Measurement device and measurement interface having a radio communication module

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 measuring device and a measuring interface including a frequency hopping radio communications module. In particular, the present invention relates to such a frequency hopping radio communications module that is used in a measuring probe of a machine tool and / or a related probe interface to enable communication of various types of measurement data.

Background Art

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

[0003] In certain situations, such as when it is difficult to directly wire a probe to a machine controller, wireless transmission systems are used to transmit trigger signals to the machine controller via a probe interface. In particular, frequency-hopping spread spectrum (FHSS) communication is known to be used between the probe and the probe interface. Such a communication protocol is described in International Publication No. 2004 / 057552 (WO2004 / 057552) and is used in the "RMP" series (range) and associated "RMI" probe interfaces of machine tool probes sold by Renishaw plc, Wotton-under-Edge, Gloucestershire, UK. A similar FHSS communication protocol is also used in the Primo series of measuring probes, also sold by Renishaw plc. The aforementioned FHSS systems have frequently been found to provide robust communications in harsh (RF) operating environments.

[0004] Frequency-hopping communication links rely on maintaining tight synchronization between both ends of the link, regardless of whether transmission is taking place. This ensures that the two base stations hop together (i.e., in synchrorinisation) 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 a measurement probe and its associated interface. Frame time (i.e., the duration 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. Frame time is chosen to balance the advantages of using shorter frame times (which allow for faster relaying of time-critical data) and the advantages of using longer frame times (which allow for the transmission of more data per frame). The inventors recognize that using such a fixed frame time method makes it difficult to use the same communication module for measuring devices that can operate in different ways to generate different amounts of measurement data.

[0005] Frequency hopping systems are also known for general applications that are not specialized for measurement. For example, U.S. Patent No. 4606040 describes a frequency hopping system employing high-speed and low-speed skip laws. [Overview of the Initiative]

[0006] According to a first aspect of the present invention, a measurement device is provided that includes a measurement sensor for generating metrology data and a frequency-hopping radio communication module for transmitting and receiving radio signals across multiple frequency channels. -This frequency-hopping radio communication module includes a clock for defining a series of base time intervals and memory for storing a hopping pattern that describes a sequence of frequency channels. -This communication module is capable of operating in at least the first, second, and third modes. - Operation in the first mode involves transmitting and / or receiving data using a series of frames having a first frame time, where the first frame time is equal to or an integer multiple thereof of the base time interval. - Operation in the second mode involves transmitting and / or receiving data using a series of frames having a second frame time, where the second frame time is an integer multiple of the first frame time. - Operation in the third mode involves transmitting and / or receiving data using a series of frames having a third frame time, where the third frame time is an integer multiple of the second frame time. - Each consecutive fundamental time interval is associated with a consecutive frequency channel in the hopping pattern sequence, and each frame uses the frequency channel associated with the fundamental time interval occurring at the start of that frame.

[0007] In this first aspect, the present invention relates to a measurement device comprising a frequency-hopping spread spectrum (FHSS) radio communication module and a measurement sensor. The radio communication module enables, for example, the establishment of a wireless FHSS radio communication link to a measurement interface that includes a similar FHSS radio communication module. In a preferred embodiment, the measurement device may be used to wirelessly transmit measurement data from a battery-powered measurement device or probe to a hardwired measurement interface that is physically wired to a machine tool. The communication module is configured to transmit and / or receive radio signals over a plurality of frequency channels. These frequency channels may be located within a particular frequency band or group of frequency bands (for example, frequency channels may be spread over a 2.4 GHz radio band). Data packets may be transmitted and received in each frame on a designated frequency channel.

[0008] This communication module includes a defining clock that defines a series of fundamental time intervals. For example, a fundamental time interval may be defined by the rising and falling edges of a square wave clock signal. Memory is also provided to store hopping patterns that describe a sequence or series of frequency channels. In other words, a hopping pattern defines the order in which a series of frequency channels can be used. Each consecutive fundamental time interval is associated with a consecutive frequency channel in the hopping pattern. In other words, each consecutive fundamental time interval is assigned the next frequency channel in the hopping pattern. The hopping pattern is continuously cyclical (i.e., repeated).

[0009] This communication module can adopt and switch between several 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, second, and 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 equal to or an integer multiple thereof of the 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 four times (i.e., four times) the basic time interval.

