Articulated probe

Abstract

The invention relates to an articulated probe. An articulated wrist for redirecting a measurement probe relative to a measurement device comprises: a support element connectable to a positioning platform of a coordinate measuring machine; a first reorientable element pivotally connected to the support element for rotation about a first axis of rotation; a first actuator actuatable to rotate the first reorientable element about a first rotational axis; a first angle encoder configured to determine an angular position of the first redirectable element relative to the support element and to generate a time series of position values, characterized in that the wrist controller receives the time series of position values, determines a desired position of the first redirectable element in real-time and commands the first actuator to move towards the desired position.

Description

Technical Field

[0001] In embodiments, the present disclosure relates to a redirectable measurement head for measuring three-dimensional coordinates of a mechanical component, and particularly, but not exclusively, to a redirectable measurement head for use on a manual or automatic machine for measuring coordinates. Background Art

[0002] Touch coordinate probes are used to check the dimensions or surfaces of machined parts and to capture the three-dimensional shape of complex parts, for example to reproduce them or model them. Touch coordinate probes usually have a moving feeler designed to come into contact with the surface of the part being measured. The sensor reacts to the slightest displacement of the feeler, generating an electrical signal that is sent to the operator of the coordinate machine or to the automatic controller of the coordinate machine.

[0003] The sensor can be a trigger circuit that produces an electrical transition whenever contact is detected, or a deflection transducer that produces deflection measurements in one, two, or three coordinates. Touch coordinate probes equipped with deflection transducers are also called scanning probes or analog probes, and can be used by programming the coordinate machine so that their feelers follow a continuous contact path on the surface of the part being measured. More commonly, those of the former type are also called trigger probes. They are typically used to collect the coordinates of a sparse set of points on a surface, and can be operated manually (e.g., through a handheld control interface such as a jog box or pendant) and automatically.

[0004] Non-contact coordinate probes are also known. They use non-contact sensors to determine, for example, the distance between the tip of the probe and the surface of the object being measured without touching it. Such sensors include laser interferometer probes, chromatic confocal probes, ultrasonic probes, cameras, line scanners, etc.

[0005] Usually, the coordinate probe is fixed on a mobile platform whose position can be determined accurately. In known bridge coordinate machines, the mobile platform is part of an accurate Cartesian coordinate system and its position relative to the reference table of the coordinate machine is read by a linear encoder. In known wrist coordinate machines and industrial robots, which are sometimes equipped with a coordinate probe for measuring purposes, positioning is achieved by a kinematic chain of rotating axes in series. It is also known to use coordinate probes in the moving parts of machine tools such as milling machines, lathes and machining centers.

[0006] The coordinate machine may be equipped with other tools than the coordinate probe, such as a surface quality probe to measure surface roughness, or an imaging device for inspection and control but also for determining coordinates and dimensions. For the purposes of this disclosure, these tools are equivalent to the coordinate probe and are interchangeable therewith.

[0007] A coordinate probe may be fixed to a movable platform of a coordinate machine for measurement. Advantageously, the coordinate probe may be attached to the movable platform by a re-orientable wrist (also referred to herein as an articulated wrist or articulated wrist) that provides various orientations of the coordinate probe. In fact, many measurements require changing the orientation of the coordinate probe to fully and satisfactorily measure the workpiece. When measuring features at the blind end of a hole, it is very useful to be able to align the axis of the feeler with the axis of the hole, for example. Many movable platforms do not provide this capability, and often the coordinate probe is mounted on a re-orientable wrist with two independent swivel joints to overcome this deficiency.

[0008] Additionally or alternatively, a rotary table beneath the workpiece may be used to reorient the probe relative to the part being measured. This may be automatically operated by the coordinate measuring machine as an additional rotational degree of freedom.

[0009] The rotational axes / axes of the redirectable wrist are usually indexed, which means that they can be locked in a large but limited number of highly repeatable predetermined positions, in particular for precise measurements in the μm range. This usually requires a locking mechanism with an indexing element or component, which usually takes the form of a periodic joint, such as a Hirth coupling (hirth disc), or a crown of a spherical surface on one side of the joint, connected to three cylindrical rollers on the opposite side of the joint. In the locked state (also indicated as a locked configuration in the present disclosure), the indexing axis is locked by pushing the two halves of the joint against each other, and in the free state (or free configuration), the indexing axis is released by setting them apart with a locking mechanism. The rotation and transition between the locked state and the free state can be manual or preferably motor-driven. Documents EP 0392660 A1 and EP 1666833 A1 describe such instruments. Indexing steps of 2.5°, 5°, 7.5° or 10° are common.

[0010] Known articulated wrists include a controller configured to drive the wrist actuator to move the measurement probe to a desired orientation. The desired orientation is transmitted from the coordinate measuring machine to the wrist during the measurement dead zone (dwell) time to prepare for continued measurement. Upon receiving the desired orientation, the wrist controller can confirm the new target configuration, unlock the rotary joints if necessary, drive them to the new orientation, lock them, and signal the coordinate machine that the reorientation is complete and effective. Only after this last signal does the coordinate machine controller move the coordinate platform to collect the new coordinates.

[0011] The wrist controller may be partially or completely located inside the body of the wrist, which is configured to protect the rotation and locking mechanism from dust and liquid projections. In other implementations, it may be partially or completely separated from the body of the wrist, such as in a separate protective housing or as a subcomponent of the coordinate machine or its controller.

[0012] In use, the articulated wrist and probe are used to measure complex mechanical equipment parts that require the acquisition of hundreds or thousands of points per unit. The coordinate machine follows a predetermined program determined taking into account the nominal shape of the unit being measured. The measurement program consists of moving the positioning platform and rotating the axes of the wrist so that the probe can acquire all the required points. At the same time, the program should avoid any collision between the movable parts of the articulated wrist and probe and other parts or accessories of the measured part or machine (such as the support of the workpiece or tool box) during the measurement and during the reorientation of the probe in the rest time. Taking into account the size of the part and the uncertainty in the actual path of the tool, the planning of the measurement path must maintain a sufficient safety distance between the moving parts and the fixed parts.

[0013] Known articulated wrists are highly repeatable and can resist considerable external torques when they are locked. When they are unlocked to turn and reorient the probe, loose guidance of the rotor is preferred, since the additional constraint introduced by a tight guidance will reduce the positioning accuracy in the locked state. Compared to a scanning probe, the operating position of a measurement probe attached to such a wrist can be uniquely determined in the free state with a lower accuracy, which is generally insufficient to provide accurate measurements, since the spatial relationship between the reorientable element with respect to the supporting element is subject to mechanical uncertainties, typically in the μm (micrometer) to mm (millimeter) range, until the rotor is locked again.

[0014] Furthermore, the time required to move from a given angular position to another angular position cannot usually be determined precisely, especially when the rotary motor must counteract the weight and moment of inertia of a long probe attached to the wrist. Therefore, planning a safe trajectory that combines translation of the XYZ stage and rotation of the wrist is not a trivial task. In many cases, the trajectory generator avoids translating the stage and reorienting the probe at the same time, and instead moves the probe away from the workpiece to a safe position where it cannot hit anything, reorients the probe while the stage is stationary, and then moves it toward the workpiece and acquires a new set of coordinates in the new orientation. This lengthens and complicates the measurement path, increasing downtime between measurements. Summary of the invention

[0015] An object of the present invention is to provide an articulated wrist that overcomes the disadvantages and limitations of the prior art.

