MEASUREMENT DEVICE HAVING RADIATION COMMUNICATION MODULE AND MEASUREMENT INTERFACE - Patent application

Abstract

A frequency hopping radio communication module (18, 26) for use in a measurement system, such as a measurement probe (10) and a measurement interface (20), is described. The module (18, 26) includes a clock for defining a series of basic time intervals and a memory for storing a hopping pattern describing an arrangement of frequency channels. The communication module (18, 26) is switchable between at least a first mode, a second mode, and a third mode. The first mode transmits and / or receives data using a series of frames having a first frame time, and the second mode transmits and / or receives data using a series of frames having a second frame time. The first frame time is equal to or an integer multiple of the basic time interval, and the second frame time is an integer multiple of the first frame time. Operation in the third mode includes transmitting and / or receiving data using a series of frames having a third frame time, and the third frame time is an integer multiple of the second frame time. Each successive basic time interval is associated with a successive frequency channel in the hopping pattern arrangement, and each frame uses the frequency channel associated with the basic time interval occurring at the start of that frame, in this manner frequency hopping synchronization is maintained even when different frame times are used.

Description

[Technical field]

[0001] The present invention relates to a measurement device and a measurement interface including a frequency hopping radio communications module, in particular for use in a measurement probe and / or an associated probe interface of a machine tool, enabling communication of various types of measurement data. [Background technology]

[0002] Coordinate positioning apparatus (such as machine tools) are often equipped with measuring devices, for example touch trigger probes, which measure the position of a point on the surface of a workpiece. A touch trigger probe has a stylus which, when deflected by contact with the surface, generates a so-called trigger signal. This trigger signal is used to freeze the output of the machine tool's measurement scales, which thereby indicate the position of the probe and, with suitable calibration, the position of a point on the workpiece surface.

[0003] In certain circumstances, for example when it is difficult to directly wire the probe to the machine controller, a radio transmission system is used to communicate the trigger signal to the machine controller via the probe interface. In particular, it is known to use frequency hopping spread spectrum (FHSS) communication between the probe and the probe interface. Such a communication protocol is described in WO 2004 / 057552 and is also used in the "RMP" range of machine tool probes and associated "RMI" probe interfaces sold by Renishaw plc, Wotton-under-Edge, Gloucestershire, UK. A similar FHSS communication protocol is also used in the Primo range of measurement probes, also sold by Renishaw plc. The FHSS system described above has been found to provide robust communications in frequently harsh (RF) operating environments.

[0004] A frequency hopping communication link relies on maintaining tight synchronisation between both ends of the link, regardless of whether a transmission is to take place. This ensures that two stations hop together (i.e. in synchhronisation) between frequency channels according to a predefined hopping pattern. Maintaining such frequency channel synchorinisation is particularly important for systems that relay time critical information, such as trigger event information transmitted between measurement probes and associated interfaces. The frame time (i.e. the period during which each frequency channel is used) is typically fixed at the time of manufacture, and both ends of the communication link use the same frame rate. The frame time is selected to balance the benefits of using a shorter frame time (allowing time critical data to be relayed more quickly) with the benefits of using a longer frame time (allowing more data to be transmitted per frame). The inventors have recognized that using such a fixed frame time approach makes it difficult to use the same communications module for measurement devices that can operate in different ways that generate different amounts of measurement data.

[0005] Frequency hopping systems are also known for general non-measurement specific applications, for example US 4606040 describes a frequency hopping system employing high-speed and low-speed skip laws. Summary of the Invention

[0006] According to a first aspect of the present invention there is provided a measurement device comprising a measurement sensor for generating metrology data and a frequency hopping radio communication module for transmitting and receiving radio signals over a number of frequency channels. The frequency hopping radio communication module includes a clock for defining a series of base time intervals and a memory for storing a hopping pattern describing a sequence of frequency channels. The communication module is operable in at least a first mode, a second mode, and a third mode. Operation in the first mode includes transmitting and / or receiving data using a series of frames having a first frame time, the first frame time being equal to or an integer multiple of a basic time interval. Operation in the second mode includes transmitting and / or receiving data using a series of frames having a second frame time, the second frame time being an integer multiple of the first frame time. Operation in the third mode includes transmitting and / or receiving data using a series of frames having a third frame time, the third frame time being an integer multiple of the second frame time. Each successive basic time interval is associated with a successive frequency channel in the hopping pattern sequence, and each frame uses the frequency channel associated with the basic time interval occurring at the start of that frame.

[0007] In this first aspect, the invention relates to a measurement device comprising a frequency hopping spread spectrum (FHSS) radio communication module and a measurement sensor. The radio communication module allows for example to establish an FHSS (wireless) radio communication link to a measurement interface including a similar FHSS radio communication module. In a preferred embodiment, the measurement device may be used to wirelessly communicate measurement data from a battery-powered measurement device or probe to a measurement interface that is hardwired to a machine tool. The communication module is configured to transmit and / or receive radio signals over multiple frequency channels. These frequency channels may be within a particular frequency band or bands (e.g., the frequency channels may be spread across the 2.4 GHz radio band). Data packets may then be transmitted and received during each frame on the designated frequency channels.

