Metrology radio communication system

Abstract

A frequency hopping radio communication system is described, the frequency hopping radio communication system comprising a measurement station (10) having a first clock and an interface station (20) having a second clock. The measurement station (10), which can form part of a measurement probe, is configured to transmit measurement information resulting from a measurement event, the measurement information comprising timing information associating the measurement event with the first clock. The interface station (20) is configured to receive the measurement information from the measurement station (10) and to generate a measurement output comprising timing information defined relative to the second clock. One of the first clock and the second clock is designated as a master clock, and the other of the first clock and the second clock is periodically performing clock adjustments to remain synchronized with the designated master clock. The timing information of the measurement output generated by the interface station (20) takes into account any periodic clock adjustments applied between the occurrence of the measurement event and the generation of the measurement output. In this way, jitter is reduced and metrology performance is improved.

Description

[0001] This invention relates to a frequency-hopping radio communication system, which includes a measurement station and an interface station. Specifically, this invention relates to a frequency-hopping radio communication system for transmitting metrological (measurement) data from a machine tool measurement probe to an associated probe interface.

[0002] Coordinate positioning equipment (e.g., machine tools) is typically equipped with measuring devices, such as contact trigger probes that measure the position of points on a workpiece surface. A contact trigger probe has a stylus that deflects upon contact with the surface, generating a trigger signal. This trigger signal is used to freeze the output of the machine tool's measuring scale, thereby indicating the probe's position and, thus, the position of points on the workpiece surface through proper calibration.

[0003] In certain situations, such as when it is difficult to wire the probe directly to the machine controller, a wireless transmission system is used to transmit the trigger signal to the machine controller via the probe interface. Specifically, a frequency-hopping spread spectrum (FHSS) communication link is known to be used between the probe and the probe interface. This communication protocol is described in WO2004 / 057552 and is also used in the “RMP” series machine tool probes and associated “RMI” probe interfaces sold by Renishaw plc of Wharton-Andedge, Gloucestershire, UK. A similar FHSS communication protocol is also used in the Primo series measuring probes, also sold by Renishaw. The aforementioned FHSS systems have been found to provide robust communication in typically harsh (RF) operating environments.

[0004] Frequency-hopping communication links rely on maintaining tight synchronization between the two stations at each end of the link, regardless of whether a transmission is taking place. This is to ensure that the two stations hop frequencies together (i.e., synchronously) between channels according to a predefined frequency-hopping pattern. Maintaining this channel synchronization is particularly important for systems that relay time-critical information, such as trigger event information transmitted between a measurement probe and its associated interface. For example, in the RMI / RMP system described above, the clock provided in the interface is periodically adjusted to maintain synchronization with the probe's master clock.

[0005] However, the inventors have discovered that the aforementioned real-time clock adjustment process may affect the metering accuracy of the FHSS communication system, especially when transmitting asynchronous measurement events such as trigger signals.

[0006] According to a first aspect of the present invention, a frequency-hopping radio communication system is provided, the frequency-hopping radio communication system comprising a measuring station having a first clock and an interface station having a second clock, wherein:

[0007] The measuring station is configured to send measurement information generated by a measurement event, the measurement information including timing information that associates the measurement event with the first clock.

[0008] The interface station is configured to receive the measurement information from the measurement station and generate a measurement output including timing information relative to the second clock definition, and

[0009] One of the first clock and the second clock is designated as the master clock, and the other of the first clock and the second clock is periodically adjusted to maintain synchronization with the designated master clock.

[0010] The characteristic feature is that the timing information of the measurement output generated by the interface station takes into account any periodic clock adjustments applied between the occurrence of the measurement event and the generation of the measurement output.

[0011] Therefore, the present invention relates to a frequency-hopping spread spectrum (FHSS) radio communication system, wherein a wireless (FHSS) radio communication link is provided between a measurement station (e.g., provided as part of a battery-powered measurement device) and an interface station (e.g., provided as part of a hardwired measurement interface to a machine tool). Both the measurement station and the interface station include their own clocks, referred to respectively as a first clock and a second clock. As described below, the first clock and the second clock may include oscillators and are arranged to output a series of clock pulses at identical nominal intervals.

[0012] The measuring station is configured to transmit measurement information generated by a measurement event. For example, the measuring station may transmit information about a contact-triggered event generated by a contact-triggered sensor. The measurement information also includes timing information that associates the measurement event with timing obtained from a first clock. The timing information may be provided as data (e.g., time values) and / or may be encoded in the transmitted message (e.g., the edges of the transmitted frame may be synchronized with the first clock). In a preferred embodiment described below, the timing information includes a clock count that defines the time (e.g., relative to the start edge of the frame) at which the measurement event occurs within the frame.