[0016] According to the present invention, these objects are achieved by an articulated wrist for reorienting a measuring probe relative to a measuring device, the articulated wrist comprising: a support element, the support element being connectable to a positioning platform of the measuring device; a first redirectable element, the first redirectable element being pivotally connected to the support element to rotate about a first rotation axis; a first actuator, the first actuator being actuatable by a wrist controller to rotate the first redirectable element about the first rotation axis; a first angle encoder, the first angle encoder being configured to determine the angular position of the first redirectable element relative to the support element and generate a read orientation; a communication interface, the communication interface being configured to receive digital commands and data, the articulated wrist being configured to selectively use any of the following Modes of operation: a locked mode in which the first redirectable element is mechanically constrained in one of a limited set of graduated orientations; a free mode in which the first actuator is capable of rotating the first redirectable element, characterized in that the wrist controller is configured to receive, through the communication interface, a positioning command expressing a series of desired orientations of the first redirectable element and a specified time for obtaining the desired orientations, and to read a first position when the articulated wrist is operating in the free mode, to select each of the desired orientations in a chronological order, and to command the first actuator to move toward the selected desired orientation at the corresponding specified time based on the difference between the read orientation and the selected desired orientation. Advantageously, the wrist controller can be configured not only to command the actuator, but also to receive such positioning commands only when the articulated wrist is in the free mode.

[0017] A positioning command may signal / indicate a specified time either explicitly (e.g., by conveying an indication of the time when the desired position should be obtained) or implicitly (also referred to herein as a "momentary configuration," e.g., the desired orientation must be obtained within a given short time interval from receipt of the command, preferably shorter than or equal to 100 ms, most preferably less than or equal to 10 ms or 1 ms).

[0018] Preferably, the communication interface is configured to resend successive values ​​of the reading orientation to a controller of the measuring device.

[0019] The first actuator may be integrated in the first redirectable element and preferably can rotate unbounded due to a slip ring in the support element, which is arranged to transmit the required power / electricity and signals and fluids (if required) between the support element and the first redirectable element. The signals may include optical signals, for example for an optical measurement probe.

[0020] The indexing in the locked configuration can be achieved by an indexing coupler between the support element and the first redirectable element, the indexing coupler having a plurality of mobile positioning elements associated with the first redirectable element and a plurality of fixed positioning elements associated with the support element. The plurality of fixed positioning elements can engage with the mobile positioning element to define a plurality of predetermined indexing orientations. The locking actuator controlled by the wrist controller sets the wrist in the free state or in the locked state. In the free state, there is an axial spacing between the mobile positioning element and the fixed positioning element, whereby the first redirectable element can be rotated by the first actuator. In the locked state, the mobile positioning element and the fixed positioning element engage with each other, and the first redirectable element presents one of the indexing orientations and is not rotatable. It is noteworthy that when the wrist is in the free mode, the wrist can be controlled to redirect the probe while the positioning platform of the wrist measurement device is translated, but the probe is only used to measure coordinates in the locked mode with enhanced accuracy. Preferably, the locking actuator comprises a hollow body or a hollow rod, which is configured to bias the mobile positioning element against the fixed positioning element in the locking mode and to separate the mobile positioning element from the fixed positioning element in the free mode, and the hollow body provides a channel for electrical and / or optical and / or fluid conductors between the support element and the first redirectable element.

[0021] The wrist controller can be configured to switch between the locked state and the free state in response to commands received through the communication interface, and vice versa. In addition to the advanced mode of constantly controlling the articulated wrist from the outside, the articulated wrist can have an optional legacy mode in which the articulated wrist can autonomously change orientation when a desired final orientation is received through the communication interface. In this mode, the wrist controller sets the wrist in the free state, commands the actuator to rotate the first redirectable element until the final orientation is reached, sets the wrist in the locked state, and optionally sends a confirmation message through the communication interface. In addition to the elements disclosed above, the articulated wrist can have additional sensors, such as one or more of the following: temperature sensor, humidity sensor, acceleration sensor, gyroscope sensor, light sensor, motor current sensor, capacitive collision sensor.

[0022] In order to achieve a more complete set of orientations, the articulated wrist may have a second redirectable element that is pivotally connected to the first redirectable element to rotate around a second rotation axis that is substantially orthogonal to the first rotation axis. The second element can be rotated around the second rotation axis by a second actuator in the first redirectable element and can have a connector for measuring a probe. A second angle encoder captures the angular position of the second redirectable element relative to the first redirectable element and provides a second read orientation for use with the first read orientation. In this dual-axis implementation of the wrist, a positioning command can specify a series of desired orientations with two parameters: a first angle of the first redirectable element relative to the support element and a second angle of the second redirectable element relative to the first redirectable element. The wrist controller reads the actual value of the angle from the encoder, selects each desired orientation in a time sequence, and commands the first actuator and the second actuator to move toward the selected desired orientation at the corresponding specified time based on the difference between the read angle and the desired orientation.

[0023] In important use cases, the measuring device is contained in a coordinate measuring machine equipped with an articulated wrist, but the wrist can also be used for machine tools and robots. All possible geometries of measuring machines (bridge, gantry, cantilever, articulated arm, etc.) are possible.

[0024] In this use case, the measuring device may comprise a mobile positioning platform to which an articulated wrist may be attached, the platform being controlled by a device controller of the measuring device, and a measuring probe may be connected to the articulated wrist for measuring a workpiece with the measuring device. Advantageously, the device controller may be configured to: determine a planned trajectory comprising a series of instantaneous configurations, each instantaneous configuration determining the position of the mobile positioning platform and the orientation of the articulated wrist carrying the measuring probe; control the positioning platform so as to translate the positioning platform in a time-sequential manner following the series of positions defined in the planned trajectory; and send commands to the wrist controller such that, while translating the positioning platform, the measuring probe rotates synchronously with a corresponding translation of the positioning platform by the articulated wrist following the series of orientations defined in the planned trajectory. Advantageously, the device controller may also be configured to send commands to the wrist controller such that the wrist controller selects the free state of the wrist when preparing to change the wrist orientation, or selects the locked state of the wrist when preparing to take a measurement with the measuring probe. Preferably, the device controller may be configured to periodically send commands to the wrist controller to provide a transient configuration, preferably regularly with a period equal to or less than 100 ms, preferably equal to or less than 10 ms, more preferably equal to 1 ms.

[0025] Advantageously, the device controller may be configured to determine the planned trajectory based on characteristics and / or capabilities and / or performance of the attached articulated wrist and / or the carried measurement probe and / or accessories thereof.

[0026] The invention also relates to a method of operating a measuring device having: a mobile positioning platform controlled by a device controller; an articulated wrist as described above, attached to the mobile platform; a measuring probe, connected to the articulated wrist to measure a workpiece with the measuring device, the method comprising: determining a planned trajectory comprising a series of instantaneous configurations, each instantaneous configuration determining the position of the mobile positioning platform and the orientation of the wrist carrying the measuring probe; controlling the positioning platform by the device controller so as to translate the positioning platform in a time-sequential manner following the series of positions defined in the planned trajectory; sending commands from the device controller to the wrist controller so that while translating the positioning platform, the measuring probe rotates synchronously with the corresponding translation of the positioning platform by the wrist following the series of orientations defined in the planned trajectory. The method may include sending commands from the device controller to the wrist controller so that the wrist controller selects the free state of the wrist when preparing to change the wrist orientation, or selects the locked state of the wrist when preparing to measure with the measuring probe. Preferably, the instantaneous configuration is periodically transmitted by the device controller to the wrist controller with a period lower than 100 ms, preferably lower than 10 ms, more preferably equal to 1 ms. The measuring device may be any kind of coordinate measuring machine, machine tool, robot or the like.