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

[0011] The present invention makes it possible to change the frame rate during operation without incurring the risk of losing the link (for example, due to a dropped transmission) and the risk of having to re-establish synchronization between both ends of the communication link from scratch. Therefore, the present invention is particularly suitable for use by a measuring device in the form of a measuring probe, which can generate different amounts of measurement data depending on the measurement task the measuring probe is performing.

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

[0013] For convenience, the first frame time is equal to the basic time interval. In other words, the basic time interval can also define the first frame time. This avoids the need to derive another timing signal from the clock signal. The second frame time can be an integer multiple of the first frame time. The second frame time can 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 The second frame time is such that N is an integer greater than or equal to 1. Therefore, the second frame time can be twice, four times, etc., the basic time interval. Preferably, the second frame time is twice the basic time interval.

[0014] If the first frame duration is equal to the basic time interval, then the frames of the first mode must follow a full hopping pattern. If the second frame duration is twice the basic time interval, then the frequency channels used in the second mode will 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), all frequency channels will be used during the two repetitions of the hopping pattern.

[0015] The ability to increase or decrease 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). Longer frame times can be used for larger data packets, and shorter frame times can be used when faster communication is required. 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 at both ends of a frequency-hopping communication link. The low power requirement of this first mode can be advantageous for maintaining battery life. The second mode may be suitable for communicating measurement data. For example, the second mode can be optimized for transmitting touch trigger data. The frame time used for communicating such touch trigger data can allow for low latency, enabling the retransmission of any data related to trigger events that were not received in the initial transmission.

[0016] The third mode has a longer frame time than the first and second modes. Therefore, the third mode can transmit larger data packets. The third mode can be thought of as a bulk data transfer mode. In a preferred embodiment, the third mode is suitable for communicating analog probe data. As described below, an analog probe may not only indicate the proximity or contact of a point on a surface, but may also contain data describing the positions of multiple points on the surface in its local coordinate system. For example, an analog probe may include a stylus for contacting an object and deflection sensors for measuring the stylus deflection in the local coordinate system. When the stylus is scanned across a surface, a stream of probe deflection data can be collected and transmitted over a communication link (i.e., using the third operating mode). When an analog probe is operating in touch trigger mode, a trigger signal should only be transmitted when stylus flex occurs as the stylus touches and moves across a surface. Such touch trigger data can be transmitted using a second mode. There are also cases where measurement is not required, but the analog probe is needed immediately. In such cases, the first mode can be used to reduce power consumption while maintaining a synchronized communications link.

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

[0018] A communication module (for example, a measuring device) may receive instructions to change mode via a communication link already established with another communication module (for example, provided within the measurement interface described below). Alternatively, a communication module may have an input for receiving such instructions to change mode and then instructing the relevant communication module to also switch modes via the already established communication link. Thus, a communication module may have an input for receiving instructions to change between a first mode and a second mode and be configured to send a message to change mode to the relevant communication module via a frequency-hopping link. A communication module acting as a transmission master or transmission slave may transmit instructions to change mode to the relevant communication module.

[0019] As described below, there may be situations where a change-in-mode instruction transmitted over a communication link needs to be accompanied by timing information. For example, if a frame in the first mode is induced on both the rising and falling edges of a clock pulse, data may need to be provided to the other end of the link regarding which edge of the clock pulse will be used to define the frame in the second mode. Therefore, a mode change message may include timing information to synchronize the base timing intervals of the communication module with the base timing intervals of the associated communication module.

[0020] While a pair of communication modules must use the same hopping pattern to communicate, communication between different pairs of communication modules may use different hopping patterns to reduce the potential for interference between systems installed in the same location. 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 relevant measurement device during the initial partnering process. Different hopping patterns (known at both ends of the link) may be used to establish the communication link initially or while the measurement device is in standby mode. For example, a hopping pattern using fewer frequency channels may be used. This helps reduce the power consumption required when the measurement device needs to repeatedly check whether it needs to exit standby mode. It should also be noted that communication protocols may include an appropriate sequence of acknowledgements with redendancy (e.g., retransmissions) to prevent non-receipt of messages due to interference or other reasons.

[0021] The communication module may be formed in an appropriate manner. For example, the module may be formed as a circuit board (e.g., an FPGA module), and / or may include a transceiver for mounting inside a measurement probe and / or inside a measurement probe interface. The circuit board may implement functions for connecting to frequency-hopping communication, or other functions for other processes. The module may include a master clock and / or a sliding correlator for reconstructing the master clock from a received signal. The module may include one or more of the features described in International Publication No. 2004 / 057552 (WO2004 / 057552).

