Motorized measuring arm device for machine tools

Abstract

A motorized measuring arm apparatus (2) for a machine tool is described. The apparatus (2) comprises a base (4; 40) for attachment to the machine tool and an arm member (6; 38) extending from the base for holding one or more sensors. The arm member (6; 38) is movable relative to the base between a stowed position (26b) and an operating position (26a), the operating position being defined by engagement of a mechanical stop arrangement (50a, 50b). The apparatus further has a motor (44) for moving the arm member (6; 38) relative to the base (4; 10) and a motor controller (52, 78) for energizing the motor (44) to move the arm member (6; 38) relative to the base (4; 40). The motor controller (52, 78) is configured to energize the motor (44) to maintain engagement of the mechanical stop arrangement (50a, 50b) when the arm member (6; 38) is in the operating position. An operating position with improved repeatability is thus obtained.

Description

Technical Field

[0001] The present invention relates to a motorized measuring arm device for machine tools, and more particularly to an improved motorized measuring arm device configured to move at least one measuring sensor into and out of an operating position for measurement. Background Technology

[0002] It is known to mount measuring arm devices on machine tools, which allow measuring sensors (such as tool measuring devices or tool setting probes) to move to an operating position as needed and as required. For example, the measuring sensor can be periodically moved into the working volume of the machine tool to measure or inspect the cutting tool, but when such tool measurement is not required, the measuring sensor can be moved to a non-operating position or a retracted position. The measuring arm is known to be manually moved by the user, or it can be motorized to allow automatic movement under the control of the machine tool.

[0003] US 5446970 describes an example of a motorized measuring arm device. A protruding measuring arm member is rotatable relative to a fixed base member, and a motion stop is used to define the operating position of the arm member. A motor and worm gear drive mechanism are used to rotate the arm member to engage with the motion stop, and a complex arrangement of tension springs is provided to maintain this engagement when the motor is deactivated after reaching the operating position.

[0004] US 6519863 describes another measuring arm that includes a stop that kinematically defines an operating or indexing position between a stationary member and an arm member. An axially biasing spring and a brake plate are used to provide a rotational force that maintains engagement of the stop after the arm member has moved to the operating position. This provides a more compact and robust device than the tension spring arrangement of US 5446970.

[0005] The inventors have discovered that, in certain circumstances, the repeatability of the index position or operating position provided by the arrangements of US 5446970 and US 6519863 may decrease. For example, the repeatability of the operating position may be affected in the presence of machine vibration, or when the arm is laboriously driven to the operating position (such as when the arm carries a heavy sensor). Any such variation in operating position will become a source of uncertainty for any position measurement made using a sensor carried by a measuring arm device. Summary of the Invention

[0006] According to the present invention, a motorized measuring arm device for a machine tool is provided, the motorized measuring arm device comprising:

[0007] The base, which is used for attachment to the machine tool,

[0008] An arm member extending from the base, used to hold one or more sensors, is movable relative to the base between a retracted position and an operating position, the operating position being defined by engagement of a mechanical stop arrangement.

[0009] A motor, used to move the arm assembly relative to the base, and

[0010] The motor controller is used to energize the motor to move the arm assembly relative to the base.

[0011] The motor controller is configured to energize the motor when the arm member is in the operating position to maintain engagement of the mechanical stop arrangement.

[0012] Therefore, the present invention provides a motorized measuring arm device for machine tools (such as metal cutting machines, machining centers, grinding machines, milling machines, or lathes). The device includes a base that can be attached to a suitable part of the machine tool. For example, the base may include multiple holes that allow the device to be attached to the bed, housing, or frame of the machine tool using bolts or the like. Any such attachment is preferably sufficiently rigid to prevent any movement of the base relative to the machine tool. An arm member extending from the base is also provided. As described below, the proximal end of the arm member can be attached to the base via a slewing joint, thereby allowing the arm member to rotate between a retracted position and an operating position. The arm member is also configured to hold one or more sensors (such as tool measuring devices or tool setting devices). The sensors (multiple) may be attached at or near the distal end of the arm member, or at any suitable location along the arm member. As also explained below, the arm member may be substantially straight, or the arm member may include one or more beveled portions. In a preferred embodiment, the arm member is L-shaped, with the sensor attached near the distal end of the arm member.

[0013] The arm member can move between a retracted position and an operating position. The arm member can also be in other positions (e.g., one or more intermediate positions). Under the control of a motor controller, a motor drives the arm member to move between the retracted and operating positions. In a preferred embodiment, the motor rotates the arm member between the retracted and operating positions. The motor controller can further interface with the controller of the associated machine tool to provide automated control of the equipment.

