Patent ID: 12255595

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the ensuing description, one or more specific details are illustrated, aimed at providing an in-depth understanding of examples of embodiments of this description. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that certain aspects of embodiments will not be obscured.

Reference to “an embodiment” or “one embodiment” in the framework of the present description is intended to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as “in an embodiment” or “in one embodiment” that may be present in one or more points of the present description do not necessarily refer to one and the same embodiment. Moreover, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments. The headings/references used herein are provided merely for convenience and hence do not define the extent of protection or the scope of the embodiments. The drawings are in simplified form and are not to precise scale.

Throughout the figures annexed herein, like parts or elements are indicated with like references/numerals and a corresponding description will not be repeated for each and every figure for brevity.

FIG.1is a diagram of an HDD device10that is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital data.

As exemplified inFIG.1, such an HDD10may comprise: one or more rigid platters12coated with magnetic material and coupled to a spindle14configured to cause the platters12to rotate rapidly about an axis perpendicular to the surface of the platters12; one or more magnetic read/write (R/W) heads20each paired with a respective rigid platter12configured to read and write data to the platter surfaces12; an actuator24having an actuator arm22coupled to the magnetic R/W head20and configured to move the actuator arm22around an actuator axis26; and a printed-circuit-board (PCB)30comprising electronic circuitry configured to control the movement of the actuator and the rotation of the disk to perform reads and writes.

As exemplified inFIG.2, electronic circuitry on the PCB board30may be coupled to the electro-mechanical actuator24and may be configured to control as a function of data received or sensed from the HDD10.

For instance, the control circuitry may comprise:

a (e.g., standard) feedback controller stage28coupled to the actuator assembly20,22,24,26configured to receive feedback from a position error signal of the HDD R/W head20;

a set of piezoelectric transducers300configured to detect rotational vibrations during HDD operation, producing an electrical signal indicative of such vibrations as a result; a processing stage38, e.g. an acceleration feed-forward controller, coupled to the piezoelectric sensors300and configured to receive the electrical signal produced by the sensors300; and a system control circuit39configured to provide feedback to the actuator assembly20,22,24,26in order to treat, for instance compensating, vibrations detected by the piezoelectric sensors300during displacement of the R/W head20with respect to the surfaces of the platters14.

In general terms (and with the exception of what will be discussed in detail in the following) the structure and operation of an HDD10as discussed herein are conventional in the art, which makes it unnecessary to provide a more detailed description herein.

FIG.3is an enlarged perspective view of a piezoelectric transducer300to which one or more embodiments may apply.

As mentioned, such a piezoelectric transducer300may be configured to detect mechanical acceleration and shock applied from outside of the HDD, producing an electrical signal indicative of such a mechanical shock as a result. For instance, the piezoelectric transducer300may detect acceleration along a direction (which may correspond to a primary axis of the sensor300) forming an angle α with the platters12.

As exemplified inFIG.4, the piezoelectric transducer300may have a certain frequency response which may vary as a function of the range of frequencies in which it is excited.

As exemplified inFIG.4, the frequency response may be substantially flat in a frequency range between a low frequency fland a high frequency fh, and it may as well present a resonant peak (such as that of a longitudinal resonant mode, for instance) at a resonance frequency fr.

While applications may exploit signals at low frequencies, that fall between fland fh, the presence of the resonance peak leads the piezoelectric transducer200to produce signals having a strong, undesired signal component at the frequency fr, representing a disturbance for the system. It may be of interest to remove the signal component at frequency fr, facilitating to relax the performance of the circuits that has to elaborate this signal.

As exemplified herein, this may be via use of a narrow band-stop or “notch” filter, for brevity, circuit tuned at the resonant frequency frand thus configured to suppress the resonance. This may involve preliminary excitation of the piezoelectric transducer300to produce a periodic signal at its resonance frequency fr. Subsequently, the notch filter may be made to oscillate producing a periodic signal at its notch frequency. As a result, the periodic signal resulting from the excitation and the periodic signal at the notch frequency may be compared to tune the notch filter to produce a periodic signal whose frequency matches that of the piezoelectric resonance frequency, as discussed in the following.

FIG.5is a diagram of an application-specific integrated circuit (ASIC)50configured to perform such a process.