[0013] The interface station is configured to receive measurement information from the measurement station. In other words, the interface station is arranged to receive measurement information sent by the measurement station (i.e., via the FHSS link). The interface station is also configured to generate measurement outputs that include timing information defined relative to a second clock. In other words, the measurement output (e.g., a trigger signal) is output from the interface station to the associated device (e.g., a machine tool) at a specific time. The interface station times all events relative to its own clock (i.e., the second clock), so the measurement output is created at a time defined relative to the second clock.

[0014] As mentioned above, the measurement station and the interface station necessarily use different clocks. Although such clocks may nominally be the same, providing clocks that maintain perfect synchronization over a long period is generally impractical or impossible. To maintain frequency hopping synchronization, it is therefore necessary to periodically align or synchronize the first and second clocks. To achieve this, one of the first and second clocks is designated as the master clock (i.e., all system timings are bound to this master clock). The other of the first and second clocks is then periodically adjusted to maintain synchronization with the designated master clock. As described below, this synchronization can be performed by periodically sending timing messages between the measurement station and the interface station. These timing messages can be sent at regular or irregular intervals. Therefore, multiple such timing messages can be sent while an FHSS communication link is established between the measurement station and the interface station. Such timing messages allow the first and second clocks to be kept synchronized in real time. This ensures that frequency hopping remains synchronized at the measurement station and the interface station, thus preventing clock drift that could otherwise lead to a gradual loss of frequency hopping synchronization. Clock synchronization protection is performed "instantaneously"; that is, periodic synchronization can be performed while measurement information is being sent from the measurement station to the interface station using the communication link.

[0015] In the prior art FHSS system described above, periodic clock synchronization is performed to maintain synchronized frequency hopping at both ends of the communication link. However, the inventors have discovered that performing such clock synchronization steps simultaneously or approximately simultaneously with the transmission of measurement information from the measurement station to the interface station introduces measurement errors. In other words, the applied clock correction is not considered when generating the measurement output (i.e., its effect is ignored). For example, fine-tuning the first clock count up or down to maintain clock synchronization may erroneously convert the time measured relative to the first clock to the time measured relative to the second clock (i.e., fine-tuning the clock count introduces timing discrepancies, which manifest as timing errors).

[0016] Therefore, the system of the present invention takes into account (i.e., uses or incorporates) any timing variations used to maintain clock synchronization when calculating the time (relative to the second clock) when the measurement output should be generated. Thus, the timing information of the measurement output generated by the interface station takes into account any periodic clock adjustments applied between the occurrence of the measurement event and the generation of the measurement output. In other words, any periodic clock adjustments applied between the occurrence of the measurement event and the generation of the measurement output are incorporated into the timing information of the measurement output generated by the interface station. Therefore, when calculating the time (relative to the second clock) when the measurement output should be generated, the interface station will include any applied timing variations. This can be considered as correcting the time (relative to the second clock) for generating the measurement output to account for the applied timing variations. In this way, clock synchronization is maintained in real time without reducing measurement accuracy.

[0017] Advantageously, the measurement information transmitted by the measurement station is timestamped relative to a time defined by a first clock. For example, the measurement information may include a time value defining when a certain measurement event occurs (as defined by the first clock). Therefore, the timestamp may include data defining the time. In a preferred embodiment, the measurement station sends information to the interface station using a series of frames, and the interface station operates using a similar series of frames. A channel can be assigned to each frame based on a cyclically repeating frequency hopping pattern or sequence known to both the measurement station and the interface station. Therefore, the measurement station can timestamp the measurement information to define the time relative to the frame edge. For example, a 250 μs frame may be subdivided into 250 counts based on the clock. In such an example, the timestamp associated with the measurement information may define the count of the measurement event that occurred during its period (i.e., a value between 0 and 249).

