In an embodiment, the attachment base721is screwed to the secondary gear.

The secondary gear731is driven by a primary gear741, which is driven by a shaft743of a motor742. In an embodiment, the motor742is a 1000:1 micro metal gear motor. Such a motor provides fine control at low speeds. In an embodiment, the motor742is attached to a rotary encoder that includes a magnet745and Hall effect sensor744. The motor742is attached to a motor mount734with motor bracket746. The motor mount734is attached to the SMR stem733. The motor mount734also supports home sensor735. In an embodiment, the home sensor735is a U-shaped micro photoelectric sensor. The photoelectric sensor emits a beam of light across the U-shaped region and provides an electrical indication when the beam is broken by a projection731A of the secondary gear731. The home sensor735, in combination with the magnet745and Hall effect sensor744, provides a convenient way to determine the rotational position of the SMR95.

In an embodiment, a housing cover701is attached to a housing base704. In an embodiment, a mounting cage706includes a cage base706A, which is attached to the housing base704. The SMR stem733is attached through a hole in the cage base706A to the housing base704. An interface board754is attached to the cage base706A. The interface board754includes many wire sockets for interconnecting electrical components within the SMR rotator700. In an embodiment, the mounting cage706includes a battery holder706B that holds a battery751. The battery is held in position by a battery cover705. In an embodiment, the battery751is a rechargeable battery such as a lithium-ion battery. In an embodiment, the mounting cage706includes a fan mount706C to support a fan755.FIG. 10shows that the housing cover701includes ventilation ports703to permit outside air to be circulated into and out of the interior of the housing cover701. There are three ventilation ports, one of which is placed on the opposite side of power switch760and hidden from view inFIG. 10. The housing cover701further includes an upper cutout702through which elements are mounted for support of the SMR95.

In an embodiment, SMR rotator700includes an electronics system750having electrical boards and components attached to the mounting cage. In an embodiment, the first electronics mount706D attaches to a computing circuit board753. In an embodiment, the computing circuit board is an Arduino Yun or Arduino Tian. In other embodiments, other types of computing circuit boards are used. In an embodiment, the mounting cage706further includes a second electronics mount706E. In an embodiment, the second electronics mount706E holds a voltage regulator756and a motor driver757. In an embodiment, the voltage regulator756takes an input voltage of up to 7.5 volts from the power management circuit board752and efficiently reduces it to 5 volts. In an embodiment, the power management circuit board752receives input voltage (for charging the battery751) from a separate platform power supply that receives input voltage from 100 to 240 VAC and outputs 19 VDC through the input ports762. In an embodiment, the power management circuit board752attaches to the outside of the battery holder706B. The housing cover701includes openings for a power switch760, a DC jack762, a multi-color status light emitting diode (LED)763, and access to an Ethernet connector753B.

In an embodiment illustrated inFIG. 11, a system1100includes three or more SMR rotators700A,700B,700C that receive signals from a system processor. A system processor might be any or all of the processors in or connected to a laser tracker10as illustrated inFIG. 5. It might be a processor in a fixed computer1110B or mobile device such as a handheld phone1110A. The signal may be transmitted via wired or wireless mediums. In an embodiment, the signals to and from the SMR rotators700A,700B,700C are routed through a network connection device1120. For the case in which wireless signals are used, the network connection device1120may be a “Wi-Fi/Ethernet Access Point.”