[0014] When the arm member is in the operating position, a mechanical stop arrangement engages. The mechanical stop arrangement may, for example, include one or more first portions of the arm member configured to engage with one or more second portions of the base. As explained below, in a preferred embodiment, this mechanical stop arrangement may include a braking mechanism that provides repeatable (e.g., kinematically defined) operating positions. In use, the operating position is arranged such that a sensor attached to the arm member is held within the machine tool in a position suitable for performing the desired measurement. For example, the operating position may position a tool measuring sensor within the working volume of the machine tool to a position suitable for tool measurement. Importantly, it should be noted that the motorized measuring arm device itself does not perform any object measurement; rather, the motorized measuring arm device is arranged to properly position the sensor in the operating position before measurement is performed using the sensor held by the arm member. In particular, the motorized measuring arm device is configured to hold a suitable sensor (e.g., a tool measuring sensor) that, when the sensor has been placed in the operating position, can be used to acquire a measurement value (e.g., a tool measurement value). As explained below, the arm component may therefore include a sensor holder that allows appropriate sensors to be attached to the arm component.

[0015] The arm component can move back and forth between an operating position and a retracted position (e.g., by rotating back and forth between the operating and retracted positions via a motor). Moving to the retracted position can, for example, remove the arm component and any attached sensors from the machine tool's working volume to ensure that the arm component and any attached sensors do not interfere with the cutting tool, workpiece, etc. The retracted position can also be referred to as the non-operating position or non-measuring position because any sensors attached to the arm component are typically not used when the arm component is in this position. Although the retracted position adopted by the arm component can be repeatable, it does not have to be repeatable because the measurement is not intended to be performed when the arm component is in this position. It should be noted that moving the arm component to the retracted position allows the arm component to retract into a housing or cavity with a door or louvers, which can then be closed during any cutting operation to protect the measuring arm device. Alternatively, the retracted position can simply position the arm assembly away from an area within the machine housing (where the arm assembly might interfere with other operations), and / or the retracted position can move any attached sensors into the protective housing or recess.

[0016] According to the invention, the motor itself is used to help maintain engagement of the mechanical stop arrangement after the arm member has been driven to the operating position. Instead of simply shutting off the motor after the arm member has moved from the retracted position to the operating position, the motor remains energized to help maintain engagement of the mechanical stop arrangement. When the arm member is in the operating position, the power (e.g., current) supplied to the motor is preferably selected to be low enough to prevent the motor from generating excessive heat. This helps prevent damage to the motor and also minimizes the effects of thermal expansion, which could otherwise affect the operating position of the arm member. Thus, the motor acts to apply force (torque) to maintain engagement of the mechanical stop, but the motor does not exhibit any further rotation. In other words, when the arm member is in the operating position, the motor stalls but remains energized to provide holding torque or force. The electrical energy supplied to the motor is preferably reduced after the mechanical stop is engaged, thereby reducing motor overheating and / or preventing damage to the motor. It should be noted that the force applied by the motor to maintain the engagement of the mechanical stop can be any force other than other forces (e.g., spring force, gravity, etc.) that can also serve to keep the mechanical stop arrangement engaged.

[0017] The arrangement of the present invention has been found to have numerous advantages. In particular, it has been found to provide a more repeatable operating position for maintaining the engagement of the mechanical stop than that obtained using purely passive (spring-based) mechanical devices. This, in turn, reduces measurement uncertainties associated with multiple measurements (e.g., tool measurements) using sensors attached to such a measuring arm device. In other words, the torque applied by a motor to maintain the engagement of the mechanical stop arrangement when the arm member is in the operating position reduces the arm member position variations that may occur in prior art devices (e.g., due to vibration, etc.). This thus provides improved metrological accuracy, especially when the arm device is used to carry heavy sensors and / or is mounted in a specific orientation.

[0018] Advantageously, the motor controller is configured to supply a starting current to the motor during a first time period following the initial engagement of the mechanical stop arrangement while the arm member moves to the operating position. Conveniently, the motor controller is also configured to supply a holding current to the motor after the first time period to maintain a firm (positive) engagement of the mechanical stop arrangement. In other words, the motor can consume a starting current when the mechanical stop arrangement is initially engaged upon reaching the operating position. In particular, a starting current limit can be applied when the motor stalls. The starting current may be quite high (i.e., if the starting current is held for too long, it may be high enough to damage the motor or cause it to overheat). After the first time period (which may be approximately a few seconds or less), a holding current is supplied to the motor, which provides holding force or torque. The first time period may be at least 0.1 seconds, or at least 0.25 seconds, or at least 0.5 seconds, or at least 1 second. The first time period may be less than 10 seconds, or less than 5 seconds, or less than 1 second. Then, while adopting the operating position, the holding current limit is maintained, so the holding current limit is preferably low enough to prevent the motor from overheating or being damaged.

[0019] Advantageously, the holding current is less than the starting current. The motor controller can also be configured to reduce the current supplied to the motor from the starting current to the holding current during a second time period. A rapid reduction from the starting current to the holding current can occur (i.e., the second time period can be very short). Advantageously, a more gradual reduction from the starting current to the holding current can occur. For example, the second time period can be at least 0.1 seconds, or 0.25 seconds, or 0.5 seconds, or 1 second. It has been found particularly advantageous to configure the motor controller to gradually reduce the current supplied to the motor from the starting current to the holding current during the second time period. In other words, the drive current can be reduced progressively or stepwise from the starting current to the holding current. This allows the good engagement of the mechanical stop, obtained when a relatively high starting current is applied, to be maintained as the current decreases to the holding current. In other words, a substantially constant engagement force (torque) can be maintained, and backward movement of the transmission (potentially inconsistent movement) can be substantially prevented.