[0022] The multiple frequency channels used by the communication module may include frequency channels within the 2.4 GHz radio frequency band (ranging from 2.4000 to 2.4835 GHz). This is also known as the Industrial, Scientific and Medical (ISM) band and is license-free in most countries. Each frequency channel has a width of 2 MHz, but it should be noted that no transmission extends beyond a portion of the frequency range of each channel. In a preferred embodiment, 39 channels (each 2 MHz wide) are provided, ranging from 2.404 GHz to 2.480 GHz. It should be noted that the present invention can 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, license-free radio frequency band. Such frequency bands may vary from country to country or over time depending on regulatory rules, but it should be noted that this does not change the advantages associated with the present invention. It should also be noted that this communication module (and therefore the measuring device) may be classified as a digital transmission system (DTS) or hybrid system, rather than an FHSS system in accordance with the formal definition of the Federal Communications Commission (FCC).

[0023] A first aspect of the present invention relates to a measuring device (e.g., a measuring probe) including the frequency-hopping radio communication module described above. The measuring device also includes a measuring sensor for generating measurement data. The measuring sensor may be of any type. For example, the measuring sensor may enable the measurement 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 sensing, etc.). In a preferred embodiment, the measuring sensor of the measuring device includes a touch trigger sensor. The touch trigger sensor may generate a trigger signal when it reaches a specific spatial relationship with respect to a point on the surface of an object. For example, a trigger signal may be generated when a stylus is flexed. The measuring probe may be for a machine tool. The trigger signal may be transmitted to the relevant interface when the communication module is operating in measurement mode. Furthermore, the measuring probe may include at least one of a stylus, shank, and battery. As described above, the measuring sensor may include an analog probe. Therefore, the measuring sensor of the measuring device may include at least one of a touch trigger sensor, scanning sensor, ultrasonic sensor, or imaging sensor. The measuring device may include multiple measuring sensors (for example, a touch trigger sensor and a temperature sensor).

[0024] This measurement device can be battery-powered. Therefore, to maximize battery life, it is advantageous for the measurement device to use as little power as possible. For this reason, the communication module of the measurement device can be configured to passively receive information (while switching channels one after another) until an activation message is received from the relevant measurement interface. The frame rate used when passively listening for the activation message can be higher than the frame rate of the relevant measurement interface. In particular, the duration of each frame used by the measurement device can be set to be at least equal to the time required for the relevant measurement interface to cycle through each of the frequency channels (e.g., one cycle through a second hopping pattern, etc.). When the activation message is received, the measurement device can send information (e.g., to confirm receipt of the activation message) to the measurement interface and start operating at a full frame rate.

[0025] The communication module of the measurement device can function as a transmission master or a transmission slave. In other words, either end of the link can become the transmission master for controlling the communication link. The measurement device can be the transmission master when measurement information is being transmitted (e.g., in the second mode and / or the third mode). The measurement interface can be the transmission 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 (e.g., a probe ID code). The hopping pattern used for communication to that measuring device can then be derived from that 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 (either through pre-programming or via a prior 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, a measuring device may receive the hopping pattern from the associated interface. The transmission of this information may occur during the initial partnering process. This ensures that both ends of the communication link can use the same hopping pattern. Each transmitted message may also include a header containing information about the measuring device to be activated (e.g., this message may include a probe ID). In this way, it can be further ensured that communication is established between the required pair of measuring devices and measuring interfaces.

[0027] A further aspect of the present invention provides a measurement interface for communicating with a measurement device in the first aspect of the present invention (i.e., using an FHSS link). This measurement interface may include a communication module (i.e., a second communication module, or a communication module of the interface) 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 machine in question. The measurement interface may be powered by mains (i.e., not by a battery). 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 with a plurality of related measurement devices. The measurement interface may have an output for passing measurement data received from the related measurement devices to a related machine (e.g., a controller of a machine tool, or an industrial PC, etc.). The measurement interface may include a plurality of different outputs for different types of measurement data. The data of the analog probe may be passed to an industrial PC for processing via Ethernet or an industrial Ethernet link. The trigger signal generated by the touch trigger sensor may be passed directly from the interface to the controller of the machine tool via a real time link. For example, such a touch trigger signal may be output by latching the voltage of a line connected to the SKIP input of the controller or by generating a pulse or a series of pulses 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 comprising a frequency-hopping radio communication module for transmitting and receiving radio signals across multiple frequency channels. The frequency-hopping radio communication module includes a clock for defining a series of fundamental time intervals, and the communication module is operable in at least a first, second, and third mode. Operation in the first mode involves 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 thereof of a fundamental time interval. Operation in the second mode involves 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 involves 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 consecutive fundamental time interval is associated with a consecutive frequency channel in a hopping pattern array, and each frame uses the frequency channel associated with the fundamental time interval occurring at the beginning of that frame. The frequency-hopping radio communication module of this measurement interface may have any of the above-described features with respect to the frequency-hopping radio communication module of the measurement device.