[0008] The communication module includes a clock defining a series of basic time intervals. For example, the basic time intervals may be defined by rising and falling edges of a square wave clock signal. A memory is also provided for storing a hopping pattern that describes a sequence or series of frequency channels. In other words, the hopping pattern defines the order in which a series of frequency channels may be used. Each successive basic time interval is associated with a successive frequency channel in the hopping pattern. In other words, each successive basic time interval is assigned the next frequency channel in the hopping pattern. The hopping pattern cycles (i.e., repeats) continuously.

[0009] The communication module can adopt and switch between different modes having different frame times (i.e., operating at different frame rates). In particular, the communication module is switchable (i.e., operable) between at least a first mode, a second mode, and a third mode having different frame times. The first mode transmits and / or receives data using a series of frames (first frames) having a first frame time that is equal to or an integer multiple of a basic time interval. The second mode transmits and / or receives data using a series of frames (second frames) having a second frame time that is an integer multiple of the first frame time. For example, if the first mode uses a frame time of t, the second mode may use a frame time of 2t, 4t, 8t, etc. In a preferred embodiment, the second frame time is twice the basic time interval. The third mode transmits and / or receives data using a series of frames (third frames) having a third frame time that is an integer multiple of the second frame time. This also means that the third frame time is an integer multiple of the basic time interval. In a preferred embodiment, the third frame time is a quadruple (i.e., four times) the basic time interval.

[0010] To provide a robust communications link, each frame (i.e., each frame in the first mode, the second mode, and the third mode) uses a frequency channel associated with a basic time interval that occurs at the beginning of that frame. Therefore, the term "frame" is used herein to collectively describe each of the first frame, the second frame, and the third frame. This ensures that the frequency channel used by a communication module always matches the frequency channel used by a similar associated communication module (e.g., inside a measurement interface, etc.) with which a communication link is established, even when different modes are used, and therefore different frame times are used. In other words, this allows frequency hopping synchronization to be maintained for associated communication modules using the same hopping pattern, even when such communication modules are operating in different modes (e.g., when one communication module is operating in a first mode and the other communication module is operating in a second mode).

[0011] The invention makes it possible to change the frame rate during operation without risking losing the link (e.g. due to a dropped transmission) and re-establishing synchronization between both ends of the communication link from scratch.The invention is therefore particularly suitable for use with a measurement device in the form of a measurement probe, which can generate different amounts of measurement data depending on the measurement task the measurement probe is performing.

[0012] It should be noted that the communication module included in the measurement device of the present invention can be implemented in various ways. For example, the communication module can include a suitably configured circuit or processor. The communication module can also include an RF antenna or be connectable to an associated RF antenna. As described below, this communication module is integrated into the measurement device (e.g., a measurement probe, etc.), but a similar communication module can be provided as part of a measurement interface to enable communication with the measurement device. The communication module can also include a processor for calculating a hopping pattern (e.g., from uniques identified as described below). Other components can be included with the communication module, and the communication module can also be operated in other modes (e.g., legacy communication modes).

[0013] Conveniently, the first frame time is equal to the basic time interval. In other words, the basic time interval may also define the first frame time. This avoids the need to derive another timing signal from a clock signal. The second frame time may be an integer multiple of the first frame time. The second frame time may also be an integer multiple of the basic time interval. Preferably, the second frame time is equal to M times the basic time interval, where M=2. N where N is an integer equal to or greater than 1. Thus, the second frame time can be two times the basic time interval, four times the basic time interval, etc. Preferably, the second frame time is two times the basic time interval.

[0014] If the first frame time is equal to the basic time interval, then the frames of the first mode have no choice but to follow the full hopping pattern. If the second frame time is twice the basic time interval, then the frequency channels used in the second mode skip every other frequency channel defined in the full hopping pattern. However, if an odd number of frequency channels are provided (as in a typical system), then all frequency channels are used during two repetitions of the hopping pattern.

[0015] The ability to increase or decrease the frame time means that the communication module can adapt to the measurement data required for communication (e.g. data received by the interface and transmitted by the measurement device). For larger data packets a longer frame time can be used, and if faster communication is required a shorter frame time can be used. Advantageously, the first mode is suitable for standby communications of non-metrology data. Such non-metrology data may include periodic timing signals that need to be exchanged to maintain synchronization of both ends of the frequency hopping communication link. The low power requirement of such a first mode may be advantageous for preserving battery life. The second mode may be suitable for communication of measurement data. For example, the second mode may be optimized for transmitting touch trigger data. The frame time used for such communication of touch trigger data may allow low latency with the ability to retransmit any data related to trigger events that are not received in the initial transmission.