[0027] The continuous values ​​of the read orientation sent from the wrist controller to the device controller can be used to determine the actual configuration of the measuring device based on the values ​​of the read orientation and the read position of the positioning platform determined by the position encoder of the measuring device, the difference between the actual configuration and the expected instantaneous configuration of the planned trajectory, and finally send instructions to the wrist controller and / or the actuator of the measuring device to move the positioning platform so as to tend to make the difference zero.

[0028] In one embodiment, the method further comprises: collecting characteristics and / or capabilities and / or performance of the attached articulated wrist and / or the carried measurement probe and / or its accessories; and determining the planned trajectory based on the collected characteristics and / or capabilities and / or performance.

[0029] An independent aspect of the invention may be an articulated wrist including environmental and operational sensors including, for example, temperature sensors, humidity sensors, acceleration sensors and / or gyroscope sensors, light sensors, current motor sensors, and housing opening sensors. Preferably, the articulated wrist is configured to transmit information collected by the environmental and operational sensors to a machine controller or another external device via a suitable digital communication interface.

[0030] The data collected by the environmental and operational sensors can be used for any purpose, including, for example, to improve the precision and accuracy of the metrology data by applying a temperature compensation process, to detect collisions, to determine the health status and preventive maintenance of the wrist, to detect unauthorized opening and tampering, and for warranty purposes. The environmental sensors are preferably positioned in each of the three sections of the wrist (the support element, the first redirectable element, and the second redirectable element).

[0031] Exchanges with the machine controller and with external devices can involve a unique identifier of the wrist stored in an unmodifiable memory in the wrist and / or a service identifier allowing quick identification of the wrist and (preferably) the connected probe, and the data can be timestamped by the wrist (if RTC is available) or by the receiving device for integrity and ease of use.

[0032] Preferably, some environmental sensors (such as light sensors, humidity sensors, accelerometers / gyroscopes) are configured for autonomous operation on an autonomous supply source when the wrist is detached, and can store environmental data internally and transmit them to the machine controller or another designated receiver when powered continuously.

[0033] The wrist equipped with environmental and operational sensors may also include all the features of the previously mentioned wrist with angle encoder, and conversely, the wrist with angle encoder may also have environmental and operational sensors in all variants and combinations disclosed herein.

[0034] In the framework of the present disclosure, the word "probe" refers to any device used to inspect a workpiece or to measure metrology-related quantities, such as coordinates of selected points on the workpiece surface, coordinates along a path on the workpiece surface, surface condition, roughness, etc. The term includes contact-based and non-contact devices as well as automated imaging systems.

[0035] In the framework of the present disclosure, the term "wrist" (and equivalent terms "articulated wrist" and "reorientable wrist") denotes a device designed to be fixed to a measuring device (e.g., a coordinate measuring machine) and to provide reorientation of an attached probe relative to the measuring device from a first orientation (e.g., angular position) to a second orientation about at least one axis of rotation between consecutive measurements.

[0036] In the framework of the present disclosure, a "slip ring" means any device that allows power and / or electrical or optical signals and, if necessary, fluids to be transmitted between a stationary structure and a rotating structure. This can include graphite or metal brushes rubbing on a (relatively) rotating collector, but also magnetic devices such as rotary transformers. Optical slip rings allow the transmission of optical signals between a stationary component and a rotating component, either unidirectionally or bidirectionally, with or without contact. Slip rings can have one or more conductors or channels to transmit as many signals or power lines as needed.

[0037] In the present disclosure, the expression "time series" means any series or sequence of data values ​​indexed in time order. Data values ​​indexed in order of appearance. "Real time" means the process of processing events and measurements within a short time after the event occurs, such as less than 100 ms, preferably equal to or less than 10 ms, and more preferably equal to or less than 1 ms.

[0038] This disclosure shows an example of the invention having two rotating joints and two corresponding rotating axes "A" and "B" because this is a common configuration, but this is not required. The invention includes variations with a single joint (e.g., only axis "B") or three or more rotating joints. For the sake of brevity, these variations are not disclosed in detail.

[0039] The above-mentioned articulated wrist is able to accurately and effectively reorient the measurement probe in one or two degrees of freedom, thereby improving the accuracy and speed of the measurement process. By including a second reorientable element and a second actuator, the wrist can perform more complex movements and reach a wider range of positions, enhancing its versatility and usability. The wrist controller ensures that the reorientation is performed with maximum accuracy and speed, reducing measurement errors and saving time. With respect to what is known in the art, the present invention provides the advantage that the change of orientation can be performed synchronously with the movement of the positioning platform, thereby reducing the dead zone / dwell time of the coordinate machine. And resulting in a higher measurement yield.

[0040] Furthermore, the present invention allows for selective reorientation and repositioning of the measurement probe along a defined trajectory at one of different possible speeds, the speed being selected as a function of one or more estimated, determined and / or sensed environmental and / or operational variables, such as:

[0041] - local concentration of objects in the vicinity of the articulated probe head and / or the measuring probe;

[0042] - loads affecting the articulated probe and / or the measuring machine;

[0043] - dimensions of the articulated probe head and / or measuring probe;

[0044] - Environmental factors that reduce the movement and / or orientation accuracy of the measurement probe.

[0045] Exemplarily, the machine controller can be operated in a safe operating mode in which reorientation and repositioning of the probe is performed more slowly, particularly in order to allow operation within an operating volume of the machine managed by an operator, or so that it can be followed in a more accurate manner compared to a normal mode in which reorientation and repositioning of the probe is performed more quickly.

[0046] Another advantage of the wrist of the present invention is that rotation about one axis (e.g., the vertical "B" axis) is not limited to restricted sectors, such as (-180°, +180°) or a limited number of revolutions. When a re-orientable wrist moves in a continuous manner and simultaneously translates around a workpiece, it is sometimes necessary to turn the wrist through large angles to make small orientation changes to avoid the physical limitations of an articulation. The rotation angle of the "B" axis of the wrist of the present invention is unrestricted / infinite, thereby avoiding this disadvantage. This feature not only makes measurement path planning simpler, but also increases the measurement throughput of the machine. Unrestricted / unrestricted rotation about the "A" and "B" axes is also possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Exemplary embodiments of the present invention are disclosed in the specification and illustrated in the accompanying drawings, in which:

[0048] Figure 1 A coordinate measuring machine having an automatically redirectable wrist of the present invention is schematically shown measuring a workpiece under the supervision of a numerical controller.

[0049] Figure 2 A redirectable wrist as used in the present invention is shown schematically.

[0050] Figure 3a and Figure 3b The redirectable wrist of the present invention is shown in a simplified manner in a locked state and a free state, respectively.

[0051] Figure 4 A re-orientable wrist is shown in a simplified schematic manner relative to its wrist controller and coordinate machine controller.

[0052] Figure 5 is an example of a trajectory selected by a coordinate measuring machine equipped with an articulated wrist of the present invention.

[0053] Figure 6 is Figure 5 A graph of control signals received by the articulated wrist during the trajectory of .