[0030] The measurement interface may include an input for receiving change instructions between a first mode, a second mode, and a third mode, and the frequency-hopping radio communication module of the measurement interface is configured to send a mode change message to the frequency-hopping communication module of the measurement device via a frequency-hopping communication link. This mode change message may include timing information to synchronize the basic time interval of the communication module in the measurement device with the basic timing interval of the communication module in the measurement interface.

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

[0032] This specification also describes frequency-hopping radio communication modules for transmitting and / or receiving radio signals using multiple frequency channels. These communication modules are capable of operating in at least a first mode and a second mode, where the frame time in the first mode is an integer multiple of the frame time in the second mode. These modules may include any of the other features described herein.

[0033] This specification also describes a method for using a frequency-hopping radio communication module for communicating measurement data. This communication module may include a clock for defining a series of fundamental time intervals. The method may include a step of using a hopping pattern that describes an array of frequency channels. The method may also include a step of switching the communication module between at least a first mode and a second mode, the first mode using a series of frames having a first frame time to transmit and / or receive data, and the second mode using a series of frames having a second frame time to transmit and / or receive data. Conveniently, the first frame time is equal to or an integer multiple thereof of a fundamental time interval, and the second frame time is an integer multiple of the first frame time. The method may also include a step of associating each consecutive fundamental time interval with a consecutive frequency channel in the hopping pattern array, and a step of using the frequency channel associated with the fundamental time interval occurring at the beginning of each frame.

[0034] This specification also describes a measurement device comprising a frequency-hopping radio communication module, which includes a measurement sensor for generating measurement data, a clock for defining a series of fundamental time intervals, and a memory for storing a hopping pattern describing an array of frequency channels. The communication module is switchable between at least a first mode and a second mode, the first mode for transmitting and / or receiving data using a series of frames having a first frame time, and the second mode for 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 thereof of a fundamental time interval, the second frame time is an integer multiple of the first frame time, each consecutive fundamental time interval is associated with a consecutive frequency channel in the hopping pattern array, and each frame uses a frequency channel associated with the fundamental time interval occurring at the beginning of that frame. The measurement device may have any one or more of the features described above.

[0035] This specification also describes a measurement interface including a communication module comprising a clock for defining a series of fundamental time intervals and a memory for storing a hopping pattern describing an array of frequency channels. This communication module is switchable between at least a first mode and a second mode, the first mode for transmitting and / or receiving data using a series of frames having a first frame time, and the second mode for transmitting and / or receiving data using a series of frames having a second frame time, where the first frame time is equal to or an integer multiple thereof of a fundamental time interval, and the second frame time is an integer multiple of the first frame time. Each consecutive fundamental time interval is associated with a consecutive frequency channel in the hopping pattern array, and each frame uses a frequency channel associated with the fundamental time interval occurring at the beginning of that frame. This measurement interface may have one or more of the features described above. The present invention also extends to a kit comprising the measurement interface and at least one measurement probe, as described above. The present invention also extends to similar methods for operating an FHSS communication module or measurement system.

[0036] This specification also describes a frequency-hopping radio communication module for a measurement system, comprising a clock for defining a series of fundamental time intervals and a memory for storing a hopping pattern describing an array 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, where the first frame time is equal to or an integer multiple thereof of a fundamental time interval. The second frame time is an integer multiple of the first frame time. Each consecutive fundamental time interval is associated with a consecutive frequency channel in the hopping pattern array, and each frame uses the frequency channel associated with the fundamental time interval occurring at the beginning of that frame. A frequency-hopping spread spectrum (FFHSS) radio communication module can be used in a measurement system to establish an FSSS (radio-stream) radio communication link between different system components. In a preferred embodiment, the communication module of the present invention may be used for wireless transmission of measurement data from a plurality of battery-powered measuring probes to a measuring interface physically wired to a machine tool. For example, the communication module may be provided as part of a measuring device and / or measuring interface. A frequency-hopping radio communication module may have any of the features described above.

