PATENT DOCUMENT

Publication Number: US-10837844-B2
Application Number: US-201816130777-A
Country: US
Kind Code: B2

Title: Haptic engine having a single sensing magnet and multiple hall-effect sensors

Abstract:
A haptic engine for measuring displacement of the haptic engine&#39;s mass uses a single sensing magnet that is carried by the mass along a driving direction. The haptic engine further uses two or more Hall-effect sensors, which are spaced apart (i) from each other along a direction parallel to the driving direction and (ii) from the single sensing magnet along a direction orthogonal to the driving direction, and are disposed adjacent to an ASIC that receives the sensors&#39; output.

Claims:
What is claimed is: 
     
       1. A haptic engine comprising:
 a frame; 
 a driving system comprising
 a first magnet that is coupled with the frame and produces a first magnetic field along a first direction, and 
 a mass supporting a coil, the mass arranged to be driven relative to the frame along a driving direction orthogonal to the first direction when a driving current is being supplied through the coil; and 
 
 a sensing system comprising
 a second magnet that is coupled with the mass and produces a second magnetic field along a second direction orthogonal to the driving direction, and 
 a first Hall-effect sensor coupled with the frame at a first location of the frame, and a second Hall-effect sensor coupled with the frame at a second location of the frame, the second location being separated from the first location along the driving direction, each of the sensors being spaced apart from the second magnet along the second direction and configured to produce a respective Hall voltage signal corresponding to changes of the second magnetic field at the location of the respective one of the sensors caused when driving the mass. 
 
 
     
     
       2. The haptic engine of  claim 1 , wherein the second direction is parallel to the first direction. 
     
     
       3. The haptic engine of  claim 1 , wherein the second direction is orthogonal to the first direction. 
     
     
       4. The haptic engine of  claim 3 , wherein
 the sensing system further comprises a third Hall-effect sensor coupled with the frame at a third location of the frame, the third location being between the first and second locations along the driving direction and laterally offset from it, and 
 the third Hall-effect sensor is configured to produce a third Hall voltage signal corresponding to changes of the second magnetic field at the third location caused when driving the mass. 
 
     
     
       5. The haptic engine of  claim 3 , wherein the sensing system further comprises
 a substrate through which the sensors are coupled with the frame, the substrate including conducting lines, and 
 an ASIC connected to the sensors through the conducting lines to process the respective Hall voltage signals produced by the sensors, the ASIC being disposed on the substrate at a location adjacent to the locations of the sensors. 
 
     
     
       6. The haptic engine of  claim 5 , wherein the frame has
 an aperture within which the sensors and the ASIC are located, and 
 a shield can that covers the aperture to shields the sensors and the ASIC from electromagnetic noise from the environment outside the haptic engine. 
 
     
     
       7. The haptic engine of  claim 3 , wherein the sensing system further comprises
 a substrate through which the sensors are coupled with the frame, and 
 a sensor-integrated ASIC disposed on the substrate, the sensor-integrated ASIC including the sensors and being configured to process the respective Hall voltage signals produced by the sensors. 
 
     
     
       8. The haptic engine of  claim 7 , wherein the frame has
 an aperture within which the sensor-integrated ASIC is located, and 
 a shield plate that covers the aperture to shields the sensor-integrated ASIC from electromagnetic noise from the environment outside the haptic engine. 
 
     
     
       9. The haptic engine of  claim 3 , wherein the mass is shaped like a cage, and the second magnet is coupled with the mass (i) on a side surface of the cage that is parallel to the driving direction and orthogonal to the second direction, and (ii) adjacent to a corner of the cage that is nearest the first and second locations of the frame. 
     
     
       10. The haptic engine of  claim 1 , wherein a gradient of the second magnetic field along the driving direction has a maximum positive value at the first location and a maximum negative value at the second location. 
     
     
       11. The haptic engine of  claim 1 , wherein
 the mass is to be driven along the driving direction over a distance that is smaller than or equal to a separation between the first and second locations, and 
 when the mass is at rest relative to the frame, the second magnet is equally spaced, along the driving direction, from the first Hall-effect sensor and the second Hall-effect sensor. 
 
     
     
       12. A displacement measurement system comprising:
 the haptic engine of  claim 1 ; and 
 a digital signal processor configured to determine tangential displacements of the mass along the driving direction based on the Hall voltage signals produced by the Hall-effect sensors. 
 
     
     
       13. The displacement measurement system of  claim 12 , wherein the digital signal processor is configured to cause supplying, based on the determined tangential displacements, the driving current through the coil. 
     
     
       14. The displacement measurement system of  claim 12 , wherein the digital signal processor is configured to
 obtain, while operating the haptic engine at an operational driving frequency, a difference signal as the difference between the Hall voltage signals, and 
 use the difference signal for determining the tangential displacements. 
 
     
     
       15. The displacement measurement system of  claim 12 , wherein the digital signal processor is configured to
 detect modes of the mass&#39; motion along the second direction, and 
 cause suppressing of the detected modes. 
 
     
     
       16. The displacement measurement system of  claim 15 , wherein the digital signal processor is configured to
 obtain, while operating the haptic engine at an operational driving frequency smaller than a maximum operational frequency, a sum signal as the sum of the Hall voltage signals, 
 obtain a spectrum of the sum signal, and 
 use the spectrum of the sum signal for detecting the modes of the mass&#39; motion along the second direction. 
 
     
     
       17. The displacement measurement system of  claim 16 , wherein the digital signal processor is configured to use for the detecting only a portion of the spectrum that is over frequencies larger than the maximum operational frequency. 
     
     
       18. The displacement measurement system of  claim 16 , wherein the digital signal processor is configured to
 access, in a data store, predetermined frequencies corresponding to the modes of the mass&#39; motion along the second direction for the haptic engine, 
 determine whether the spectrum of the sum signal has spectral features at one or more frequencies that match respective ones of the predetermined frequencies, and if so 
 identify each detected mode based on its matching predetermined frequency. 
 
     
     
       19. The displacement measurement system of  claim 18 , wherein the digital signal processor is configured to
 obtain respective sum signals for multiple driving frequencies lower than the maximum operational frequency, 
 obtain a spectrum for each respective sum signal, 
 identify, using portions of the spectra that are over frequencies larger than the maximum operational frequency, one or more frequencies of spectral features corresponding to respective modes of the mass&#39; motion along the second direction, and 
 store the identified frequencies as the predetermined frequencies for the haptic engine. 
 
     
     
       20. A computing system that includes the displacement measurement system of  claim 12 . 
     
     
       21. The computing system of  claim 20  comprises one of a smartphone, a tablet, a laptop and a watch. 
     
     
       22. A device comprising:
 a haptic interface; 
 a haptic engine coupled with the haptic interface, the haptic engine comprising
 a frame; 
 a first magnet that is coupled with the frame and produces a first magnetic field along a first direction, 
 a mass supporting a coil, the mass arranged to be driven relative to the frame along a driving direction orthogonal to the first direction when a driving current is being supplied through the coil, 
 a second magnet that is coupled with the mass and produces a second magnetic field along a second direction orthogonal to the driving direction, and 
 a first magnetic field sensor coupled with the frame at a first location of the frame, and a second magnetic field sensor coupled with the frame at a second location of the frame, the second location being separated from the first location along the driving direction, each of the sensors being spaced apart from the second magnet along the second direction and configured to produce a respective sensor signal corresponding to changes of the second magnetic field at the location of the respective one of the sensors caused when driving the mass; and 
 
 a digital signal processor communicatively coupled with the haptic engine, the digital signal processor configured to determine tangential displacements of the mass along the driving direction based on the sensor signals produced by the magnetic field sensors. 
 
     
     
       23. The device of  claim 22 , wherein the second direction is parallel to the first direction. 
     
     
       24. The device of  claim 22 , wherein the second direction is orthogonal to the first direction. 
     
     
       25. The device of  claim 24 , wherein the mass is shaped like a cage, and the second magnet is coupled with the mass (i) on a side surface of the cage that is parallel to the driving direction and orthogonal to the second direction, and (ii) adjacent to a corner of the cage that is nearest the first and second locations of the frame. 
     
     
       26. The device of  claim 22 , wherein the magnetic field sensors are Hall-effect sensors. 
     
     
       27. The device of  claim 22 , further comprising
 a driver module coupled with the digital signal processor and the haptic engine, the driver module configured to supply, based on the determined tangential displacements, the driving current through the coil. 
 