[0020] Advantageously, the motor controller is configured to monitor the current supplied to the motor. For example, the motor controller may include a current measuring device or circuitry. In this way, the motor controller can sense any increase in current (i.e., starting current) that may occur when the mechanical stop engages. Monitoring the current can also be used to determine whether the boom member has made (e.g., unintentional) contact with an external object. For example, if the boom member is moving, any sudden increase in the current consumed by the motor may indicate that the boom member has struck an obstacle. In this example, the motor can be stopped to prevent damage or injury. As explained below, if an encoder is also provided to measure the orientation of the boom member, the encoder output can also be used to distinguish whether the arm has reached the operating position or has contacted an unintended obstacle.

[0021] The current supplied to the motor can also be monitored when the arm component is in the operating position. If the motor begins to draw more current than the expected holding current, it can be determined that an external force is being applied to the arm component. This external force could be a machine operator attempting to manually move the arm component from the operating position (e.g., if the machine tool is being reset after a power failure, collision, etc.). In response to determining that such an external force is being applied to the arm component for a certain period of time, the motor controller can cut off the holding current to allow manual movement (i.e., release) of the arm component without having to overcome the holding force applied by the motor. In particular, the motor controller is preferably configured to de-energize the motor in the event of an external force applied to the movable arm. However, it should be remembered that transient forces may arise due to vibration, so the arm component is preferably only released when an external force of a certain magnitude is continuously applied for a certain period of time.

[0022] As explained in more detail below, the device may include an encoder (e.g., a rotary encoder) for measuring the position of the movable arm. Advantageously, the motor controller is configured to monitor the output of the rotary encoder and thereby determine whether there are any unintended changes in the position or speed of the arm member indicating that an external force is being applied to the arm member. In other words, the measurement by the encoder can be used to sense any unintended changes in position (e.g., when the arm member is expected to be stationary) or speed of movement of the arm member (e.g., when the arm is moving between an operating position and a retracted position) caused by an external force being applied to the arm. Instead of or supplementing monitoring of changes in the supplied current, the motor controller may also use any such unintended changes in position or speed, as measured by the encoder, to indicate that an external force has been applied to the arm member, thereby de-energizing the motor.

[0023] When the arm member is in the operating position, the mechanical stop arrangement preferably defines a repeatable position of the arm member relative to the base. Preferably, the stop mechanism is located inside the motorized measuring arm device, but alternatively, a separate external stop (e.g., directly attached to a part of the machine tool) may be provided. In a preferred embodiment, the mechanical stop arrangement includes a first portion attached to the arm member and a second portion attached to the base. The first and second portions may each include multiple elements (e.g., three elements) that engage to define a repeatable relative position when the first and second portions are engaged.

[0024] Advantageously, the first and second parts provide a kinematically defined relative position upon engagement. In other words, the first and second parts define a kinematically constrained operating position. This kinematic constraint means that each of the six degrees of freedom of motion between the first and second parts is constrained by only one point of contact. This defines a highly repeatable relative position between the first and second parts. Various types of kinematic connectors and mounts are known and described, for example, in HJJ Braddick's "Mechanical Design of Laboratory Apparatus," published in 1960 by Chapman & Hall in London. Such kinematic constraints can include quasi-kinematic mounts or partially degenerate kinematic mounts.

[0025] The operating position is defined by the engagement of a mechanical stop arrangement, which preferably allows the boom member to obtain a highly repeatable position relative to the base. In the retracted position, repeatable positioning is typically not required because position measurements are typically not performed when the boom member is in the retracted position. However, a repeatable retracted position can also be defined (e.g., by providing another mechanical stop arrangement). The precision of defining any repeatable position provided in the retracted position may be lower than the precision of defining the repeatable position provided in the operating position.

[0026] The motor of the device can be of any suitable type. Advantageously, the motor includes a brushless motor, and / or the motor can be a direct current (DC) motor. The motor can include a stepper motor. The device may also include a gearbox (i.e., the motor can transmit motion to the arm member via the gearbox). The arm member can move linearly relative to the base. In a preferred embodiment, the arm member is attached to the base via a slewing joint. Thus, the motor can rotate the arm member between a retracted position and an operating position. The rotation can be directly driven or gearbox-driven. Any suitable rotation angle can be provided between the operating position and the retracted position. Advantageously, the rotation between the retracted position and the operating position needs to be greater than 45°, or greater than 60°, or at least 90°. The amount of angular rotation between the retracted position and the operating position can be adjustable. For example, the absolute angle of at least one of the retracted position and the operating position can be adjustable. This adjustment can be made by the user. Alternatively, the angle defining the retracted position and / or the operating position can be set during manufacturing or by an installation engineer.

