JP2008275548A - Stress measuring device and actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stress measuring device capable of accurately measuring the magnitude of a stress, and to provide an actuator equipped with such the stress measuring device. <P>SOLUTION: When an AC voltage is applied to a coil 23 by using an AC voltage applying circuit 51, AC voltages are generated across a coil 22 and comb-shaped electrodes 42, 43, whereby a portion between a piezo-electric substrate 41 and the comb-shaped electrodes 42, 43 is vibrated. This vibration is reflected by a reflector 44 and returns to a portion between the comb-shaped electrodes 42, 43, and AC voltages are generated across the comb-shaped electrodes 42, 43 and the coil 22, and furthermore an AC voltage is generated across the coil 23. The AC voltages are detected by an AC voltage detecting circuit 52. When a stress is applied to the substrate by a suction nozzle, a shaft is compressed, whereby the piezo-electric substrate 41 is also compressed. Therefore, a period from a time when the AC voltage is applied by the AC voltage applying circuit 51 to a time when the AC voltage is detected by the AC voltage detecting circuit 52 is varied according to the magnitude of the stress. The magnitude of the stress is calculated from the period by using a stress calculating circuit 53. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a stress measuring device that measures external stress, and an actuator including the stress measuring device.

  In the chip mounter described in Patent Document 1, an electric current is passed through the coil of the main body of the linear actuator to generate a thrust force on the shaft, thereby moving the shaft and pressing the substrate with a tip fitting provided at the tip of the shaft. As a result, the semiconductor chip adsorbed on the tip fitting is bonded to the substrate. Here, when the shaft moves, a force is generated in the direction opposite to the moving direction by the magnetic spring force. Therefore, in the linear actuator of Patent Document 1, the current flowing through the coil is controlled in accordance with the position of the shaft in order to apply a desired stress to the substrate. At this time, the position of the shaft is detected from the positional relationship between the mover provided at the end opposite to the end fitting of the shaft and the stator fixed to the main body of the linear actuator.

JP 2005-318769 A

  Here, in the chip mounter described in the cited document 1, the positional relationship between the mover and the stator is changed even when the linear actuator is rattled, which affects the stress control according to the position. give. Also, the bearing of the linear actuator has a mechanical loss, which affects the stress control. On the other hand, when the parts to be handled are reduced in size, the applied stress is also reduced. Therefore, when a component is downsized, the difference between the applied stress and the effects of rattling or mechanical loss of the linear actuator is reduced, making it impossible to apply the desired stress to the board and the component. There is a risk that.

  An object of the present invention is to provide a stress measurement device capable of accurately detecting stress and an actuator including such a stress measurement device.

  The stress measuring device of the present invention is a stress measuring device for measuring a stress applied to an object to be measured having a deformed portion that is deformed by applying a stress, the piezoelectric substrate disposed on the surface of the deformed portion, and the piezoelectric substrate A pair of comb-shaped electrodes arranged to face each other and the one surface of the piezoelectric substrate, and have propagated through the one surface of the piezoelectric substrate A SAW sensor having a reflector that reflects surface acoustic waves, a movable coil connected to the pair of comb-shaped electrodes, and a fixed member that is opposed to the movable coil and is not in contact with the object to be measured. A coil, an AC voltage application circuit for applying an AC voltage to the fixed coil, an AC voltage detection circuit for detecting an AC voltage generated in the fixed coil, and a detection result in the AC voltage detection circuit. And a, a stress calculating circuit for calculating the magnitude of the stress applied to the object to be measured (claim 1).

  When an AC voltage is applied to the fixed coil by the AC voltage application circuit, the AC voltage is also applied to the movable coil and a pair of comb electrodes connected to the movable coil. When an AC voltage is applied to the pair of comb electrodes, the portion of the piezoelectric substrate sandwiched between the pair of comb electrodes vibrates, and this vibration is reflected by the reflector and returns to the pair of comb electrodes. Come. An AC voltage is generated in the movable coil connected to the pair of comb-shaped electrodes and the pair of comb-shaped electrodes due to the returned vibration, whereby an AC voltage is also generated in the fixed coil. The AC voltage detection circuit detects this AC voltage.

  Here, when stress is applied to the object to be measured and the deformed part of the object to be measured is deformed, the piezoelectric substrate disposed on the surface of the deformed part is also deformed, so that the detection result in the AC voltage detection circuit depends on the amount of deformation of the deformed part. Changes.

  Therefore, according to the present invention, the magnitude of the stress applied to the object to be measured can be calculated from the detection result in the AC voltage detection circuit.

  In addition, the detection result in the AC voltage detection circuit changes depending on the deformation amount of the deformed portion and does not change depending on the rattling of the object to be measured. Therefore, even when the stress measuring device is downsized, the magnitude of the stress is reduced. It can be detected accurately.