[0037] This specification also describes a frequency-hopping radio communication module. This frequency-hopping radio communication module may be suitable for measurement systems. This module may include a clock. This clock may be suitable for defining a series of fundamental time intervals. This module may include memory. This memory may be for storing a hopping pattern describing an array of frequency channels. This communication module may include a transceiver. This communication module may include means for transmitting and / or receiving RF signals. This communication module (e.g., a transceiver) may be switchable (i.e., operable) 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 a fundamental time interval. The second frame time may be an integer multiple of the first frame time. Each consecutive fundamental time interval may be associated with consecutive frequency channels in the hopping pattern array. Each frame may use a frequency channel associated with a fundamental time interval occurring at the start of that frame. The communication module may include a processor for controlling the communication process. For example, such a processor may control the transceiver to enable radio communication in a first mode, a second mode, and an optional third mode. The communication module may have one or more of the features described elsewhere in this specification. [Brief explanation of the drawing]

[0038] Herein, the present invention will be described only illustratively with reference to the attached drawings. [Figure 1] This diagram illustrates measuring probes and probe interfaces for machine tools. [Figure 2] This figure shows the synchronized hopping of lobes and interfaces. [Figure 3] This figure shows synchronized hopping with changes in frame rate. [Figure 4] This diagram shows how sync hopping is lost when the frame rate changes. [Figure 5] This figure shows frame rate adjustment using the technology of the present invention. [Figure 6] This figure shows the resilience of such frame rate adjustments against interference that prevents message reception. [Figure 7] This diagram shows the adjustments made between three different frame rates. [Figure 8A] This diagram illustrates the implementation of the change between a frame duration of 0.25ms and a frame rate of 0.5ms. [Figure 8B] This diagram illustrates the implementation of the change between a frame duration of 0.25ms and a frame rate of 0.5ms. [Figure 9] This figure shows an operation with a frame rate of 0.5ms. [Figure 10] This diagram illustrates the implementation of the change between a frame duration of 0.5ms and a frame rate of 1.0ms. [Figure 11] This figure shows an operation with a frame rate of 1.0ms. [Modes for carrying out the invention]

[0039] First, referring to Figure 1, a touch-trigger type measuring probe 10 attached to the spindle 12 of a machine tool is illustrated. The measuring probe 10 has a delectable stylus 14 with a workpiece-contacting tip 16. The measuring probe also includes a first frequency-hopping radio communication module 18, which is usually integrated into the body of the measuring probe but is shown separately in Figure 1 for clarity. The measuring probe interface 20 is attached to a statinary part 22 in the structure of the machine tool and is connected to the machine tool controller 24 (usually via a cable). The measuring 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 synchronously switch between frequency channels in succession to enable the establishment of the communication link. The sequence in which various different frequency channels are used is commonly called a "hopping pattern." In conventional systems, a hopping pattern describes the order or sequence in which different frequency channels will always be used (regardless of 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 are using the same frame rate). In other words, a hopping pattern describes the sequence of "hopping" between different frequency channels.

[0041] Therefore, for brevity, no further details of the system, such as how communication timing is established to ensure synchronous frequency hopping and how the reliability of data transmission from the measurement probe to the probe interface can be improved by enabling data retransmission, are described in this application. Further details of such functions are referenced to International Publication No. 2004 / 057552 (WO2004 / 057552), the contents of which are incorporated herein by reference.

[0042] In frequency-hopping systems, both ends of a link (probe and interface) must maintain tight synchronization. When one frame rolls over to the next, both ends of the link switch to the next channel in the hopping array, regardless of whether a transmission is to occur. This ensures that both ends of the link are ready to create and receive data packets on the correct channel at the correct time.

[0043] Figure 2 schematically illustrates the hopping sequence employed by a frequency-hopping system of the type described with reference to Figure 1. The communication module in the probe (labeled P) and the interface (labeled I) circulates the frequency channels together. Each channel is used for a frame time (t). There may be no data exchange within each frame, and messages may be exchanged periodically to maintain synchronization (i.e., to maintain frame-time consistency).