[0027] Advantageously, the arm device includes at least one rotary encoder. The rotary encoder can be an optical encoder, an inductive encoder, or a magnetic encoder, etc. The rotary encoder can be used to measure the rotation of the arm component relative to the base. An encoder can be provided for the motor, or the encoder can be integrated into the motor. For example, the motor can include an integrated encoder (e.g., including one or more Hall sensor elements) to measure the amount of motor rotation.

[0028] Alternatively or additionally, an encoder can be mounted on a suitable part of the measuring arm device to measure the relative position (e.g., angle) of the arm member relative to the base. The motor controller can receive position information from the encoder, enabling it to operate in response to the relative position (e.g., angle) of the arm member relative to the base. Thus, the arm member's speed can be slowed down as it approaches the operating or retracted position. This reduces damage or wear to the equipment and also mitigates vibration or oscillation of the arm member that might otherwise occur upon reaching the operating position. If the arm member's movement speed can be slowed down before reaching the desired position, the arm member's movement speed can also be increased.

[0029] In a preferred embodiment, the base includes a housing that accommodates a rotary joint, a motor, and a mechanical stop arrangement. The arm member can then extend from the housing. A rotatable hub can be provided for supporting the arm member. In a preferred embodiment, the motorized measuring arm device may include a braking mechanism as described in US 6519863 (the contents of which are hereby incorporated by reference). Specifically, the base may include a hub having a movable portion having three radially (outwardly) protrusions that rotate within an orifice of the base, which also has three radially inwardly protrusions. These protrusions together provide a mechanical stop that defines not only the operating position of the arm member but also its retracted position. The orifice may also have three axially raised regions on an annular flange that support an annular shoulder on the hub. In this way, there are six contact points between the hub and the base member in each of the operating and retracted positions. A spring bias arrangement may be provided, comprising a brake plate fastened to the orifice and a planar spring fastened to the hub through its central region. The ball bearing can be loosely held in two opposing lugs on the spring and extends around the brake plate between two pairs of brake holes. In the operating and retracted positions, the ball bearing rests on the radially extending edges of the brake holes (see, for example, US 6519863). Figure 5 And therefore the axial force of the spring also provides a force component in the tangential direction, thereby generating a rotational force.

[0030] As mentioned above, a motorized measuring arm device may include a gearbox connecting a motor to the arm component. This allows the rotation of the motor to be converted to provide the desired speed and torque. The gear ratio may be fixed or variable. The gear ratio may be set to provide sufficient torque to rotate the arm component (and any sensors mounted on the arm component) at the desired speed between the retracted and operating positions. The device preferably does not include a clutch or similar mechanism. The motor is preferably arranged to stall and stop (i.e., not rotate) when energized to maintain engagement of the mechanical stop arrangement (e.g., by applying a holding current).

[0031] Advantageously, the base includes an attachment mechanism for securing the device to a machine tool. For example, the base may include an attachment mechanism with multiple holes to allow attachment to the machine tool using bolts or the like. Alternatively, other attachment devices (e.g., custom mounts, mounting blocks, etc.) may be provided. The arm member preferably includes at least one sensor holder to which a sensor can be attached. Preferably, the sensor is detachably mounted to the sensor holder. At least one sensor holder may be located at or near the distal end of the arm member. Each sensor holder may be arranged to receive one or more sensors. For example, the sensor holder may be configured to allow tool measuring sensors (e.g., non-contact or contact tool setting devices or tool measuring devices) to be attached to the movable arm. The motorized measuring arm device may also include sensors mounted (e.g., detachably mounted) to the arm member (e.g., via the sensor holders of the arm member).

[0032] The motorized measuring arm device may include only one axis of motion (e.g., a rotation axis) between its base and the distal end of the arm components. The device is preferably not an articulated robot or the like. Only the operating position is suitable for the measurement purpose (i.e., the retracted position and any other positions may not be sufficiently defined to allow for measurements at an acceptable level of accuracy or repeatability). The device may include other features that allow the use of attached measuring sensors. For example, appropriate cabling (e.g., through-device routing) may be provided to allow the attached measuring sensors to communicate with, for example, an associated interface. Visual indicators (e.g., LEDs or displays) may be provided to indicate the status of the device (e.g., whether the device is in the operating or retracted position, and whether the motors are powered).

[0033] The device may also include one or more sensors attached to the arm member. As explained above, the sensors may be detachably attached to a sensor holder on the arm member. The sensors are preferably independent or separate sensors that move the arm member into and out of the operating position. The arm member is preferably stationary when the sensor takes a measurement. The arm member is preferably moved to the operating position before the sensor takes a measurement. The attached sensors(s) may include measurement probes with deflectable styluses. For example, analog or contact-triggered measurement probes may be provided. The attached sensors(s) may include tool measurement sensors. Tool measurement sensors may be contact tool measurement sensors with deflectable styluses (e.g., with a disk, square, etc. at their distal end). Tool measurement sensors may be non-contact sensors. For example, optical or laser-based tool measurement sensors. The measurement sensor may be a beam-interrupting laser tool setter, such as the NC4 system sold by Renishaw PIC, Wotton-Under-Edge, UK. The measuring sensor can be a reflective tool measuring device, such as the TRS2 system also sold by Renishaw. The device may also include a protective housing or recess for the sensor when it is moved to the retracted position.