[0018] Advantageously, the first clock and the second clock each generate clock counts. For example, each clock may include an oscillator that increments the clock count value. Such clock count values ​​may be cyclical. One of the first clock and the second clock may be designated as the master clock. Periodic clock adjustments may then include incrementing or decrementing the clock count of the other of the first clock and the second clock to maintain synchronization with the designated master clock (i.e., maintaining synchronization of both clock counts). In this way, the measuring station and the probe station can generate a series of clock counts that are aligned (synchronized) with each other. A frame may be defined by a plurality of such clock counts (e.g., these clock counts may be 250 clock counts of duration 1 μs defining a 250 μs frame), and the edges of such frames will therefore also remain synchronized. Thus, the system can allow the first clock and the second clock to be (and remain) synchronized within a timeframe of 1 ms, more preferably within a timeframe of 250 μs, more preferably within a timeframe of 100 μs, or more preferably within a timeframe of 10 μs.

[0019] Periodic clock adjustments can be performed in any suitable manner. Conveniently, periodic clock adjustments involve exchanging messages containing timing information between the measuring station and the interface station. For example, the measuring station may send its current clock count value to the interface station. Alternatively, the measuring station may send a message at a specific time (or clock count) defined by its (first) clock. The interface station may receive the transmission from the probe station and compare the timing information provided by the received message within a time defined by its (second) clock. This will allow any counting discrepancies between the first and second clocks to be determined. After any timing (e.g., counting) discrepancy is established, the interface station may then instruct the probe station to change its first clock to eliminate the discrepancy. For example, the probe station may receive instructions to add a clock count to a frame or skip a clock count in a frame to bring the counts of the first and second clocks back into synchronization.

[0020] Periodic clock adjustments can be performed at irregular intervals; for example, on demand or when messages are exchanged between the probe station and the interface station (e.g., messages transmitting measurement information). Preferably, periodic clock adjustments are performed at regular (periodic) intervals. This ensures that the probe station and the interface station remain synchronized even if they are not exchanging other messages. In addition to any regular clock adjustments, temporary clock adjustments can also be performed (e.g., when transmitting measurement information). Therefore, multiple such clock adjustments can be performed.

[0021] Either the first clock or the second clock can be used as the master clock for system timing. Advantageously, the second clock is the master clock, and periodic clock adjustments include adjusting the first clock to maintain synchronization with the second clock. The master clock can therefore be the (second) clock provided in the interface station. The second clock can also be used to define the timing of other components of the system, such as the timing of devices to which the interface station is connected.

[0022] Advantageously, the measuring station can be provided as part of the measuring device. The measuring device may also include a measuring sensor. The measuring sensor can generate metrological data. The measuring sensor can be of any type. For example, the measuring sensor may include at least one of a contact trigger sensor, a scanning sensor, an ultrasonic sensor, or an imaging sensor. The measuring sensor can allow the measurement of dimensions, position, temperature, etc. The measuring sensor can be a contact sensor (i.e., it can physically contact the object being measured), or it can be a non-contact sensor (e.g., it can use optical, inductive, capacitive, or other sensing methods).

[0023] In a preferred embodiment, the measuring sensor of the measuring device includes a contact-triggered sensor. The contact-triggered sensor can sense a trigger event when a specific spatial relationship is established with a point on the surface of an object. For example, a trigger event can be sensed when a stylus deflects. The measuring device can be provided as a measuring probe for a machine tool. The measuring device can be battery-powered. Therefore, advantageously, the measuring device uses as little power as possible to maximize battery life. The measuring probe may also include at least one of a stylus, a shank, and a battery.

[0024] Measurement information sent by the measurement station can be correlated with contact-triggered events sensed by the contact-triggered sensor. Such contact-triggered measurement events can occur at any point in time. The measurement output generated by the interface station can include a trigger signal. For example, such a contact-triggered signal can 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 delivered to the SKIP input. The trigger signal can alternatively be transmitted to the controller via a digital data bus (e.g., as described in WO2018 / 134585). Therefore, measurement events can include asynchronous measurement events. In other words, instead of recording a measurement at a specific time, the measurement event may occur at an undefined point in time (e.g., when the stylus contacts an object). Therefore, the time of occurrence of such a measurement event can be used to measure the position of a point on the surface of an object. Therefore, preferably, the delay between the probe station recording the asynchronous measurement event and the interface station generating the measurement output is not affected by any periodic clock adjustments applied between the measurement event and the generation of the measurement output. In other words, the system delay is preferably not affected by the periodic clock adjustment process.