     
     
       28. The device of  claim 22  is a smartphone, a tablet, a laptop and a watch.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This disclosure claims the benefit of the priority of U.S. Provisional Patent Application No. 62/560,130, filed on Sep. 18, 2017. The above-identified application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     This specification relates generally to haptic engine architectures, and more specifically, to a haptic engine in which a single sensing magnet carried by the engine&#39;s moving mass between two or more Hall-effect sensors provides a varying magnetic field used for sensing the motion of the mass. 
     Background 
     A haptic engine (also referred to as a vibration module) is a linear resonant actuator that determines one of acceleration, velocity and displacement of a moving mass.  FIG. 11A  shows a plan view, e.g., in the (x,y)-plane, and  FIG. 11B  shows a cross-section view, in the (x,z)-plane, of a conventional haptic engine that has a frame, one or more magnets affixed to the frame, and a mass arranged to move inside the frame. Here, the mass includes a stainless steel or tungsten cage that holds one or more coils corresponding to the static magnets. The mass further includes an array of two or more sensing magnets that are attached to the cage to form, along the x-axis, a row in which adjacent sensing magnets have opposing polarities. The conventional haptic engine further includes a flexible printed circuit (FPC) that holds a pair of Hall-effect sensors, HES 1  and HES 2 , and an application-specific integrated circuit (ASIC) coupled through electrical conductors of the FPC with the HES 1  and HES 2 . In the example illustrated in  FIG. 11A , the ASIC is encapsulated in a shield can, and the FPC folds up, out-of-page and parallel to the (x,z) plane. The HES 1  and HES 2  are (i) spaced apart from the sensing magnets along the z-axis, and (ii) disposed within the magnetic field provided by the array of sensing magnets. As such, a displacement of the mass of the conventional haptic engine, when the mass is vibrated along the x-axis, is encoded in the magnetic field provided by the array of sensing magnets. The HES 1  and HES 2  output voltage signals V H     1    and V H     2    to be used by a processor to determine the mass&#39; displacement ΔX along the x-axis and the mass&#39; displacement ΔZ along the z-axis as:
 
Δ X∝V   H     1     +V   H     2     (1),
 
Δ Z∝V   H     1     −V   H     2     (2).
 