[0016] The third mode has a longer frame time than the first and second modes. As such, the third mode may convey larger data packets. The third mode may be considered a bulk data transfer mode. In a preferred embodiment, the third mode is suitable for communication of analogue probe data. As described below, an analogue probe may not only indicate the proximity or contact of a point on a surface, but may also include data describing the location of multiple points on the surface in its local coordinate system. For example, an analogue probe may include a stylus for contacting an object and deflection sensors that measure stylus deflection in the local coordinate system. When scanning a stylus across a surface, a stream of probe deflection data may be collected and transmitted over a communication link (i.e., using the third mode of operation). When an analogue probe is operating in touch trigger mode, it only needs to send a trigger signal if a deflection of the stylus occurs when the stylus is moved in contact with a surface. Such touch trigger data can be conveyed using the second mode. There are also cases where no measurements are required but the analogue probe is needed immediately. In such instances the first mode can be used to reduce power consumption but maintain a synchronised communications link.

[0017] Advantageously, the basic time interval is at least 0.25 ms. In the embodiment described below, the basic time interval is 0.25 ms. The first mode then has a frame time of 0.25 ms, the second mode has a frame time of 0.5 ms, and the optional third mode has a frame time of 1 ms.

[0018] A communication module (e.g. of a measurement device) may receive an instruction to change mode via an already established communication link with another communication module (e.g. provided in a measurement interface described below). Alternatively, the communication module may have an input for receiving such an instruction to change mode and then instructing an associated communication module to also perform a mode switch via an already established communication link. Thus, a communication module may have an input for receiving an instruction to change between a first mode and a second mode and may be configured to transmit a message to change mode to an associated communication module via a frequency hopping link. A communication module acting as a transmission master or a transmission slave may communicate the instruction to change mode to an associated communication module.

[0019] As will be explained below, there may be situations where a change in mode instruction conveyed over a communication link needs to be accompanied by timing information. For example, if frames in a first mode are triggered on both the rising and falling edges of a clock pulse, it may be necessary to provide data to the other end of the link as to which edge of the clock pulse is to be used to define frames in a second mode. Thus, a change in mode message may include timing information for synchronizing base timing intervals of a communication module with those of an associated communication module.

[0020] Although the same hopping pattern must be used for a pair of communication modules to communicate, communication between different pairs of communication modules may use different hopping patterns to reduce the possibility of interference between co-located systems. For example, a measurement interface may use different hopping patterns to communicate with different measurement devices. Alternatively, each measurement interface may use a specific (e.g., predefined) hopping pattern that the measurement interface passes to each associated measurement device during the initial partnering process. Different hopping patterns (known to both ends of the link) may be used to initially establish a communication link or while the measurement device is in standby mode. For example, a hopping pattern that uses fewer frequency channels may be used. This contributes to reducing the power consumption required when the measurement device needs to repeatedly check whether it should exit standby mode. It should also be noted that the communications protocol may include an appropriate sequence of acknowledgements, with redundancy (e.g., retransmissions, etc.) to prevent non-receipt of a message due to interference, etc.

[0021] The communication module may be formed in any suitable manner. For example, the module may be formed as a circuit board (e.g., an FPGA module, etc.) and / or may include a transceiver for mounting inside the measurement probe and / or inside the measurement probe interface. The circuit board may implement other functions connected to frequency hopping communication or for other processes. The module may include a master clock and / or a sliding correlator for recovering the master clock from the received signal. The module may include any one or more of the features described in WO2004 / 057552.

[0022] The multiple frequency channels used by the communication module may include frequency channels within the 2.4 GHz radio frequency band (spanning 2.4000-2.4835 GHz). This is also known as the Industrial, Scientific and Medical (ISM) band and is license free in most countries. It should be noted that each frequency channel is 2 MHz wide, but any transmission only spans a portion of each channel's frequency range. In a preferred embodiment, 39 channels (each 2 MHz wide) are provided, spanning from 2.404 GHz to 2.480 GHz. It should be noted that the present invention may be used in any radio frequency band and is not limited to operation in the ISM band. Preferably, the module is configured to operate on a standard and license-free radio frequency band. It should be noted that such frequency bands may vary from country to country or over time depending on regulatory rules, but this does not change the advantages associated with the present invention. It should also be noted that this communications module (and therefore the measurement device) may be classified as a digital transmission system (DTS) or hybrid system rather than an FHSS system according to the official Federal Communications Commission (FCC) definition.

[0023] A first aspect of the present invention relates to a measurement device (such as a measurement probe) including the frequency hopping radio communication module described above. The measurement device also includes a measurement sensor for generating metrology data. The measurement sensor may be of any type. For example, the measurement sensor may enable measurements of dimensions, position, temperature, etc. The sensor may be a contact sensor (i.e., the sensor may physically contact the object being measured) or a non-contact sensor (e.g., the sensor may use optical, electromagnetic induction, capacitive, etc. sensing). In a preferred embodiment, the measurement sensor of the measurement device includes a touch trigger sensor. The touch trigger sensor may generate a trigger signal when a particular spatial relationship is reached with respect to a point on the surface of the object. For example, a trigger signal may be generated when a stylus is deflected. The measurement probe may be for a machine tool. The trigger signal may be communicated to an associated interface when the communication module is operating in a metrology mode. Also, the measurement probe may include at least one of a stylus, a shank, and a battery. As described above, the measurement sensor may include an analog probe. Thus, the measurement sensor of the measurement device may include at least one of a touch-trigger sensor, a scanning sensor, an ultrasonic sensor, or an imaging sensor. The measurement device may include multiple measurement sensors (e.g., a touch-trigger sensor and a temperature sensor, etc.).