In an embodiment, a laser tracker10is used to measure 3D coordinates of a probe tip1202of a six-DOF probe1200as illustrated inFIGS. 12A, 12B. Many types of six-DOF probes are possible, and the six-DOF probe1200illustrated inFIGS. 12A, 12Bis only one of many embodiments for which the present invention is applicable and the claims should not be so limited. In an embodiment, the probe tip1202is a part of a shaft1210that may be used to measure points hidden from the view of the tracker10as well as points not hidden from the view of the tracker10. Examples of hidden points include points in holes or points on rear surfaces of an object. In an embodiment, the tracker10sends a beam of light to a retroreflector1220. The light reflected from the retroreflector1220back into the tracker10is used to determine 3D coordinates of the retroreflector. In an embodiment, the tracker includes a structural frame1225that supports all elements of the six-DOF probe1200, including the retroreflector and an LED assembly1230. In an embodiment, the light-target assembly includes a support element1231on which are mounted light targets1232such as light-emitting diodes (LEDs)1232. Additional light targets such as light targets1233and1234may be mounted on the structural frame1225. A camera coupled to the tracker10, for example, with the camera placed within the tracker, records an image of the light targets and, from the pattern of the recorded positions of the imaged light targets, determines orientation angles of the six-DOF probe1200. Such orientation angles may be described in a variety of ways. One common way to describe such angles is as pitch, yaw, and roll angles. Having determined three translation degrees of freedom (for example, x, y, z) and three orientational degrees of freedom (for example, pitch angle, yaw angle, roll angle), a processor coupled to the tracker may determine the 3D coordinates of the probe tip1202.

In an embodiment, a laser tracker10and non-contact six-DOF probe1235are used cooperatively to measure 3D coordinates of a projected line of light1242as illustrated inFIGS. 12C, 12D, 12E. Many types of non-contact six-DOF probes are possible, and the six-DOF probe1235illustrated inFIGS. 12C, 12D, 12Eis only one of many embodiments for which the present invention is applicable. In an embodiment, a tracker10measures the 3D coordinates of the retroreflector1220, while at the same time capturing with a camera coupled to the tracker an image of the illuminated points of light such as the points of light1232,1233,1234. As explained in the preceding paragraph, this collected information is sufficient to enable the laser tracker10to determine the six degrees-of-freedom of the non-contact six-DOF probe1235. In an embodiment, a line scanner1240coupled to the six-DOF probe1240determines 3D coordinates of points on an object that are intersected by a line of light1242. In an embodiment, the line of light is projected in a plane approximately perpendicular to a line connecting a projector1241and a camera1245. In an embodiment, the projector1241includes a light source1243and a lens1244. The light source may be a laser, superluminescent diode, LED, or other device. In an embodiment, the camera images the beam of light1242on an object surface with the camera1247. In an embodiment, light passes through a camera lens1247, which images the light on a photosensitive array1248. In an embodiment, a processor coupled to the tracker10evaluates the image of the captured 2D image of the stripe of light to determine the distances and angles to the object points illuminated by the line of light. In other embodiments, other types of illumination patterns may be used. For example, in another approach, light is projected in an area rather than a line, thereby enabling a collection of 3D coordinates to be determined for an area rather than a line.

In another embodiment, a six-DOF probe is not handheld by an operator but instead is mounted on a machine tool or robotic device. In an embodiment, a system1250includes a robotic mechanism1252operable to hold a six-DOF probe1260. The robotic mechanism may include mechanical links may be adjusted in multiple degrees-of-freedom. In an embodiment illustrated inFIG. 12F, the six-DOF probe1260includes protective windows1262placed over retroreflectors having the lines marked on the retroreflectors. In an embodiment, the lines include intersection lines between reflecting mirror elements darkened so as to be visible to a camera coupled to the laser tacker10. By recording the 3D coordinates of the retroreflectors and by analyzing the orientations of the pattern of lines, the six degrees-of-freedom of the six-DOF probe1260may be determined. Such six-DOF values may then be used to determine 3D coordinates of a probe tip1267. In an embodiment, the system further includes a line scanner1272of the sort sometimes used on articulated arm CMMs. In an embodiment, the line scanner1272includes a line projector1275and a two-dimensional (2D) camera1272, which includes a lines1273. Used together, the six-DOF probe1260and the line scanner1270may be used to determine 3D coordinates of points intersected by the projected line of light within a frame of reference of the tracker10, even as the robotic end effector is moved to different locations. The six-DOF probe1260and the line scanner1270may be electrically and mechanically connected through a connector1269. Additional electrical connections may be provided through an electrical cable1268or through wireless signals.