[0025] The communication link between the probe station and the interface station is preferably a bidirectional communication link. The probe station and the interface station preferably transmit and receive radio signals on multiple channels, which are preferably distributed across a specific frequency band (e.g., the 2.4 GHz radio band). Thus, data packets can be transmitted and received during each frame on a designated channel. The probe station and the interface station can operate in a variety of different modes. For example, multiple communication modes using different frame rates can be implemented. Multiple different frequency hopping patterns can also be used. For example, the interface station can use different frequency hopping patterns to communicate with different measurement stations. However, it should be remembered that both the probe station and the interface station communicating with each other need to use the same frequency hopping pattern to maintain frequency hopping synchronization. In other words, the measurement station and the probe station preferably include a frequency hopping spread spectrum modem operating using the same frequency hopping pattern. An acquisition mode can also be implemented, in which the measurement station passively receives information (while hopping between channels) until an activation message is received from the measurement station.

[0026] The probe station and interface station may include communication modules implemented in various ways. For example, such a communication module may include appropriately configured circuitry or a processor. The communication module may also include an RF antenna, or be connectable to an associated RF antenna. The communication module may also include a processor for calculating a frequency-hopping pattern (e.g., based on a unique identifier). The communication module may be configured as a circuit board (e.g., an FPGA) for mounting within the measurement probe and / or the measurement probe interface. The circuit board may implement additional functions connected to frequency-hopping communication or for other processes. Other components may be included within the probe station or interface station.

[0027] The system may use multiple channels within the 2.4 GHz radio frequency band (extending from 2.4000 GHz to 2.4835 GHz). This is also known as the Industrial, Scientific, and Medical (ISM) band, which is unlicensed in most countries. Each channel may be 2 MHz wide, but it should be noted that any transmission may only occur on a portion of the frequency range of each channel. In a preferred embodiment, 39 channels (each 2 MHz wide) extending from 2.404 GHz to 2.480 GHz are provided. It should be noted that the invention can be used in any radio frequency band and is not limited to ISM band operation. Preferably, the system is configured to operate on standard unlicensed radio bands. It should be noted that such bands may vary depending on the country or over time, depending on regulatory rules, but this will not alter the benefits associated with the invention. It should also be noted that frequency-hopping radio communication systems and their components may be classified as Digital Transmission System (DTS) or hybrid systems, rather than as FHSS systems as formally defined by the Federal Communications Commission (FCC).

[0028] According to a second aspect of the invention, a method is provided using a frequency-hopping radio communication system, the system comprising a measuring station having a first clock and an interface station having a second clock, the method comprising the steps of: transmitting measurement information from the measuring station to the interface station, the measurement information transmitted by the measuring station being generated by a measurement event and including timing information associating the measurement event with the first clock; receiving the measurement information at the interface station and generating a measurement output including timing information associated with the second clock; and designating one of the first clock and the second clock as a master clock, and periodically adjusting the other of the first clock and the second clock to maintain synchronization with the designated master clock, characterized in that any periodic clock adjustment applied between the measurement event and the generation of the measurement output is taken into account when generating the timing information of the measurement output generated by the interface station. In other words, the method may include the step of incorporating any periodic clock adjustment applied between the occurrence of the measurement event and the generation of the measurement output into the timing information of the measurement output (i.e., which is generated by the interface station). The method may also include any features described above in conjunction with the associated devices.

[0029] This document also describes a frequency-hopping radio communication system. The system may include a measurement station. The measurement station may have a first clock. The system may include an interface station. The interface station may have a second clock. The measurement station may be configured to transmit measurement information generated by a measurement event (e.g., a contact-triggered event). This measurement information may include timing information associating the measurement event with the first clock. The interface station may be configured to receive measurement information from the measurement station. The interface station may be configured to generate a measurement output including timing information associating the measurement event with the second clock. One of the first and second clocks may be designated as the master clock, and the other of the first and second clocks may be periodically clock-adjusted to maintain synchronization with the designated master clock. The timing information of the measurement output generated by the interface station may take into account any periodic clock adjustments applied between the occurrence of the measurement event and the generation of the measurement output. In other words, timing corrections taking into account clock adjustments may be implemented.

[0030] The invention will now be described by way of example only, with reference to the accompanying drawings, in which;

[0031] Figure 1 The machine tool measuring probe and probe interface were demonstrated.

[0032] Figure 2 The clock count for the frame is shown.

[0033] Figure 3 It demonstrates the possibility of probe and interface clock drift and how to periodically correct this situation. Figure 4 This demonstrates how to create a trigger output from an interface using trigger events measured by a probe, and...

[0034] Figure 5 This demonstrates how clock drift correction can be considered when generating trigger outputs.