[0054] Reference numerals appearing in the accompanying drawings:

[0055] AK position along the trajectory of the positioning platform

[0056] X, Y Cartesian coordinates

[0057] Β Rotation angle of "B" connector

[0058] 10 Articulated wrist

[0059] 10a-10d Position of the articulated wrist

[0060] 15 Wrist Controller

[0061] 16 Desired wrist configuration

[0062] 17 Wrist instantaneous configuration

[0063] 19 Lock / Unlock Commands

[0064] 20 Communication Interface

[0065] 22 Machine Cartesian Actuator

[0066] 23 Machine Linear Encoder

[0067] 25 Machine Controller

[0068] 30 Workpieces

[0069] 33 Edge

[0070] 40 Coordinate Measuring Machine (CMM)

[0071] 41 Bridge

[0072] 42 Bracket

[0073] 43 Workbench

[0074] 45 Z- plunger, sleeve shaft, positioning platform

[0075] 60 "A" axis (horizontal)

[0076] 70 "B" axis (vertical)

[0077] 100 Support elements

[0078] 103 Connectors

[0079] 107 Slip ring device, slip ring housing

[0080] 109 Axis

[0081] 114 Upper cable

[0082] 115 Cable Harness

[0083] 120 Indexing Unit, Hirt Coupling, "B" Axis

[0084] 125 Indexing Unit, Hirt Coupling, "A" Shaft

[0085] 150 Positioning platform trajectory

[0086] 160 Collision detector, capacitive sensor

[0087] 175 Compression spring

[0088] 190° Angle Encoder, "B" Axis

[0089] 195 Angle encoder, "A" axis

[0090] 200 First redirectable element

[0091] 220 Visual Indicator

[0092] 224 Rotational Actuator at Wrist

[0093] 225 Wrist Angle Encoder

[0094] 226 Wrist lock / unlock actuator

[0095] 230 Rotary Actuator, "A" Axis

[0096] 232 Anti-rotation fingers, "B" shaft

[0097] 233 Anti-rotation fingers, slip rings

[0098] 237 Gear

[0099] 240 Rotary Actuator, "B" Axis

[0100] 250 Positioning platform trajectory

[0101] 252 "B" bearing

[0102] 253 "B" axis

[0103] 254 "A" bearing

[0104] 255 "A" axis

[0105] 270 Crank

[0106] 272 Tie rod, "B" axis

[0107] 274 Tie rod, "A" axis

[0108] 300 Second Redirectable Element

[0109] 350 Expected Angle

[0110] 360 lock signal

[0111] 370 X displacement

[0112] 380 Y displacement

[0113] 400 Stylus, tip sensor

[0114] 415 Touch Tip

[0115] In the drawings, significant elements are identified by reference numerals that are repeated in the text. The same reference numerals may be used to identify different elements that are identical, similar, or technically equivalent. When there are many identical, similar, or equivalent elements in a figure, some reference numerals may be omitted to avoid overcrowding the figure. DETAILED DESCRIPTION

[0116] Figure 1 A coordinate measuring system comprising a coordinate measuring machine 40 of a known type is shown. The coordinate measuring machine 40 has a horizontal table 43 on which the workpiece 30 to be measured rests. A bridge 41 moves on the table 43 along a first linear axis Y, and a carriage 42 moves along a second linear axis X orthogonal to the first linear axis. A vertical spindle 45 (also called a quill or Z-plunger according to different conventions) moves on a third orthogonal axis Z, so that the end of the spindle 45 terminates in a positioning platform that can be positioned at any desired point in the measurement volume of the machine (i.e., in the volume in which the CMM is able to provide measurements of the surface of an object). Suitable encoders (not shown) read the position of the bridge 41, the carriage 42 and the spindle 45 along the measurement axes X, Y, Z. Most CMM machines are automatic, and the movement of the bridge 41, the carriage 42 and the spindle 45 is determined by electric motors, but there are also manual machines. The machine controller 25 is programmed to command the motors according to a predefined measurement plan designed taking into account the shape of the workpiece 30.

[0117] Figure 1 A touch probe 400 is shown having a spherical tip 415 designed to contact the workpiece 30 at a desired point. The touch probe 400 is typically a trigger probe and is configured to generate an electrical signal upon contact. The controller 25 uses this signal to store the instantaneous values ​​of X, Y, and Z and calculate the corresponding coordinates of the contact point by known methods.

[0118] The trigger probe 400 may be replaced by another coordinate probe, such as an optical non-contact probe, a scanning probe, a "hard" probe, etc., without departing from the scope of the present invention. The shape and length of the stylus are also not limited.

[0119] Although common, Figure 1The bridge structure is not the only possible structure. The invention is not limited to this execution, but includes all the various shapes and structures found in coordinate measurement systems. The invention explicitly includes systems where the carriage slides along a horizontal beam that is cantilevered rather than supported at both ends, articulated arm machines based only on rotational degrees of freedom rather than linear articulated arm machines such as articulated arm coordinate machines and robots, parallel robots such as delta robots and Stewart platforms, etc.

[0120] The size of the machine may also vary from a benchtop machine to a large device for measuring vehicles, aircraft or turbines without departing from the scope of the invention. The articulated probe head may be mounted vertically or horizontally on the positioning platform of the system. The invention explicitly includes systems comprising a movable platform, such as a rotary table, to movably support a workpiece during operation (e.g., measurement).

[0121] The precision and accuracy of CMMs range from sub-micron precision for laboratory equipment to 10-100 μm in some industrial applications.The invention is applicable to all variants disclosed herein, and in general to any kind of mobile stage that can be moved with suitable repeatability and precision.

[0122] Figure 2 The general structure of an articulated wrist in combination with a general purpose coordinate measuring machine as used in the present invention is shown. The wrist includes a support element 100, which is configured to be fixed to a positioning platform of the coordinate measuring machine. In many embodiments including a Cartesian coordinate machine, the support element 100 will be translated by the coordinate machine along a desired trajectory without rotation, and the articulated wrist is used to redirect the measurement probe as required, for example to insert the probe into a hole or between the aerodynamic blades of a turbine. In other cases, the movement of the positioning platform to which the wrist is fixed may include rotations, and in these cases, the wrist can be used to compensate for them. The connection between the wrist and the positioning platform can be obtained in any suitable manner.

[0123] Importantly, the wrist has a connector 103 to power and control the internal actuators that are responsible for redirecting the probe and for powering and reading the coordinate probe itself. In the simple case where the coordinate probe is a touch-trigger probe, the only connection required is a current loop that is opened once the probe touches the workpiece, but more complex power supply and signaling modes can be used. The connector 103 can also include a fiber optic connection, for example in combination with an optical probe to measure the distance to the workpiece by interferometry, triangulation, time of flight, chromaticity, focus change, or in any other suitable manner. This does not mean that the connector 103 is necessary. For example, the wrist of the present invention can completely get rid of the connector 103 using batteries and some form of wireless data transmission. The connector 103 may include an optical channel, or the wrist may have an additional connector for optical signals. Alternatively, an optical probe equipped on the wrist can be connected to a dedicated measurement device via an optical fiber that bypasses the wrist.

[0124] The support element 100 is pivotally connected to a first redirectable element that is rotatable relative to the support element about an axis "B". Axis "B" is drawn vertically in the figure, and this is its conventional orientation; therefore, it may also be referred to as a "vertical rotation axis", although the wrist may be used in any orientation in space.

[0125] The angle of rotation about axis "B" is adjustable by an internal actuator in the wrist and is controlled by a digital signal, as will be explained below. Importantly, the axis is of the indexing variety, which means that in addition to a "free" state in which the redirectable element can rotate about axis "B", the wrist also has a locked state in which the relative position of the first rotor 200 with respect to the support element is determined by an internal periodic joint. In the locked state, the rotor is fixed relative to the support element 100 at one of a predetermined plurality of precise and repeatable angles.

[0126] Preferably, the wrist also includes a second redirectable element 300 pivotally attached to the first redirectable element. The second redirectable element 300 can rotate around a second axis "A", which is preferably orthogonal to the first axis "B" and is therefore generally horizontal. As in the case of the other axis, the rotation of the second redirectable element 300 is preferably indexed.