     For example, for a separation between HES 1  and HES 2  of X H  and for a mass range of motion of ±X 0 , the requirements that (i) the array of sensing magnets has a size along the x-axis that is at least 4X 0 +2X H , while (ii) the array of sensing magnets must be spaced apart from the static magnets, e.g., by a minimum separation X MS , to avoid interaction with the static magnets, can lead to challenging size constraints for the conventional haptic engine. Moreover, the FPC used by the conventional haptic engine tends to have a large area and complicated electrical routing that allows for the HES 1  and HES 2  to be placed near the array of sensing magnets along the y-axis. All of these considerations lead to increased engine material cost. 
     Although the conventional haptic engine can sense both the X travel and the Z travel of the mass, yaw modes cannot be reliably sensed unless the sensing magnets are very narrow in the y-axis direction. Using sensing magnets with such an aspect ratio can be a reliability concern especially when the engine is dropped and the moving mass assembly is permanently shifted in the y-axis direction due to plastic deformation of the mechanical flexures. The ability to sense engine modes in the X-Y plane, such as the yaw mode, is critical in engine design because these modes are difficult to damp and is a dominant source of acoustic noise. This is applicable to all resonant actuators with a suspended mass assembly. 
     SUMMARY 
     This specification describes technologies for measuring displacement of a mass of a haptic engine by using a sensing geometry in which a single sensing magnet is carried by the mass along a driving direction. Two or more Hall-effect sensors, which are spaced apart (i) from each other along a direction parallel to the driving direction and (ii) from the single sensing magnet along a direction orthogonal to the driving direction, are disposed adjacent to an ASIC that receives the sensors&#39; output. 
     In general, one innovative aspect of the subject matter described in this specification can be embodied in a haptic engine that includes (a) a frame; (b) a driving system including (i) a first magnet that is coupled with the frame and produces a first magnetic field along a first direction, and (ii) a mass supporting a coil, the mass arranged to be driven relative to the frame along a driving direction orthogonal to the first direction when a driving current is being supplied through the coil; and (c) a sensing system comprising (i) a second magnet that is coupled with the mass and produces a second magnetic field along a second direction orthogonal to the driving direction, and (ii) a first Hall-effect sensor coupled with the frame at a first location of the frame, and a second Hall-effect sensor coupled with the frame at a second location of the frame, the second location being separated from the first location along the driving direction, each of the sensors being spaced apart from the second magnet along the second direction and configured to produce a respective Hall voltage signal corresponding to changes of the second magnetic field at the location of the respective one of the sensors caused when driving the mass. 
     Other embodiments of this aspect include corresponding displacement measuring systems, and computing devices, each configured to perform the actions performed by the disclosed haptic engine. For a system or a device to be configured to perform particular operations or actions means that the system or the device has installed on it software, firmware, hardware, or a combination of them that in operation cause the system or the device to perform the operations or actions. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one implementation includes all the following features in combination. In some implementations, the second direction can be parallel to the first direction. 
     In some implementations, the second direction can be orthogonal to the first direction. In some cases, the sensing system can include a third Hall-effect sensor coupled with the frame at a third location of the frame, the third location being between the first and second locations along the driving direction and laterally offset from it; and the third Hall-effect sensor is configured to produce a third Hall voltage signal corresponding to changes of the second magnetic field at the third location caused when driving the mass. In some cases, the sensing system can include (i) a substrate through which the sensors are coupled with the frame, the substrate including conducting lines; and (ii) an ASIC connected to the sensors through the conducting lines to process the respective Hall voltage signals produced by the sensors, the ASIC being disposed on the substrate at a location adjacent to the locations of the sensors. Here, the frame can have (i) an aperture within which the sensors and the ASIC are located, and (ii) a shield can that covers the aperture to shields the sensors and the ASIC from electromagnetic noise from the environment outside the haptic module. In some cases, the sensing system can include (i) a substrate through which the sensors are coupled with the frame, and (ii) a sensor-integrated ASIC disposed on the substrate, the sensor-integrated ASIC including the sensors and being configured to process the respective Hall voltage signals produced by the sensors. Here, the frame can have (i) an aperture within which the sensor-integrated ASIC is located, and (ii) a shield plate that covers the aperture to shields the sensor-integrated ASIC from electromagnetic noise from the environment outside the haptic module. In some cases, the mass can be shaped like a cage, and the second magnet is coupled with the mass (i) on a side surface of the cage that is parallel to the driving direction and orthogonal to the second direction, and (ii) adjacent to a corner of the cage that is nearest the first and second locations of the frame. 
     In some implementations, a gradient of the second magnetic field along the driving direction has a maximum positive value at the first location and a maximum negative value at the second location. In some implementations, the mass can be driven along the driving direction over a distance that is smaller than or equal to the separation between the first and second locations, and when the mass is at rest relative to the frame, the second magnet is equally spaced, along the driving direction, from the first Hall-effect sensor and the second Hall-effect sensor. 
     In some implementations, a displacement measurement system can include the above-noted haptic engine, and a digital signal processor configured to determine tangential displacements of the mass along the driving direction based on the Hall voltage signals produced by the Hall-effect sensors. In some cases, the digital signal processor can be configured to cause supplying, based on the determined tangential displacements, the driving current through the coil. In some cases, the digital signal processor can be configured to (i) obtain, while operating the haptic engine at an operational driving frequency, a difference signal as the difference between the Hall voltage signals, and (ii) use the difference signal for determining the tangential displacements. 
     In some cases, the digital signal processor can be configured to (i) detect modes of the mass&#39; motion along the second direction, and (ii) cause suppressing of the detected modes. For example, the digital signal processor can be configured to (i) obtain, while operating the haptic engine at an operational driving frequency smaller than a maximum operational frequency, a sum signal as the sum of the Hall voltage signals, (ii) obtain a spectrum of the sum signal, and (iii) use the spectrum of the sum signal for detecting the modes of the mass&#39; motion along the second direction. Here, the digital signal processor can be configured to use for the detecting only a portion of the spectrum that is over frequencies larger than the maximum operational frequency. Also here, the digital signal processor can be configured to (i) access, in a data store, predetermined frequencies corresponding to the modes of the mass&#39; motion along the second direction for the haptic engine, (ii) determine whether the spectrum of the sum signal has spectral features at one or more frequencies that match respective ones of the predetermined frequencies, and if so (iii) identify each detected mode based on its matching predetermined frequency. For example, the digital signal processor can be configured to (i) obtain respective sum signals for multiple driving frequencies lower than the maximum operational frequency, (ii) obtain a spectrum for each respective sum signal, (iii) identify, using portions of the spectra that are over frequencies larger than the maximum operational frequency, one or more frequencies of spectral features corresponding to respective modes of the mass&#39; motion along the second direction, and (iv) store the identified frequencies as the predetermined frequencies for the haptic engine. 
     In some implementations, a computing system can include the above-noted displacement system. For instance, the computing system can be one of a smartphone, a tablet, a laptop and a watch. 
     Another innovative aspect of the subject matter described in this specification can be embodied in a device that includes (a) a haptic interface; (b) a haptic engine coupled with the haptic interface, the haptic engine including (i) a frame; (ii) a first magnet that is coupled with the frame and produces a first magnetic field along a first direction, (iii) a mass supporting a coil, the mass arranged to be driven relative to the frame along a driving direction orthogonal to the first direction when a driving current is being supplied through the coil, (iv) a second magnet that is coupled with the mass and produces a second magnetic field along a second direction orthogonal to the driving direction, and (v) a first magnetic field sensor coupled with the frame at a first location of the frame, and a second magnetic field sensor coupled with the frame at a second location of the frame, the second location being separated from the first location along the driving direction, each of the sensors being spaced apart from the second magnet along the second direction and configured to produce a respective sensor signal corresponding to changes of the second magnetic field at the location of the respective one of the sensors caused when driving the mass; and (c) a digital signal processor communicatively coupled with the haptic engine, the digital signal processor configured to determine tangential displacements of the mass along the driving direction based on the sensor signals produced by the magnetic field sensors. 
     Implementations can include one or more of the following features. In some implementations, the above-noted device can include a driver module coupled with the digital signal processor and the haptic engine, the driver module configured to supply, based on the determined tangential displacements, the driving current through the coil. In some implementations, the above-noted device can be a smartphone, a tablet, a laptop and a watch. In some implementations, the magnetic field sensors can be Hall-effect sensors. 
     In some implementations, the second direction can be parallel to the first direction. In some implementations, the second direction can be orthogonal to the first direction. Here, the mass can be shaped like a cage, and the second magnet is coupled with the mass (i) on a side surface of the cage that is parallel to the driving direction and orthogonal to the second direction, and (ii) adjacent to a corner of the cage that is nearest the first and second locations of the frame. 
     The subject matter described in this specification can be implemented in particular embodiments so as to realize one or more of the following advantages. For example, the area of the FPC used to implement the disclosed technologies can be significantly reduced relative to the FPC used to implement the above-noted conventional haptic engine. As such, reductions in the FPC&#39;s cost, and improvements in the FPC&#39;s manufacturability also are possible. 
     As another example, the disclosed technologies enable that yaw, Y, and Z modes can be sensed, in addition to the X mode. This is possible because of the arrangement of the single sensing magnet ensures the Hall-effect sensors always experience non-zero sensing-flux produced by the single sensing magnet. Any sensing-flux variation caused by non-X mode motion can therefore be decoupled and sensed. As the disclosed haptic engine can detect unwanted yaw modes, it can be configured to proactively damp the yaw modes by using active electronic damping of the unwanted modes. Additionally, the sensing magnet can be disposed closer to the static magnets of the haptic engine without compromising the sensitivity of the displacement measurements performed by the haptic engine, because the sensing magnetic field oriented in the (x,y) plane does not couple with the driving magnetic field provided by the static magnets in a plane (x,z) perpendicular to the plane of motion (x,y). The closer proximity between the sensing magnet and the static magnets allows for reductions in the size of the haptic engine. 
     As yet another example, due to the Hall sensor placement relative to the geometry of the disclosed haptic engine, the sensing magnet is small compared to maximum X travel. This is in contrast with the conventional haptic engine in which the array of sensing magnets is extended over the entire maximum X travel. As yet another example, the Hall sensors are placed adjacent to the controlling ASIC. The Hall sensors&#39; close proximity to the ASIC improves routing and signal integrity. It also gives an opportunity to integrate the Hall sensors into future designs of the ASIC itself. 
     The details of one or more embodiments of the subject matter of this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1B  show aspects of a first example of a haptic engine. 
         FIG. 1C  shows an example of a displacement measurement system that includes a haptic engine. 
         FIGS. 2A-2B  show aspects of a second example of a haptic engine. 
         FIGS. 3A-3B, 4 and 5  show respective examples of a transducer sub-system that can be used to replace the transducer system of the haptic engine shown in  FIG. 2A . 
         FIGS. 6A-6B  show aspects of a sensing system that can be used in either of the haptic engines shown in  FIGS. 1A-1B  and  FIGS. 2A-2B . 