In an embodiment illustrated inFIG. 13A, a laser tracker10may be part of a system1300operable to move the tracker10from location to location. In embodiments, the stand may be a portable stand pushed by an operator or a motorized stand under processor control. In an embodiment, the tracker10is mounted on a portable stand which is pushed by an operator from location to location. In another embodiment illustrated inFIG. 13A, the stand includes a motorized carriage1314. In an embodiment, the motorized carriage1314includes a structural support1312, a collection of wheels1316, motors1318to turn the wheels1316, and a controller1314to provide the signals to drive the wheels1316.

A situation often encountered in making 3D measurements with a laser tracker is the need to measure an object from multiple sides. A way to do this is to place retroreflectors in kinematic nests in fixed locations around the object to be measured. As the measurement proceeds and the tracker is moved from the location to location, the tracker measures the 3D coordinates of at least three common retroreflectors from two different locations of the tracker. A mathematical procedure may then be performed to place any measurements made by the tracker in the first and second locations to be combined into a common frame of reference. There are many equivalent mathematical procedures for obtaining such a transformation of collected 3D values into a common frame of reference and the claims should not be so limited, but one term often used for obtaining such transformations is by means of “transformation matrices.”

In some embodiments, the acceptance angle of a spherically mounted retroreflector is limited. For example, for an SMR95having a cube-corner retroreflector with three mutually perpendicular mirror reflectors in air, the acceptance angle of the SMR95is approximately +/−25 degrees, which is to say that if the retroreflector is tilted at a larger angle relative to the beam of light90from the laser tracker10, the beam will begin to clip and eventually light will not be reflected into the laser tracker10. To get around this potential issue as the tracker is moved from location to location, in prior art tracker systems a procedure was used where an operator rotated each SMR in each nest to face the laser tracker10. For tracker measurements manually performed by an operator, such additional rotation slows down measurement. Embodiments provided herein provide advantages in allowing tracker measurements to performed automatically, some method is needed to automatically rotate the SMRs in each kinematic nest to face the tracker10as the tracker10moves from location to location.

In an embodiment, the SMR rotator illustrated inFIG. 7A,FIG. 7B,FIG. 8,FIG. 9,FIG. 10andFIG. 11may be used to obtain automatic, high accuracy tracker registration. To obtain high accuracy, in an embodiment, the SMR95is rotated while being kept in contact with a fixed kinematic nest. In this embodiment, the center of an SMR may be held at fixed 3D coordinates, as measured by the laser tracker10, even as the SMR95is rotated.

Some examples are now given for a few applications in which the SMR rotator700is usefully employed. In an embodiment illustrated inFIG. 13B,FIG. 13C,FIGS. 13D and 13E, a laser tracker10measures an object under test1330, in this case an automobile body-in-white, with a laser tracker10moved on a motorized carriage1310around the object. To enable such a measurement to be performed automatically, each time the motorized carriage1310is moved, the tracker10reestablishes its frame of reference in relation to the frame of reference of the tracker10in each of its other locations.FIG. 13Billustrates the case in which a tracker10measures the six degrees-of-freedom of a six-DOF probe1260, which is rigidly coupled to a line scanner1270. The pose of the line scanner1270is known in relation to the pose of the six-DOF probe1260. Hence, by measuring the six degrees of freedom of the six-DOF probe1260with the tracker, the six degrees-of-freedom of the line scanner1270is also determined. In an embodiment, the line scanner1270and six-DOF probe1260are both mounted on a multi-segment robotic arm1252, which in turn is mounted on a mobile platform1254. The mobile measurement system1290includes the six-DOF probe1260, the line scanner1270, the robotic arm1252, and the mobile cart1254. In other embodiments, other measuring devices are attached to the robotic arm1252. In an embodiment, the mobile measurement system1290moves the robotic arm to measure features of interest on the object1330with the line scanner1270, while measuring at the same time the six degrees-of-freedom of the line scanner1270. The mobile platform1254moves to continue the measurements of the object1330. When the six-DOF probe1260is outside the view of the laser tracker10, the laser tracker10is moved to from its first location inFIG. 13Bto its second location inFIG. 13D. To make this move without losing track of the pose of the line scanner1270, a registration procedure is performed as illustrated inFIG. 13CandFIG. 13D.