[0127] The coordinate probe 400 is attached to the second redirectable element (when present). The figure shows a contact probe that generates a contact signal whenever the ball 415 contacts the workpiece, or a deflection signal when the ball sliding on the surface of the workpiece moves away from its resting position. The wrist can be equipped with any kind of contact-based or non-contact coordinate probe, or with other probes, such as a surface quality probe or a camera.

[0128] By a series of rotation angles around axes "B" and "A", the probe 400 can be aligned to any desired orientation in space. Preferably, the rotation around axis "B" spans more than one turn, and even more preferably it is not limited. The rotation of the second redirectable element around axis "A" may have an upward inhibition sector, as is common with wrists, which is of little importance when the wrist is attached below the positioning platform.

[0129] Optionally, the redirectable wrist may have one (or more) visual indicators 220 that may be activated autonomously by the controller of the coordinate machine or by the wrist controller circuitry. For example, this may be used to signal contact by the touch probe 415. Complementarily or alternatively, the visual indicator 220 may be activated by the controller of the wrist, such as the operational configuration of the wrist (for example) and / or the operational state or configuration of the wrist and / or sensed environmental factors (e.g., locked or free configuration of the wrist, below / above a given humidity or temperature level, abnormal operation of an active part of the wrist (such as an actuator).

[0130] Figure 3a and Figure 3b A partial cross section of a reorientable wrist is shown. The drawings are simplified: only the essential elements are shown, and in a schematically idealized manner. Figure 3a shows the probe in a locked indexing state, and Figure 3b The probe is shown in a state where it can rotate freely. In this embodiment, axes "A" and "B" are locked or released together. This is not a necessary feature. Variations can be designed in which axes "A" and "B" can be released, locked and / or operated independently of each other if this is advantageous in a particular use case.

[0131] The signals and power levels from and to the connector 103 are routed to the slip ring arrangement 107 inside the support element 100. The body of the slip ring enclosure 107 does not rotate and is connected to the connector by a short upper cable harness 114. The axis 109 of the slip ring follows the rotation of the first orientable element due to the anti-rotation fingers 233 and is the origin of the wire harness 115 that enters the first redirectable element 200 as well as the second redirectable element 300 to provide the required energy and signal paths. In the drawings, the harness 115 is drawn as having no branches and going directly to the probe connector 340, but this is a simplification of the actual configuration.

[0132] The operation of the redirectable wrist is controlled by an electronic wrist controller, which is not drawn to avoid confusing the accompanying drawings. The wrist controller may be included in one or more circuit boards in the support element 100 and / or in the first redirectable element 200 and / or in the second redirectable element 300. The wrist controller receives power and commands by wire harness 115, and commands determine the motor of the rotation of the redirectable element, reads the actuator measuring the corresponding rotation angle, and switches between a locked state and a state capable of free rotation, as will be disclosed below. In possible variations, the wrist controller may be separated from the redirectable wrist instead of being embedded, and communicates with the actuator and sensors in the wrist by wire harness and connector 103. The wrist controller may also be present in a group of electronic modules that communicate with each other, partially embedded in the wrist and partially external.

[0133] The slip ring enclosure 107 will be equipped with sufficient conductive circuits, such as 12 or more rings, to carry all the power and signal lines required for the application. If necessary, the slip ring enclosure 107 may also include pneumatic slip rings to transmit fluids such as compressed air, and / or optical circuits to transmit optical signals. Suitable electrical and electronic slip ring enclosures can be obtained from Moflon, Shenzhen, China, Moog, Elma, New York, etc.

[0134] Advantageously, the slip ring device 107 is located inside the support element 100, and the size of the support element 100 is selected to at least partially enter the hollow Z spindle of the coordinate measuring machine. In fact, the articulated wrist can be advantageously designed and specified to be mounted on a mobile platform with a central cavity, such as most of the Z spindle of the coordinate measuring machine. In this configuration, the articulated wrist can be advantageously designed to accommodate the support element 100 completely or at least partially within the gap and unused cavity. Fixing to the mobile platform can be achieved by a dedicated interface that encapsulates the shape of the Z spindle, or by a dedicated fixing mechanism that operates on a portion of the Z spindle (such as a wall and / or side). In this way, the assembly is more compact and the height of the measurable volume is not reduced.

[0135] The wiring harness 115 enters the first redirectable element through the central hole of a hollow rod 272 connected to a crank 270 and used to lock and release the first redirectable element 200. In the locked state, the position of the first redirectable element 200 relative to the support element 100 is defined by a periodic connector 120, which can be a Hirth connector (also called an end tooth disk or a rat tooth disk) or any other similar device. For example, the angular resolution of the Hirth connector can be 144 positions equally spaced 2.5°, or any other desired combination. The mating surfaces of the Hirth connector are biased against each other by a rod 272, which is kept taut by the crank 270, with the contact force being determined by a compression spring 175.

[0136] This synergy between the locking mechanism and the mechanism providing unrestricted / infinite rotation (i.e., a cavity or recess through the locking actuator 272 for the passage of optical signals and / or power and / or cables 115 between the support element and the first redirectable element) allows the articulated wrist to have a more compact and robust design.

[0137] The position of the second redirectable element 300 relative to the first redirectable element in the locked state is defined by an arrangement similar to that of the first redirectable element 200. The second periodic coupler 125 can be a second Hirth coupler having the same resolution as the first periodic coupler, or a different device as desired. When the mating surfaces of the first periodic coupler 120 are biased by the hollow rod 272, the pull rod 274 coupled to the crank 270 simultaneously biases the mating surfaces of the periodic couplers against each other.

[0138] Since the rotation of the second redirectable element is limited, the harness 270 is threaded into the second redirectable element, allowing sufficient length to allow the second redirectable element 300 to rotate within the expected range. However, a second slip ring device (with optical and electrical circuits if necessary) and a hollow rod can be provided to allow unlimited rotation around the "A" axis. The harness arrives at a connector 340 at the distal end of the second redirectable element, to which an interchangeable probe can be connected.

[0139] Figure 3b The wrist is shown in an unlocked state. Unlocking is determined by rotation of the crank 270 by an actuator not shown (e.g., a brushed DC motor with an appropriate speed reducer). In the unlocked state, the rods 272, 274 push the first redirectable element 200 away from the support element 100 and / or push the second redirectable element 300 away from the first redirectable element 200. The mating surfaces of the first Hirth coupling 120 and the second Hirth coupling 125 are separated, allowing rotation.

[0140] The first redirectable element 200 is guided in its rotation about the "B" axis by a bearing comprising an outer sleeve 252 and an inner shaft 253 which can pivot and slide axially in the outer sleeve to accommodate rotation and transition between a locked state and a free state. Notably, the bearing surfaces are shaped so that the minimum distance between the shaft and the sleeve is greater in the locked state than in the free state. Due to this feature, the rotation of the redirectable element 200 is guided with sufficient accuracy, but when the wrist is locked, the bearing does not introduce any lateral forces or torques that could change the indexing given by the periodic connector 120.

[0141] When the wrist is in the unlocked configuration, the spatial relationship between the first redirectable element 200 and the support element 100 is determined by the bearing surfaces, which ensure that the mechanical (radial and axial) position errors are typically in the range of a few μm (micrometers) to mm (millimeters). Therefore, compared with scanning probes, the geometric configuration of the wrist and the uncertainty of the position of the measurement probe prevent accurate measurement of coordinates (for example, in the μm range).

[0142] The electric motor 230 generates rotation about the "B" axis via a pair of gears 237. The electric motor 230 (which may be a brushed DC motor) is mounted on a collar that is free to rotate about a sleeve 252 (the sleeve 252 is connected to the support element 100 and does not rotate) and drives the body of the first redirectable element 200 via an anti-rotation pin 232. Importantly, the pin can slide axially in the corresponding hole to allow conversion between the free state and the locked state, and the connection of the pin in the hole is relatively loose to avoid any influence on the indexing position.

