Rotational and linear vibration sensing

In accordance with certain embodiments, a method is provided for sensing linear vibration and rotational vibration. The method includes generating a combined linear vibration and rotational vibration signal. The combined linear vibration and rotational vibration signal may then be processed with an adaptive filter.

PRIORITY CLAIM

This application claims the benefit under 35 U.S.C. section 119 of U.S. provisional patent application Ser. No. 61/712,651 filed on Oct. 11, 2012 and entitled “Rotational and Linear Vibration Sensing” which is hereby incorporated by reference in its entirety for all purposes.

BACKGROUND

Vibrational forces can lead to problems in the operation of electronic devices. For example, disk drives can encounter vibration during use that can impact the performance of the drive. The vibration is often referred to as having a linear vibration component and rotational vibration component. As technology has advanced, both linear vibration and rotational vibration have become of greater interest to counteract.

SUMMARY

This Summary is provided to introduce a selection of concepts in simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other features, details, utilities, and advantages of the claimed subject matter will be apparent from the following more particular written Detailed Description of various implementations and implementations as further illustrated in the accompanying drawings and defined in the appended claims.

In accordance with certain embodiments, a method is provided for sensing linear vibration and rotational vibration. The method includes generating a combined linear vibration and rotational vibration signal. The combined linear vibration and rotational vibration signal may then be processed with an adaptive filter.

These and various other features and advantages will be apparent from the following detailed description.

DETAILED DESCRIPTION

Electronic devices can experience vibrational forces from external and internal sources. The vibration is often referred to as linear vibration and rotational vibration.FIG. 1illustrates an example of vibrational forces being exerted on a device. In the illustration ofFIG. 1, a disc drive is used as the example device.

InFIG. 1, system100is shown as responding to vibrational forces. A disc drive platter104and actuator108are shown. These components experience both rotational vibration Vrand linear vibration VL. Sensors112and116are shown positioned on different ends of the device. The sensors112and116can sense the vibrational forces and be used by a feed forward controller120to adjust the positioning of the actuator108. A feedback controller124can also be used to position the actuator108.

Rotational vibration, Vr, has typically been the greater concern with devices like disc drives because platters are rotated away from the position of heads of the actuator. In contrast, linear vibration, VL, tends to move platters and heads of the actuator together in the same direction such that there is less of a concern about error. However, as the frequency range of disc drive technology has increased, linear vibration has become more of an issue.

FIG. 2illustrates an example of a system200that can be used to measure rotational vibration and linear vibration. The system ofFIG. 2shows vibration sensors204and208. These sensors can be positioned, for example, as they are shown inFIG. 1at the opposite ends of a device. Each sensor includes a sensor element that responds to vibrational forces. One example of a sensor element used by the sensors is a piezoelectric sensor element.

FIG. 2shows that a linear vibration signal, LV, can be generated from a single sensor serving as an input to a charge amplifier circuit214. The charge amplifier circuit214is shown comprised of operational amplifier216and impedance Z2. An input, Vref, can be used as a voltage supply for the sensors in the circuit214and impedance Zrefcan be used to limit the current.

FIG. 2also shows that a rotational vibration signal, RV, can be generated from multiple sensors. InFIG. 2, sensor204serves as an input to a charge amplifier circuit comprised of operational amplifier212and impedance Z1. The sensor204is oriented so that it has the opposite polarity of sensor208. Because of the reversal of the polarity, when an output of the first charge amplifier circuit210and an output of the second charge amplifier circuit214are input into a differential amplifier220(with feedback impedance Z3), the sum rather than the difference of the sensor outputs can be generated. This sum can be used as the rotational vibration signal. Thus, the system shown inFIG. 2shows how separate signals indicative of rotational vibration and linear vibration can be generated using at least two charge amplifier circuits210and214.

Referring now toFIG. 3, a system300is shown in accordance with certain embodiments of the present disclosure. A first vibration sensor circuit302is shown comprised of a sensor304and a capacitor C coupled in series. A second sensor circuit306is shown comprised of sensor308by itself. Outputs of these sensor circuits302and306are shown coupled together. Orientation of the polarity of the sensor circuits is reversed relative to one another. As a result, the magnitude of one of the sensor circuit's outputs is effectively subtracted from the other.FIG. 3also shows a reference voltage Vref and impedance Z1.