The laser tracker10is in a first location inFIG. 13Cand is moved to a second location inFIG. 13D, for example, by activating the motorized carriage1310or by having an operator manually push the tracker10from the first location inFIG. 13Cto the second location inFIG. 13D. While the laser tracker10is in the first location inFIG. 13C, the tracker measures the positions of SMRs in each of a collection of SMR rotators700.FIG. 13Cillustrates the case in which the tracker measures the 3D coordinates of the center of the SMR in the SMR rotator700C. It continues by measuring the 3D coordinates of the centers of SMRs in a number of other SMR rotators such as the SMR rotator700D,700E,700A,700B. The SMR rotators700may be mounted on the floor (for example, by using hot glue) or may be attached to stands that raise the height of the SMR rotators700. This decision is made according to the visibility of the SMRs in the SMR rotators700to the laser tracker10in each of its expected locations.

Following the measuring of the 3D coordinates of the SMRs in the setup ofFIG. 13C, the laser tracker is moved to the second location as illustrated inFIG. 13D.FIG. 13Dshows the laser tracker10again measuring the SMR in the SMR rotator700C. The laser tracker continues to measure the SMRs in the other rotators such as the SMR rotators700D,700E,700A,700B. In an embodiment, the laser tracker10measures at least three common SMRs in the first location ofFIG. 13Cand the second location ofFIG. 13D.

Besides moving the tracker10to the second location, the mobile measurement system1290also moves to a new location as shown inFIG. 13E. In the illustration ofFIG. 13E, the tracker measures the six degrees of freedom of the six-DOF probe1260, thereby placing the line scanner1270into position to measure interior features of the object1330. In an embodiment, the determined 3D coordinates measured by the line scanner1270are transformed into the frame of reference of the tracker10in the second location ofFIG. 13Ebased on the six-DOF measurements made by the tracker in combination with the six-DOF probe1260.

The 3D coordinates of the object obtained by the tracker inFIG. 13Bare then combined with the 3D coordinates of the objected obtained by the tracker inFIG. 13Eby placing the measured 3D coordinates a common frame of reference. In an embodiment, a mathematical method is used to determine the six-DOF pose of the tracker in the second location ofFIG. 13DandFIG. 13Ein relation to the pose of the tracker in the first location ofFIG. 13BandFIG. 13C. To do this, the tracker10at the first location and the second location must measure the 3D coordinates of at least three common SMRs700. For example, the tracker in the first location ofFIG. 13Cand the second location ofFIG. 13Dmay both measure the SMRs in SMR rotators700A,700C,700E. Following these measurements of the SMRs in the SMR rotators, any 3D measurements of an object1330by the tracker in the first location ofFIG. 13Bor the second location ofFIG. 13Emay be placed in a common frame of reference. For example, the 3D measurements of the object1330by the laser tracker10at the second location ofFIG. 13Emay be transformed into the frame of reference of the laser tracker10at the first location ofFIG. 13C. In another embodiment, the 3D measurements of the object1330by the tracker at the first location ofFIG. 13Cmay be transformed into the frame of reference of the laser tracker10at the second location ofFIG. 13D. In still another embodiment, the 3D measurements of the object1330by the tracker at the first and second locations may be transformed into a common frame of reference not corresponding to the frame of reference of the tracker at the first location or the second location. In the illustrated embodiment, the minimum requirement to perform a transformation into a common frame of reference is for 3D measurements to be obtained for three common SMRs in the first location ofFIG. 13Cand the second location ofFIG. 13D. This method of combining measured 3D coordinates into a common frame of reference based on measurement of commonly positioned SMRs was described herein above in reference toFIG. 6.