         FIG. 7  shows a process for identifying unwanted vibration modes induced in a haptic engine like the ones shown in  FIGS. 1A-1B  and  FIGS. 2A-2B  and for damping the identified modes. 
         FIGS. 8A-8D  show results of identifying unwanted vibration modes. 
         FIGS. 9A-9B  show results of correcting displacement signals produced by a haptic engine like the ones shown in  FIGS. 1A-1B  and  FIGS. 2A-2B . 
         FIG. 10  an example mobile device architecture that uses a haptic engine as the ones described in reference to  FIG. 1-9 , according to an embodiment. 
         FIGS. 11A-11B  show aspects of a conventional haptic engine. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1A  is a plan view, e.g., in the (x,y)-plane, and  FIG. 1B  is a cross-section view, in the (x,z)-plane, of an example of a haptic engine  100  that includes a sensing system  105  with a single sensing magnet  114  and a pair of Hall-effect sensors  108 A,  108 B. The haptic engine  100  has a frame  102  and further includes a driving system  101  and a mass  110  that are enclosed inside the frame. 
     The driving system  101  includes a stationary part and a moving part. In the example illustrated in  FIGS. 1A-1B , the moving part includes a pair of coils  112 , each of which being formed from a winding parallel to the (x,y)-plane. Moreover, the mass  110  is implemented as a cage (e.g., made from steel or tungsten) having enclosures configured to hold the coils  112 . In the example illustrated in  FIG. 1A , the cage is constrained to move along the driving direction by using flexures  109 A,  109 B. In this manner, the moving part of the driving system  101  will be carried by the mass  110 , e.g., when the mass is driven along a driving direction, here the x-axis. The stationary part of the driving system  101  includes a pair of magnetic plates  104  affixed to the opposing side surfaces of the frame  102  that are parallel to the (x,y)-plane. As such, the cage is sandwiched along the z-axis by the magnetic plates  104 . Each of the magnetic plates  104  is formed from magnetic tiles that are distributed across the (x,y)-plane to produce, inside the cage, a magnetic field B Z  oriented along the z-axis, orthogonal to the driving direction. More specifically, for each coil held by the cage, the magnetic plates  104  produce the magnetic field B Z  that is parallel to the z-axis over a half of the coil winding, and anti-parallel to the z-axis over the other half of the coil winding. A power source (not shown in  FIGS. 1A-1B ) supplies to the coils  112  currents having opposite circulations. For instance, when a counter-clockwise current is supplied to one of the coils  112 , a clockwise current is supplied to the other one of the coils. As such, for the configuration of the magnetic field B Z  produced by the magnetic plates  104  and at a time instance when the current circulation in the coils  112  is as illustrated in  FIG. 1B , the coils experience a Lorentz force anti-parallel to the x-axis (i.e., to the left of the page) and will move, along with the mass  110 , in that direction. In this manner, as the power source supplies alternating currents of opposite circulations to the coils  112 , a periodic Lorentz force will drive, along the x-axis, the mass  110 , which includes the coils. An amplitude and a frequency of the displacement ΔX of the mass  110  along the driving direction depend from the amplitude and the frequency of the alternating currents supplied to the coils  112 . 
     In the example illustrated in  FIGS. 1A-1B , the sensing system  105  includes a flexible printed circuit (FPC)  106  that is affixed to one of the side surfaces of the frame  102  parallel to the (x,y)-plane. The Hall-effect sensors  108 A,  108 B are mounted on the FPC  106  at locations X A , X B  that are separated from each other, along the x-axis, by a separation of the order of a maximum X travel. Here, the maximum X travel is the maximum distance 2X 0  that the mass  110  is expected to travel when driven by the driving system  101  between coordinates ±X 0  along the x-axis. The sensing system  105  further includes an ASIC  122  mounted on the FPC  106  and electrically coupled with the Hall-effect sensors  108 A,  108 B through conducting lines of the FPC. In the example illustrated in  FIG. 1A , the FPC  106  extends through a slot  103  of the frame  102 . Here, the portion of the FPC  106  that is outside of the frame  102  folds along a side surface of the frame that is parallel to the (x,z)-plane. Moreover, a ferretic shield can  124  encompasses the slot  103  and the ASIC  122  to shield the interior of the frame  102  and the ASIC from electromagnetic noise and magnetic coupling from the environment outside the haptic module  100 . 
     The sensing magnet  114  of the sensing system  105  is affixed to one of the side surfaces of the mass  110  parallel to the (x,y)-plane that faces the Hall-effect sensors  108 A,  108 B. As the mass  110  is implemented as a cage, the sensing magnet  114  can be held in an enclosure of the cage or in a recess of the side surface of the cage, or can be attached on the cage&#39;s side surface itself. In this manner, the sensing magnet  114  of the sensing system  105  illustrated in  FIGS. 1A-1B  produces a sensing magnetic field B oriented along the z-axis, i.e., along a direction that is orthogonal to the driving direction and parallel to the direction of the magnetic field B Z  produced by the stationary part of the driving system  101 . A profile B(X) along the x-axis of the sensing magnetic field B corresponds to the profile of a single magnet, as described below in connection with  FIGS. 6A-6B . Moreover, when the mass  110  is at rest, the sensing magnet  114 &#39;s location is equally spaced, along the driving direction, here the x-axis, from the locations X A , X B  of the Hall-effect sensors  108 A,  108 B. As the mass  110  is being driven by the driving system  101  along the x-axis, the Hall-effect sensors  108 A,  108 B will sense changes in the sensing magnetic field B produced by the sensing magnet  114  as the sensing magnet is being carried by the mass. Hall voltage signals V H     1   , V H     2   , that are output by the Hall-effect sensors  108 A,  108 B in response to the changes in the sensing magnetic field B, are provided by the haptic engine  100  to a digital signal processor to (i) determine the displacement ΔX of the mass  110 , and (ii) detect the mass&#39; unwanted displacements ΔZ, ΔY and ΔΦ, as described below in connection with  FIGS. 6A-6B . 
       FIG. 1C  shows a displacement measurement system  150  that includes the haptic engine  100  and a computing module  155  coupled to the haptic engine through a sensing channel  152 . The computing module  155  includes the above-noted digital signal processor, which uses the Hall voltage signals V H     1   , V H     2    output by the Hall-effect sensors  108 A,  108 B, to (i) determine the displacement ΔX of the mass  110 , and (ii) detect the mass&#39; unwanted displacements ΔZ, ΔY and ΔΦ. In some implementations, when the computing module  155  receives the Hall voltage signals V H     1   , V H     2    as analog signals, the computing module includes analog-to-digital converters (ADCs) to digitize the received analog signals, so the digital signal processor uses the digitized Hall voltage signals V H     1   , V H     2    for calculating the mass displacement(s). In other implementations, the ASIC  122  of the haptic engine  100  digitizes the Hall voltage signals V H     1   , V H     2    prior to transmitting them to the computing module  155  over the sensing channel. In this manner, the calculated mass displacements ΔX and/or the detected mass&#39; unwanted displacements ΔZ, ΔY and ΔΦ can be provided by the displacement measurement system  150  to a driver module  170 , which in turn suitably uses the provided information to control the driving system  101  of the haptic engine  100 . Alternatively or additionally, the mass displacements ΔX and/or the mass&#39; unwanted displacements ΔZ, ΔY and ΔΦ can be provided by the displacement measurement system  150  for display or storage to a presentation/storage module  160 . Moreover, the displacement measurement system  150  can be integrated in a computing device  180 , e.g., in a smartphone, tablet, watch or any other electronic device that uses an LRA module for haptic feedback, either by itself or along with one or both of the driver module  170  and the presentation/storage module  160 . 
     Referring again to  FIGS. 1A-1B , note that as the sensing magnetic field B is parallel to the magnetic field B Z  produced by the static magnetic plates  104 , the magnetic fields B and B Z  will interact and their interaction causes mechanical motion along the z-axis, which in turn can produce undesirable acoustic noise. This motion can be stronger for cases when the separation X A −X B  is comparable to a distance X MS  (between the static magnetic plates  104  and the Hall-effect sensors) then for cases when the distance X MS  is large compared to the separation X A −X B . Instead of increasing the distance X MS  to reduce the interaction between the parallel magnetic fields B and B Z , a new geometry of the haptic engine is described below, in which the magnetic fields B and B Z  are orthogonal, so their interaction can be substantially eliminated, for any distance X MS . Such a geometry of the haptic engine, that enables further miniaturization thereof, is described below in connection with  FIGS. 2A-2B . 
       FIG. 2A  is a plan view, e.g., in the (x,y)-plane, of another example of a haptic engine  200  that includes a sensing system  205  with a single sensing magnet  214  and a pair of Hall-effect sensors  208 A,  208 B. Note that the haptic engine  200  can be used in the displacement measurement system  150  in conjunction with, or instead of, the haptic engine  100 . The haptic engine  200  has a frame  202  and further includes a driving system  201  and a mass  210  that are enclosed inside the frame. The driving system  201  is implemented, and therefor functions, as the driving system  101  described above in connection with  FIGS. 1A-1B . For example, the coils  212  of the moving part of the driving system  201  correspond to the coils  112  of the moving part of the driving system  101 . The mass  210  is implemented as a cage that holds the coils  212  and carries them when the mass is driven along a driving direction, here the x-axis, as described for the mass  110  and the corresponding components of the driving system  101 . Here, the cage is constrained to move along the driving direction by using flexures  209 A,  209 B. Although not shown in  FIG. 2A , the stationary part of the driving system  201  is implemented, and therefore functions, as the stationary part of the driving system  101  described above in connection with  FIGS. 1A-1B . As such, the stationary part of the driving system  201  produces, inside the cage, a magnetic field B Z  oriented along the z-axis (out of page), orthogonal to the driving direction. In this manner, as a power source (not shown in  FIG. 2A ) supplies alternating currents of opposite circulations to the coils  212 , a periodic Lorentz force will drive, along the x-axis, the mass  210 , which includes the coils. 
     In the example illustrated in  FIG. 2A , the sensing system  205  includes an FPC  206  that is affixed to one of the side surfaces of the frame  202  parallel to the (x,z)-plane. The Hall-effect sensors  208 A,  208 B are mounted on the FPC  206  at locations X A , X B  that are separated from each other, along the x-axis, by a separation of the order of a maximum X travel 2X 0 . The sensing system  205  further includes an ASIC  222  mounted on the FPC  206  and electrically coupled with the Hall-effect sensors  208 A,  208 B through conducting lines of the FPC. In the example illustrated in  FIG. 2A , the FPC  206  is disposed outside of the frame  202 , and the locations X A , X B  of the Hall-effect sensors  208 A,  208 B are within a slot  203  of the frame. As further illustrated in  FIG. 2B , the locations X A , X B  of the Hall-effect sensors  208 A,  208 B are adjacent to a location of the ASIC  222  on the FPC  206 . This allows for a transducer sub-system  207 , which includes the Hall-effect sensors  208 A,  208 B and the ASIC  222 , to be more compact than a corresponding transducer sub-system of the sensing system  105 . Note that for the transducer sub-system of the sensing system  105 , the ASIC  122  is not disposed adjacent to the Hall-effect sensors  108 A,  108 B. Accordingly, routing and signal integrity will be increased for the transducer sub-system  207  relative to the corresponding to corresponding transducer sub-system of the sensing system  105 . Moreover, a shield can  224  encompasses the slot  203  and the transducer sub-system  207  to shield the interior of the frame  202  and the components of the transducer sub-system from electromagnetic noise and magnetic coupling from the environment outside the haptic module  200 . 
     Referring again to  FIG. 2A , the sensing magnet  214  of the sensing system  205  is affixed to one of the side surfaces of the mass  210  parallel to the (x,z)-plane that faces the Hall-effect sensors  208 A,  208 B through the slot  203 . As the mass  210  is implemented as a cage, the sensing magnet  214  can be held in an enclosure of the cage or in a recess of the side surface of the cage, or can be attached on the cage&#39;s side surface itself. In this manner, the sensing magnet  214  of the sensing system  205  illustrated in  FIG. 2A  produces a sensing magnetic field B oriented along the y-axis, i.e., along a direction that is orthogonal to the driving direction and orthogonal to the direction of the magnetic field B Z  produced by the stationary part of the driving system  201 . A profile B(X) along the x-axis of the sensing magnetic field B corresponds to the profile of a single magnet, as described below in connection with  FIGS. 6A-6B . Moreover, when the mass  210  is at rest, the sensing magnet  214 &#39;s location is equally spaced, along the driving direction, here the x-axis, from the locations X A , X B  of the Hall-effect sensors  208 A,  208 B. As the mass  210  is being driven by the driving system  201  along the x-axis, the Hall-effect sensors  208 A,  208 B will sense changes in the sensing magnetic field B produced by the sensing magnet  214  as the sensing magnet is being carried by the mass. Hall voltage signals V H     1   , V H     2   , that are output by the Hall-effect sensors  208 A,  208 B in response to the changes in the sensing magnetic field B, are provided by the haptic engine  200  to a digital processor (e.g., of the computing module  155 ) to (i) determine the displacement ΔX of the mass  210 , and (ii) detect the mass&#39; unwanted displacements ΔZ, ΔY and ΔΦ, as described below in connection with  FIGS. 6A-6B . 