[0035] Original Reference Figure 1 This image shows a contact-triggered measuring probe 10 mounted to the spindle 12 of a machine tool. The measuring probe 10 has a deflectable probe 14 with a workpiece contact end 16. The measuring probe also includes a first frequency-hopping radio communication module or station 18, which is typically integrated into the main body of the measuring probe, but is shown separately for clarity. Figure 1 Shown separately. The measurement probe interface 20 is mounted on a fixed part 22 of the machine tool structure and is connected (typically via cable) to the machine tool controller 24. The measurement probe interface 20 also includes a second frequency-hopping radio communication module or station 26.

[0036] 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 synchronize their hopping between channels to allow the communication link to be established. The sequence followed when using various different channels is generally referred to as a "frequency-hopping pattern". In prior art systems, a frequency-hopping pattern describes the order or sequence that is always followed when using different channels and is used to ensure that, after proper synchronization, both ends of the radio link transmit / receive on the same channel at the same time (assuming both ends use the same frame rate). In other words, a frequency-hopping pattern describes the order in which different channels are "hopped". For further information, refer to WO2004 / 057552, the contents of which are incorporated herein by reference.

[0037] In frequency hopping systems, both ends of the link (i.e., the probe station and the interface station) need to maintain close synchronization. As one frame rolls to the next, both ends of the link will switch to the next channel in the frequency hopping sequence or pattern, regardless of whether a transmission is scheduled. This ensures that both ends of the link are ready to create and receive data packets on the correct channel and at the correct time.

[0038] Reference Figure 2 The image shows multiple frames (F1 to F8) from the probe station. According to a so-called frequency hopping pattern, the channel used to transmit / receive information changes every frame. In this example, each frame lasts 250 μs. This frame duration is timed using a clock within the probe, which counts from 0 to 249 in 1 μs intervals. Figure 2 As illustrated in the illustration, the 250 counts generated by the probe clock define each frame. Clock count 0 defines the start of a frame, while clock count 249 is the last count for that frame. Therefore, the clock count increments from 0 to 249 and then resets to zero at the start of the next frame.

[0039] In the aforementioned system where the probe and associated interface communicate via a frequency-hopping link, different clocks will exist within the probe and interface. Most oscillators used in electronic circuits to provide clock signals are characterized under certain defined conditions. Under these defined operating parameters, the oscillator will have a tolerance (i.e., an acceptable deviation from the ideal operating frequency), which varies from oscillator device to device. Any deviation from the defined conditions, such as a deviation in operating temperature, will result in a difference in oscillation frequency. This difference will be more pronounced if the probe and interface are used in a way that the temperature of one unit differs from that of the other. The crystal used in the oscillator is also prone to change in oscillation frequency over time (drift); this is known as aging. Therefore, it is necessary to design a system that can tolerate crystal drift and compensate for it during operation, so that the final metrological accuracy is not affected even after many years of use.

[0040] refer to Figure 3 This demonstrates the effect of a very small difference in the oscillation frequency of the clock provided within the probe and interface. Frames F1 through F9 of the probe are shown together with their corresponding frames F1' through F9' of the interface. Although roughly aligned in time, Figure 3 The illustration shows that the drift between the probe clock and the interface clock causes a slight offset in the start time of frames F2 and F2', as indicated by arrow 36. Although this slight misalignment of frames is unlikely to affect data communication, it may worsen (cumulatively) over time until the frames of the probe and interface are no longer aligned, at which point the probe and interface will no longer use the same channel (i.e., frequency hopping synchronization will be lost) and communication will fail.

[0041] The clock drift problem has been previously solved in the aforementioned prior art frequency hopping systems. In particular, periodic transmission between the probe and the interface is known. Figure 3 The probe (marked as 38) is used to resynchronize the clock. Simply put, the probe can send a message at a specific count within a frame. For example, the probe can send a status message at count 74 within a specific frame. The interface can read this message and compare the probe's clock count with its own count. If the counts differ, the interface can send a message back to the probe, instructing it to adjust its clock count to synchronize with the interface's clock count. For example, the interface can instruct the probe to skip or add a specific number of counts to the next frame to provide the necessary clock realignment.

[0042] Consider a more concrete example: a probe might send a so-called heartbeat message to its associated interface every 32ms (regardless of the frame rate). If the message is lost, the probe will retry in each frame. The interface will wait until one of two things happens: (a) the interface receives the message sent by the probe, or (b) no heartbeat message is received after 63ms, in which case the interface will output an error. After outputting an error, the interface will begin searching for probes to reconnect to (i.e., the interface will attempt to establish a communication link from scratch).