To measure 3D coordinates of a retroreflector98embedded in an SMR95with a laser tracker10, the SMR95is positioned to face a laser beam90from the laser tracker10(e.g. the mirrored surfaces of the SMR are oriented in a direction towards the laser tracker10). A method for rotating an SMR95with an SMR rotator700to face the laser tracker10is now described. In an embodiment, a laser tracker illuminates light sources such as the light sources76B,78B as illustrated inFIG. 3. Light from these light sources travel to retroreflectors and is reflected into cameras such as the cameras76,78. The light from the light sources76B,78B may be flashing to enable easy identification of retroreflectors in the images on the photosensitive arrays76A,76B of the cameras76,78. In an embodiment illustrated inFIG. 13F, a retroreflector95on an SMR rotator700is rotated about a vertical axis1390of the SMR rotator1390. When the retroreflector rotates into a position to reflect some of the light from the light sources76B,78B as reflected beams77,79, respectively, into the cameras76,78, respectively, flashing spots appear on the photosensitive arrays76A,78A, respectively. When this occurs, in an embodiment, the laser tracker turns to face the retroreflector95. In addition, in an embodiment, the SMR rotator continues to turn to face the cameras76,78. In response, the illuminated spots move toward the center of the photosensitive arrays76A,78A. In an embodiment, the tracker10locks onto the SMR95with a beam of light90from the laser tracker10, as shown inFIG. 1. Lock on is achieved when the position-detector assembly460of the laser tracker10receives the reflected beam of light92and the tracker steering mechanism is adjusted to keep the beam centered on the position detector. Once lock-on occurs, the tracker10may measure the 3D coordinates of the SMR95.

In an embodiment, the cameras76,78have a field-of-view (FOV) of between 30 and 60 degrees. Any retroreflectors95within the FOV of the cameras76,78are captured by the photosensitive arrays76A,76B whenever the SMRs95are rotated to approximately align with the cameras76,78. Hence, as the SMRs95are rotated about the axis1390, they will appear as flashing spots of light on the photosensitive arrays76A,78A whenever they point toward the laser tracker10. Once an acceptable rotation angle has been found for each SMR rotator700, the SMR95may stop rotating and the tracker10used to measure the 3D coordinates of the centers of the SMR95. If some SMRs are outside the FOV of the cameras76,78on the laser tracker10, the tracker may be rotated about the axes12,14shown inFIG. 2to look for SMRs95in different regions of space.

FIG. 14shows an exemplary triangulation scanner having a projector1403and two cameras1406,1407installed in a frame1402. In other embodiments, a triangulation scanner includes only one camera rather than two cameras. In an embodiment, the projector projects a pattern of light. Such a pattern of light may project pattern elements recognizable in images captured by the cameras1406,1407. By making a correspondence among the camera such as camera1406,1407and pattern elements projected by a projector1403, a triangulation calculation may be performed to determine 3D coordinates of the corresponding pattern elements as they appear on an object. To do the triangulation calculation, a baseline distance is established between the projector perspective center and a camera perspective center. Trigonometric relations are used to determine the 3D coordinates of the object point. In another embodiment, the corresponding pattern elements are recognized in images on each of the cameras1406,1407. A baseline distance between the two cameras1406,1407is then used to perform a triangulation calculation to determine 3D coordinates of identified pattern elements on images captured by the cameras1406,1407. The method of matching pattern elements in two cameras or a projector and a camera enables 3D coordinates to be determined in a single shot.