  It should be noted that stress is applied to the object to be measured because not only is stress applied to the object to be measured from the outside, but also stress is applied to the object to be measured by reaction when the object to be measured applies stress to the outside. Is also included.

  In the stress measurement device of the present invention, a first storage circuit that stores a relationship between a detection result in the AC voltage detection circuit and an ambient temperature when no stress is applied to the object to be measured, and a plurality of peripherals A second memory circuit for storing a relationship between a stress applied to the object to be measured and a detection result in the AC voltage detection circuit at a temperature; a relationship stored in the first memory circuit; and a stress applied to the object to be measured. From the detection result in the AC voltage detection circuit in the absence of the ambient temperature, the ambient temperature calculation circuit that calculates the ambient temperature, the ambient temperature calculated by the ambient temperature calculation circuit, and the relationship stored in the second storage circuit And a calculation method setting circuit for setting a stress calculation method in the stress calculation circuit.

  Since the characteristics of the SAW sensor change depending on the ambient temperature, when the ambient temperature changes, the correspondence between the stress applied to the object to be measured and the detection result in the AC voltage detection circuit changes. However, the ambient temperature detection circuit By detecting the ambient temperature and setting the stress calculation method in the stress calculation circuit by the calculation method setting circuit, the magnitude of the stress can be accurately detected even when the ambient temperature changes.

  Further, in the stress measuring device of the present invention, an offset for setting a detection result in the AC voltage detection circuit in a state where no stress is applied to the object to be measured as a reference for calculating the stress in the stress calculation circuit. It is preferable to further include a setting circuit.

  Since the characteristics of the SAW sensor change depending on the ambient temperature, if the ambient temperature changes, the detection result in the AC voltage detection circuit when no stress is applied to the object to be measured changes. Since the detection result in the AC voltage detection circuit when no stress is applied to the object is set as a reference, the stress calculation circuit can accurately calculate the magnitude of the stress even if the ambient temperature changes.

  In the stress measuring apparatus of the present invention, the SAW sensor has one reflector, and the stress calculation circuit applies an AC voltage from the fixed coil by the AC voltage application circuit. The stress applied to the object to be measured may be calculated from the time until the AC voltage is detected by the AC voltage detection circuit.

  When the piezoelectric substrate is deformed by deforming the deformed portion of the object to be measured, the distance between the pair of comb electrodes and the reflector changes. Therefore, depending on the amount of deformation of the piezoelectric substrate, the time until the vibration propagates from the comb electrode to the reflector and returns to the comb electrode changes. Therefore, the magnitude of the stress applied to the object to be measured can be calculated from the time from when the AC voltage is applied by the AC voltage application circuit until the AC voltage is detected by the AC voltage detection circuit.

  Alternatively, in the stress measuring device of the present invention, the SAW sensor has the two reflectors arranged so as to sandwich the pair of comb-shaped electrodes on the one surface of the piezoelectric substrate, The AC voltage detection circuit and the fixed coil constitute an oscillation circuit, and the stress calculation circuit determines the magnitude of stress applied to the object to be measured from the frequency of the AC voltage detected by the AC voltage detection circuit. (Claim 5).

  According to this, the SAW sensor constitutes a resonator, and when a stress is applied to the object to be measured and the deformed portion is deformed, the circuit constant of the resonator changes. Due to the change in the circuit constant, the oscillation frequency of the oscillation circuit also changes. Therefore, the magnitude of the stress applied to the object to be measured can be measured from the frequency of the AC voltage detected by the AC voltage detection circuit.

  The actuator of the present invention is deformed by a reaction when the stress measuring device according to any one of claims 1 to 5, a stress applying unit that applies external stress, and the stress applying unit applies external stress. And the piezoelectric base material of the stress measuring device is disposed on the surface of the deformable portion (Claim 6). According to this, the magnitude of the stress applied to the outside from the stress applying portion in the actuator can be accurately measured by the stress measuring device.

  The actuator of the present invention further includes a stress control device that controls the magnitude of the stress applied to the outside by the stress applying unit according to the magnitude of the stress calculated by the stress calculation circuit of the stress measuring device. It is preferable to provide (Claim 7). According to this, by controlling the magnitude of the stress applied from the stress applying part to the outside according to the magnitude of the stress calculated by the stress calculating circuit, the desired magnitude of stress is applied from the stress applying part to the outside. be able to.

  Embodiments according to the present invention will be described below.