[0034] This document also describes a motorized measuring arm device. The device can be configured for use on a machine tool. The device may include a base for attachment to the machine tool. The device may include an arm member extending from the base. The arm member may be configured to hold one or more sensors. The arm member may be movable relative to the base. This movement may include moving to a retracted position. This movement may include moving to an operating position. The operating position may be defined by engagement of a mechanical stop arrangement. A motor may be provided for moving the arm member relative to the base. A motor controller may be provided for energizing the motor to move the arm member relative to the base. The motor controller is configured to energize the motor when the arm member is in the operating position to maintain engagement of the mechanical stop arrangement. The motor controller may be configured to supply a holding current to the motor when the arm member is in the operating position to maintain engagement of the arm member with the mechanical stop. The holding current may be less than the drive current used to move the arm member. Any one or more other features described herein may also be provided.

[0035] A method for operating a motorized measuring arm device for a machine tool is also described, the device comprising: a base for attachment to the machine tool; an arm member extending from the base for holding one or more sensors, the arm member being movable relative to the base between a retracted position and an operating position, the operating position being defined by engagement of a mechanical stop arrangement; and a motor for moving the arm member relative to the base, the method comprising the step of energizing the motor to maintain engagement of the mechanical stop arrangement when the arm member is in the operating position. The method may also include any features described with reference to similar devices. Attached Figure Description

[0036] The invention will now be described by way of example only, with reference to the accompanying drawings, in which;

[0037] Figure 1 The motorized arm device of the present invention is shown.

[0038] Figure 2 Showing the installation on the lathe Figure 1 Motorized boom equipment,

[0039] Figure 3A to Figure 3C These are different views of the motorized arm device of the present invention.

[0040] Figure 4 This is an exploded view of the base end of the mechanized boom assembly.

[0041] Figure 5 A variation of the motorized arm device for holding two sensors is shown.

[0042] Figure 6 The machined arm device mounted on the lathe was showcased.

[0043] Figure 7 The variation of motor current over time is shown when the first controlled movement enters the operating position.

[0044] Figure 8 The variation of motor current over time is shown when the second controlled movement enters the operating position, and

[0045] Figure 9 The variation of motor current over time is shown in the case of the third controlled movement into the operating position. Detailed Implementation

[0046] refer to Figure 1The diagram schematically illustrates a motorized arm device 2. The motorized arm device includes a base 4 and a movable arm member 6. The proximal end of the arm member 6 is attached to the base 4 via a hub 8, which allows the arm member 6 to rotate relative to the base 4. A tool-setting probe 10 is attached to the distal end of the movable arm member 6. A motor (not shown) is disposed within the base 4 for driving the movable arm member 6 to rotate about an axis R via a planetary gearbox (not shown) that can be reverse-driven. The movable arm member 6... Figure 1 The movable arm component is shown in the operating position or "arm ready" position, but as explained below, it can be rotated from the operating position to the retracted position or the non-operating position.

[0047] The motor used to drive the rotation is a brushless DC motor with built-in Hall sensors, which allow for the measurement of motor rotation. Specifically, the generated Hall sensor pulses provide a direct measurement of the amount of motor rotation and therefore a direct measurement of the movement of the arm member 6. In this embodiment, the arm member 6 can rotate 90° from the shown operating position or "arm ready" position to the retracted position. Figure 1 (Not shown in the diagram). The gearbox ratio is 216:1, and there are eight Hall sensor pulses per motor revolution, so 432 Hall sensor pulses are provided as the arm sweeps from the operating position to the retracted position. Counting the Hall pulses and timing the gaps between them allows information about the arm's position and speed to be determined (e.g., by a motor controller as described below).

[0048] For further reference Figure 2 The image shows a motorized arm device 2 mounted on a lathe. Of course, the motorized arm device can be mounted on any other type of machine tool. The lathe includes a chuck 12 for holding the workpiece and a tool holder 14 carrying multiple cutting tools 16 for cutting the workpiece (not shown) held in the chuck 12. The motorized arm device 2... Figure 2 The image shows the motorized arm device in the operating position or "arm-ready" position, where the tool-setting probe 10 is positioned within the lathe's working volume to measure one or more cutting tools 16. However, it can be seen that if the tool-setting probe 10 is held in this operating position, it will obstruct the cutting process. Therefore, before performing the cutting process, the motorized arm device 2 is activated to rotate the movable arm component 6 to the retracted position. Although Figure 2 Not shown, but moving to the retracted position involves rotating the arm member until the tool setting probe 10 is positioned or stopped within the protective storage box 18. The lathe can then cut the workpiece held in the chuck 12 without obstruction from the tool setting probe 10.