[0043] For such an example, the maximum acceptable drift between the two periodic oscillators would occur in the latter case (b). To calculate this drift, some details about the crystals used to drive the modems on both the probe and the interface can be used. For example, the oscillation frequency is 32 MHz, and the calibration tolerance is ±15 ppm. The frequency stability over the temperature range of -20 to 85 °C is ±15 ppm, and the annual aging effect is less than ±3 ppm. If the worst-case scenario is considered, the following assumptions can be made: (i) the probe and interface are at opposite ends of the calibration tolerance, (ii) the probe and interface are at opposite ends of the usable temperature range, and (iii) this relates to the opposite ends of the frequency stability range. Additionally, (iv) both the probe and interface have been used for five years and have been aged according to the worst-case scenario, with the aging directions opposite to each other.

[0044] Considering all the factors mentioned above, for this example, there will be approximately 2.8 ps of drift per clock cycle between two clock cycles. Assuming the maximum number of clock cycles that could occur between calibrations (adjustments) is approximately 2 million cycles, the possible drift would be around 5.67 μs. This drift becomes more severe as the probe is used longer, potentially reaching as high as 7.56 μs for a probe used for ten years.

[0045] The aforementioned prior RMI / RMP and Primo metrology probe systems adjust for this clock drift to maintain frame timing and robust communication. However, these small adjustments are not compensated for when metrology points occur nearby or simultaneously. The inventors have discovered that this manifests as jitter, i.e., small variations in switching time, which will appear as small differences in measurement location. To achieve the most repeatable and accurate system, the present invention compensates for any timing adjustments when distributing metrology points. Roughly speaking, and ignoring other effects, this has been found to improve the timing accuracy of metrology events by about twenty times. This will now be described in more detail.

[0046] refer to Figure 4 This will demonstrate the use of the aforementioned probe and interface to collect contact trigger points. As described above, the probe and interface cycle through a series of frames together. Figure 4The image shows that probe frames F1 to F14 are aligned with interface frames F1' to F14'.

[0047] The probe may sense a trigger event at any point in time. In this example, trigger event 40 occurs during frame F2. The clock count within frame F2 when the trigger event is detected is recorded (i.e., the clock count measured using the probe clock). Accurate contact-triggered measurement relies on the interface always emitting a trigger signal at a specific (constant) time after the trigger event occurs. In this example, trigger signal 44 is emitted by the interface during interface frame F13'. Figure 4 In the diagram, the delay (or time delay) between trigger event 40 and trigger signal 44 is marked as "t". 时延 ".

[0048] Information about the trigger event is exchanged between the probe and the interface via message exchange. For example, in frame F4, the probe can send message 42 notifying the interface that a measurement event has been detected and that the measurement event occurred at a specific clock count within frame F2. This message can be sent several frames after the event and can be retransmitted multiple times in case of communication failure on a channel (e.g., due to interference). The interface can acknowledge receipt of the message (i.e., the probe knows the message has been safely received). The interface can then act on the information in the message. Specifically, it then knows the frame in which the trigger event occurred and the clock count within that associated frame. This allows the interface to calculate the time required to send the trigger signal 44 (i.e., the frame and the clock count within that frame) to ensure it is delayed t relative to the trigger event. 时延 ).

[0049] The above relies on the synchronization of the probe clock and the interface (i.e., because the interface needs to map the timing of the probe clock to the timing relative to its own (interface) clock). Therefore, it can be seen that the accuracy of the clocks used in the probe and interface will directly affect the final metrological capability of the system, since changes in probe state (i.e., contact points) are transmitted as timestamps relative to the start of the synchronization frame edge.

[0050] While clock adjustment has been previously used to maintain clock synchronization, this existing technology separates clock synchronization from trigger event information communication. In other words, the clock adjustment (i.e., synchronization) process can occur at any point in time relative to the trigger event communication (such a trigger event is an asynchronous event that can occur at any time). Therefore, clock timing may change at or before / after recording metering points. Consequently, the clock adjustment process has been found to increase latency errors, which manifest as jitter in the trigger signal. As will now be described in detail, the present invention eliminates this source of error by taking into account any clock adjustment when generating the trigger signal.

[0051] Next reference Figure 5 This describes a technique (also known as RMI-QE) that takes into account clock adjustment and drift when transmitting contact-triggered events from the probe to the interface.