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

[0045] Therefore, there is a demand for operation using different frame times. For example, longer frames can be used to send larger data payloads. However, switching frame times (from shorter to longer, or vice versa) requires coordination from both ends of the link; otherwise, channel synchronization may be lost and communication between the two ends may fail.

[0046] Normal operating communications consist of a message sent from the probe to the interface, followed by an acknowledgment sent back from the interface to the probe. When the probe receives an acknowledgment as a reply, it can be assumed that the original message (from the probe to the interface) was successfully transmitted. As shown in Figure 3, such a message sent from one end of a communication 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, the interface transmits again, but the probe does not receive. In this situation, the probe will retransmit, but the interface is unaware that the probe did not receive the message. If the interface receives the next transmission from the probe, it can retransmit the data. However, if the interface does not receive the next transmission from the probe, the interface will assume that the 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 illustrated in Figure 4. For example, if only the probe changes the frame rate, there is one more frame (indicated by the arrow) in which communication is possible between the probe and the interface, but thereafter the probe and the interface cycle through hopping patterns at different rates, and the synchronization of the hopping is lost.

[0049] Figure 5 illustrates a method, according to the present invention, for maintaining synchronization of frequency hopping during frame rate changes with resilience in case transmission is not received. A clock signal is used to generate 0.25 ms timing intervals and sequentially assign each frequency channel in the hopping pattern to each timing interval. The basic timing intervals and associated frequency channels are encoded as 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 allow timing corrections or operational data to be passed between the different ends of the link.

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

[0052] Referring to Figure 6, the various advantages of using frequency channels assigned to the basic timing interval are clearly illustrated. In particular, it can be seen that even if one end of the link (i.e., the interface in this example) changes the frame time to 0.5 ms, there is still a period of time when both ends of the link (indicated by arrows) operate on the same frequency channel. This allows for multiple retransmissions of the frame time change instruction, thereby maintaining synchronization during hopping.

[0053] In a preferred embodiment, three different frame times are used. These are the 0.25 ms (standby) communication mode and the 0.5 ms frame time mode mentioned above. A 1.0 ms frame is also provided for large-scale "bulk transfer" communications, such as the transmission of scan data or image data. The ratio of these frame times is 1:2:4. This allows the three operating frames to use either single hop, double hop, or quadruple hop between the frequency channels of the hopping pattern, respectively. Using this method, even if communication is lost when changing the frame rate, the interface does not change to the new rate, and even if the probe changes to the new rate, the probe and interface still maintain channel synchronization. A key 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 occurs on the same edge of the frame clock.

[0054] Figure 7 illustrates that frequency hopping synchronization can be maintained even when using three different frame times. Before the probe switches to a 0.5ms frame, it is shown to operate using 0.25ms frames for 10 basic time intervals (i.e., 2.5ms). The interface operates using 0.25ms frames for 2 basic time intervals, then using 0.5ms frames for 6 basic time intervals, and then using 1ms frames. In either case, for each of the probe and interface frames, the frequency channel used by them is the frequency channel assigned to the basic time interval at the start of that frame. It is used for at least part of the longer frames that enable communication between the probe and interface, which can be used to ensure that the same frequency channel switches together to use the same frame time despite the different frame times.

[0055] Next, referring to Figures 8A through 811, a more detailed illustration of the transition between different frame times is provided.

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

[0057] Next, when the probe communicates (encoded as 88), the so-called RMI-QE interface will respond with a request to switch to the operating mode. In RMI-QE, the modem will set the frame offset bit according to the frame clock edge for the current frame. If the current frame is driven from a rising edge (the clock is high), the offset bit will be 0. If the frame is driven from a falling edge (the clock is low), the offset will be 1. In this way, the modem in the probe can be ensured 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 necessary systems in the probe, but transmission must occur as quickly as possible at the correct frame timing.

[0058] Figure 9 illustrates the operation in an operating mode with a frame time of 500 μs.

[0059] Figure 10 shows the frame clock and various line statuses at the probe and interface when operating with a 0.5ms frame time (operating mode) and being instructed to transition to a 1ms frame time (high-capacity transfer mode).