[0024] The measurement device may be battery powered. Therefore, to maximize battery life, it is advantageous for the measurement device to use as little power as possible. To that end, the communication module of the measurement device may be configured to passively receive information (switching between channels) until an activation message is received from the associated measurement interface. The frame rate used when passively listening for the activation message may be greater than the frame rate of the associated measurement interface. In particular, the duration of each frame used by the measurement device may be set to be at least equal to the time required for the associated measurement interface to cycle through each of the frequency channels (e.g., one cycle through the second hopping pattern). Once the activation message is received, the measurement device may transmit information to the measurement interface (e.g., to confirm receipt of the activation message) and begin operating at the full frame rate.

[0025] The communication module of the measurement device may function as a transmitting master or a transmitting slave. In other words, either end of the link may be a transmitting master for controlling the communication link. The measurement device may be a transmitting master when measurement information is being transmitted (e.g., in the second mode and / or the third mode). The measurement interface may be a transmitting master when measurement information is not being communicated (e.g., in the first mode).

[0026] In a preferred embodiment, each measuring device includes a unique identifier. For example, each measuring device may be assigned a unique identification code (such as a probe ID code). The hopping pattern used for communication to the measuring device may then be derived from the unique code. From this it can be seen that in such an example, the unique identifier must be known by the measuring device and the associated interface (by pre-programming or via a previous pairing process). Alternatively, one communication module may transmit the hopping pattern to the other communication module during the initial pairing or partnering process. For example, the measuring device may receive the hopping pattern from the associated interface. The transmission of this information may be performed during the initial partnering process. This allows both ends of the communication link to use the same hopping pattern. Each transmitted message may also include a header containing information about the measuring device to be activated (for example, the message may include a probe ID). In this way, it can be further ensured that communication is established between the required measuring device and measuring interface pair.

[0027] According to a further aspect of the invention, there is provided a measurement interface for communicating (i.e. using an FHSS link) with a measurement device in the first aspect of the invention. The measurement interface may include a communication module (i.e. a second communication module, or an interface communication module) having some or all of the features described above in relation to the communication module of the measurement device. The measurement interface may be physically wired to the associated machine. The measurement interface may be mains (i.e. not battery) powered. For example, the measurement interface may be connected (physically wired) to a controller of a machine tool.

[0028] Advantageously, the measurement interface is for communication to a number of associated measurement devices. The measurement interface may have an output for passing measurement data received from the associated measurement devices to an associated machine (e.g. a machine tool controller, or an industrial PC, etc.). The measurement interface may include a number of different outputs for different types of measurement data. Analogue probe data may be passed to an industrial PC for processing via an Ethernet or industrial Ethernet link. A trigger signal generated by the touch trigger sensor may be passed directly from the interface to the machine tool controller via a real time link. For example, such a touch trigger signal may be output by latching a voltage on a line connected to a SKIP input of the controller, or by generating a pulse or series of pulses that are passed to the SKIP input. Alternatively, the trigger signal may be passed to the controller via a digital data bus (e.g., as described in WO2018 / 134585).

[0029] In a preferred embodiment, a measurement interface is provided that includes a frequency hopping radio communication module for transmitting and receiving radio signals over a plurality of frequency channels. The frequency hopping radio communication module includes a clock for defining a series of basic time intervals, the communication module being operable in at least a first mode, a second mode, and a third mode. Operation in the first mode includes transmitting and / or receiving data using a series of frames having a first frame time, the first frame time being equal to or an integer multiple of the basic time interval. Operation in the second mode includes transmitting and / or receiving data using a series of frames having a second frame time, the second frame time being an integer multiple of the first frame time. Operation in the third mode includes transmitting and / or receiving data using a series of frames having a third frame time, the third frame time being an integer multiple of the second frame time. Each successive basic time interval is associated with a successive frequency channel in a hopping pattern arrangement, and each frame uses a frequency channel associated with a basic time interval occurring at the start of that frame. The frequency hopping radio communication module of the measurement interface may have any of the features described above for the frequency hopping radio communication module of the measurement device.

[0030] The measurement interface may include an input for receiving an indication to change between the first mode, the second mode, and the third mode, and the frequency hopping radio communication module of the measurement interface is configured to transmit a mode change message over the frequency hopping communication link to the frequency hopping communication module of the measurement device, The mode change message may include timing information for synchronizing a basic time interval of the communication module of the measurement device with a basic timing interval of the communication module of the measurement interface.

[0031] The invention also extends to a measurement system comprising one or more measurement devices and a measurement interface. Each component of the measurement system (i.e. each measurement device and measurement interface) may include a communication module of the invention. Legacy communication protocols may also be provided in such modules. In a preferred embodiment, the measurement system is for use in a machine tool.