[0052] As described above, the goal of the metering system is to enable the RMI-QE's SKIP or status output (i.e., the trigger signal output from the interface) to be valid after a fixed delay following the probe receiving the trigger. The delay must be as short as possible and the jitter very low. The delay is shown as t in the diagram. 时延 And in this example, it is 2.5ms.

[0053] Both the probe and the interface have frame timers running at 250μs, resulting in 10 frames within a 2.5ms delay. This allows for 1 frame for triggering, 1 "housekeeping" frame for scheduling transmission, 1 frame for sending the message, and 7 frames for retries.

[0054] In this example, the probe initially sends a normal periodic message to the RMI-QE interface. Periodic messages from the probe are always sent with a specific offset within the frame (t...). 探头_发送 In this example, the offset is 74 μs. The RMI-QE modem (interface) receives this message at the end of the 75th microsecond and calculates that the probe has drifted by -1 μs, and an adjustment of -1 μs needs to be applied (t). 调整 This synchronizes the two frame timers. A few microseconds later, the RMI-QE sends an adjustment message to the probe, and the probe applies the adjustment, which takes effect at the end of the next frame.

[0055] At the end of the next frame, a trigger (t) is received. 触发 This is shown at 247μs within the frame. Note that the adjustments made to keep the frame length consistent with the RMI-QE frame timer have not yet taken effect. To reduce jitter, it is clear from the figure that although the trigger occurs at 247μs on the probe frame timer, the RMI-QE needs to calculate that it occurs at 249μs on its own frame timer.

[0056] In the second frame after the trigger occurs, the probe will send a timestamp (t). 触发 ), and the adjustment it applies (t) 调整 The RMI-QE also calculates the number of retries by the modem in the RMI-QE. In this example, because the probe frame timer is drifting, it has drifted again to the 75th microsecond, so the RMI-QE calculates that the probe has drifted by 1 μs (t). 漂移 ).

[0057] It should be noted that, preferably, no frame timer adjustment is applied in the frame after the trigger event and before an event acknowledgment is received from the RMI-QE interface. For example, if the trigger event occurs in the same frame as a periodic message containing probe adjustment values, no adjustment should be applied. Instead, the interface will calculate the required drift compensation upon receiving the event message, and this will be used to correct for latency.

[0058] The confirmation of the event message will include the probe's adjustment value, which can then be used to correct the clock in the probe. At a Serial Peripheral Interface (SPI) interval (225μs in this example), sometime later in the frame, the modem will send all this information back to the FPGA at the RMI-QE interface. The information sent is:

[0059] t 触发 =247

[0060] t 调整 =-1

[0061] t 漂移 =-1

[0062] Retry = 0

[0063] After the FPGA receives this data, it will calculate until the SKIP output (t) is required. 定时器 The remaining time before it becomes effective. Therefore, it is calculated from the delay (t). 时延 Subtract all delays in the transmission system from (2.5ms). The delay is denoted as t. 偏移 As can be seen from the graph, t 偏移 It consists of the following: the intra-frame offset (t) of the FPGA's startup time. 定时器_启动 (225μs in the example) and timestamp (t) 触发 The distance (t) between it and the end of its frame 触发_INV (and any retries that have already occurred.)

[0064] To run the timer in the FPGA with the smallest possible latency and allow for the maximum possible clock drift, the timer also needs to be started at least 20μs before the end of the frame in which the event data is received: t 定时器启动_最大 = 230μs. If this is not possible, a drift allowance needs to be added to the timer to prevent requests for negative timer values.

[0065] It should also be noted that the timestamp from the probe needs to be fine-tuned (t). 触发 To obtain the correct timestamp (249μs), we need to subtract the adjustment and drift values ​​from this timestamp.

[0066] t 时间戳 -t调整 -t 漂移

[0067] =247--1--1

[0068] =249

[0069] Therefore, calculate t 定时器 :

[0070] t 定时器 =t 时延 -t 定时器启动 -·t 触发INV -·R×t 帧

[0071] t 时延 The value will vary depending on whether the computation is performed within the RMI-QE interface. For RMI-QE, this will be:

[0072] t 时延 =t 输出_时延 -(n 接收(RX)_之前_帧 ×t 帧 )

[0073] t 时延 = 2.5ms - (2 × 250μs)

[0074] t 时延 =2.0ms

[0075] t 触发INV It can be calculated by subtracting the trigger timestamp from the frame length.