As exemplified inFIG.5, such an ASIC50may be configured to be coupled to a circuit40comprising the piezoelectric sensor300having a first input node302coupled to a first series RC circuit comprising a first resistor RN and a first capacitor CN, and a second input node304of the sensor300being coupled to a second series RC circuit comprising a second resistor Rp and a second capacitor Cp.

As exemplified inFIG.5, the ASIC may be coupled the test circuit40for the sensor300via a plurality of input nodes SO, SN, SP, SR, comprising a first pair of input nodes SN, SP configured to be coupled to the electrodes302,304of the piezoelectric transducer300, and a second pair of input nodes SO, SR each configured to be coupled to series RC circuits Rn, Cn, Rp, Cp coupled at the electrodes of the sensor300respective test circuit40Rn, Cn, Rp, Cp for the sensor300, a first input node SR configured to be at a reference voltage level.

As exemplified inFIG.5, such an ASIC50may comprise: a control logic block51, for instance a digital IP core, configured to generate510at least one pulse electrical signal, for instance one or more pulsed signals P+, P−, and to set512a frequency for a notch filter58, as discussed in the following; and a first (charge) amplifier stage52, such as an operational amplifier520having non-inverting520aand inverting520binput nodes and an output node, for instance. The first amplifier stage52may have its input nodes520a,520bcoupled to the control logic51and to the first pair of input nodes SN, SP, the nodes520a,520bbeing thus configured to receive the input signal P+, P− from the controller51and to apply it input nodes SN, SP. Notch filter58may be implemented using notch filter circuits known in the art. In some embodiments, notch filter58may be implemented using an active notch filter. Programmability of the stopband of notch filter58may be achieved using selectable components, such as selectable capacitors and/or selectable resistances.

The first amplifier stage52may further comprise, for instance: a feedback branch520ccoupling the output node to the input node SO of the ASIC50and to the inverting input node520bof the amplifier520via a resistor RfNand a first switch SN; and a further branch520dselectively couplable, via a second switch SWpto the second input node SR via a second resistor Rfpbetween the second input node SP of the ASIC50and the second input node of the first amplifier52.

In one or more embodiments, such switches SWn, SWpmay be controllable between an open and closed state as a function of a control signal EN_TIA which may be produced by the control logic block51; closing the feedback branch520cbetween input520band the output node of amplifier520may enable a fast settling time of the charge amplifier, which may be turned to a transimpedance amplifier configured to receive an input electric current signal to produce an output amplified voltage signal VOUT1at the output node.

During oscillation, the fast settling mode facilitates speeding up the settling time of the oscillation, and rejecting the low frequency noise where a large part of the random vibrations of the external environment sensed by piezoelectric sensor300are present, whereas such disturbances would otherwise affect measurement precision.

As exemplified inFIG.5, the resistors Rfp, Rfnare put in parallel to external resistors Rn, Rpwithout changing the resonance frequency.

As exemplified inFIG.5, the ASIC may further comprise: a second amplifier stage54, such as a fully differential inverting amplifier, coupled to the output node OUT1of the first amplifier stage52and to a second node SR at a reference voltage level, the second amplifier stage54being configured to apply amplification processing520to the voltage signal VOUT1output from the first amplifier stage52, producing a pair of output voltage signals; a comparator stage56, such as a comparator with hysteresis, for instance, having input nodes coupled to the second amplifier stage54and an output node coupled to the controller circuit51, the comparator56configured to “square” the signal from the second amplifier stage54making it compatible with digital processing from the control circuit51; and a tunable notch filter stage58, such as a digitally programmable “notch” filter, for instance, having its output selectively couplable to the input of the second amplifier stage54via feed-back branches540a,540b; the notch filter58may also be coupled to the control circuit51, wherein the tunable notch filter58has a stopband frequency value which may be programmable, for instance set via a control signal W from the control logic51.

The notch filter stage58may be configured to apply very narrow band-stop filtering at the set notch frequency to the input signal VOUT2N, VOUT2Preceived from the second amplifier stage54.

The ASIC50may further comprise a third amplifier stage59coupled to the notch filter stage58and configured to apply amplification processing to the filtered signal, which may be provided at the output node RV of the ASIC to further user circuits, for instance to the processing stage38on the board30of the HDD10.