  FIG. 1 is a schematic configuration diagram of a linear actuator according to the present embodiment. As shown in FIG. 1, the linear actuator 1 includes a fixed portion 11, a movable portion 12, a suction nozzle 13, a SAW sensor 21, coils 22 and 23, and a control circuit 24. In the linear actuator 1, the movable portion 12 receives thrust from the fixed portion 11 in a state where a semiconductor chip or the like is sucked to the suction nozzle 13 attached to the tip of the movable portion 12, as will be described later. By moving in the left-right direction, the semiconductor chip sucked by the suction nozzle 13 is pressed against the substrate. An adhesive is applied to either the semiconductor chip or the substrate, whereby the semiconductor chip is bonded to the substrate.

  At this time, as will be described later, when the semiconductor chip is pressed against the substrate by the SAW sensor 21, the coils 22, 23 and the control circuit 24, the stress applied to the substrate (stress applied to the outside by the linear actuator) is measured. At the same time, the magnitude of the stress applied to the substrate is controlled according to the measured stress.

  Next, the fixed part 11 and the movable part 12 will be described in detail. FIG. 2A is a cross-sectional view schematically showing the configuration of the fixed portion 11 and the movable portion 12 of FIG. 2B is a cross-sectional view when viewed from the direction of arrow B in FIG.

  As shown in FIGS. 2A and 2B, the fixed portion 11 includes a yoke 31, coils 33 and 34, and permanent magnets 35 to 38. The yoke 31 is configured by laminating metal thin plates, and includes a frame portion 31a and projecting portions 31b and 31c. The frame portion 31 a is a substantially rectangular cylindrical body and forms the outer peripheral portion of the yoke 31. The protruding part 31b protrudes downward from the upper end part of the frame part 31a. The protruding portion 31c protrudes upward from the lower end portion of the frame portion. The protrusions 31b and 31c face each other, and a shaft 30 (to be described later) of the movable part 12 passes between them. The coils 33 and 34 are wound around the protrusions 31b and 31c, respectively.

  The permanent magnets 35 and 36 are fixed to the lower surface of the protruding portion 31b, and are arranged adjacent to each other so that the permanent magnet 36 is located on the left side of the permanent magnet 35 in FIG. The permanent magnet 35 is arranged so that the upper end in FIG. 2 is an N pole and the lower end is an S pole, and the permanent magnet 36 is arranged so that the upper end in FIG. 2 is an S pole and the lower end is an N pole.

  The permanent magnets 37 and 38 are fixed to the upper surface of the protrusion 31c, and are arranged adjacent to each other so that the permanent magnet 38 is located on the left side of the permanent magnet 37 in FIG. The permanent magnet 37 is arranged so that the upper end in FIG. 2 is an N pole and the lower end is an S pole, and the permanent magnet 38 is arranged so that the upper end in FIG. 2 is an S pole and the lower end is an N pole. Yes.

  Since the permanent magnets 35 to 38 are arranged as described above, the permanent magnets 35 and 36 and the permanent magnets 37 and 38 respectively rotate counterclockwise on the paper surface of FIG. Magnetic fields M1 and M2 are generated, and an upward magnetic field M3 is generated on the paper surface of FIG. 2A by the permanent magnets 35 and 37, and the permanent magnets 36 and 38 in FIG. A downward magnetic field M4 is generated on the paper surface.

  The movable part 12 includes a shaft 30 and a metal member 29. The shaft 30 is a rod-like body extending in the left-right direction in FIG. 2A, extends in the left-right direction in FIG. 2A, and passes between the protruding portions 31b and 31c of the fixed portion 11. The metal member 29 is provided at a substantially central portion of the shaft 30 so as to surround the shaft 30.

  Next, the principle that the movable part 12 moves by receiving a thrust from the fixed part 11 will be described. FIG. 3 is a schematic diagram showing the principle that the movable part 12 receives thrust from the fixed part 11.

  When no current flows through the coils 33 and 34, the magnetic fields M1 to M4 are generated by the permanent magnets 35 to 38 as described above. In this state, when a current is passed through the coils 33 and 34 in the direction shown in FIG. 3A, as shown in FIG. , M13, and counterclockwise magnetic fields M12, 14 are generated at the left ends of the coils 33, 34 on the paper surface, respectively.

  At this time, the direction of the portion of the magnetic field M11 passing through the protruding portion 31b and the direction of the portion of the magnetic field M13 passing through the protruding portion 31c are both upward on the paper in the vertical direction of FIG. Since the direction of the magnetic field M3 described above is also upward on the paper surface of FIG. 3A, the magnetic fields M11 and M13 are guided to the magnetic field M3 and pass through the metal member 29 and the shaft 30 from the protruding portion 31c as a whole. Thus, the magnetic field M15 reaches the protruding portion 31b. This increases the magnetic flux density at the right end of the metal member 29. The magnetic field M15 passes from the protruding portion 31a through the frame portion 31a to the protruding portion 31c at a position (not shown), and is a loop-shaped magnetic field as a whole.