[0049] The motor controller is configured to control the motor and interface with the lathe's digital controller. In this embodiment, the motor controller is configured as a combination of a circuit system within a separate interface box and a circuit board integrated within the base 4 (the circuit board in the base is connected to the circuit system in the interface box via a cable). However, those skilled in the art will understand that the motor controller can be implemented in various different ways; for example, all motor controller electronics may be included in the base or as an interface circuit system independent of the base. Furthermore, wired or wireless connections may be provided between any distributed components of the motor controller. The motor controller is arranged to activate the motor as needed and when required (i.e., by supplying appropriate power) to move the arm member between the operating position and the retracted position. Specifically, the motor controller controls and monitors the drive signals (e.g., drive current) applied to the motor and receives Hall sensor pulses output by the motor (i.e., measuring rotational speed and degree of rotation). The motor controller is also arranged to receive instructions from the lathe's digital controller. The motor controller can move the arm member from the retracted position to the operating position upon receiving an instruction indicating that measurement of the tool is to be performed, and can return the arm member to the retracted position upon receiving an instruction indicating that measurement is no longer needed.

[0050] Therefore, it can be seen that each time a tool measurement is required, the arm component needs to be repeatedly moved into and out of the operating position. This tool measurement can be performed at specific times during each cutting operation, between each cutting operation, or periodically (e.g., when the tool may be severely worn, or during setup at the start of a job). Therefore, it is important to define the operating position, and thus the position of the tool probe 10, within the lathe's local coordinate system as precisely and repeatably as possible. This is because any error or deviation in the operating position during each measurement will translate into tool measurement error, which in turn will introduce the corresponding cutting error into the dimensions of the workpiece manufactured by the lathe.

[0051] As mentioned above, existing motorized arms typically employ precise (e.g., kinematic) mechanical stop arrangements in conjunction with spring mechanisms to provide an operating position after the arm components have been driven to such a position by the motor. However, the inventors have realized that relying solely on such mechanical spring force is not always sufficient to obtain a sufficiently repeatable operating position.

[0052] Therefore, the motor controller of this device is configured to apply a holding current to the motor when the movable arm member has reached the operating position. This holding current serves to maintain the engagement of the mechanical stop arrangement, even in the presence of severe vibration, if the arm carries a heavy sensor or if the arm is mounted in an orientation unfavorable to gravity (e.g., inverted). This holding current is selected to generate sufficient torque to keep the mechanical stop tightly engaged without damaging or overheating the motor. Preferably, as explained in more detail below, the holding current applied to the motor when the mechanical stop is engaged is less than the initial starting current applied when the arm member moves to the operating position (thus engaging the mechanical stop). Several alternative conversion methods from starting current to holding current are described below. The device can also achieve controlled deceleration as the arm approaches the end of the sweep (e.g., when the arm reaches the operating or retracted position), as also explained below. This deceleration improves aesthetics (i.e., prevents a loud “dull metallic sound” when reaching the desired position), reduces wear (e.g., wear on components of the mechanical stop arrangement), and minimizes vibrations (e.g., bounce oscillations) that occur when the arm reaches the end stop.

[0053] The motor controller can also perform other functions. As explained above, in this embodiment, the motor controller can monitor the movement speed or position of the arm component. The motor controller can also monitor the current supplied to the motor. The motor controller can use any one or both of these measurements to provide additional functionality to assist the user of the device. Examples of these situations are outlined below.

[0054] First, if the arm component is found to be moving faster than expected (e.g., because someone is pushing it) or moving too slowly (e.g., because someone is trying to stall it, or because it is colliding with an object), the motor can be de-energized. The movable arm can then be moved manually without having to overcome the force applied by the motor. This allows, for example, a user to manually move the arm to the desired position and / or prevent damage in the event of contact with an obstacle. If such an event occurs, a warning signal can be issued (e.g., to the lathe's digital controller and / or directly to the user via an alarm, etc.).

[0055] If the boom member is held in the operating position by the holding current, its position (i.e., as measured by an encoder) can be monitored. Although vibration and shock may cause brief changes in position, the motor controller is arranged to disengage the motor if the boom member appears to have been manually actuated slightly (e.g., as measured by an encoder integrated into the motor). This allows the user to manually retract the boom member. This ability to manually move the boom member is useful during initial installation and in the event of a control malfunction. If the boom member is manually moved back to the operating position, the holding current can be reconnected. However, it is preferable that the return to the operating position is performed under motorized control in any case to ensure a repeatable operating position.

[0056] As explained above, the motor controller can receive commands from the digital controller of the host machine (i.e., the lathe in this example) and send status signals to the digital controller. For example, the device can send a "arm ready" signal when in the operating position. It can also send a "machine ready" signal when the arm is in the retracted position. The position of the arm can be measured by counting pulses emitted by the Hall sensor in the motor, or a separate position encoder can be provided to measure the rotation angle of the arm relative to the base. One or more reed switches or similar devices may also be present to indicate that a certain position has been reached (e.g., operating position or retracted position).