[0143] The second redirectable element rotates about the "A" axis by a similar arrangement including a bearing (which includes shaft 255 and sleeve 254), motor 240, and pin 242.

[0144] The articulated wrist of the present invention also includes a capacitive sensor 160 that is responsive to the average distance between the support element 100 and the first redirectable element 200. The capacitive sensor can be used to ensure that the indexing connector 120 surfaces are completely separated before starting rotation, and to detect unwanted collisions of the wrist or probe during the movement of the wrist. Preferably, the capacitive sensor 160 is effective in both the free state and the locked state. A similar capacitive sensor 160 provides the same function for the "A" axis between the first redirectable element 200 and the second redirectable element 300.

[0145] The rotary encoder 190 provides the relative angular position between the support element 100 and the first redirectable element 200. The rotary encoder 190 can utilize a resistance transducer, an optical encoder, an inductive or inductive encoder, a magnetic or reluctance encoder, or any other suitable angle measurement device. Preferably, the angle transducer 190 is an absolute encoder. The angle transducer 190 is used to control the instantaneous rotation in the free state, as will be explained below, but it can also be optionally effective in the locked state. There is also a corresponding angle transducer 195 to sense the rotation of the second redirectable element 300 relative to the first redirectable element.

[0146] Figure 4 There is schematically shown a reorientable wrist 10 mounted on a movable platform 20 in contacting relationship with a workpiece 30. The platform can be translated at will within a predetermined measurement space by a machine controller 25 driving suitable actuators 22. In the common case of a bridge CMM, the actuators 22 will be three motors producing three linear movements, each along one of the three Cartesian directions X, Y, Z, but other configurations are possible. The machine controller 25 also receives position data from a position encoder 23, which provides the instantaneous position of the positioning platform at any given time. Referring again to a conventional bridge CMM, the encoder 23 can be embodied by an optical linear transducer which measures the range of the above three linear movements and provides the position of the positioning platform as a 3D vector of values ​​X, Y, Z.

[0147] The re-orientable wrist 10 is managed by an electronic wrist controller 15, which may be embedded in the wrist itself, preferably, or provided as a separate unit. The wrist controller may be in the form of HW and / or SW, for example comprising one or more dedicated electronic circuits and / or enabled by one or more sets of instructions run by computer hardware (e.g. a microprocessor, microcomputer, digital signal processor or programmable electronic unit) as part of the wrist and / or coordinate machine, the instructions preferably being stored in a non-volatile memory of the wrist or coordinate machine.

[0148] like Figure 4 As shown, the wrist controller 15 operates the motor 224 that produces the rotation of the redirectable element of the wrist and the actuator 226 that locks and unlocks the wrist, reading the angular encoders 225 of the axes "A" and "B" and the capacitive collision sensor 160. The wrist controller 15 can be programmed to transmit the instantaneous internal state of the wrist to the machine controller 25 (arrow 17) and to receive from the machine controller the desired values ​​of the angular parameters and the locking state (arrow 16, arrow 19).

[0149] Thus, the wrist controller 15 may include a data transmission interface 20 for transmitting the instantaneous internal state 16 to the machine controller 25 and / or for receiving desired configuration values ​​from the machine controller 25. The data transmission interface may be configured to send and / or receive data according to a wired or wireless based communication standard (advantageously, a digital and industrial standard, such as an Ethernet based fieldbus), ultimately relying on a signal and / or power supply cable 114 and / or a dedicated cable passing through the connector 103 or another bus connector to send and / or receive data.

[0150] The internal state of the wrist may include joint parameters, in particular the angular position of the first redirectable element and the second redirectable element encoded in a digital manner, a locked state / free state, a touch flag indicating whether the touch probe is in contact with the workpiece 30, or the distance between the probe and the part, a collision flag generated by the capacitive sensor 160, and any other state variables.

[0151] The internal state transmitted to the machine controller can be accomplished by values ​​acquired by various sensing elements in the wrist, such as:

[0152] Temperature sensors for collecting the temperature of selected portions of the wrist. These temperature data can be used in the machine controller for thermal compensation of measurements or for diagnosing the health of the wrist. Preferably, each of the three sections of the wrist (support element, first redirectable element, and second redirectable element) has at least one temperature sensor.

[0153] One or more humidity sensors for collecting humidity values ​​of selected parts of the wrist. For example, these data can be used to determine tampering and / or assess the validity of a warranty.

[0154] • Acceleration and / or gyroscopic sensors for detecting shocks and / or impacts involving the wrist. Advantageously one sensor of this nature is provided in each section of the wrist or at least in each redirectable element.

[0155] Light sensor for detecting tampering and confirming maintenance operations. The light sensor may be effectively located within the first redirectable element 200, which is normally enclosed. Detection of light above a specified threshold may be used to determine if the wrist has been tampered with, unauthorized repaired, or modified.

[0156] Motor current sensing to determine operating status and for predictive maintenance.

[0157] The sensing and usage data are sent to the CMM controller 25 and in particular data related to misuse and authorization are sent to external devices via a suitable communication module (not shown). The exchanges with the machine controller 25 and external devices may involve a unique identifier of the wrist stored in an unmodifiable memory in the wrist and / or a service identifier allowing quick identification of the wrist and (preferably) the connected probe.

[0158] To ensure data integrity and simplify further data use, the wrist controller 15 may include a real-time clock module for time stamping the data. Alternatively, the time stamping may be performed in the machine controller 25 or in an external device.

[0159] Sensing devices, especially those that should detect abnormal tampering, can be configured to operate independently using an autonomous energy source and maintain their measured state, at least until it can be transmitted to the machine controller 25 or an external device. For example, if the wrist is disconnected and detached, it can be configured to sense opening through its light sensor and transmit relative operating information to the machine controller 25 when it is next powered on.

[0160] According to an important aspect of the invention, the wrist controller is configured to reorient and reposition the measurement probe along a desired trajectory in the operating volume of the CMM. The trajectory is defined by digital commands received from an external unit (such as a controller of a coordinate machine) and is followed in a deterministic manner. Deviations from the trajectory are limited by known errors at any time.

[0161] While many articulated wrists are configured to respond to general instructions that specify only the desired final values ​​of angles α and β, the articulated wrist of the present invention may preferably follow a trajectory that specifies not only the final parameters, but also a series of intermediate configurations along that path to be reached at specified points in time based on the received digital commands.

[0162] This can be achieved in many ways. Figure 4 , the machine controller can be configured to issue commands to the wrist controller that cause the wrist controller to switch from a locked state to a free state and vice versa from a free state to a locked device, and to provide the wrist controller with a desired orientation of the redirectable elements (arrow 16), as described above. The desired orientation can be expressed by an angle β of the first redirectable element relative to the support element and an angle α of the second redirectable element relative to the first redirectable element, or in any other suitable manner that allows the desired values ​​of α and β to be determined. The wrist controller 15 is programmed to drive an actuator 224 that rotates the first redirectable element and the second redirectable element so that their orientation matches the commands received from the machine controller 25.

[0163] Preferably, the wrist controller 15 implements a digital loop (feedback-based) control method configured to read the instantaneous angle value from the encoder 225, compare it with the desired angle value, and operate the actuator 224 to achieve and maintain the desired angle value. The control method can be implemented as a PD controller, a PID controller, or in any other suitable manner.