  On the other hand, the direction of the portion of the magnetic field M12 that passes through the protruding portion 31b and the direction of the portion of the magnetic field M14 that passes through the protruding portion 31c are both upward on the paper in the vertical direction of FIG. On the other hand, since the direction of the magnetic field M4 described above is downward on the paper surface of FIG. 3A, the magnetic fields M12 and M14 and the magnetic field M4 cancel each other. Thereby, in the left end part of the metal member 29, magnetic flux density falls.

  As a result, the metal member 29 and the shaft 30 to which the metal member 29 is fixed move to the right in FIG.

  On the other hand, when a current is passed through the coils 33 and 34 in the direction opposite to that shown in FIG. 3A, the counterclockwise magnetic fields M21 and M23 are respectively formed at the right ends of the coils 33 and 34 as shown in FIG. At the same time, clockwise magnetic fields M22 and M24 are generated at the left ends of the coils 33 and 34, respectively.

  At this time, the direction of the portion of the magnetic field M22 passing through the protruding portion 31b and the direction of the portion of the magnetic field M24 passing through the protruding portion 31c are both downward on the paper with respect to the vertical direction of FIG. Since the direction of the magnetic field M4 is also downward on the paper surface of FIG. 3A, the magnetic fields M22 and M24 are guided to the magnetic field M4 and pass through the metal member 29 and the shaft 30 from the protruding portion 31b as a whole. Thus, the magnetic field M25 reaches the protruding portion 31c. As a result, the magnetic flux density increases at the left end of the metal member 29. Note that the magnetic field M25 passes from the protruding portion 31c through the frame portion 31a to the protruding portion 31b at a position not shown, and is a loop-shaped magnetic field as a whole.

  On the other hand, the direction of the portion of the magnetic field M21 passing through the protruding portion 31b and the direction of the portion of the magnetic field M23 passing through the protruding portion 31c are both downward on the paper surface in the vertical direction of FIG. On the other hand, since the direction of the magnetic field M3 described above is upward on the paper surface of FIG. 3B, the magnetic fields M21 and M23 and the magnetic field M3 cancel each other. Thereby, in the right end part of the metal member 29, magnetic flux density falls.

  As a result, the metal member 29 and the shaft to which the metal member 29 is fixed move to the left in FIG. As described above, the movable portion 12 receives thrust from the fixed portion 11.

  Next, the SAW sensor 21, the coils 22, 23, and the control device 24 will be described in detail with reference to FIGS. FIG. 4 is a circuit diagram of the SAW sensor 21, the coils 22, 23, and the control device 24 of FIG.

  As shown in FIG. 4, the SAW (Surface Acoustic Wave) sensor 21 includes a piezoelectric substrate 41, a pair of comb-shaped electrodes 42 and 43, and a reflector 44. The piezoelectric substrate 41 is a substantially rectangular plate-shaped body made of a piezoelectric material, and is fixed to the surface of the shaft 30 of the movable portion 12. The pair of comb-shaped electrodes 42 and 43 have a substantially U-shaped planar shape and are arranged on one surface of the piezoelectric substrate 41 so as to face each other. The reflector 44 is provided on one surface of the piezoelectric substrate 41 and reflects vibration (surface acoustic wave, SAW) propagating along the one surface of the piezoelectric substrate 41.

  The coil (movable coil) 22 is wound around a shaft 30 and both ends thereof are connected to comb electrodes 42 and 43, respectively. The coil (fixed coil) 23 is disposed so as to surround the coil 22, and the coil 22 and the coil 23 constitute a transformer. The coil 23 has a length in the left-right direction in FIG. 1 longer than that of the coil 22, and as described above, even if the shaft 30 moves in the left-right direction in FIG. It is comprised so that it may oppose. Thereby, the characteristic of the transformer constituted by the coils 22 and 23 is always constant.

  The control circuit 24 includes an alternating voltage application circuit 51, an alternating voltage detection circuit 52, a stress calculation circuit 53, an offset setting circuit 54, a storage circuit 55, a temperature calculation circuit 56, a calculation method setting circuit 57, and a stress control circuit 58. . In addition, what remove | excluded the stress control circuit 58 from the SAW sensor 21, the coils 22, 23, and the control circuit 24 mentioned above is equivalent to the stress measuring device of this invention.

  The AC voltage application circuit 51 is connected to the coil 23 and applies an AC voltage to both ends of the coil 23 for a predetermined time. The AC voltage detection circuit 52 is connected to the coil 23 and detects the voltage across the coil 23.