[0032] Also described herein is a frequency hopping radio communication module for transmitting and / or receiving radio signals using multiple frequency channels, the communication module operable in at least a first mode and a second mode, the frame time of the first mode being an integer multiple of the frame time of the second mode, and may include any of the other features described herein.

[0033] Also described herein is a method for using a frequency hopping radio communication module for communicating measurement data. The communication module may include a clock for defining a series of basic time intervals. The method may include using a hopping pattern describing an arrangement of frequency channels. The method may also include switching the communication module between at least a first mode and a second mode, the first mode transmitting and / or receiving data using a series of frames having a first frame time, and the second mode transmitting and / or receiving data using a series of frames having a second frame time. Conveniently, the first frame time is equal to or an integer multiple of the basic time interval, and the second frame time is an integer multiple of the first frame time. The method may also include associating each successive basic time interval with a successive frequency channel in the hopping pattern arrangement, and using for each frame the frequency channel associated with the basic time interval occurring at the start of that frame.

[0034] Also described herein is a measurement device including a frequency hopping radio communication module including a measurement sensor for generating measurement data, a clock for defining a series of basic time intervals, and a memory for storing a hopping pattern describing an arrangement of frequency channels. The communication module is switchable between at least a first mode and a second mode, the first mode transmitting and / or receiving data using a series of frames having a first frame time, and the second mode transmitting and / or receiving data using a series of frames having a second frame time. The first frame time is equal to or an integer multiple of the basic time interval, the second frame time is an integer multiple of the first frame time, each successive basic time interval is associated with successive frequency channels in the hopping pattern arrangement, and each frame uses a frequency channel associated with the basic time interval occurring at the start of that frame. The measurement device may have any one or more of the features described above.

[0035] Also described herein is a measurement interface including a communication module with a clock for defining a series of basic time intervals and a memory for storing a hopping pattern describing an arrangement of frequency channels. The communication module is switchable between at least a first mode and a second mode, the first mode transmitting and / or receiving data using a series of frames having a first frame time, and the second mode transmitting and / or receiving data using a series of frames having a second frame time, the first frame time being equal to or an integer multiple of the basic time interval, and the second frame time being an integer multiple of the first frame time. Each successive basic time interval is associated with a successive frequency channel in the hopping pattern arrangement, and each frame uses a frequency channel associated with the basic time interval occurring at the start of that frame. The measurement interface may have any one or more of the features described above. The invention also extends to a kit comprising a measurement interface and at least one measurement probe as described above. The invention also extends to a similar method of operating an FHSS communication module or measurement system.

[0036] Also described herein is a frequency hopping radio communication module for a measurement system, comprising a clock for defining a series of basic time intervals and a memory for storing a hopping pattern describing an arrangement of frequency channels. The communication module is switchable between at least a first mode and a second mode. The first mode transmits and / or receives data using a series of frames having a first frame time, and the second mode transmits and / or receives data using a series of frames having a second frame time, the first frame time being equal to or an integer multiple of the basic time interval. The second frame time being an integer multiple of the first frame time. Each successive basic time interval is associated with a successive frequency channel in the hopping pattern arrangement, and each frame uses a frequency channel associated with the basic time interval occurring at the beginning of that frame. The frequency hopping spread spectrum (FFHSS) radio communication module can be used in the measurement system to establish a FSSS (wireless) radio communication link between different system components. In a preferred embodiment, the communication module of the present invention may be used for wireless communication of measurement data from a plurality of battery-powered measurement probes to a measurement interface that is physically wired to the machine tool. For example, the communication module may be provided as part of the measurement device and / or the measurement interface. The frequency hopping radio communication module may have any of the characteristics described above.

[0037] Also described herein is a frequency hopping radio communication module. The frequency hopping radio communication module may be suitable for a measurement system. The module may include a clock. The clock may be suitable for defining a series of basic time intervals. The module may include a memory. The memory may be for storing a hopping pattern describing an arrangement of frequency channels. The communication module may include a transceiver. The communication module may include means for transmitting and / or receiving RF signals. The communication module (e.g., transceiver, etc.) may be switchable (i.e., operable in) between at least a first mode and a second mode. The first mode may be for transmitting and / or receiving data using a series of frames having a first frame time. The second mode may be for transmitting and / or receiving data using a series of frames having a second frame time. The first frame time may be equal to or an integer multiple of the basic time interval. The second frame time may be an integer multiple of the first frame time. Each successive basic time interval may be associated with a successive frequency channel in the hopping pattern arrangement. Each frame may use a frequency channel associated with a basic time interval occurring at the beginning of that frame. The communication module may include a processor for controlling the communication process. For example, such a processor may control a transceiver to enable radio communication in a first mode, a second mode, and an optional third mode. The communication module may have any one or more of the features described elsewhere herein. [Brief description of the drawings]