[0076] Therefore (RMI-QE):

[0077] t 定时器 =t 时延 -t 定时器启动 -(t 帧 -(t 时间戳 -t 调整 -t 漂移 ))-R×t 帧

[0078] t 定时器 =2.0ms-230μs-(250μs-(247μs--1μs--1μs))-0×250μs

[0079] t 定时器 =2000μs-230μs-(250μs-(249μs))

[0080] t 定时器 =2000μs-(231μs)

[0081] t定时器 =1769μs

[0082] Therefore, the above technology allows for clock adjustment to ensure that the probe and interface clocks remain synchronized, and this operation can be performed without affecting metrological accuracy. In particular, it eliminates the jitter previously observed due to the clock adjustment process.

[0083] Although the above examples relate to contact-triggered measurement probes and associated probe interfaces, the same technology can be used for the transmission of any measurement data. For example, ultrasonic waves, scan points, or other metrological data can be transmitted. Similarly, operation in the 2.4 GHz radio band is provided by way of example only and is not intended to limit the scope of the invention. Other features of WO2004 / 057552 may also be included in the system.

Claims

1. A frequency-hopping radio communication system, the frequency-hopping radio communication system comprising a measuring station having a first clock and an interface station having a second clock, wherein: The measuring station is configured to send measurement information generated by asynchronous measurement events, the measurement information including timing information that associates the asynchronous measurement events with the first clock. The interface station is configured to receive the measurement information from the measurement station and generate a measurement output including timing information relative to the second clock definition, and The frequency-hopping radio communication system is configured such that one of the first clock and the second clock is designated as the master clock, and the other of the first clock and the second clock is periodically clock-adjusted to maintain synchronization with the designated master clock within a millisecond. The interface station is characterized in that it is configured to correct the timing information of the measurement output generated by the interface station for any periodic clock adjustments applied between the occurrence of the asynchronous measurement event and the generation of the measurement output.

2. The frequency-hopping radio communication system according to claim 1, wherein, The measurement information sent by the measurement station is timestamped relative to the time defined by the first clock.

3. The frequency-hopping radio communication system according to claim 2, wherein, The measurement station sends information to the interface station using a series of frames, and the measurement information is timestamped to define the time relative to the edge of the sent frame.

4. The frequency-hopping radio communication system according to any of the preceding claims, wherein, The first clock and the second clock each generate a clock count, wherein one of the first clock and the second clock is designated as the master clock, and the periodic clock adjustment includes incrementing or decrementing the clock count of the other of the first clock and the second clock to maintain synchronization with the designated master clock.

5. The frequency-hopping radio communication system according to any of the preceding claims, wherein, The periodic clock adjustment includes exchanging messages containing timing information between the measuring station and the interface station.

6. The frequency-hopping radio communication system according to any of the preceding claims, wherein, The periodic clock adjustments are performed at regular intervals.

7. The frequency-hopping radio communication system according to any of the preceding claims, wherein, The second clock is the master clock, and the periodic clock adjustment includes adjusting the first clock to keep it synchronized with the second clock.

8. The frequency-hopping radio communication system according to any of the preceding claims, further comprising a measuring device, the measuring device including the measuring station and a measuring sensor.

9. The frequency-hopping radio communication system according to claim 8, wherein, The measurement sensor includes a contact trigger sensor.

10. The frequency-hopping radio communication system according to claim 9, wherein, The asynchronous measurement events include contact-triggered events sensed by the contact-triggered sensor.

11. The frequency-hopping radio communication system according to claim 10, wherein, The measurement output generated by the interface station includes a trigger signal.

12. The frequency-hopping radio communication system according to any of the preceding claims, wherein, The measurement station and the interface station include frequency-hopping spread spectrum modems that operate using the same frequency-hopping pattern.

13. A method using a frequency-hopping radio communication system, the system comprising a measuring station having a first clock and an interface station having a second clock, the method comprising the steps of: Measurement information is sent from the measurement station to the interface station. The measurement information sent by the measurement station is generated by an asynchronous measurement event and includes timing information that associates the asynchronous measurement event with the first clock. The interface station receives the measurement information and generates a measurement output including timing information related to the second clock. One of the first clock and the second clock is designated as the master clock, and the other of the first clock and the second clock is periodically adjusted to maintain synchronization with the designated master clock within a millisecond. The method is characterized by the following steps: using any periodic clock adjustment applied between the asynchronous measurement event and the generation of the measurement output to correct the timing information of the measurement output generated by the interface station.

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