  Here, a process from when the AC voltage is applied to the coil 23 by the AC voltage application circuit 51 to when the AC voltage is detected by the AC voltage detection circuit 52 will be described.

  When an AC voltage is applied to the coil 23 by the drive voltage application circuit 51 for a predetermined time, an AC voltage is applied to both ends of the coil 22 arranged to face the coil 23, and the comb shape is connected to both ends of the coil 22. An AC voltage is generated between the electrodes 42 and 43. When an alternating voltage is generated between the comb electrodes 42 and 43, a portion of the piezoelectric substrate 41 sandwiched between the comb electrodes 42 and 43 vibrates. This vibration propagates on the surface of the piezoelectric substrate 41, is reflected by the reflector 44, returns to the portion between the comb electrodes 42 and 43 of the piezoelectric substrate 41, and the comb electrodes 42 and 43 of the piezoelectric substrate 41 The part between is vibrated.

  When the portion between the comb-shaped electrodes 42 and 43 of the piezoelectric substrate 41 vibrates, an alternating voltage is generated between the comb-shaped electrodes 42 and 43 and is applied to both ends of the coil 22 connected to the comb-shaped electrodes 42 and 43. An alternating voltage is applied. As a result, an AC voltage is also applied to the coil 23 disposed opposite to the coil 22, and the AC voltage detection circuit 52 detects this AC voltage.

  The stress calculation circuit 53 is connected to the AC voltage detection circuit 52. As described above, after the AC voltage is applied to the coil 53 by the AC voltage application circuit 51, the AC voltage is detected by the AC voltage detection circuit 52. The magnitude of the stress that presses the substrate is calculated from the time (hereinafter, referred to as detection time) (the detection result in the AC voltage detection circuit 52) until the time when the substrate is pressed.

  The offset setting circuit 54 sets a reference when the stress calculation circuit 53 calculates the stress. Specifically, the detection time in a state where no stress is applied to the substrate is set as a reference for measuring the stress. The stress calculation circuit 53 calculates the magnitude of the stress from the difference between the detection time set by the offset setting circuit 54 and the detection time at the time of stress measurement.

  Since the characteristics of the SAW sensor 21 change depending on the ambient temperature, the detection time changes when the ambient temperature changes. Therefore, the stress calculation circuit 53 can accurately calculate the magnitude of the stress by setting the detection time when the stress is not applied to the substrate in the offset setting circuit 54 as a reference for measuring the stress. it can.

  The memory circuit (first memory circuit, second memory circuit) 55 stores the relationship between the detection time (the detection result in the AC voltage detection circuit 52) and the ambient temperature when no stress is applied to the substrate. In addition, the relationship between the stress applied to the substrate and the detection time at each ambient temperature is stored.

  The temperature calculation circuit 56 calculates the ambient temperature from the detection time when no stress is applied to the substrate and the relationship stored in the storage circuit 55. The calculation method setting circuit 57 sets a stress calculation method in the stress calculation circuit 53 from the ambient temperature calculated in the temperature calculation circuit 56 and the relationship stored in the storage circuit 55.

  Since the characteristics of the SAW sensor 21 change depending on the ambient temperature, the detection time changes when the ambient temperature changes. For this reason, in the stress calculation circuit 53, it is necessary to change the stress calculation method according to the ambient temperature. Therefore, by setting the stress calculation method in the stress calculation circuit 53 according to the ambient temperature by the calculation method setting circuit 57, the magnitude of the stress can be accurately calculated.

  The stress control circuit 58 compares the magnitude of the stress calculated by the stress calculation circuit 53 with the set value (the magnitude of the stress desired to be applied to the substrate) input by the user, and according to the comparison result, the coil 33. , 34 is controlled. More specifically, when the magnitude of the stress calculated in the stress calculation circuit 53 is larger than the set value, the value of the drive current is decreased, and the magnitude of the stress calculated in the stress calculation circuit 53 is the set value. If it is smaller, the value of the drive current is increased. This makes it possible to apply a desired amount of stress to the substrate.

  Next, a method for bonding the semiconductor chip to the substrate using the linear actuator 1 while controlling the stress applied to the substrate will be described.

  In the linear actuator 1, before the semiconductor chip is bonded to the substrate, an AC voltage is applied to the coil 23 for a predetermined time by the AC voltage application circuit 51 without applying stress to the substrate, as described above. At the same time, the AC voltage applied to the coil 23 is detected by the AC voltage detection circuit 52. As described above, the offset setting circuit 54 sets the detection time at this time as a reference for measuring the stress in the stress calculation circuit 53. At the same time, the temperature calculation circuit 56 calculates the ambient temperature from the detection time at this time. A method for calculating stress in the stress calculation circuit 53 is set by the calculation method setting circuit 57 in accordance with the calculated ambient temperature.