[0060] As illustrated (see reference numeral 90 in Figure 10), when scan enable is high, the FPGA notifies the ARM core by raising the data ready line. Following the communication transaction, the ARM core requests a frame time change. The frame rate change request is sent to the FPGA in the RMI-QE interface in the next available communications slot (see reference numeral 92). Upon receiving the frame rate change request (reference numeral 94), the RMI-QE interface requests the frame rate change from the modem in the next SPI communications slot. Upon receiving the frame change request, the modem switches to a 1ms frame time and does not respond to communications from the probe unless the communication from the probe occurs on the rising edge of the frame clock (reference numeral 96). For a 1ms 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. As encoded as 100, the probe will retransmit in the next 500 μs frame because it did not receive a response in the previous transmission, which will occur immediately at the start of the frame. The interface will respond to the probe with a request to change the frame rate. Upon receiving this change request, the probe will switch to transmitting in a 1 ms bulk data frame type 102.

[0062] While 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 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 frequency-hopping radio communication modules in measurement probes and probe interfaces should share the same hopping pattern, such modules do not need to be completely identical in all respects. For example, one or all modules may include functions as described in International Publication No. 2004 / 057552 (WO2004 / 057552).

Claims

1. A measurement system comprising one or more measuring devices and a measuring interface for communicating with the one or more measuring devices, The one or more measuring devices include a measuring sensor for generating measurement data and a first frequency-hopping radio communication module for transmitting and receiving radio signals across multiple frequency channels. The first frequency-hopping radio communication module includes a clock for defining a series of basic time intervals and a memory for storing a first hopping pattern that describes an array of frequency channels. The first frequency-hopping radio communication module is configured to operate in operating modes including at least a first mode, a second mode, and a third mode. The operation in the first mode includes transmitting and / or receiving data using a series of frames having a first frame time, wherein the first frame time is equal to or an integer multiple thereof of the basic time interval. The operation in the second mode includes transmitting and / or receiving data using a series of frames having a second frame time, wherein the second frame time is an integer multiple of the first frame time. The operation in the third mode includes transmitting and / or receiving data using a series of frames having a third frame time, wherein the third frame time is an integer multiple of the second frame time. Each consecutive basic time interval is associated with a consecutive frequency channel in the sequence of the first hopping pattern, and each frame uses the frequency channel associated with the basic time interval occurring at the start of that frame. The measurement interface includes an output for transferring the measurement data received from one or more measuring devices to an associated machine tool, and includes a second frequency-hopping radio communication module for transmitting and receiving radio signals across multiple frequency channels. The second frequency-hopping radio communication module includes a clock for defining a series of basic time intervals and a memory for storing a second hopping pattern that describes an array of frequency channels. The second frequency-hopping radio communication module is configured to operate in at least the first mode, the second mode, and the third mode, Each consecutive basic time interval is associated with a consecutive frequency channel in the second hopping pattern sequence, and each frame uses the frequency channel associated with the basic time interval occurring at the start of that frame. For each of the one or more pairs between the one or more measuring devices and the measuring interface, the first hopping pattern and the second hopping pattern have the same configuration between the first frequency-hopping radio communication module and the second frequency-hopping radio communication module, a frequency-hopping communication link is established, and frequency-hopping synchronization corresponding to the basic time interval is maintained whether the operating modes of these two frequency-hopping radio communication modules are the same or different from each other. A measurement system characterized by the following features.

2. The measurement system according to claim 1, characterized in that the first frame time is equal to the basic time interval.

3. The measurement system according to claim 1, characterized in that the second frame time is equal to M times the basic time interval, where M = 2N and N is an integer of 1 or more.

4. The measurement system according to claim 1, characterized in that the second frame time is twice the basic time interval.

5. The measurement system according to claim 1, characterized in that the third frame time is four times the basic time interval.

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

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

8. The measurement system according to claim 1, characterized in that the second mode is used for communication of touch trigger data.

9. The measurement system according to claim 1, characterized in that the third mode is used for data communication of an analog probe.

10. The measurement system according to claim 1, characterized in that the measurement sensor includes at least one of a touch trigger sensor, a scanning sensor, an ultrasonic sensor, and an image sensor.

11. The measurement system according to claim 1, comprising an input for receiving instructions to change between the first mode, the second mode, and the third mode, wherein the second frequency-hopping radio communication module is configured to transmit a mode change message to the first frequency-hopping radio communication module via the frequency-hopping communication link.

12. The measurement system according to claim 11, characterized in that the mode change message includes timing information for synchronizing the basic time interval of the first frequency-hopping radio communication module with the basic time interval of the second frequency-hopping radio communication module.

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