     Note that as the sensing magnetic field B is orthogonal to the magnetic field B Z  produced by the stationary part of the driving system  201 , the magnetic fields B and B Z  will not interact, or will do so only minimally. Accordingly, the Hall voltage signals V H     1   , V H     2    output by the Hall-effect sensors  208 A,  208 B will be less noisy than the ones output by the Hall-effect sensors  108 A,  108 B of the sensing system  105 . 
     In some implementations, displacements of the mass of a haptic engine along a direction orthogonal to the driving direction, e.g., the displacements ΔY of mass  110  along the y-axis or the displacements ΔZ of the mass  210  along the z-axis, can be determined simultaneously to the determining of displacements along the driving direction, e.g., the displacements ΔX along the x-axis, by adding one or more additional Hall-effect sensors to the sensing system of the haptic engine, as described below in connection with  FIGS. 3A-3B . 
       FIG. 3A  is a plan view, e.g., in the (x,z)-plane, of an example of a transducer sub-system  307 A, and  FIG. 3B  is a plan view, e.g., in the (x,z)-plane, of another example of a transducer sub-system  307 B, either of which can replace the transducer sub-system  207  of the haptic system  200  to simultaneously sense Z modes in addition to X, Y and/or Φ modes.  FIG. 3A  shows that the transducer sub-system  307 A includes an FPC  306 A, Hall-effect sensors  308 A,  308 B,  308 C and an ASIC  322  mounted on the FPC. The Hall-effect sensors  308 A,  308 B,  308 C are located on the FPC  306 A to have spatial separation along the z-axis, such that  308 C is offset along the z-axis from a line parallel to the x-axis along which  308 A,  308 B are located. Note that when the mass  210  is at rest, the sensing magnet  214 &#39;s location coincides with the center of the smallest rectangle that bounds the Hall-effect sensors  308 A,  308 B,  308 C. The ASIC  322  is disposed at a location adjacent to the locations of  308 A,  308 B,  308 C on the FPC  306  making the transducer sub-system  307 A compact within the (x,z)-plane. A shield can  324 A is used to shield the components of the transducer sub-system  307 A from electromagnetic noise and magnetic coupling from the environment outside the haptic module  200 . 
     The compact arrangement of the transducer sub-system  307 A can be made even more compact in the (x,z)-plane, as exemplified by the transducer sub-system  307 B.  FIG. 3B  shows that the transducer sub-system  307 B includes an ASIC  323  with CMOS integrated Hall-effect sensors  309 A,  309 B,  309 C, and an FPC  306 B onto which the ASIC has been mounted. The spatial arrangement of the CMOS integrated Hall-effect sensors  309 A,  309 B,  309 C on the ASIC  323  is similar to, but smaller in area than, the spatial arrangement of the Hall-effect sensors  308 A,  308 B,  308 C of the transducer sub-system  307 A. Also, when the mass  210  is at rest, the sensing magnet  214 &#39;s location coincides with the center of the smallest rectangle that bounds the Hall-effect sensors  309 A,  309 B,  309 C on the ASIC  323 . A shield can  324 B, that has a smaller extent in the (x,z)-plane than the shield can  324 A, is used to shield the components of the transducer sub-system  307 B from electromagnetic noise from the environment outside the haptic module  200 . 
     Referring again to  FIGS. 2A-2B , note that the Hall-effect sensors  208 A,  208 B of the transducer sub-system  207  are mounted adjacent to the ASIC  222  on the FPC  206 . In  FIG. 4 , another example of a transducer sub-system  407  includes an FPC  406 , Hall-effect sensors  408 A,  408 B mounted on the FPC within the slot  403  of the frame  402 , and an ASIC  422  mounted on the opposing side of the FPC from the sensors. In this manner, the transducer sub-system  407  is more compact in the (x,z)-plane than the transducer sub-system  207 . Also, a shield can  424 , that has a smaller extent in the (x,z)-plane than the shield can  224 , is used to shield the components of the transducer sub-system  407  from electromagnetic noise from the environment outside the haptic module  200 . 
     Note that the transducer sub-system  407  protrudes, along the y-axis, from the frame  202  of the haptic engine  200  (because the ASIC  422 , which is mounted on the side of the FPC  406  opposing the slot  403 , has a finite thickness), and is covered by the shield can  424  that has a finite height along the y-axis (so it can encompass the ASIC). The shield can  424  could be replace with a flat shield plate if the ASIC were mounted on the same side with the sensors. In order to keep the transducer sub-system compact in the (x,z)-plane and remove the shield can, another example of transducer sub-system  507  is proposed, as shown in  FIG. 5 . In  FIG. 5 , the transducer sub-system  407  includes an ASIC  523  with CMOS integrated Hall-effect sensors, and an FPC  506  onto which the ASIC has been mounted. In this manner, the transducer sub-system  507  is about as compact in the (x,z)-plane as the transducer sub-system  407 . However, the transducer sub-system  507  uses a flat shield plate  525 , which has a protrusion along the y-axis from the frame  506  that is smaller than the height of any of the previously described shield cans. The shield plate  525  shields the components of the transducer sub-system  507  from electromagnetic noise and magnetic coupling from the environment outside the haptic module  200 . In this manner, when the example of transducer sub-system  507  is used in conjunction with the haptic engine  200 , the frame  202  can have matchbox shape, as the height of the shield has been reduced to substantially zero. 
       FIG. 6A  and  FIG. 6B  show aspects of a sensing magnetic field B produced by a sensing magnet ( 114 ;  214 ) that is used in conjunction with a pair of Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B) in a sensing system ( 105 ;  205 ) of a haptic engine ( 100 ;  200 ).  FIG. 6B  shows that the sensing magnet ( 114 ,  214 ) is spaced apart, along the z-axis, from the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B), and produces the sensing magnetic field B having field lines characteristic to a single magnet polarized along the z-axis. The first Hall-effect sensor ( 108 A;  208 A) is located at X A , and the second Hall-effect sensor ( 108 B;  208 B) is located at X B . Here, the sensor locations X A , X B  are fixed relative to a frame ( 102 ;  202 ) of the haptic engine ( 100 ;  200 ), and are equally spaced from X=0. The sensing magnet ( 114 ;  214 ) is attached to a mass ( 110 ;  210 ) of the haptic engine ( 100 ;  200 ). When the mass ( 110 ;  210 ) is not being driven, the sensing magnet ( 114 ;  214 ) is at rest relative to the frame ( 102 ;  202 ) at X=0. The maximum X travel of the sensing magnet ( 114 ,  214 ) is defined by the center-to-center distance between the Hall-effect sensors  208 A and  208 B. 
       FIG. 6A  shows a profile B(X)  602  along the x-axis (blue curve) of the sensing field B, when the sensing magnet ( 114 ;  214 ) is located at X=0. Note that the sensing magnet  214  is sized to provide best sensitivity, e.g., to produce a gradient dB/dX of BZ(X)  602  that has largest magnitude, at each of the sites X A , X B  of the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B). Note that the representation of the profile B(X)  602  will be shifted left-and-right, in  FIG. 6A , as the mass ( 110 ;  210 ) of the haptic engine ( 100 ;  200 ), which carries the sensing magnet ( 114 ;  214 ), is driven left-and-right along the x-axis. 
       FIG. 6A  further shows a first Hall-voltage signal V H     1      604  output by the first Hall-effect sensor ( 108 A;  208 A) located at X A , and a second Hall-voltage signal V H     2      606  output by the second Hall-effect sensor ( 108 B;  208 B) located at X B , when the sensing magnet ( 114 ;  214 ) moves left-and-right along with the driven mass ( 110 ;  210 ). Note that the first Hall-voltage signal V H     1      604  has a maximum value and the second Hall-voltage signal V H     2      606  has a minimum value when the sensing magnet ( 114 ;  214 ) is above the second Hall-effect sensor ( 108 B;  208 B); and the first Hall-voltage signal V H     1      604  has a minimum value and the second Hall-voltage signal V H     2      606  has a maximum value when the sensing magnet ( 114 ;  214 ) is above the first Hall-effect sensor ( 108 A;  208 A). 
     The sensing system ( 105 ,  205 ) senses the X travel of the mass ( 110 ;  210 ) using a difference signal  615  shown in  FIG. 6A  as the difference between the first Hall-voltage signal V H     1      604  and the second Hall-voltage signal V H     2      606 . By using the difference signal  615 , which has a slope steeper than the slope of each of the individual Hall-voltage signals  604 ,  606 , the size along the x-axis of the single sensing magnet ( 114 ;  214 ) can be reduced relative to the size of the array of sensing magnets of the conventional haptic engine. That allows for a smaller separation between the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B) to the magnetic plates ( 104 ) of the haptic engine ( 100 ,  200 ). As such, for the same distance between the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B) and the magnetic plates ( 104 ) of the haptic engine ( 100 ,  200 ), the sensing magnet ( 114 ;  214 ) is further away from the magnetic plates ( 104 ) compared to that of the conventional haptic engine. Thus, the interaction between the magnetic plates and the sensing magnet ( 114 ;  214 ) can be beneficially reduced compared to that of the conventional haptic engine because the sensing magnet now vibrates at an effectively large distance along the x-axis relative to the magnetic plates. 
     Note that, concurrently to sensing the X travel of the mass ( 110 ;  210 ) based on the difference signal  615 , the sum signal  625  of the first Hall-voltage signal V H     1      604  and the second Hall-voltage signal V H     2      606  can be used to sense travel of the mass along a direction parallel to the separation between a plane of the X travel (in which the motion of the sensing magnet ( 114 ;  214 ) takes place) and the sensing plane (that includes the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B)). With reference to  FIGS. 6A and 1A-1B , for the haptic engine  100 , in which the plane of the X travel and the sensing plane are spaced apart along the z-axis, the sum signal  625  can be used to sense Z travel of the mass  110 . Here, the sum signal  625  increases (decreases) when the mass  110  carrying the sensing magnet  114  moves along the z-axis closer to (farther from) the Hall-effect sensors  108 A and  108 B. 
     In some implementations of the haptic engine  100 , the motion of its mass  110  along the z-axis can be constrained by using a lubricant, e.g., a ferrous liquid/oil. However, unwanted translations ΔY and/or unwanted yaw, i.e., rotations ΔΦ about the z-axis, of the mass  110  cannot be prevented by the lubricant. As such, it is beneficial to sense the unwanted in-plane motion ΔY and ΔΦ of the mass  110 , and then apply corrective procedures to suppress them. Note that the sum signal  625  can also be used to sense Y travel and/or yaw motion of the mass  110 . That is because the sum signal  625  also decreases (increases) when the mass  110  carrying the sensing magnet  114  moves along the y-axis away from (back towards) the Hall-effect sensors  108 A and  108 B. 
     Referring now to  FIGS. 6A and 2A , for the haptic engine  200 , in which the plane of the X travel and the sensing plane are spaced apart along the y-axis, the sum signal  625  can be used to sense Y travel and/or yaw motion of the mass  210 . Here, the sum signal  225  increases (decreases) when the mass  210  carrying the sensing magnet  214  moves along the y-axis closer to (farther from) the Hall-effect sensors  208 A and  208 B. Note that for the haptic engine  200 , the sensing system  205  (that includes the sensing magnet  214  and the Hall-effect sensors  208 A and  208 B) can be positioned along the x-axis anywhere relative to a corner of the mass  210 . However, the amplitude of the yaw modes will increase (decrease) by placing the sensing system  205  closer to a corner (the middle) of the mass  210 . 
     Further note that it has been determined experimentally, for both haptic engines  100 ,  200 , that it is possible to tell apart whether the changes in the sum signal  625  are due to Z modes, Y modes or yaw modes of the mass ( 110 ;  210 )&#39;s motion because they occur at different vibration frequency ranges, e.g., 320&lt;f Z &lt;343 Hz, 353&lt;f Y &lt;450 Hz, and 513&lt;f YAW &lt;523 Hz, respectively, for the particular design that has been studied here. Experimental results for detecting the frequencies f Z , f Y  and f YAW  are presented below in connection with  FIGS. 8A-8D . For other designs, these frequency ranges can be determined from finite element analysis simulation or factory calibration. 
     Referring again to  FIG. 6A , note that prior to (i) determining the displacement ΔX of the mass ( 110 ;  210 ) of the haptic engine ( 100 ;  200 ) along the driving direction based on the difference signal  615 , and/or (ii) performing spectral analysis of the sum signal  625  to detect whether unwanted modes have been induced in the motion of the mass, a digital signal processor is used to apply a set of corrections to the Hall voltage signals V H     1   , V H     2   , that are output by the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B). In some implementations, a digital signal processor is integrated in the ASIC ( 122 ;  222 ) of the sensing system ( 105 ;  205 ) of the haptic engine ( 100 ;  200 ). In some implementations, the ASIC ( 122 ;  222 ) that is part of the sensing system ( 105 ;  205 ) simply digitizes the Hall voltage signals V H     1   , V H     2    and then transmits the digitized signals to a digital signal processor that is external to the haptic engine ( 100 ;  200 ). 
     In this manner, a digital signal processor that receives the Hall-voltage signals V H     1   , V H     2    can determine a displacement ΔX of the mass ( 110 ;  210 ) along the driving direction (e.g., the x-axis) as a tangential-displacement signal H ∥ , where H ∥  is calculated as
 