  Next, as described above, the suction nozzle 13 that sucks the semiconductor chip is pressed against the substrate, and an AC voltage is applied to the coil 23 by the AC voltage application circuit 51 for a predetermined time. At this time, stress is applied to the suction nozzle 13 and the shaft 30 as a reaction of the force pressing the substrate, and the shaft 30 is compressed according to the magnitude of the stress. Accordingly, the piezoelectric substrate 31 fixed to the surface of the shaft 30 is also compressed, and the distance between the pair of comb-shaped electrodes 42 and 43 of the piezoelectric substrate 41 and the reflector 44 is shortened. Note that the portion of the shaft 30 to which the piezoelectric substrate 41 is fixed corresponds to the deformed portion according to the present invention.

  When the distance between the pair of comb-shaped electrodes 42 and 43 and the reflector 44 is shortened, the vibration generated between the comb-shaped electrodes 42 and 43 is reflected by the reflector 44 so as to be between the comb-shaped electrodes 42 and 43. The time until it returns to is shortened, and as a result, the detection time is shortened. The stress calculation circuit 53 calculates the magnitude of the stress applied to the substrate from the difference between the detection time detected by the AC voltage detection circuit 52 and the detection time set by the offset setting circuit 54.

  Here, since the detection time varies depending on the compression amount of the piezoelectric substrate 41 and does not vary depending on the rattling of the linear actuator 1 or the like, the linear actuator 1 is a small one used for bonding the semiconductor chip to the substrate. Even in this case, the magnitude of the stress can be accurately calculated.

  Then, the stress control circuit 58 compares the magnitude of the stress calculated by the stress calculation circuit 53 with the magnitude (set value) of the stress set by the user, and controls the drive current as described above. By repeating the operation as described above, a stress having a magnitude set by the user can be applied to the substrate.

  According to the embodiment described above, the following effects can be obtained.

  When an AC voltage is applied to the coil 23 by the AC voltage application circuit 51, the AC voltage is also applied to the coil 22 facing the coil 23 and the comb electrodes 42 and 43 connected to the coil 22. When an alternating voltage is applied to the comb-shaped electrodes 42 and 43, the portion sandwiched between the comb-shaped electrodes 42 and 43 of the piezoelectric substrate 41 vibrates, and this vibration is reflected by the reflector 44 and is reflected by the comb-shaped electrodes 42 and 43. Come back to. An AC voltage is generated in the comb-shaped electrodes 42 and 43 and the coil 22 connected to the comb-shaped electrodes 42 and 43 due to the returned vibration, whereby an AC voltage is also generated in the coil 23. Then, the AC voltage detection circuit 52 detects this AC voltage.

  Here, when stress is applied to the suction nozzle 13 and the shaft 30 by pressing the substrate, the shaft is compressed, and the piezoelectric substrate 31 disposed on the surface of the shaft 30 is also compressed. Thereby, the distance between the comb-shaped electrodes 42 and 43 and the reflector 44 in the piezoelectric substrate 41 is shortened, and accordingly, the detection time is shortened. And this detection time changes with the stress which presses a board | substrate.

  Therefore, the magnitude of stress with which the suction nozzle 13 presses the substrate can be calculated from the detection time.

  The detection time changes depending on the amount of compression of the shaft 30 (piezoelectric substrate 41) and does not change depending on the rattling of the linear actuator 1, etc. Therefore, the linear actuator 1 is a small size used for bonding the semiconductor chip to the substrate. The stress can be accurately detected even if it is a thing.

  Further, since the characteristics of the SAW sensor 11 change depending on the ambient temperature, when the ambient temperature changes, the correspondence between the stress applied to the substrate and the detection time changes. However, when the ambient temperature changes by calculating the ambient temperature in the ambient temperature detection circuit 56 and setting the stress calculation method in the stress calculation circuit 52 in accordance with the calculated ambient temperature in the calculation method setting circuit 57. Even stress can be detected accurately.

  Further, since the characteristics of the SAW sensor 11 change depending on the ambient temperature, if the ambient temperature changes, the detection time when no stress is applied to the substrate changes. However, before the stress is detected, the offset is changed. The detection time when no stress is applied to the substrate by the setting circuit 54 is set as a reference for calculating the stress in the stress calculation circuit 53, so that even if the ambient temperature changes, it is given to the substrate. The magnitude of stress can be detected accurately.

  Further, by controlling the magnitude of the current applied to the coils 33 and 34 in accordance with the magnitude of the stress calculated by the stress calculation circuit 53, the magnitude of the stress applied to the board is controlled, so that a desired value can be applied to the board. Can be applied.