[0038] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 2 illustrates a measurement probe and probe interface of a machine tool. [Diagram 2] FIG. 1 illustrates synchronous hopping of lobes and interfaces. [Diagram 3] FIG. 2 illustrates synchronized hopping with frame rate change. [Figure 4] FIG. 1 illustrates how synchronous hopping is lost when the frame rate changes. [Diagram 5] FIG. 2 illustrates frame rate adjustment using the techniques of the present invention. [Figure 6] FIG. 1 illustrates the resilience of such frame rate adjustment to interference that prevents reception of a message. [Figure 7] FIG. 1 illustrates adjustment between three different frame rates. [Figure 8A] A diagram illustrating an implementation of a change between a 0.25 ms frame time and a 0.5 ms frame rate. [Figure 8B] A diagram illustrating an implementation of a change between a 0.25 ms frame time and a 0.5 ms frame rate. [Figure 9] FIG. 1 illustrates operation with a frame rate of 0.5 ms. [Figure 10] A diagram illustrating an implementation of a change between a 0.5 ms frame time and a 1.0 ms frame rate. [Figure 11] FIG. 1 illustrates operation with a frame rate of 1.0 ms. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Referring initially to Figure 1, there is illustrated a touch-trigger type measurement probe 10 mounted on a machine tool spindle 12. The measurement probe 10 has a deflectable stylus 14 having a workpiece-contacting tip 16. The measurement probe also includes a first frequency-hopping radio communication module 18 which would normally be integrated within the body of the measurement probe but which is shown separately in Figure 1 for clarity. A measurement probe interface 20 is mounted to a statinary part 22 of the machine tool structure and is connected (typically via a cable) to the machine tool controller 24. The measurement probe interface 20 also includes a second frequency-hopping radio communication module 26.

[0040] Data is transmitted between the measurement probe 10 and the probe interface 20 via a frequency hopping radio communication link established between the first frequency hopping radio communication module 18 and the second frequency hopping radio communication module 26. As described above, the first and second frequency hopping radio communication modules need to switch between frequency channels in a synchronized manner to allow the establishment of the communication link. The sequence in which the various different frequency channels are used is usually called a "hopping pattern". In prior art systems, a hopping pattern describes the order or sequence in which the different frequency channels will always be used (irrespective of the frame rate) and is used to ensure that, after proper synchronization, both ends of the radio link are transmitting or receiving on the same frequency channel at the same time (assuming both ends use the same frame rate). In other words, the hopping pattern describes the sequence of "hopping" between the different frequency channels.

[0041] Therefore, for brevity, additional details of the system, such as how communication timing is established to ensure synchronous frequency hopping, and how reliability of the transmission of measurement data from the measurement probe to the probe interface can be improved by enabling retransmission of data, will not be described in any detail in this application. For further details of such functionality, reference is made to WO2004 / 057552, the contents of which are incorporated herein by reference.

[0042] In a frequency hopping system, both ends of the link (probe and interface) must maintain tight synchronization. As one frame rolls over to the next, both ends of the link will change to the next channel in the hopping sequence, regardless of whether a transmission is to take place. This allows both ends of the link to be ready to create and receive data packets on the correct channel at the correct time.

[0043] Figure 2 illustrates generally the hopping arrangement employed by a frequency hopping system of the type described with reference to Figure 1. The communication modules in the probe (labelled P) and interface (labelled I) cycle through frequency channels together. Each channel is used for a frame time (t). There may be no exchange of data during each frame, and messages may be exchanged periodically to maintain synchronization (i.e., to preserve frame time alignment).

[0044] To preserve battery life, the length of the frame size can be reduced to accommodate only the data required for the type of measurement sensor being used. However, certain measurement devices, such as the latest generation of so-called analogue probes, have multiple modes of operation. For example, an analogue probe may operate in a touch-trigger mode (i.e., when the probe signals its proximity to a surface) or in a scanning mode (i.e., when a stream of surface position measurements is generated). Such analogue probes may therefore also include video sensors or ultrasonic (flaw) detectors, etc. This type of analogue probe therefore requires a larger communication bandwidth when making "anlogue" measurements than would be required for touch-trigger measurements, for example.

[0045] Therefore, there is a desire to operate with different frame times, e.g., longer frames can be used to transmit larger data payloads, but switching frame times (from shorter to longer or vice versa) requires coordination from both ends of the link, otherwise the channel may lose synchronization and communication between the two ends may fail.

[0046] Normal operating communications consist of a message being sent from the probe to the interface, followed by an acknowledgement being sent from the interface back to the probe. If the probe receives an acknowledgement in return, then it can assume that the original (probe to interface) message got through. As shown in Figure 3, such a message sent from one end of a communications link can be used to instruct the other end of the link to change the frame time. However, this has low resilience to transmission errors.

[0047] As explained above, if the probe transmits, the interface receives, the interface sends an acknowledgment, and the probe receives that acknowledgment, then everything is fine. However, consider the case where the probe transmits, the interface receives, and the interface transmits but the probe does not receive. In this situation, the probe will retransmit, but the interface does not know that the probe did not receive the message. If the interface receives the next transmission from the probe, it can retransmit the data from the interface. However, if the interface does not receive the next transmission from the probe, the interface will assume that its previous acknowledgment was actually transmitted. If this message contained an instruction to change the frame rate or channel number, then synchronization may be lost.