A method60suitable for operating the ASIC50as exemplified inFIG.5may include: a first stage62comprising exciting the resonant frequency frof the piezoelectric sensor300, and a second stage64comprising (auto-)tuning the notch filter58, iteratively (re-)setting the notch filter frequency to match with the resonant frequency frof the sensor300.

As exemplified inFIG.6, the first stage62of the method60may include stimulating (see block620) a resonance of the piezoelectric sensor300, hence obtaining a (resonant) oscillation of the piezoelectric sensor300; this may be via an electrical signal P+, P− such as pulses P+, P− produced by the control circuit51, as exemplified inFIG.6A; the control circuit51may control parameters of such a stimulus P+, P− in order to control oscillation amplitude of the response of the piezoelectric sensor300.

For instance, the control circuit51may control the amount of charge injected into the piezoelectric transducer300by means of a programmable current pulse P+, P− having a programmable magnitude and/or pulse width.

The stimulus P+, P− provided to the piezoelectric sensor300may produce an electric current signal Isn, Isp which may be detected at respective input nodes SN, SP as exemplified inFIG.6B.

The first stage62of the method as exemplified inFIG.6may further comprise:

applying transimpedance amplification (see block624) to the response from the piezo, for instance sending a signal EN_TIA to the switches SWn, SWpin order to change their status from an open state to a closed stage.

As a result, the charge of the piezoelectric sensor300flows through the resistance Rfin the feedback branch520cof the first amplifier stage52and no more through the capacitors Cpn, Cp. Subsequently, a voltage signal VOUT1as exemplified inFIG.6Cmay be present at the output node of the first amplifier stage52as a result of such an operation624.

In one or more embodiments, varying the feedback of the first amplifier52may lead to several advantages. For instance, these maybe: a reduction of time constant of the system, previously determined by capacitors CN, CP and resistors RN, RP; a reduction of the settling time of the amplifier52, so that the amplifier52, after entering a saturation state due to the excitation of the resonance frequency fr, quickly desaturates; and a transfer function of the amplifier52becomes less sensitive to the low frequencies. Also, the system may be much less sensitive to any disturbances that may otherwise impact the first stage62of the method60.

As exemplified inFIG.6D, the signal VOUT1is then amplified by the second amplifier stage54. The first stage of the method60exemplified by block62may include: digitizing, squaring the (amplified) signals VOUT2N, VOUT2P, resulting from the stimulated resonant oscillation to produce therefrom, via the comparator stage56, for instance, a square wave signal VOUT3(as exemplified inFIG.6E); and measuring the frequency of the square wave signal VOUT3, for instance via a digital counter512included in the control logic51, suitable to count a time interval between a pair of edges with a digital clock, which may generally have a frequency of tens of MHz.

For instance, the digital core51may measure the time interval by counting how many clock periods are present between two consecutive rising edges of the square signal VOUT3.

Such a counting operation may produce signals as exemplified inFIG.6F, with the digital counter512producing a final count value as a result of counting time intervals between edges of the signal Vout.

As exemplified inFIG.6, the second stage64of the method60may include: setting (see block640) the stopband frequency of the notch filter to an initial, coarse, value (e.g., a frequency value in the middle of the tunability range of the filter); this may be performed via a control word W transmitted from the control circuit51to the notch58, in ways per se known; controlling (see block642) the feedback branches540a,540bbetween output nodes of the notch filter58to be closed and input nodes of the second amplifier stage54, obtaining as a result that a virtual ground condition is imposed between such input and output nodes (see, e.g.,FIG.8, representing a portion of the circuit ofFIG.5); this may induce as a result an oscillatory signal to be produced by the amplifier54, with the oscillatory signal having a frequency equal to the stop-band frequency set for the notch filter (see block644); detecting such an oscillatory signal having a frequency equal to that of the notch filter58at nodes VOUT2N, VOUT2P; and comparing, e.g., via the control logic block51the detected oscillatory signal ΔV having a frequency value dependent on the set stopband frequency value of the notch filter58with the resonant frequency frmeasured at stage62; and iteratively varying (see block646) the notch word W to re-set the stopband frequency of the notch filter as a function of the result of the comparison, until the set stopband frequency matches as closely as possible the measured value of the resonant frequency frof the sensor300as processed at stage62of the first stage62.