 H   ∥   =H   1   −H   2   (3a).
 
In EQ. (3a), the terms H 1  and H 2  are obtained by performing the following corrections on the Hall voltage signals V H     1   , V H     2   :
 
 H   1   =V   H     1     −H   01 −η 1   I   (3b),
 
 H   2   =V   H     2     −H   02 −η 2   I   (3c).
 
In EQs. (3b), (3c), each of the Hall voltage signals V H     1   , V H     2    (expressed in counts) is corrected by a respective offset H 01 , H 02  (expressed in counts), that represents the signal output by a Hall-effect sensor ( 108 A,  108 B;  208 A,  208 B) when the sensor is at rest. Additionally, each of the Hall voltage signals V H     1   , V H     2    (expressed in counts) is further corrected by a respective coupling term, that represents a strength of the coupling between the current I in the driving coil ( 112 ;  212 ) and the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B). Each of the coupling terms is obtained as a product of a respective electromagnetic coupling factor η 1 , η 2  (expressed in counts/A), and an intensity (expressed in A) of the current I in the driving coil ( 112 ;  212 ). Note that, because the electromagnetic coupling factors η 1 , η 2 , can have similar values, the coupling terms from EQs. (3b), (3c) mostly cancel out in EQ. (3a). Note that the tangential-displacement signal H ∥  obtained based on EQ. (3a) represents a corrected version of the difference signal  615  shown in  FIG. 6A .
 
     The digital signal processor that receives the Hall-voltage signals V H     1   , V H     2    can detect displacements of the mass that are orthogonal to the displacement ΔX along the x-axis, e.g., the displacement ΔZ along the z-axis, the displacement ΔY along the z-axis and the yaw ΔΦ about a rotation axis parallel to the z-axis. These orthogonal displacements are detected by performing spectral analysis of an orthogonal-displacement signal H ⊥  obtained based on the following equation: 
     
       
         
           
             
               
                 
                   
                     H 
                     ⊥ 
                   
                   = 
                   
                     
                       
                         
                           H 
                           1 
                         
                         + 
                         
                           H 
                           2 
                         
                       
                       