  Next, modified examples in which various changes are made to the present embodiment will be described. However, components having the same configuration as in the present embodiment are denoted by the same reference numerals, and description thereof is omitted as appropriate.

  In one modification, as shown in FIG. 5, the SAW sensor 60 includes a reflector 64 on one surface of the piezoelectric substrate 41 in addition to the piezoelectric substrate 41, the comb-shaped electrodes 42 and 43, and the reflector 44 similar to those of the embodiment. The reflector 64 is arranged so that the comb-shaped electrodes 42 and 43 are sandwiched between the reflector 64 and the reflector 44. In addition to the circuits 51 to 58 similar to those of the embodiment, the control circuit 70 is connected in parallel with the coil 23 and in parallel with the two capacitors 71 and 72 connected in series with each other. And a transistor 73 connected between the capacitors 71 and 72. (Modification 1).

  In this case, the coil 23, the capacitors 71 and 72, and the transistor 73 constitute a Colpitts type oscillation circuit. Further, vibration (surface acoustic wave) propagating on the surface of the piezoelectric substrate 41 is reflected by the reflectors 44 and 64 to resonate between the reflectors 44 and 64. At this time, the comb electrodes 42 and 43 are resonated. An AC voltage corresponding to this resonance frequency is generated between That is, the SAW sensor 60 forms a resonator that exhibits the same electrical characteristics as the oscillation circuit.

  In this case, when the shaft 30 is compressed by applying stress to the substrate, and the piezoelectric substrate 41 fixed to the shaft 30 is compressed, the comb-shaped electrodes 42 and 43 and the reflectors 44 and 64 And the resonance frequency of the SAW sensor 60 (resonator) changes. As a result, the oscillation frequency of the oscillation circuit including the coil 23, the capacitors 71 and 72, and the transistor 73 connected to the SAW sensor 60 via the coil 22 also changes. Therefore, in this case, the AC voltage detection circuit 52 detects the oscillation frequency of the AC voltage applied to the coil 23, and the stress calculation circuit 53 uses the detected oscillation frequency (the detection result in the AC voltage detection circuit 52) to generate the substrate. The magnitude of the stress applied to can be calculated.

  In the first modification, the offset setting circuit 54 calculates the stress in the stress calculation circuit 53 using the oscillation frequency detected in the AC voltage detection circuit 52 in a state where no stress is applied to the substrate. Set as standard for Further, the storage circuit 55 includes the relationship between the ambient temperature and the oscillation frequency (detection result in the AC voltage detection circuit 52) detected by the AC voltage detection circuit 52 in a state where no stress is applied to the substrate, and The relationship between the magnitude of the stress applied to the substrate and the oscillation frequency detected by the AC voltage detection circuit 52 at the ambient temperature is stored. Then, the temperature calculation circuit 56 calculates the ambient temperature from the oscillation frequency detected by the AC voltage detection circuit 52 in a state where no stress is applied to the substrate and the relationship stored in the storage circuit 55, and sets the calculation method. The circuit 57 sets a method for calculating the stress in the stress calculation circuit 53 based on the calculated ambient temperature, the detected ambient temperature, and the relationship stored in the storage circuit 55.

  In the first modification, a Colpitts type oscillation circuit is formed by the coil 23, the capacitors 71 and 72, and the transistor 73 in the control device 70. However, another type of oscillation circuit including the coil 23 is formed in the control device. May be.

  In the present embodiment, the length of the coil 23 is made longer than the length of the coil 22, and the entire coil 22 is always opposed to the coil 23 even if the shaft 30 moves. On the contrary, as shown in FIG. 6, the length of the coil (movable coil) 82 connected to the SAW sensor 21 is made longer than the length of the coil (fixed coil) 83 connected to the control circuit 24. Even if 30 moves, you may comprise so that the whole coil 83 may always oppose the coil 82 (modification 2). Even in this case, the characteristics of the transformer constituted by the coil 82 and the coil 83 are always constant.

  In the present embodiment, the coil 22 is wound around the shaft 30 and the coil 23 is disposed so as to surround the coil 22. However, even if the shaft 30 moves, the entire one of the coils 22, 23 is always maintained. However, another arrangement may be used as long as it is arranged to face the other.

  In the present embodiment, the offset setting circuit 54 and the calculation method setting circuit 57 perform the setting according to the ambient temperature before the stress measurement, but the stress is always used under a constant temperature condition. In such a case, the offset setting circuit 54, the storage circuit 55, the temperature calculation circuit 56, and the calculation method setting circuit 57 may not be provided.

  In the present embodiment, the stress control circuit 58 controls the magnitude of the stress by comparing the magnitude of the stress calculated by the stress calculation circuit 53 with the magnitude of the stress set by the user. The stress control circuit 58 is not provided, and the user may manually adjust the stress while looking at the magnitude of the stress calculated in the stress calculation circuit 53.