For instance, iterations of operation646may be halted when the notch filter58is finely tuned to the desired frequency fr, namely when the programming word W adequately matches the frequency value frtarget.

For instance, a dichotomic routine (SAR routine, reverse SAR, sub-binary SAR for instance) may be suitable to perform such a matching process646. See, for instance, the entries for “Dichotomic_search” or “Successive_approximation_ADCa” in Wikipedia® at wikipedia.org.

As exemplified inFIG.6G, while the notch58and the second amplifier stage54are in the closed feedback loop540a,540b, an electrical signal oscillating at the notch frequency may be sensed at the output of the second amplifier stage54, such as a voltage difference ΔV, for instance ΔV=VOUT2N−VOUT2P. Causing the notch filter to oscillate in this manner advantageously allows for an easy measurement of the resonant frequency of the notch filter. In the embodiment depicted inFIG.5, feedback loops540aand540bmay be closed via switches (not shown) coupled in series with each feedback loop540aand540b, thereby allowing for the activation and deactivation of feedback loops540aand540bwith very little additional hardware. In some embodiments, signal path between piezoelectric sensor300and signal VOUT1may be disabled when feedback loops540aand540bare activated.

As exemplified inFIG.6G, such a signal ΔV is substantially sinusoidal and that has a same frequency of the notch frequency set by the programming word W, for instance a word consisting of 9-bits.

Subsequently, the comparator56and the counter512may be used to measure frequency of the signal ΔV in a manner substantially similar to what discussed with respect to the measurement of the resonant frequency of the piezoelectric sensor300, that is by counting the number of clock periods between a pair of edges of the signal V our3and obtaining a measurement of at least one period (see, e.g., the discussion with reference toFIG.6F). The control logic51may then compare such a measured notch frequency and vary the programming word W, configured to set the notch frequency of the notch filter58, until the measured notch frequency matches the resonance frequency of the piezoelectric sensor300measured in stage62.

As exemplified herein, both the resonance frequency frof the piezoelectric transducer300and the notch frequency of the filter58may be measured using substantially the same measurement arrangement involving at least one amplifier52,54, the comparator56and the logic unit51. This may advantageously facilitate substantially compensating non-idealities involved in the measuring system and related measuring errors, so that it may be possible to use relatively simple measuring system, bringing further benefits therewith such as a reduction of design-complexity, current consumption and area footprint, for instance.

As exemplified inFIG.6F, the comparator56as exemplified inFIG.5is used to access the digital domain where the control unit51(digitally) measures and processes both the resonance frequency frof the piezoelectric sensor300and the stopband frequency of the notch58. Such a measurement may be performed during a first stage DMt, reaching a final value in a second stage DMf.

FIGS.7A and7Bare exemplary diagrams of the circuit50when the feedback loop540a,540bis closed, in particular of the respective loop gain (FIG.7A) and phase (FIG.7B).

As exemplified inFIGS.7A,7Bthe circuit50will oscillate at the notch frequency because the phase of the loop transfer function reaches 180 degrees and the magnitude is bigger than 0 dB (in line with the so-called Barkhausen stability criterion, for instance).

A method as exemplified herein includes:

providing a piezoelectric transducer (for instance,300) configured to transduce mechanical vibrations into transduced electrical signals at a pair of sensor electrodes (for instance,302,304), wherein the piezoelectric transducer has a resonance frequency (for instance, fr), and coupling to the piezoelectric transducer, a notch filter (for instance,58) configured to receive the transduced electrical signals and to produce filtered signals (for instance, RV) from the transduced electrical signals, the notch filter having a tunable stopband frequency. The method comprises: stimulating (for instance,510,620) resonant oscillation of the piezoelectric transducer applying to the pair of electrodes at least one pulse electrical stimulation signal (for instance, P+,P−); detecting (for instance,52,54,622), at the pair of electrodes, at least one electrical signal (for instance, ISN, ISP, VOUT, VOUT2N, VOUT2P) resulting from the stimulated resonant oscillation, wherein the at least one electrical signal resulting from the stimulated resonant oscillation oscillates at a resonance frequency (for instance, fr) of the piezoelectric transducer; measuring (for instance,56,512,624) the frequency of oscillation of the at least one electrical signal resulting from the stimulated resonant oscillation, obtaining a measurement of the resonance frequency of the piezoelectric transducer as a result; and tuning (for instance,64, W), iteratively varying, for instance, the stopband frequency of the notch filter to match the measured resonance frequency of the piezoelectric transducer.