                         
                           H 
                           01 
                         
                         + 
                         
                           H 
                           02 
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In EQ. (4), the terms H 1 , H 2  are obtained using EQs. (3b), (3c), respectively. EQ. (4) can be used to detect which of the orthogonal displacements ΔZ, ΔY and ΔΦ of the mass ( 110 ;  210 ) are present at a given time by detecting respective high order modes of the signal H ⊥ . Note that the orthogonal-displacement signal H ⊥  obtained based on EQ. (4) represents a corrected version of the sum signal  625  shown in  FIG. 6A . 
     Note that the sensing systems ( 105 ,  205 ) described here use Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B) to detect changes in the sensing magnetic field produced by a single sensing magnet ( 114 ,  214 ). However, any magnetic field sensors, e.g., fluxgates, magneto-resistors, etc., can be used in conjunction with, or instead of, the above-noted Hall-effect sensors. In such cases, the Hall voltage signals V H     1   , V H     2   , that are output above by the Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B), are respectively replaced by sensing signals V SENSOR     1   , V SENSOR     2   , which are output by the corresponding magnetic field sensors. 
       FIG. 7  shows a process  700  for identifying unwanted vibration modes induced in a haptic engine ( 100 ;  200 ) and for damping the identified modes. The process  700  can be performed by one or more digital signal processors in conjunction with the haptic engine ( 100 ;  200 ). The process  700  includes a calibration portion  705  followed by an operational portion  735 . 
     The calibration portion  705  of the process  700  can be performed during the fabrication of the haptic engine ( 100 ;  200 ) or during the fabrication of a computing device, e.g., smartphone, laptop, watch, etc., that includes the haptic engine. 
     At  710 , respective sum signals  625 ( j ) are acquired for multiple driving frequencies f(j), where j=1 . . . N&gt;1 and f MIN &lt;f(j)&lt;f MAX . Each sum signal  625  is acquired using a pair of Hall-effect sensors ( 108 A,  108 B;  208 A,  208 B) in a sensing system ( 105 ;  205 ) of the haptic engine ( 100 ;  200 ). The minimum frequency f MIN  can be 0, 10, 20 or 30 Hz. The maximum frequency f MAX  can be 400, 600, 800 or 1000 Hz. In some implementations, each sum signal  625 ( j ) is corrected based on EQ. (4) to obtain an orthogonal-displacement signal H ⊥ . 
       FIG. 8A  shows a false-color plot of the orthogonal-displacement signal H ⊥  (along the axis perpendicular to the page) as a function of time (along the horizontal axis) and driving frequency (along the vertical axis). The data plotted in  FIG. 8A  was generated for the haptic engine  100  during a driving-frequency sweep corresponding to the response  800 A of the orthogonal-displacement signal H ⊥ . During this sweep, the driving frequency is changed linearly in time, over a time interval of 6 s, from a minimum frequency of 25 Hz to a maximum frequency 325 Hz. In addition to the response  800 A, a set  802 A of higher frequency modes have been induced during the driving-frequency sweep. For instance, along a vertical section of the false-color plot, e.g., at t=2s, the orthogonal-displacement signal H ⊥  has a direct response at the driving frequency, e.g., f=100 Hz, and a series of harmonics at 200 Hz, 300 Hz, 400 Hz, etc., having smaller and smaller amplitudes. Note that for some modes, e.g., at f Z =343 Hz, f Y =405 Hz and f Φ =513 Hz, all of which are larger than the maximum frequency of the driving-frequency sweep, the response stretches in time, indicating that these are resonant modes. In the example illustrated in  FIG. 8A , the foregoing resonant modes correspond, respectively, to a displacement ΔZ along the z-axis, a displacement ΔY along the y-axis and a displacement ΔΦ corresponding to yaw (i.e., rotation about an axis parallel to the z-axis). 
       FIG. 8B  shows a false-color plot of the orthogonal-displacement signal H ⊥  (along the axis perpendicular to the page) as a function of time (along the horizontal axis) and driving frequency (along the vertical axis). The data plotted in  FIG. 8B  was generated for the haptic engine  100  during a sequence  802 B of five taps separated by a period 0.5 s. The response  800 C for each of the taps includes many frequencies spanning beyond the upper bound, e.g., 300 Hz, of an operational frequency range. Note that for some modes, e.g., at f Z =322 Hz, f Y =358 Hz and f Φ =523 Hz, all of which are larger than the maximum operational frequency, the response stretches in time, indicating that these are resonant modes. In the example illustrated in  FIG. 8B , the foregoing resonant modes correspond, respectively, to a displacement ΔZ along the z-axis, a displacement ΔY along the y-axis and a displacement ΔΦ corresponding to yaw (i.e., rotation about an axis parallel to the z-axis). 
     Referring again to  FIG. 7 , at  720 , a spectrum S(f) is obtained for each respective sum signal  625 ( j ). For instance, spectral analysis can be performed, e.g., Fast Fourier transform, etc., to identify the type of the unwanted modes that are responsible for an increase or decrease of the sum signal  625 ( j ). In the implementations in which each sum signal  625 ( j ) has been corrected based on EQ. (4) to obtain the orthogonal-displacement signal H ⊥ , the spectrum S(f) is obtained for the orthogonal-displacement signal H ⊥ . 
       FIG. 8C  shows an overlay of a spectrum  810 A of the orthogonal-displacement signal H ⊥  for the driving-frequency sweep illustrated in  FIG. 8A , and a spectrum  820 A of the corresponding tangential-displacement signal H ∥ .  FIG. 8D  shows an overlay of a spectrum  810 B of the orthogonal-displacement signal H ⊥  for a tap illustrated in  FIG. 8B , and a spectrum  820 B of the corresponding tangential-displacement signal H ∥ . 
     Referring again to  FIG. 7 , at  730 , one or more resonant frequencies are identified based on the obtained spectra, e.g., frequency f(Z)&gt;f MAX  for Z-motion mode, frequency f(Y)&gt;f(Z) for Y-motion mode, and f(Φ)&gt;f(Y) for yaw mode. For example, the spectrum  810 A illustrated in  FIG. 8C  clearly shows a peak at f Φ =513 Hz corresponding to a yaw mode of a haptic engine like the haptic engine  100 . As another example, the spectrum  810 B illustrated in  FIG. 8D  clearly shows a peak at f Z =328 Hz corresponding to a ΔZ mode, a peak at f Y =359 Hz corresponding to a ΔY mode, and a peak at f Φ =515 Hz corresponding to another yaw mode of a haptic engine like the haptic engine  100 . 
     Referring again to  FIG. 7 , at  732 , the identified one or more resonant frequencies f Z , f Y  and/or f Φ  are stored in a data store, either locally to the haptic engine ( 100 ;  200 ) or external from the haptic engine. The stored data can be retrieved by one or more digital signal processors that perform the operational portion  735  of the process  700 . 
     The operational portion  735  of the process  700  can be performed iteratively during operation of a haptic engine ( 100 ;  200 ), e.g., as the haptic engine of a computing device, e.g., smartphone, laptop, watch, etc., is being started from rest, driven and/or brought to rest. 
     At  740 , the haptic engine ( 100 ;  200 ) is operated at an operational driving frequency f OP . While doing so, a sum signal  625 ( f   OP ) is acquired. 
     At  750 , a spectrum s(f) is obtained for the sum signal  625 ( f   OP ). For example, the spectrum s(f) can be obtained by applying a fast-Fourier transform (FFT) to the sum signal  625 ( f   OP ). 
     At  760 , the spectrum s(f) of the sum signal  625 ( f   OP ) is parsed to determine whether any modes are present that have a frequency larger than f MAX . For instance, the driving frequency f of the haptic engine ( 100 ;  200 ) can have a specified upper bound, e.g., f MAX =300 Hz. Here, one or more digital signal processors retrieve, from the data store, a value for f MAX . At  760 N, no action will be taken, and the operational portion  735  of the process  700  is restarted from  740 . 
     At  760 Y, the portion of the spectrum s(f) for frequencies larger than f MAX  is parsed, at  770 , to determine whether any modes are present that have a frequency that matches a previously identified resonant frequencies f Z , f Y  and/or f Φ  corresponding to unwanted modes of Z-motion, Y-motion and/or yaw. Here, one or more digital signal processors retrieve, from the data store, the values for f Z , f Y  and/or f Φ . At  770 N, no action will be taken, and the operational portion  735  of the process  700  is restarted from  740 . 
     At  770 Y, the identified one or more unwanted modes of the portion of the spectrum s(f) for frequencies larger than f MAX  are suppressed, at  780 , by applying an appropriate damping signal to the haptic engine. Examples of damping signals include anti-phase signals corresponding to the unwanted identified modes. Anti-phase signals and other noise cancellation signals are reserved signals, i.e., developers will not be allowed to drive the haptic engine at frequencies in the range of the frequencies of the reserved signals. 
     Note that the tangential-displacement signal H ∥ , that has been obtained above using EQ. (3a), for determining displacement ΔX of the mass ( 110 ;  210 ) of the haptic engine ( 100 ;  200 ) along the driving direction can be further corrected, as described next. 
     For example, a look up table (LUT), which is produced based on EQ. (3a), can be used to obtain the displacement of the mass ΔX along the x-axis. However, in some implementations, the tangential-displacement signal H ∥  can be distorted due to changes in the sensing magnetic field B caused by off-axis movement of the mechanical flexures ( 109 / 209 ), or due to the interaction of the sensing magnetic field B with the static field B Z  produced by the magnetic plates  104 . Here, the off-axis movement can be potentially due to an out-of-plane flexure force. Either of these reasons causes the slope dB/dX of the sensing magnetic field profile B(X)  602  to decrease, which in turn leads to a decrease in the sensitivity of the displacement measurements.  FIG. 9A  shows an overlay of (i) a tangential-displacement signal H ∥   910  obtained based on Hall sensing measurements, in accordance with EQ. (3a), and (ii) a reference tangential-displacement signal  920  obtained based on back-electromotive force (bEMF) measurements. Distortions  930  of the tangential-displacement signal H ∥   910  are highlighted in  FIG. 9A  as differences relative to the reference signal  920 . 
     To compensate for the off-axis movement, the tangential-displacement signal H ∥ , and the LUT in which it is used, can be compensated to obtain a compensated tangential-displacement signal H COMP  that satisfies the following equation: 
                     H   comp     =         H   ∥       1   +     KH   ⊥         .             (   5   )               
In EQ. (5), the tangential-displacement signal H ∥  is obtained using EQ. (3a), and the orthogonal-displacement signal H ⊥  is obtained using EQ. (4). Here, K is an adjustable gain factor. For the haptic engine ( 100 ;  200 ) described in this specification, the gain factor K=1 has been found to produce good results. Note that K can be calibrated for each haptic engine ( 100 ;  200 ) during production test.
 