[0057] Diagnostic and status indicators can also be set for the device. For example, one or more LEDs can be placed on the interface board, with light guides leading to the outside of the interface box. In one example, based on angle counts derived from Hall sensor pulses, a flashing red LED can be used to indicate that the arm component has stopped in the operating or retracted position, but no reed switch activation is detected (suggesting a reed switch malfunction). A flashing red / blue LED can indicate a motor drive problem, while a solid yellow LED can indicate that the arm component has stopped in an uncontrolled position, either due to the movement command being changed during movement or as a result of manual movement (the arm being pulled or pushed). A slow flashing yellow LED can indicate that the arm component has stopped in an uncontrolled position after movement because the commanded movement speed was too slow (this is, for example, indicating a stall stop / collision). A fast flashing yellow LED can indicate that the arm component has stopped in an uncontrolled position after movement because the commanded movement speed was higher than expected (this is, for example, indicating that the arm component has been manually accelerated or pushed). A flashing blue LED can indicate that the movable arm is powered but has entered an unknown position (i.e., the movable arm did not retract properly when opened, which may indicate an obstruction in the probe recess). A constantly lit green LED indicates that the power is on and everything is working as expected.

[0058] Next, refer to Figure 3A to... Figure 3C Figure 3A shows a variation of the motorized boom device of the present invention in the operating position and the retracted position. It is a side view of the device, showing the base 24 and the boom member in the operating and retracted positions. When shown in the operating position, the boom member is labeled 26a, and when shown in the retracted position, the boom member is labeled 26b. Figure 3B shows the same device, but viewed from above. Figure 3C A 3D view is shown.

[0059] Next reference Figure 4 An exploded view of the base 36 and the proximal end of the movable arm 38 is shown. The base includes a housing 40 having bolt holes 42 for securing the base to a machine tool. A motor, gearbox, and mounting structure 44 are provided, mounted via a central aperture in a spring and brake plate 46. The proximal end of the movable arm 38 is attached to a hub 48, which is rotatable relative to the housing 40. Corresponding protrusions 50a and 50b on the housing 40 and hub 48 respectively provide mechanical stop arrangements that define the operating position (i.e., in a manner similar to that described in US 6519863). Motor control electronics 52, protected by an end cap 54, are also included within the structure.

[0060] refer to Figure 5 , showed Figure 4 The assembled base 36 and the entire movable arm component 38. The movable arm component 38 is generally L-shaped and has two sensor supports 64 and 66 near its distal end. Figure 5 In the diagram, a universal tool sensor is shown attached to a sensor holder. In a preferred embodiment, sensor holders 64 and 66 can be arranged to hold the transmitting and receiving modules of the non-contact tool setting device. Alternatively, two separate sensors can be mounted to arm member 38.

[0061] refer to Figure 6 The above-mentioned device is shown when mounted on a lathe. Specifically, the above reference is shown when the device is mounted for measuring a cutting tool used to cut a workpiece held in the chuck 70 of the lathe. Figure 5 The described device. The arm member is shown in the operating position, and sensor recesses 72 and 74 are also shown, in which the sensors carried by the arm member will be located when the arm member is moved to the retracted position. (See above reference...) Figure 4As explained, motor control electronics 52 are housed within the base 36. These motor control electronics are connected via cable 76 to additional motor control electronics housed within an interface box 78. This interface box 78 is connected via another cable 80 to the lathe's digital controller 82. The electronics within the interface box 78 and the motor control electronics 52 within the base 36 together form a motor controller that operates the arm device upon receiving appropriate control commands from the lathe's digital controller 82.

[0062] Next reference Figures 7 to 9 Further details will be provided regarding how the motor controller controls the motor as the arm moves from the retracted position to the operating position.

[0063] First refer to Figure 7 The figure shows the motor drive current (in amperes) as the movable arm is driven by the motor from the retracted position to the operating position over time (in seconds). As can be seen from the figure, the current peaks in the first 0.2 seconds as the arm moves toward the operating position with the aid of gravity, and then decreases. After approximately 2.1 seconds, the mechanical stop makes initial contact, the motor stalls and stops, causing the motor drive current to increase. The motor controller is configured to detect when the drive current increases in this manner (i.e., due to the initial contact of the mechanical stop) and subsequently apply a holding current limit of approximately 0.55A.

[0064] It should be noted that a drive current peak of approximately 1A exists before applying the holding current limit, but slight inconsistencies in the amplitude of this peak have been observed. While acceptable positional accuracy was achieved, slight inconsistencies were found in the motor stall stop positions. This rapid switching to holding current also occurred while the boom tube was still exhibiting significant resonance, and in some cases, the motor was found to relax back to a slightly variable position after switching to holding current. However, this arrangement eliminates the need to measure the position of the boom components during rotation to the operating position.

[0065] Figure 8The diagram shows the motor drive current (in amperes) as the movable arm is driven from a retracted position to an operating position by the motor over time (in seconds). In this example, the motor controller also monitors the position of the arm member based on pulses generated by the motor's Hall sensor. The motor controller uses the measured arm member position to determine when the mechanical stop arrangement should initially engage, confirming this by increasing the time between each Hall sensor pulse. Specifically, when the arm member has moved to the position where the mechanical stop arrangement is initially engaged, the motor controller applies a so-called starting current of approximately 1.6 A. This starting current is maintained for approximately 500 ms before applying a lower holding current limit of approximately 0.5 A. This maximizes the holding current while keeping it below the thermal limits of the motor and its surrounding environment. It has been found that applying the starting current for a short period (e.g., approximately 500 ms) before applying the lower holding current allows for a reduction in the amplitude of arm resonance.