[0048] This is also illustrated in Figure 4. For example, if only the probe changes frame rate, then there is one more frame (indicated by the arrow) during which communication is possible between the probe and the interface, but after that the probe and the interface cycle through the hopping pattern at different rates and hopping synchronization is lost.

[0049] Figure 5 illustrates a method for maintaining frequency hopping synchronization during frame rate changes with resilience in the event that no transmission is received, in accordance with the present invention. A clock signal is used to generate 0.25 ms timing intervals and assign each frequency channel in the hopping pattern to each timing interval in turn. The basic timing interval and associated frequency channel are coded HP in this figure. It should be noted that the hopping pattern is repeated.

[0050] In the first mode, a frame time of 0.25 ms is used by both the probe (P) and the interface (I). Such a frame time is used for standby communications. For example, this is a low power consumption mode used for housekeeping communications that allows timing corrections or operational data to be passed between different ends of the link.

[0051] In the second mode, a frame time of 0.5 ms is used by both the probe and the interface. This is used for touch-triggered communication or for communication of measurements containing a relatively small amount of data. In this second mode, all other frequency channels in the hopping pattern are skipped (note that if there is an odd number of frequency channels overall, the skipped channels will be used in the next repetition of the hopping pattern). In other words, each frame uses the frequency channel that is assigned to the time interval that coincides with the start of the associated frame. In the example of Figure 5, it can be seen that frequency channel 3 is used for the first 0.5 ms frame.

[0052] With reference to Figure 6, various advantages of using frequency channels assigned to basic timing intervals are evident. In particular, it can be seen that even if one end of a link (i.e., the interface in this example) changes to a frame time of 0.5 ms, there will still be a period of time during which both ends of the link operate on the same frequency channel (indicated by the arrows). This allows the frame time change indication to be retransmitted multiple times, so that hopping synchronization can be maintained.

[0053] In the preferred embodiment, three different frame times are used. These are the 0.25 ms (standby) communication mode mentioned above, and the 0.5 ms frame time modes. A 1.0 ms frame is also provided for large "bulk transfer" communications, such as the transmission of scan or image data. The ratio of these frame times is 1:2:4. This allows the three operating frames to use either a single hop, a double hop, or a quadruple hop, respectively, between the frequency channels of the hopping pattern. Using this method, even if communication is lost when making a frame rate change, the probe and interface will still maintain channel synchronization when the probe changes to a new rate without the interface also changing to the new rate. An important requirement for this embodiment is that when switching to a lower frame rate, the interface also sends "phase" information to the probe to ensure that the start of the new slower frame will occur on the same edge of the frame clock.

[0054] FIG. 7 illustrates that frequency hopping synchronization can be maintained even when three different frame times are used. Before the probe changes to a 0.5 ms frame, the probe is shown operating with a 0.25 ms frame for 10 basic time intervals (i.e., 2.5 ms). The interface operates with a 0.25 ms frame for two basic time intervals, then operates with a 0.5 ms frame for six basic time intervals, and then operates with a 1 ms frame. In either case, the frequency channel used by the probe and the interface for each of their frames is the frequency channel assigned to the basic time interval at the start of that frame. Despite the different frame times, the same frequency channel is used for at least a portion of the longer frame that allows communication between the probe and the interface, which can be used to ensure that they switch together to use the same frame time.

[0055] 8A through 11, a more detailed illustration of the transition between different frame times is shown.

[0056] 8A and 8B show the frame clock and the status of the various lines at the probe and interface when operating with a 0.25 ms frame time and being commanded to transition to a 0.5 ms frame time. A command 80 is applied to the status line to request a change from standby mode (i.e., 250 μs frame time) to operating mode (i.e., 500 μs frame time). The mode change indication is propagated up the chain to the modem as encoded by 82 and 86. When the interface FPGA receives the request to change to operating mode 84, it will switch to the 500 μs frame time by synchronizing only on the rising edge of the clock frame.

[0057] The next time the probe communicates (encoded 88), the so-called RMI-QE interface will respond with a request to switch to the operational mode. The modem in the RMI-QE will set the frame offset bit according to the frame clock edge for the current frame. If the current frame is driven from the rising edge (clock is high), the offset bit will be 0. If the frame is driven from the falling edge (clock is low), the offset will be 1. In this way, the modem in the probe can be sure to reinitialize its frame timer to use the correct edge. The exact delay required depends on the amount of time needed to initialize all the required systems in the probe, but it is necessary to transmit as soon as possible with the correct frame timing.

[0058] FIG. 9 illustrates operation in an operating mode having a frame time of 500 μs.

[0059] FIG. 10 shows the frame clock and status of various lines at the probe and interface when operating using a 0.5 ms frame time (operating mode) and being commanded to transition to a 1 ms frame time (large capacity transfer mode).