     If it is desired to use a digital signal processor that does not support division, the compensated tangential-displacement signal H COMP  can be approximated using the following equation: 
                       H   comp     ≈       H   ∥     ⁡     (     1   -     KH   ⊥       )         =         H   ∥     ⁡     (     1   -     K   ⁢         H   1     +     H   2           H   01     +     H   02             )       .             (   6   )               
In EQ. (6), the factor
 
             1       H   01     +     H   02             
is consistent and can be precomputed.
 
     By applying one of EQs. (5) or (6) to calculate a compensated tangential-displacement signal H COMP , the distortions of this signal can be significantly smaller than the distortions of the tangential-displacement signal H ∥  calculated in accordance with EQ. (3a). This is illustrated in  FIG. 9B , which shows an overlay of (i) a tangential-displacement signal H COMP    912 ′ obtained based on Hall sensing measurements, in accordance with EQ. (5), and (ii) a reference tangential-displacement signal  920 ′ obtained based on bEMF measurements, for a driving frequency of 125 Hz. Here, the error between the tangential-displacement signal H COMP    912 ′ and the reference signal  920 ′ is about 3%. 
     In summary, the disclosed haptic engines include one sensing magnet, and multiple sensors for sensing mass motion. In some of the disclosed haptic engines, a sensing magnet flux direction is orthogonal to the static magnet flux direction. Various implementations of the disclosed haptic engines include two, three or more sensors to distinguish between X, Y/yaw, Z movements of the sensing magnet. In some implementations of the disclosed haptic engines, the one or more sensors are integrated inside an ASIC to save space and cost. In some implementations of the disclosed haptic engines, the two or more sensors, and in some cases the ASIC, can be mounted on the inside of the engine to save space. 
       FIG. 10  is a diagram of an example of mobile device architecture that uses one of the haptic engines described in reference to  FIGS. 1-9 , according to an embodiment. Architecture  1000  may be implemented in any mobile device for generating the features and processes described in reference to  FIGS. 1-9 , including but not limited to smart phones and wearable computers (e.g., smart watches, fitness bands). Architecture  1000  may include memory interface  1002 , data processor(s), image processor(s) or central processing unit(s)  1004 , and peripherals interface  1006 . Memory interface  1002 , processor(s)  1004  or peripherals interface  1006  may be separate components or may be integrated in one or more integrated circuits. One or more communication buses or signal lines may couple the various components. 
     Sensors, devices, and subsystems may be coupled to peripherals interface  1006  to facilitate multiple functionalities. For example, motion sensor(s)  1010 , light sensor  1012 , and proximity sensor  1014  may be coupled to peripherals interface  1006  to facilitate orientation, lighting, and proximity functions of the device. For example, in some embodiments, light sensor  1012  may be utilized to facilitate adjusting the brightness of touch surface  1046 . In some embodiments, motion sensor(s)  1010  (e.g., an accelerometer, rate gyroscope) may be utilized to detect movement and orientation of the device. Accordingly, display objects or media may be presented according to a detected orientation (e.g., portrait or landscape). 
     Haptic engine  1017 , under the control of haptic engine instructions  1072 , provides the features and performs the processes described in reference to  FIGS. 1-9 , such as, for example, implementing haptic feedback (e.g., vibration). Haptic engine  1017  can include one or more actuators, such as piezoelectric transducers, electromechanical devices, and/or other vibration inducing devices, which are mechanically connected to an input surface (e.g., touch surface  1046 ). Drive electronics (e.g.,  170 ) coupled to the one or more actuators cause the actuators to induce a vibratory response into the input surface, providing a tactile sensation to a user touching or holding the device. 
     Other sensors may also be connected to peripherals interface  1006 , such as a temperature sensor, a barometer, a biometric sensor, or other sensing device, to facilitate related functionalities. For example, a biometric sensor can detect fingerprints and monitor heart rate and other fitness parameters. In some implementations, a Hall sensing element in haptic engine  1017  can be used as a temperature sensor. 
     Location processor  1015  (e.g., GNSS receiver chip) may be connected to peripherals interface  1006  to provide geo-referencing. Electronic magnetometer  1016  (e.g., an integrated circuit chip) may also be connected to peripherals interface  1006  to provide data that may be used to determine the direction of magnetic North. Thus, electronic magnetometer  1016  may be used to support an electronic compass application. 
     Camera subsystem  1020  and an optical sensor  1022 , e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, may be utilized to facilitate camera functions, such as recording photographs and video clips. 
     Communications functions may be facilitated through one or more communication subsystems  1024 . Communication subsystem(s)  1024  may include one or more wireless communication subsystems. Wireless communication subsystems  1024  may include radio frequency receivers and transmitters and/or optical (e.g., infrared) receivers and transmitters. Wired communication systems may include a port device, e.g., a Universal Serial Bus (USB) port or some other wired port connection that may be used to establish a wired connection to other computing devices, such as other communication devices, network access devices, a personal computer, a printer, a display screen, or other processing devices capable of receiving or transmitting data. 
     The specific design and embodiment of the communication subsystem  1024  may depend on the communication network(s) or medium(s) over which the device is intended to operate. For example, a device may include wireless communication subsystems designed to operate over a global system for mobile communications (GSM) network, a GPRS network, an enhanced data GSM environment (EDGE) network, IEEE802.xx communication networks (e.g., Wi-Fi, Wi-Max, ZigBee™), 3G, 4G, 4G LTE, code division multiple access (CDMA) networks, near field communication (NFC), Wi-Fi Direct and a Bluetooth™ network. Wireless communication subsystems  1024  may include hosting protocols such that the device may be configured as a base station for other wireless devices. As another example, the communication subsystems may allow the device to synchronize with a host device using one or more protocols or communication technologies, such as, for example, TCP/IP protocol, HTTP protocol, UDP protocol, ICMP protocol, POP protocol, FTP protocol, IMAP protocol, DCOM protocol, DDE protocol, SOAP protocol, HTTP Live Streaming, MPEG Dash and any other known communication protocol or technology. 
     Audio subsystem  1026  may be coupled to a speaker  1028  and one or more microphones  1030  to facilitate voice-enabled functions, such as voice recognition, voice replication, digital recording, and telephony functions. In an embodiment, audio subsystem includes a digital signal processor (DSP) that performs audio processing, such as implementing codecs. 
     I/O subsystem  1040  may include touch controller  1042  and/or other input controller(s)  1044 . Touch controller  1042  may be coupled to a touch surface  1046 . Touch surface  1046  and touch controller  1042  may, for example, detect contact and movement or break thereof using any of a number of touch sensitivity technologies, including but not limited to, capacitive, resistive, infrared, and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with touch surface  1046 . In one embodiment, touch surface  1046  may display virtual or soft buttons and a virtual keyboard, which may be used as an input/output device by the user. 
     Other input controller(s)  1044  may be coupled to other input/control devices  1048 , such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port, and/or a pointer device such as a stylus. The one or more buttons (not shown) may include an up/down button for volume control of speaker  1028  and/or microphone  1030 . 
     In some embodiments, device  1000  may present recorded audio and/or video files, such as MP3, AAC, and MPEG video files. In some embodiments, device  1000  may include the functionality of an MP3 player and may include a pin connector for tethering to other devices. Other input/output and control devices may be used. 
     Memory interface  1002  may be coupled to memory  1050 . Memory  1050  may include high-speed random access memory or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices, or flash memory (e.g., NAND, NOR). Memory  1050  may store operating system  1052 , such as Darwin, RTXC, LINUX, UNIX, OS X, iOS, WINDOWS, or an embedded operating system such as VxWorks. Operating system  1052  may include instructions for handling basic system services and for performing hardware dependent tasks. In some embodiments, operating system  1052  may include a kernel (e.g., UNIX kernel). 
     Memory  1050  may also store communication instructions  1054  to facilitate communicating with one or more additional devices, one or more computers or servers, including peer-to-peer communications. Communication instructions  1054  may also be used to select an operational mode or communication medium for use by the device, based on a geographic location (obtained by the GPS/Navigation instructions  1068 ) of the device. 
     Memory  1050  may include graphical user interface instructions  1056  to facilitate graphic user interface processing, including a touch model for interpreting touch inputs and gestures; sensor processing instructions  1058  to facilitate sensor-related processing and functions; phone instructions  1060  to facilitate phone-related processes and functions; electronic messaging instructions  1062  to facilitate electronic-messaging related processes and functions; web browsing instructions  1064  to facilitate web browsing-related processes and functions; media processing instructions  1066  to facilitate media processing-related processes and functions; GNSS/Navigation instructions  1068  to facilitate GNSS (e.g., GPS, GLOSSNAS) and navigation-related processes and functions; camera instructions  1070  to facilitate camera-related processes and functions; and haptic engine instructions  1072  for commanding or controlling haptic engine  1017  and to provide the features and performing the processes described in reference to  FIGS. 1-9 . 
     Each of the above identified instructions and applications may correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. Memory  1050  may include additional instructions or fewer instructions. Furthermore, various functions of the device may be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits (ASICs). Software instructions may be in any suitable programming language, including but not limited to: Objective-C, SWIFT, C# and Java, etc. 
     While this document contains many specific implementation details, these should not be construed as limitations on the scope what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub combination or variation of a sub combination. Logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.

Metadata:
Filing Date: 20180913
Publication Date: 20201117
Grant Date: 20201117
Priority Date: 20170918
Inventors: CHEN, DENIS G.
LEE, ALEX M.
YONEOKA, SHINGO
Assignee: APPLE INC
CPC Classifications: [{"code": "G01D5/145", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01D5/145", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01D5/145", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/12", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 65720021