More accurate methods than single-shot methods are possible if multiple patterns are projected and captured. In one example of such an approach, the optical power of projected light is varied sinusoidally, for example, with the light varying sinusoidally in intensity from left to right on an object surface. With this approach the sinusoidal pattern is shifted in phase from left to right, for example, to have phases of 0, 120, and 240 degrees. At each point on the photosensitive array of a camera such as a camera1406,1407, the level of the received light is determined. From the levels received for each of the phases, a correspondence may be determined between points projected by a projector such as the projector1403and the points captured by the camera or cameras such as1406,1407. A triangulation calculation in the multiple-image case may then be performed as in the single-shot case.

As a further example of how SMR rotators700may be usefully employed, a 3D measurement of points performed using an array1510of triangulation scanners is illustrated inFIG. 15A. In an embodiment, the array1510includes a plurality of triangulation scanners1520mounted on a structure1515. In an embodiment, the triangulation scanner1520includes a projector1522, a camera1524, and a processor1526. In an embodiment, the plurality of triangulation scanners1520are compensated so as to enable the captured 3D images to be combined into a single 3D image in a common frame of reference. In an embodiment, the plurality of triangulation scanners further cooperate with a processor1530, which may connect with additional processors off the array1510. In an embodiment, the structure1515is attached to an end effector of a robot1540operable to move the array1510, enabling measurement of different portions of an object1330with the array of triangulation scanners. In an embodiment, a controller1542is used to control motion of the robot1540. In an embodiment, the robot1540is moved along a track1550.

In an embodiment, a laser tracker10is moved from a first location inFIGS. 15A, 15Bto a second location inFIGS. 15C, 15D. At the first location inFIG. 15A, the tracker measures three or more retroreflectors95on the structure1515as shown inFIG. 15A. In addition, in the first tracker location, the tracker10measures SMRs on three or more SMR rotators700as shown inFIG. 15B. Possible SMR rotators that may be measured include700A,700B,700C,700D,700E,700F,700G,700H. After 3D coordinate data has been collected by the array1510in the initial robot location shown inFIG. 15A,FIG. 15BandFIG. 15C, the robot1540is moved to a later robot location shown inFIG. 15D. InFIG. 15D, with the tracker10in its second location, the tracker10measures the 3D coordinates of SMRs95on the structure1515. In addition, at the second tracker location, the tracker10measures the 3D coordinates of SMRs on a collection of SMR rotators700as shown inFIG. 15C. The 3D coordinates of at least three of the SMRs on the SMR rotators700are measured in common by the tracker in its first location and its second location. In an embodiment, these measured 3D coordinates are used by a processor to place any tracker measurements in the first and second tracker locations into a common frame of reference. In this way, the SMRs95measured by the tracker10in its first and second locations enable measurements performed by the array1510in the initial and final locations of the robot1540to be combined in a common frame of reference. In other words, in an embodiment, the tracker measurements performed as inFIG. 15A,FIG. 15B,FIG. 15CandFIG. 15Denable the 3D measurements obtained by the triangulation scanners1520with the array1510at two different robot locations to be combined in a common frame of reference.

Commonly owned U.S. Patent Application No. 62/595,745 ('745), which is incorporated herein by reference, describes a method in which one or more cameras attached to a laser tracker may be used to obtain a 3D image showing edges of an object captured by the one or more cameras with the laser tracker positioned in three or more poses. The method described in the patent application '745 is applicable even to obtain 3D coordinates of continuous edges of objects, where no discrete points are identifiable in the multiple camera images captured in the three of more poses. A portion of the method described in the patent application '745 is to establish the relative pose of the laser tracker in each of the three or more poses. One way to determine the relative poses is to measure 3D coordinates of three or more common SMRs in each of the three or more tracker poses.