[0066] It has been found that applying such a controlled starting current results in a kinematically consistent torque in the mechanical stop arrangement and a consistent starting position. Holding the starting current for a short period also allows for reduced vibration of any arm components, thus decreasing the tendency for the arm components to slack backward. However, a slight shock may occur when the drive current drops rapidly from the starting current to the holding current (i.e., from 1.6A to 0.5A), causing a slight reverse drive to the motor and gearbox (e.g., no more than about a quarter of the motor speed). This may reduce the kinematic push-in torque of the mechanical stop arrangement and introduce a slight variability in the final steady position of the motor (e.g., about 1 / 16 of the motor speed). This variability, though small, can manifest as a few micrometers of variation in the end position of the movable arm.

[0067] Figure 9 The motor drive current (in amperes) also varies over time (in seconds) as the movable arm is driven from the retracted position to the operating position by the motor. In this example, the motor controller also monitors the position of the arm member based on pulses generated by the motor's Hall sensor to determine when the mechanical stop arrangement initially engages (i.e., by detecting when the Hall pulses become less frequent). In this example, when the arm member first engages the mechanical stop arrangement, the motor controller applies an initial starting current of approximately 1.6 A for several hundred milliseconds. However, the transition from the starting current to a lower holding current (approximately 0.65 A) is not abrupt but comprises a steady, gradual descent over a period of approximately one second. This gradual descent provides a smooth release without causing any reverse winding of the motor, unlike the referenced above. Figure 8 It dropped suddenly as described.

[0068] It has been discovered, for reference Figure 9The described arrangement provides a consistent starting position that does not change after transitioning to holding current. It also maintains high starting torque, resulting in robust kinematic engagement and improved repeatability.

[0069] It should be remembered that the above examples are merely preferred embodiments of the invention, and those skilled in the art will recognize many variations and alternatives. For example, the lathe is only one example of a machine tool, and the arm device can be used with any machine tool. The use of a slewing arm is also only an example, and other movements of the arm relative to its base (e.g., linear movements) are possible. Any sensor can be attached to the movable arm component, not just a tool measuring device. Variations of the device can also be provided to carry different loads or sensors or to operate in different operating environments.

Claims

1. A motorized measuring arm device for machine tools, comprising: Base, the base being used for attachment to the machine tool, An arm member extending from the base, the arm member for holding one or more sensors, the arm member being movable relative to the base between a retracted position and an operating position, the operating position being defined by engagement of a mechanical stop arrangement. A motor, the motor being used to move the arm member relative to the base, and A motor controller is configured to energize the motor to move the arm member relative to the base. The motor controller is configured to energize the motor when the arm member is in the operating position to maintain engagement of the mechanical stop arrangement. The motor controller is configured to supply a starting current to the motor during a first time period following the initial engagement of the mechanical stop arrangement while the arm member is moved to the operating position. The motor controller is also configured to supply a holding current to the motor after the first time period to maintain engagement of the mechanical stop arrangement, the holding current being less than the starting current. The motor controller is configured to reduce the current supplied to the motor from the starting current to the holding current during a second time period.

2. The device according to claim 1, wherein, The motor controller is configured to gradually reduce the current supplied to the motor from the starting current to the holding current during the second time period.

3. The device according to claim 1, wherein, The mechanical stop arrangement includes a first portion attached to the arm member and a second portion attached to the base, the first portion and the second portion being arranged in a repeatable relative position when forming an engagement.

4. The device according to claim 3, wherein, The first and second portions provide a kinematically defined relative position when engaged.

5. The device according to claim 1, wherein, The motor includes a brushless direct current (DC) motor.

6. The device according to claim 1, wherein, The arm component is attached to the base via a slewing joint.

7. The device of claim 6, further comprising a rotary encoder for measuring the rotation of the arm member relative to the base.

8. The device according to claim 7, wherein, The motor includes an integrated rotary encoder for measuring the amount of motor rotation.

9. The device according to claim 7, wherein, The motor controller is configured to monitor the output of the rotary encoder and thereby determine whether there are any unexpected changes in the position or speed of the arm member that indicate that an external force is being applied to the arm member.

10. The device according to claim 9, wherein, The motor controller is configured to de-energize the motor when an external force is applied to the arm member.

11. The device according to claim 6, wherein, The base includes a housing that accommodates the rotary joint, the motor, and the mechanical stop arrangement.

12. The device of claim 1, further comprising a gearbox that connects the motor to the arm member.

13. The device according to any one of claims 1 to 12, wherein, The base includes an attachment mechanism for securing the device to the machine tool, and at least one sensor bracket is disposed at or near the distal end of the arm member.

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