  In the present embodiment, the magnitude of the stress applied to the outside is detected in the linear actuator and the magnitude of the stress is controlled, but the actuator has a portion that deforms when the stress is applied to the outside. If so, the present invention can be applied to other types of actuators.

  Further, in the above description, the case where the stress measuring device according to the present invention is arranged in an actuator has been described. However, as long as it has a deforming portion that is deformed when stress is applied from the outside, the device other than the actuator is used. It is also possible to provide a stress measuring device according to the present invention.

It is a schematic block diagram of the linear actuator which concerns on embodiment in this invention. (A) It is one sectional view which showed typically the fixed part and movable part of Drawing 1, and (b) is a sectional view when (a) is seen from the direction of arrow B. It is a figure which shows operation | movement of the fixed part and movable part in FIG. It is a circuit diagram of the SAW sensor, coil, and control circuit of FIG. FIG. 6 is a view corresponding to FIG. 4 of Modification 1; FIG. 10 is a view corresponding to FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Linear actuator 21 SAW sensor 22, 23 Coil 24 Control circuit 30 Shaft 41 Piezoelectric substrate 42, 43 Comb-shaped electrode 44 Reflector 51 AC voltage application circuit 52 AC voltage detection circuit 53 Stress calculation circuit 54 Offset setting circuit 55 Memory circuit 56 Temperature Calculation circuit 57 Calculation method setting circuit 58 Stress control circuit 60 SAW sensor 64 Reflector 71, 72 Capacitor 73 Transistor 82, 83 Coil

Claims (7)

A stress measuring device that measures stress applied to an object to be measured having a deformed portion that deforms when stress is applied,
A piezoelectric substrate disposed on the surface of the deformable portion, a pair of comb-shaped electrodes disposed on one surface of the piezoelectric substrate so as to face each other, and disposed on the one surface of the piezoelectric substrate A SAW sensor having a reflector that reflects a surface acoustic wave that has propagated through the one surface of the piezoelectric substrate;
A movable coil connected to the pair of comb electrodes;
A fixed coil arranged to face the movable coil and not to contact the object to be measured;
An AC voltage application circuit for applying an AC voltage to the fixed coil;
An AC voltage detection circuit for detecting an AC voltage generated in the fixed coil;
A stress calculation circuit for calculating the magnitude of stress applied to the object to be measured from the detection result in the AC voltage detection circuit;
A stress measuring device comprising: A first storage circuit for storing a relationship between a detection result in the AC voltage detection circuit and an ambient temperature in a state in which no stress is applied to the object to be measured;
A second storage circuit for storing a relationship between a stress applied to the object to be measured at a plurality of ambient temperatures and a detection result in the AC voltage detection circuit;
An ambient temperature calculation circuit that calculates an ambient temperature from the relationship stored in the first storage circuit and the detection result in the AC voltage detection circuit in a state in which no stress is applied to the object to be measured;
A calculation method setting circuit for setting a stress calculation method in the stress calculation circuit from the ambient temperature calculated by the ambient temperature calculation circuit and the relationship stored in the second storage circuit;
The stress measuring device according to claim 1, further comprising:   It further comprises an offset setting circuit for setting a detection result in the AC voltage detection circuit in a state where no stress is applied to the object to be measured as a reference when calculating stress in the stress calculation circuit. The stress measuring device according to claim 1 or 2. The SAW sensor has one of the reflectors;
The stress calculation circuit is
The magnitude of stress applied to the object to be measured is calculated from the time from when the AC voltage is applied by the fixed coil by the AC voltage application circuit until the AC voltage is detected by the AC voltage detection circuit. It is comprised, The stress measuring device of any one of Claims 1-3 characterized by the above-mentioned. The SAW sensor has the two reflectors arranged so as to sandwich the pair of comb-shaped electrodes on the one surface of the piezoelectric substrate,
An oscillation circuit including the fixed coil;
The stress calculation circuit is configured to calculate the magnitude of stress applied to the object to be measured from the frequency of the AC voltage detected by the AC voltage detection circuit. The stress measuring device according to any one of the above. The stress measuring device according to any one of claims 1 to 5,
A stress applying portion for applying stress to the outside;
The deformed portion deformed by a reaction when the stress applying portion applies stress to the outside;
With
The actuator, wherein the piezoelectric base material of the stress measuring device is disposed on a surface of the deforming portion.   The apparatus further comprises a stress control device that controls the magnitude of the stress applied to the outside by the stress applying unit according to the magnitude of the stress calculated by the stress calculation circuit of the stress measuring device. Item 7. The actuator according to Item 6.

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