In the method described in the patent application '745 the SMRs to be measured may not be facing the laser tracker attempting to measure their 3D coordinates. In other words, the laser tracker may not be aimed at the SMR to within the acceptance angle of the retroreflector of the SMR. A way around this difficulty is illustrated inFIG. 16. In an embodiment, a laser tracker10moves from a location A to a location B and then to a location C. This is indicated inFIG. 16by labeling the tracker10at these three locations as10A,10B, and10C. The tracker at each of these locations is mounted on a cart1310, which may be pushed by hand or moved by a motorized mechanism. The cart1310holds the tracker10at the three locations A, B, C as indicated by labeling the cart at these locations1310A,1310B,1310C, respectively. In an embodiment, the laser tracker10at the locations A, B, C captures with one or more of its cameras 2D images over a region1600of a portion1602of an object1330. At each of the three poses of the tracker10A,10B,10C, the tracker further measures three or more of SMRs on SMR rotators700, which may be any of SMR rotators700A,700B,700C,700D,700E,700F,700G,700H in the example ofFIG. 16. In each case, the SMR rotator rotates its SMR to face the laser tracker to enable the 3D coordinates of the SMR to be determined. With these 3D coordinates of the SMRs on the SMR rotators700obtained, in an embodiment, the edges of the portion1602of the object1330are determined and displayed, for example, according to the method of the patent application '745. In an embodiment, the laser tracker10continues to move around the object1330and to use its one or more cameras to obtain 3D images of the edges of the object1330.

In an embodiment illustrated inFIG. 17AandFIG. 17B, the 2D images obtained from one or more cameras on a laser tracker10are again used to obtain a 3D image of an object1330according to the method described in patent application '745. InFIG. 17A, the object1330is moved past a first laser tracker10R and a second laser tracker10L. In an embodiment, the object1330is moved along by a conveyor belt1702, which travels in a direction1704, while the trackers10R,10L are stationary. In an embodiment, multiple SMR rotators700are placed on the conveyor belt1702, for example, the SMR rotators700A,700B,700C,700D,700E,700F,700G,700H. In an embodiment, at a first location of the conveyor belt, the laser tracker10R measures the 3D locations of SMRs in the SMR rotators700B,700C,700D. With the conveyor belt at a new second location, the laser tracker10L further captures 2D image of a portion1702of the object1330with its one or more cameras. In addition, it again measures the 3D coordinates of SMRs on the SMR rotators700B,700C,700D. A processor uses the 3D coordinates of the SMRs in the SMR rotators700B,700C,700D in the first location and the second location of the conveyor belt to move the 2D images for the regions1702,1703into a common frame of reference. To finally obtain 3D coordinates for the edges of the object1330, the method will be repeated to at least a third location in which the conveyor belt has further progressed in its path1704. The 3D coordinates of the SMRs in the SMR rotators for at least three poses of the laser tracker relative to the moving conveyor belt1702is sufficient to enable the obtained 2D images to be converted to 3D coordinates of edge points, even continuous edge points.

FIG. 18shows an embodiment in which a rotating camera assembly1800includes a rotating camera1810mounted on a cart1310, which might be a motorized cart. In an embodiment, the rotating camera1810includes a camera1820coupled to a payload assembly1830that rotates in a rotation pattern1846about a horizontal axis1844, as shown inFIG. 18. The payload assembly1830is in turn mounted on a yoke assembly that rotates in a rotation pattern1842about a vertical axis1840to a tracker base1834. The yoke assembly rotates relative a base1834, which is stationary relative to the cart1310. In an embodiment, the rotating camera1810further includes one or more light sources1826proximate the camera1820. Such light sources1826may be used to illuminate a reflector such as a retroreflector. Light reflected by the illuminated reflector may then appear in an image of the camera1820. The payload1830and yoke1832may be turned by motors, with the angles of rotation measured to relatively high accuracy with angular transducers such as angular encoders similar to those found in the laser tracker10. Hence the rotating camera assembly1810may cover a wide system field-of-view (FOV) by rotating about the axes1840,1844to relatively accurate angles while at the same time obtaining high resolution 2D image data by restricting the camera FOV1822to a small angular value about a camera pointing direction1824. In this way, the rotating camera assembly1810may obtain relatively higher accuracy image data over a wider FOV than is possible within an ordinary stationary camera.