As a result of this configuration inFIG. 3, when linear vibration is encountered sensors of equal sensitivity, positioned as shown for example inFIG. 1, would experience the same output. If the gain of sensor circuits302and306were not adjusted, for example by capacitor C inFIG. 3, the coupling of the outputs of sensor circuits302and306together would cause the signals from the two sensors to cancel one another. By adjusting the gains of the two sensor circuits302and306to be different from one another, no complete cancellation takes place—so a combined signal remains to indicate linear vibration.

When rotational vibration is encountered and the sensors304and308are located on opposite sides of the axis of rotation of the rotational vibration, the output signals from the sensors304and308will be out of phase. Thus, the configuration shown inFIG. 3will create a superposition that is effectively an addition of the magnitudes of the signals produced by the two sensor circuits302and306, if the sensors are located on opposite sides of the center of rotation.

The outputs of the two sensor circuits in system300are shown coupled to a charge amplifier circuit310comprised of operational amplifier312and impedance Z2. The output from the charge amplifier circuit310can be input to a bandpass filter circuit314shown comprised of operational amplifier316and impedance Z3and reference voltage Vref. The resulting output from the bandpass filter circuit, Vo, is a signal that represents both linear vibration and rotational vibration.

The use of the capacitor, C, in combination with sensor element304allows the gain of the sensor circuit302comprised of sensor element304and capacitor, C, to be adjusted, relative to the gain of the sensor circuit306that is comprised of sensor308by itself. This is but one way in which the gains of the sensor circuits302and306may be adjusted relative to one another. By adjusting the gain of the sensor circuits302and306to be different from one another, one is able to ensure that the output signal, Vo, contains a component indicative of linear rotation. If two sensor circuits were used, where each had the same gain, the output of the sensors inFIG. 3would cancel one another out for purposes of linear rotation.

As can be seen by comparing the systems ofFIG. 3andFIG. 2, the embodiment shown inFIG. 3saves space and reduces the number of components. The system shown inFIG. 2requires a second charge amplifier as well as supporting components. But a second charge amplifier is not required for the system shown inFIG. 3. Thus, the embodiment ofFIG. 3saves on components, space on a circuit board, and cost in manufacturing. The embodiment inFIG. 3saves the cost of the additional operational amplifier that would be required and also the cost of supporting components that would be required.

FIG. 3also shows that the output signal, Vo, can be processed by an adaptive filter320. An adaptive filter is a filter that self-adjusts its transfer function according to an optimization algorithm driven by an error signal. The implementation of the adaptive filter320can vary in accordance with the desired adjustments for a particular signal. The input signal to the adaptive filter has a signal that includes both a component indicative of rotational vibration and a component indicative of linear vibration.

FIGS. 4 and 5illustrate examples of how the gain of the two vibration sensor circuits can be adjusted. InFIG. 4, two sensors,404and408, are positioned for use at opposite ends of a device in order to detect vibration. The sensors404and408are shown oriented such that they are not in parallel alignment. Parallel alignment should be understood to include co-linear alignment. As a result, respective sensor elements in sensors404and408are also not in parallel alignment. Thus, when the sensors404and408experience linear vibration, outputs from each sensor404and408will be different from the other (assuming the sensors404and408have the same sensitivity to begin with). One example of a sensor element used by the sensors404and408is a piezoelectric sensor element.

FIG. 5shows a different arrangement of sensors. InFIG. 5, sensors504and508are shown. The sensors504and508are shown positioned for use at opposite ends of a device. Each sensor has been selected, however, to have a predetermined gain that is different relative to the other sensor. Thus, sensor508is shown with a gain Av=1.0 and sensor504is shown with a gain Av=1.12. When referring specifically to a sensor device, the gain of the sensor device is sometimes referred to as the “sensitivity” of the sensor device. However, since the sensor device can be combined with other components, the gain of the “sensor circuit” is typically used herein. When the sensors are aligned along the same axis, as shown inFIG. 5, making sure that the sensors do not have the same gain ensures that the linear vibration value, LV, such as that computed inFIG. 2, does not equal zero.

Referring now toFIG. 6, a flow chart600illustrating a method of detecting vibration can be seen. In block604of flow chart600, a combined linear vibration and rotational vibration signal is generated. In block,608, the combined linear vibration and rotational vibration signal is processed with an adaptive filter.

FIGS. 7A and 7Billustrate another embodiment. In flow chart700ofFIGS. 7A and 7B, block704shows that a first vibration sensor circuit may be provided. Similarly, block708shows that a second vibration sensor circuit may be provided. The gain of the first vibration sensor circuit and the gain of the second vibration sensor circuit may be intentionally mismatched, as shown by block712. Thus, the two circuits have predetermined mismatched gains.