[0164] The expected values ​​of the angles α and β can be transmitted to the wrist controller in the form of a series of target positions to be reached at said time (e.g., formatted as a timetable) relative to a system clock or a local clock accessible to the wrist controller. The time information can be specified or given implicitly for each individual target point (e.g., under the following agreement: if the link between the machine controller 25 and the wrist controller 15 ensures a predictable reception time, the target point should be reached when the next target is expected to be transmitted). Possibly, the wrist controller can be configured to generate additional expected values ​​of the angles by interpolating the trajectory between the target point and the next point at a constant speed or at a given acceleration / deceleration or following an original curve or arc. In this way, the wrist controller causes the probe to follow a trajectory connecting a time series of target points received from the machine controller at said time. A known synchronized time reference system between the machine controller 25 and the wrist controller 15 can be used.

[0165] In a possible embodiment, a machine controller having obtained or generated a measurement plan including a trajectory of the positioning platform 20 and a series of orientations of the wrist sends a time series of desired orientations to the wrist controller 15 while driving the actuator 22 of the positioning platform 20. The controller 15 tracks the variable angle values ​​provided by the machine controller 25 so that at any given moment along the trajectory, the full kinematic configuration of the reorientable wrist is predictable within a determined error. In an embodiment, the repetition rate of the time series / sequence may be comprised between 10 Hz and 10 kHz, although higher or lower rates may be appropriate in special cases. The inventors have determined that 1 kHz is suitable for most metrology applications.

[0166] The actual values ​​of the angles α and β provided by the encoder 225 can be fed back to the machine controller, which supervises the motion of the five axes (X, Y, Z, α, β) of the system in real time. The machine controller 25 supervises the motion of the positioning platform 20 of the CMM and the orientation of the articulated wrist. In the case of a Cartesian CMM, the machine controller implements 5-axis control with position feedback, the axes being the Cartesian axes X, Y, Z and the rotation angles α and β of the rotation axes A and B of the wrist.

[0167] Advantageously, the wrist controller 15 may be configured to send a warning message to the machine controller 25 in determined circumstances, such as:

[0168] - the expected orientation is not received within a given deadline after the command to unlock the wrist;

[0169] - No further direction has been received within a given cutoff time after the previously desired direction.

[0170] In both cases, the cut-off time may preferably be set between 1 ms and 100 ms, preferably between 2 ms and 10 ms, for example 5 ms.

[0171] Preferably, the trajectory of the positioning platform 20 and the continuous orientation of the wrist are calculated by the machine controller 25 or by a dedicated preprocessor in a manner that ensures that all desired measurements are collected, the measurement time is optimized, and no collisions occur under reasonable assumptions about the true size and position of the workpiece being measured. Several algorithms can be used to achieve this result, provided that the kinematic configuration of the reorientable wrist should always be determinable with sufficient accuracy.

[0172] In other words, the better the kinematic configuration of the redirectable wrist is known, the closer the probe can be held to the workpiece, and the lower the measurement time will be. In the opposite case where the kinematic configuration of the wrist is only poorly known - as is the case in a conventional automatic indexing wrist - collisions can be avoided with certainty simply by moving the positioning stage to a position spaced from the workpiece, reorienting the probe while the positioning stage is not moving, and then resuming the motion of the positioning stage (which necessarily results in longer times). The inventors have determined that tight closed-loop control of joint angles and precision mechanical joints are beneficial because they allow faster measurements, even if no coordinate measurements are being made while the redirectable element is rotating, because this reduces dwell time.

[0173] Therefore, it is desirable to control the rotational position of such a reorientable wrist to a sufficiently precise degree that when the rotational axes are at or near a new desired relative orientation, the relative joints of such axes can be locked together by a locking mechanism, and then the accuracy of the desired indexing position for supporting measurement is provided by an indexing element or component of the locking mechanism and ultimately by a separate or identical calibration process of the desired indexing position.

[0174] To better illustrate this, Figure 5 An example is shown in which a coordinate machine equipped with a re-orientable wrist of the present invention is used to probe two orthogonal sides of a prismatic workpiece 30. In this simple example, for simplicity, only the X, Y coordinates of the positioning platform 20 and the "B" joint of the wrist are variable, but this is not required. The machine controller 25 is configured to control the configuration of the CMM machine, which for a Cartesian CMM includes the configuration of the axes X, Y, Z and the articulated wrist, including the rotation angles α, β and locked / unlocked state of the wrist.

[0175] The trajectory of the positioning stage is plotted as 250, and four consecutive positions of the wrist along the trajectory are shown as 10a-10d. Starting from position "A", the wrist in a locked state travels parallel to the first face of the workpiece 30. In this segment, the probe travels parallel to the nominal surface with a determined gap without touching the nominal surface. At point "B", the positioning stage moves closer, the probe taps the surface and collects measurement points. The wrist and probe travel along the initial line in "C", tap the surface again in "D", and travel along the initial line again until it reaches point "E" which has been predetermined as the start of the re-orientation maneuver. In contrast to other measurement systems in which the orientation of the probe is continuously variable, the measurement points are collected while the axes "A" and "B" are locked, and the orientation of the probe is fixed in a graduated configuration.

[0176] At point "E", optionally, the positioning platform is moved slightly away to increase the clearance between the wrist and the workpiece, thus preparing to unlock the wrist. This is reasonable because the dimensions of the wrist change slightly in the transition between the locked state and the free state, and because the geometric uncertainty in the free state is always higher. This additional clearance is exaggerated in the figures to make it obvious and is achieved at point "F" where the wrist receives the unlock command. At the same time, the platform continues to move in the "X" direction towards the edge of the face.

[0177] At point "G", the positioning platform deviates from its previous substantially straight trajectory, following an arc of rotation about edge 33 (represented as a double line), and simultaneously the machine controller sends a series of desired orientations to the wrist controller, which causes the first redirectable element to rotate so that the probe follows a smaller arc (not drawn) about the same edge without contacting the workpiece 30.

[0178] Point "H" is the end of the arc. The positioning stage resumes its linear motion, this time in the "Y" direction, in which the face to the left of edge 33 is located, and a lock command is given to the wrist. After a period of time, the optional additional clearance is withdrawn and the positioning stage is moved closer to the workpiece 30. At point "I", the reorientation maneuver is completed and the measurement continues with the acquisition of two new data points at "J" and "K".

[0179] Figure 6 3 is a graph of the commands received by the wrist for the "B" axis (curve 350) and the locked state (curve 360) along the trajectory of the previous example, superimposed on the instantaneous "X" and "Y" positions (curves 370, 380) of the platform 20. The machine controller sends the desired value of the β angle synchronously with the corresponding movement of the positioning platform so that the orientation of the wrist follows a series of orientations predefined in the trajectory.

[0180] In possible embodiments, the machine controller may be configured to collect characteristics, capabilities (e.g., predefined capabilities) and / or performance (e.g., evaluated capabilities) of an attached articulated wrist, a carried measurement probe and / or its accessories in view of supporting and / or determining a planned trajectory (ultimately via a wrist controller) based on data collected as follows.

[0181] The present invention allows a machine controller or a dedicated preprocessor to calculate (and operate) a measurement plan with reorientation of the articulated wrist synchronously with the movement of the positioning platform 20 through a series of expected orientations having time information or linked to time information (particularly a time series of expected orientations), which will be provided to the wrist controller 15 for execution.

[0182] Furthermore, the invention also allows a machine controller or a dedicated pre-processor to optimize the reorientation of the articulated wrist not only based on the level of knowledge of the kinematic configuration of the articulated wrist, but also based on the estimated risk of collision due to, for example, a local concentration of objects in the measurement volume of the measurement device (particularly in the vicinity of the articulated wrist and the attached coordinate probe). Thus, a measurement plan can be calculated (or executed) to selectively operate the reorientation of the measurement probe in a first operating mode (e.g., when there is a risk of collision and the kinematic configuration of the wrist is less favorable (e.g., due to significant loads caused by the attached coordinate probe), where the repositioning of the probe is performed in a slower but more accurate manner) and in a second operating mode (when the risk of collision is estimated to be low, where the repositioning of the probe is performed faster but in a less accurate manner).