[0060] As illustrated (see 90 in FIG. 10), when the scan enable goes high, the FPGA will notify the ARM core by raising the data ready line. Following the communication transaction, the ARM core will request a frame time change. The frame rate change request is sent to the FPGA on the RMI-QE interface in the next available communications slot (see 92). Upon receiving the frame rate change request (94), the RMI-QE interface requests a frame rate change from the modem during the next SPI communications slot. Upon receiving the frame change request, the modem switches to a 1 ms frame time and will not respond to communications from the probe unless the communications occur on the rising edge of the frame clock (96). For a 1 ms frame, the rising edges of both clocks indicate the start of the frame.

[0061] Figure 11 illustrates operation in an operating mode with a frame time of 1000 μs. Since no response was received in the previous transmission, as coded 100, the probe will retransmit in the next 500 μs frame, which will occur immediately at the start of the frame. The interface will respond to the probe with a request for a frame rate change. Having received this request, the probe will switch to transmitting a 1 ms bulk data frame type 102.

[0062] Although the above examples relate to measurement probes and probe interfaces, the same frequency hopping radio communication modules can be used in other measurement devices. Similarly, operation in the 2.4 GHz radio band is provided merely as an example and is not intended to limit the scope of the invention. It should also be noted that while the frequency hopping radio communication modules in the measurement probe and probe interface should share the same hopping pattern, it is not necessary that such modules be completely identical in all respects. For example, one or all of the modules may include functionality as described in WO2004 / 057552.

Claims

1. 1. A measurement device comprising: a measurement sensor for generating measurement data; and a frequency hopping radio communication module for transmitting and receiving radio signals over a plurality of frequency channels, the frequency hopping radio communication module includes a clock for defining a series of basic time intervals and a memory for storing a hopping pattern describing an arrangement of frequency channels; the communication module is operable in at least a first mode, a second mode, and a third mode; operating in the first mode includes transmitting and / or receiving data using a series of frames having a first frame time, the first frame time being equal to or an integer multiple of the basic time interval; operating in the second mode includes transmitting and / or receiving data using a series of frames having a second frame time, the second frame time being an integer multiple of the first frame time; operating in the third mode includes transmitting and / or receiving data using a series of frames having a third frame time, the third frame time being an integer multiple of the second frame time; Each successive basic time interval is associated with a successive frequency channel in the sequence of the hopping pattern, and each frame uses the frequency channel associated with the basic time interval occurring at the start of that frame. A measuring device comprising:

2. 2. The measuring device of claim 1, wherein the first frame time is equal to the basic time interval.

3. 2. The measuring device of claim 1, wherein the second frame time is equal to M times the basic time interval, where M=2N, N being an integer greater than or equal to 1.

4. 2. The measuring device of claim 1, wherein the second frame time is twice the basic time interval.

5. 2. The measuring device according to claim 1, wherein the third frame time is four times the basic time interval.

6. 2. The measuring device according to claim 1, characterized in that the basic time interval is at least 0.25 ms.

7. 2. The measuring device according to claim 1, characterized in that the first mode is used for standby communication of non-measurement data.

8. 2. The measuring device of claim 1, wherein the second mode is used for communication of touch-trigger data.

9. 2. The measuring device of claim 1, wherein the third mode is used for communication of analog probe data.

10. The measuring device of claim 1 , wherein the measurement sensor comprises at least one of a touch-trigger sensor, a scanning sensor, an ultrasonic sensor, and an image sensor.

11. 2. A measurement interface for communicating with a measuring device according to claim 1, including an output for passing the measurement data received from the measuring device to an associated machine tool.

12. a frequency hopping radio communication module for transmitting and receiving radio signals across a plurality of frequency channels; the frequency hopping radio communication module includes a clock for defining a series of basic time intervals and a memory for storing a hopping pattern describing an arrangement of frequency channels; the communication module is operable in at least a first mode, a second mode, and a third mode; operating in the first mode includes transmitting and / or receiving data using a series of frames having a first frame time, the first frame time being equal to or an integer multiple of the basic time interval; operating in the second mode includes transmitting and / or receiving data using a series of frames having a second frame time, the second frame time being an integer multiple of the first frame time; the third mode includes transmitting and / or receiving data using a series of frames having the third frame time, the third frame time being an integer multiple of the second frame time; Each successive basic time interval is associated with a successive frequency channel in the sequence of the hopping pattern, and each frame uses the frequency channel associated with the basic time interval occurring at the start of that frame. Measurement interface according to claim 11, characterized in that

13. 13. The measurement interface of claim 12, further comprising an input for receiving instructions to change between the first, second, and third modes, and wherein the frequency hopping radio communication module in the measurement interface is configured to send a mode change message over the frequency hopping communication link to the frequency hopping communication module in the measurement device.

14. 14. The measurement interface of claim 13, wherein the mode change message includes timing information for synchronizing the basic time interval of the communication module in the measurement device with the basic time interval of the communication module in the measurement interface.

15. A measuring system, characterized in that it comprises one or more measuring devices according to any one of claims 1 to 10 and a measuring interface according to any one of claims 11 to 14.

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