As exemplified herein, the tuning the stopband frequency of the notch filter to match the measured resonance frequency of the piezoelectric transducer (300) comprises: providing (for instance,642) a feedback signal path (for instance,54,540a,540b) from the output to the input of the notch filter via a gain stage (for instance,52,54) to produce oscillation of the gain stage, wherein the gain stage oscillates at an oscillation frequency which is a function of the stopband frequency set for the notch filter; measuring (for instance,644) the oscillation frequency of an oscillatory output signal (for instance, ΔV) from the gain stage, obtaining a measurement of the stopband frequency of the notch filter as a result; and performing a comparison (for instance,56) between the measured resonance frequency of the of the piezoelectric transducer and the measured stopband frequency of the notch filter, obtaining a difference therebetween as a result.

As exemplified herein, the measuring the frequency of oscillation of the at least one electrical signal resulting from the stimulated resonant oscillation and the measuring the oscillation frequency of the oscillatory output signal from the gain stage are performed at a same gain stage (for instance,52,54), obtaining a measurement of the resonance frequency of the piezoelectric transducer and a measurement of the stopband frequency of the notch filter as respective results.

As exemplified herein, performing the comparison comprises: producing a first square wave signal having a first frequency equal to the measured resonance frequency; producing a second square wave signal having a frequency equal to the measured stopband frequency; and checking that a pair of corresponding rising and/or falling edges in the first and second squared signals have a same time interval therebetween.

As exemplified herein, the method includes pre-setting (for instance,512,640) the stopband frequency of the notch filter (58) to an initial value (for instance, W) approximating the calculated resonant frequency of the piezoelectric transducer.

As exemplified herein, the method comprises iteratively re-setting (for instance,512,646) the stop-band frequency of the notch filter to at least one further value (for instance, W) approximating the calculated resonant frequency of the piezoelectric transducer as a function of the difference, obtained as a result of comparison (for instance,56), between the measured oscillation frequency of the gain stage and the measured resonance frequency of the piezoelectric transducer.

As exemplified herein, the method comprises: detecting (for instance,620) the at least one electrical signal resulting from the stimulated resonant oscillation as an electrical current signal (for instance, Isn, Isp); and applying transimpedance amplification (for instance,52) to the electrical current signal and producing therefrom at least one electric voltage signal (for instance, VOUT1).

As exemplified herein, the method comprises stimulating (for instance,510,620) resonant oscillation of the piezoelectric transducer applying to the pair of electrodes (for instance,300,302, Sn, Sp) an electrical stimulation signal (for instance, P+, P−) configured to control an amplitude of the resonant oscillation of the piezoelectric transducer.

A circuit (for instance,50) as exemplified herein, couplable to a piezoelectric transducer (for instance,300) configured to transduce mechanical vibrations into transduced electrical signals at a pair of sensor electrodes (for instance,302,304), wherein the piezoelectric transducer has a resonance frequency (for instance, fr) and has coupled therewith a notch filter (for instance,58) configured to receive the transduced electrical signals and produce filtered signals (for instance, RV) from the transduced electrical signals, the notch filter (58) having a tunable stopband frequency, comprises calibration circuitry (for instance,51,52,54,56,58) configured to: stimulate (for instance,51,510) resonant oscillation of the piezoelectric transducer applying to the pair of electrodes at least one pulse electrical stimulation signal; detect (for instance,52,54), at the pair of electrodes, at least one electrical signal (for instance, ISN, ISP, VOUT1, VOUT2N, VOUT2P) resulting from the stimulated resonant oscillation, wherein the at least one electrical signal resulting from the stimulated resonant oscillation oscillates at a resonance frequency (for instance, fr) of the piezoelectric transducer; measure (for instance,56,512,624) the frequency of oscillation of the at least one electrical signal resulting from the stimulated resonant oscillation, obtaining a measurement of the resonance frequency of the piezoelectric transducer as a result; and tune (for instance,64, W) the stopband frequency of the notch filter to match the measured resonance frequency of the piezoelectric transducer.