Claims

1. An articulated wrist for reorienting a measurement probe relative to a measurement device, the articulated wrist comprising: A support element, which can be connected to a positioning platform of a measuring device; a first redirectable element pivotably connected to the support element for rotation about a first axis of rotation; a first actuator actuatable by a wrist controller to rotate the first redirectable element about the first rotational axis; a first angle encoder configured to determine an angular position of the first redirectable element relative to the support element and to generate a read orientation; a communications interface configured to receive digital commands and data, The articulated wrist is configured to selectively operate in any of the following modes: ○ a locked mode in which the first redirectable element is mechanically constrained in one of a finite set of indexed orientations; ○ a free mode in which the first actuator is capable of rotating the first redirectable element, Features: The wrist controller is configured to receive, through the communication interface, a positioning command expressing a series of desired orientations of the first redirectable element and a specified time for obtaining the desired orientations, and to read a first position when the articulated wrist is in the free mode, to continuously select each of the desired orientations in chronological order, and to command the first actuator to move toward the selected desired orientation at a corresponding specified time based on a difference between the read orientation and the selected desired orientation.

2. The articulated wrist according to claim 1, wherein: The communication interface is configured to resend successive values ​​of the reading orientation to a controller of the measurement device.

3. The articulated wrist according to claim 1, wherein: The first actuator is contained in the first redirectable element and is capable of unlimited rotation, and the support element includes one or more slip rings for transmitting power and / or electrical actuation contacts from the support element to the first redirectable element.

4. The articulated wrist according to claim 3, wherein: The slip ring also transmits an optical signal and / or a pressurized fluid from the support element to the first redirectable element.

5. The articulated wrist of claim 1 having an indexing coupler between the support element and the first redirectable element, the indexing coupler comprising a plurality of mobile positioning elements associated with the first redirectable element, a plurality of fixed positioning elements associated with the support element and engageable with the mobile positioning elements to define a plurality of predetermined indexed orientations of the first redirectable element relative to the support element, the articulated wrist further comprising a locking actuator controlled by the wrist controller, the locking actuator being actuatable to cause one of: in the free mode, an axial separation between the mobile positioning element and the fixed positioning element, whereby the first redirectable element can be rotated relative to the support element by the first actuator, or - In said locked mode, mutual engagement between said mobile positioning element and said fixed positioning element, whereby said first redirectable element assumes one of said indexed orientations.

6. An articulated wrist according to claim 5, wherein the locking actuator comprises a hollow body configured to bias the mobile positioning element against the fixed positioning element in the locking mode and to separate the mobile positioning element from the fixed positioning element in the free mode, the hollow body providing a passage for electrical and / or optical and / or fluid conductors between the support element and the first redirectable element.

7. The articulated wrist of claim 1, the wrist controller being configured to switch between the locked state and the free state in response to commands received through the communication interface, and conversely to switch between the free state and the locked state.

8. The articulated wrist according to claim 1, wherein: The wrist controller is configured to operate in a conventional mode, wherein upon receiving a final orientation via the communication interface, the wrist controller places the wrist in the free state, commands the actuator to rotate the first redirectable element until the final orientation is reached, places the wrist in the locked state, and optionally sends a confirmation message via the communication interface.

9. The articulated wrist of claim 1, comprising at least one sensor from the following group: a temperature sensor, a humidity sensor, an acceleration sensor, a gyroscope sensor, a light sensor, a motor current sensor, a capacitive collision sensor.

10. The articulated wrist of claim 1, comprising: a second redirectable element pivotably connected to the first redirectable element for rotation about a second axis of rotation substantially orthogonal to the first axis of rotation; a second actuator in the first redirectable element, the second actuator being actuatable to rotate the second redirectable element about the second rotational axis; a connector on the second redirectable element, the connector being used to secure the measurement probe; a second angle encoder configured to determine an angular position of the second redirectable element relative to the first redirectable element and generate a second read orientation, ·The positioning command specifies a series of desired orientations of the first redirectable element relative to the support element and a series of desired orientations of the second redirectable element relative to the first redirectable element, and the wrist controller is configured to read the read orientation and the second read orientation, continuously select each of the desired orientations of the first redirectable element relative to the support element and the second redirectable element relative to the first redirectable element in a chronological order, and based on the difference between the read orientation and the selected orientation of the first redirectable element relative to the support element and the difference between the second read orientation and the selected orientation of the second redirectable element relative to the first redirectable element, command the first actuator and the second actuator to move toward the selected desired orientation at the corresponding specified time.

11. A measuring device, the measuring device being included in a coordinate measuring machine in a machine tool or a robot, the measuring device comprising: A mobile positioning platform controlled by a device controller; An articulated wrist according to any one of the preceding claims, attached to the mobile positioning platform; and a measuring probe connected to the articulated wrist for measuring a workpiece using the measuring device; Wherein, the device controller is configured to: determine a planned trajectory including a series of instantaneous configurations, each instantaneous configuration determining the position of the mobile positioning platform and the orientation of the articulated wrist carrying the measuring probe; control the positioning platform so as to translate the positioning platform in a time-sequential manner following the series of positions defined in the planned trajectory; and send a command to the wrist controller so that while translating the positioning platform, the measuring probe rotates synchronously with the corresponding translation of the positioning platform through the articulated wrist following the series of orientations defined in the planned trajectory.

12. The measuring device according to claim 11, wherein The device controller is configured to send a command to the wrist controller so that the wrist controller selects the free state of the wrist when preparing to change wrist orientation, or selects the locked state of the wrist when preparing to take a measurement with the measurement probe.

13. A method of operating a measurement device having: a mobile positioning platform controlled by a device controller; an articulated wrist according to any one of claims 1 to 10, the articulated wrist being attached to the mobile platform; a measuring probe connected to the articulated wrist for measuring a workpiece using the measuring device, the method comprising: determining a planned trajectory comprising a series of instantaneous configurations, each instantaneous configuration determining a position of the mobile positioning platform and an orientation of the wrist carrying the measurement probe; The positioning platform is controlled by the device controller so as to translate the positioning platform in a time-sequential manner following a series of positions defined in the planned trajectory; a command is sent from the device controller to the wrist controller so that while the positioning platform is translated, the measurement probe is rotated by the wrist in synchronization with the corresponding translation of the positioning platform following the series of orientations defined in the planned trajectory.

14. A method according to claim 13, the method comprising sending a command from the device controller to the wrist controller so that the wrist controller selects the free state of the wrist when preparing to change the wrist orientation, or selects the locked state of the wrist when preparing to measure with the measurement probe.

15. The method according to claim 13, wherein: The transient configuration is periodically transmitted by the device controller to the wrist controller with a period lower than 100 ms, preferably lower than 10 ms, more preferably equal to 1 ms.

16. The method according to claim 13, comprising: retransmitting a continuous value of the read orientation from the wrist controller to the device controller; determining the actual configuration of the measuring device based on the value of the reading orientation and the reading position of the positioning stage determined by a position encoder of the measuring device; A difference between the actual configuration and a desired instantaneous configuration of the planned trajectory is determined; and an instruction is sent from the device controller to the wrist controller and / or to an actuator of the measurement device to move the positioning platform so as to tend to zero the difference.

17. The method according to claim 13, wherein: The measuring device is composed of a coordinate measuring machine, a machine tool or a robot.

Images