FIG. 19shows a 3D measuring device1900having a handheld triangulation line scanner1910, on which is mounted an electronics assembly1920and a light target array1930. In an embodiment, the handheld triangulation line scanner1910includes a handle1912and a triangulation line scanner comprising a projector1914and camera1916mounted in a frame1918. In an embodiment, an optional electronics assembly1920is attached to the line scanner1910through an electrical and mechanical interface1919, as shown inFIG. 19. In an embodiment, the electronics assembly1920includes in a body1922that houses the electronics used to support the line scanner1910and the light target array1930. In an embodiment, elements of the electronics assembly1920include a processor1924, a frame, and optionally a tactile probe tip1926. In an embodiment, the light target array1930is mounted on the electronics assembly1920. In an embodiment, the light target assembly includes a structure1932on which are mounted targets such as the targets1934and targets1936. In an embodiment, the targets1934are light sources such as LEDs mounted on the structure1932, and the targets1936are light sources mounted on pedestals1938. In other embodiments, the targets are not light sources but instead are small retroreflectors or target elements made of a reflective material.

In an embodiment illustrated inFIGS. 20A, 20B, a first rotating camera assembly1800A and a second rotating camera assembly1800B cooperate with a 3D measuring device1900to determine 3D coordinates of an object1330. In an embodiment, the first rotating camera assembly1800A and the second rotating camera assembly1800B measure at least three common SMRs that are rotated on SMR rotation assemblies700, which may include700A,700B,700C,700D,700E,700F, for example. InFIG. 20A, the rotating camera assemblies1800A,1800B are each measuring 3D coordinates of an SMR in the SMR rotator700A. In an embodiment, the rotating camera assemblies are mounted on carts1310A,1310B, respectively.FIG. 20Bshows the rotating camera assemblies1310A,1310B measuring targets on the light target array of the 3D measuring device1900. By each of the rotating camera assemblies1310A,1310B having measured 3D coordinates of at least three common SMRs on the SMR rotation assemblies700, the pose of the cameras of the rotating camera assemblies1310A and1310B may be put into a common frame of reference by a processor. This enables the baseline distance between perspective centers of the cameras in the rotating camera assemblies1310A,1310B to be determined and in addition the relative orientation of the cameras in the rotating camera assemblies1310A,1310B to be determined. This information enables a processor to perform triangulation calculations to the 2D images obtained by the cameras in the rotating camera assemblies1310A,1310B. The result of such calculations is 3D coordinates of points on the object1330measured by the 3D measuring device1900. Such 3D measurement of points on the object may be obtained even as the 3D measuring device1900is moved from location to location, measuring different portions of the object1330.

In other embodiments, the SMRs held by the SMR rotators may be replaced with spherical target elements that included centered light sources, such as LEDs, or centered reflective targets, such as circular reflective targets. Such spherical target elements include at least a portion of a spherical surface—for example, a hemisphere. In an embodiment, SMRs may be mixed with spherical target elements having light sources or reflective targets. In such cases, a laser tracker10may be used to measure the 3D coordinates of the SMRs in the SMR rotators700to establish 3D coordinates of some SMRs in an environment. Such 3D measurements may be used to establish scaled measurements by rotating camera assemblies such as1800A,1800B. As a rule of thumb, by measuring six such spherical target elements with a rotating camera assembly1800A, the pose of a rotating camera assembly1800A may be robustly determined relative to a rotating camera assembly1800B. In an embodiment, rotating camera assemblies1800A,1800B further measure targets mounted on background structures such as walls or on test objects to obtain a large number of 3D coordinates within the environment.