Various manners of mismatching the gains of the sensor circuits in response to the same vibrational force may be utilized. For example, block716shows that a capacitor in series with a first vibration sensor element may be utilized as the first vibration sensor circuit. Blocks720and724illustrate that the sensitivity of the two sensors used in the sensor circuits be selected to be different so that the gain of the two sensor circuits is different. And, block728illustrates that the axes of the two sensors could be placed in non-parallel alignment on a device. The non-parallel alignment would cause sensors of the same sensitivity to respond differently to the same vibrational force with respect to their respective outputs.

In block732, the output of the first vibration sensor circuit may be subtracted from the output of the second vibration sensor circuit. This could effectively be accomplished, for example, by wiring the sensor circuits together in parallel but with reversed polarity.

In block736, a single charge amplifier may be used to generate the combined linear vibration and rotational vibration signal. And, in block740, the combined linear vibration and rotational vibration signal may be processed with an adaptive filter. The adaptive filter may then be used as desired to provide feed forward correction to the positioning of an actuator, for example.

Thus, this system may be utilized to provide feed forward correction in response to both linear and rotational vibration forces.

FIG. 8illustrates a plan view of an example disc drive800. The disc drive800includes a base802to which various components of the disc drive800are mounted. A top cover804, shown partially cut away, cooperates with the base802to form an internal, sealed environment for the disc drive in a conventional manner. The components include a spindle motor806that rotates one or more storage medium discs808at a constant high speed. Information is written to and read from tracks on the discs808through the use of an actuator assembly810, which rotates during a seek operation about a bearing shaft assembly812positioned adjacent the discs808. The actuator assembly810includes a plurality of actuator arms814that extend towards the discs808, with one or more flexures816extending from each of the actuator arms814. Mounted at the distal end of each of the flexures816is a head818that includes an air bearing slider enabling the head818to fly in close proximity above the corresponding surface of the associated disc808. The distance between the head818and the storage media surface during flight is referred to as the fly height.

During a seek operation, the track position of the head818is controlled through the use of a voice coil motor (VCM)824, which typically includes a coil826attached to the actuator assembly810, as well as one or more permanent magnets828which establish a magnetic field in which the coil826is immersed. The controlled application of current to the coil826causes magnetic interaction between the permanent magnets828and the coil826. As the coil826moves, the actuator assembly810pivots about the bearing shaft assembly812, and the transducer heads818are caused to move across the surfaces of the discs808.

The spindle motor806is typically de-energized when the disc drive800is not in use for extended periods of time. The transducer heads818are moved away from portions of the disk808containing data when the drive motor is de-energized. The transducer heads818are secured over portions of the disk not containing data through the use of an actuator latch arrangement and/or ramp assembly844, which prevents inadvertent rotation of the actuator assembly810when the drive discs808are not spinning.

A flex assembly830provides the requisite electrical connection paths for the actuator assembly810while allowing pivotal movement of the actuator assembly810during operation. The flex assembly830includes a printed circuit board834to which a flex cable connected with the actuator assembly810and leading to the head818is connected. The flex cable may be routed along the actuator arms814and the flexures816to the transducer heads818. The printed circuit board834typically includes circuitry for controlling the write currents applied to the transducer heads818during a write operation and a preamplifier for amplifying read signals generated by the transducer heads818during a read operation. The flex assembly830terminates at a flex bracket for communication through the base deck802to a disc drive printed circuit board (not shown) mounted to the bottom side of the disc drive800.

The disc drive800also includes two vibration sensors837and836mounted on circuit board834. The sensors836and837could be located at other positions on the device800, as desired.

It is also noted that many of the structures, materials, and acts recited herein can be recited as means for performing a function or step for performing a function. Therefore, it should be understood that such language is entitled to cover all such structures, materials, or acts disclosed within this specification and their equivalents, including any matter incorporated by reference.

It is thought that the apparatuses and methods of embodiments described herein will be understood from this specification. While the above description is a complete description of specific embodiments, the above description should not be taken as limiting the scope of the patent as defined by the claims.

It will be understood that while embodiments have been described in conjunction with specific examples, the foregoing description and examples are intended to illustrate, but not limit the scope of the invention. Other aspects, advantages, and modifications will be apparent to those of ordinary skill in the art to which the claims pertain. The elements and use of the above-described embodiments can be rearranged and combined in manners other than specifically described above, with any and all permutations within the scope of the disclosure.

The implementations described above and other implementations are within the scope of the following claims.