As exemplified herein, the tunable notch filter comprises a digitally programmable notch filter.

As exemplified herein, the circuit comprises: a feedback signal path (for instance,54,540a,540b) activatable from the output to the input of the notch filter via a gain stage (for instance,52,54) to produce an oscillatory output signal (for instance, ΔV), wherein the oscillatory output signal from the gain stage oscillates at an oscillation frequency equal to the stopband frequency set for the notch filter; and a measuring circuit (for instance,51) configured to measure the oscillation frequency of the gain stage, obtaining a measurement of the stopband frequency of the notch filter as a result.

As exemplified herein, the circuit comprises a frequency setting control circuit (for instance,512) of the stopband frequency of the notch filter, the frequency setting control circuit configured to be set to an initial value (for instance, W) approximating the calculated resonant frequency of the piezoelectric transducer, wherein the frequency setting control circuit of the stopband frequency of the notch filter is configured to re-set the stop-band frequency of the notch filter to at least one further value (for instance, W) approximating the calculated resonant frequency of the piezoelectric transducer as a function of the difference between the oscillation frequency of the gain stage and the calculated resonant frequency of the piezoelectric transducer.

As exemplified herein, the calibration circuitry is further configured to detect, at the pair of electrodes, at least one electrical signal (for instance, ISN, ISP, VOUT1, VOUT2N, VOUT2P) resulting from the stimulated resonant oscillation, via the gain stage of the feedback signal path activatable from the output to the input of the notch filter.

As exemplified herein, the circuit comprises: at least one square wave generator (for instance,51,510) configured to produce a first squared signal having a first frequency equal to the measured resonance frequency, and a second squared signal having a frequency equal to the measured stopband frequency; and a measuring circuit (for instance,51,512) configured to check that a pair of corresponding rising and/or falling edges in the first and second squared signals have a same time interval therebetween.

As exemplified herein, the circuit comprises a charge amplification stage (for instance,520) coupled to the pair of sensor electrodes of the piezoelectric transducer, where an output of the charge amplification stage couplable (for instance, EN_TIA, Sn, Sp) to at least one electrode (for instance,302) of the pair of sensor electrodes of the piezoelectric transducer, where the charge amplification stage is configured to apply transimpedance amplification (for instance,52) to the electrical current signal (for instance, Isn, Isp) and produce therefrom at least one electric voltage signal (for instance, VOUT1).

As exemplified herein, the calibration circuitry is configured to stimulate (for instance,51,510) resonant oscillation of the piezoelectric transducer applying to the pair of electrodes an electrical stimulation signal (for instance, P+, P−) configured to control an amplitude of the response of the piezoelectric sensor.

An apparatus as exemplified herein, includes: a piezoelectric transducer (for instance,300) configured to transduce mechanical vibrations into transduced electrical signals at a pair of sensor electrodes (for instance,302,304), wherein the piezoelectric transducer has a resonance frequency (for instance, fr) and has coupled therewith a notch filter (for instance,58) configured to receive the transduced electrical signals and produce filtered signals (for instance, RV) from the transduced electrical signals, the notch filter having a tunable stopband frequency; and a circuit (for instance,50) as exemplified herein, wherein the circuit comprises calibration circuitry (for instance,51,52,54,56,58) coupled to the pair of electrodes configured to apply to the pair of electrodes the electrical stimulation signal (for instance, P+, P−) and detect at the pair of electrodes (302,304), the at least one electrical signal (for instance, Isn, Isp, VOUT1, VOUT2N, VOUT2P) resulting from the stimulated resonant oscillation.

One or more embodiments may present one or more of the following advantages: facilitated circuit self-tuning; reduced burden on clock precision used for measurement; increased robustness with respect to low-frequency disturbances; and robustness to process spread, and reduced testing time.

It will be otherwise understood that the various individual implementing options exemplified throughout the figures accompanying this description are not necessarily intended to be adopted in the same combinations exemplified in the figures. One or more embodiments may thus adopt these (otherwise non-mandatory) options individually and/or in different combinations with respect to the combination exemplified in the accompanying figures.

Without prejudice to the underlying principles, the details and embodiments may vary, even significantly, with respect to what has been described by way of example only, without departing from the extent of protection. The extent of protection is defined by the annexed claims.