Optical force sensor

Abstract

According to the present invention, a light-emitting unit emits light in the direction of a directional axis. A portion of the light diffusely reflected at a target that intersects the directional axis is received by a first light reception unit. At least one optical waveguide has an input end at a position at which a portion of the light generated by the light-emitting unit is incident. A second light reception unit is provided at a position at which a portion of the light outputted from an output end of the optical waveguide is incident. Displacement of a displacement member by external force changes the power of the light outputted from the output end of the optical waveguide and received by the second light reception unit. A reference light reception unit is provided at a position at which a portion of the light generated by the light-emitting unit as propagated by a reference propagation path that is unaffected by displacement of the displacement member is incident.

Description

Optical force sensor

[0001] This invention relates to an optical force sensor.

[0002] A tactile and proximity sensor that detects contact and proximity of an object based on the result of light reception is known (Patent Document 1). This tactile and proximity sensor comprises a light source, a light receiving unit, and an elastic member. The elastic member is made of an elastic material that deforms in response to an external force and comprises a reflective part that reflects light and a transmissive part that transmits light. A portion of the light emitted from the light source passes through the transmissive part of the elastic member and is diffusely reflected by the target. A portion of the light diffusely reflected by the target is received by the light receiving unit. The proximity of the target is detected from this light reception result. A portion of the light emitted from the light source and reflected by the reflective part of the elastic member is received by the light receiving unit. When an external force is applied to the elastic member, the position and orientation of the reflective part change, which changes the light reception result by the light receiving unit. Contact is detected by this change.

[0003] International Publication No. 2020 / 166185

[0004] To detect the proximity of a target, a portion of the light emitted from the light source must reach the target. In conventional sensors, a transparent section is provided in the elastic member to allow the light emitted from the light source to reach the target. As a result, external light enters the light-receiving section through the transparent section. Alternatively, when the target comes into contact with the elastic member, the light that has reached the target through the transparent section is reflected by the target, and a portion of the reflected light is received by the light-receiving section. Thus, in addition to the reflected light from the reflective section of the elastic member, external light and reflected light from the target enter the light-receiving section. This reduces the accuracy of the contact sensor.

[0005] The object of the present invention is to provide an optical force sensor that is less susceptible to the influence of external light and reflected light from a target when detecting contact.

[0006] According to one aspect of the present invention, an optical force sensor is provided comprising: a light-emitting unit that emits light in the direction of a directional axis; a first light-receiving unit that receives a portion of the light diffusely reflected by a target intersecting the directional axis; at least one optical waveguide having an input terminal at a position into which a portion of the light generated by the light-emitting unit is incident; a second light-receiving unit positioned at a position into which a portion of the light output from the output terminal of the optical waveguide is incident; a displacement member that changes the power of the light output from the output terminal of the optical waveguide and received by the second light-receiving unit by being displaced by an external force; and a reference light-receiving unit positioned at a position into which a portion of the light generated by the light-emitting unit propagates through a reference propagation path unaffected by the displacement of the displacement member and is incident.

[0007] Based on the light received by the first light receiving unit, it is possible to detect when a target is approaching. If there is external light or reflected light from the target, the external light or reflected light is detected by the first light receiving unit and the reference light receiving unit through the optical waveguide and the reference propagation path. When the target comes into contact with the displacement member and the displacement member is displaced, the light received level of the second light receiving unit changes. The light received level of the reference light receiving unit can be used as information to remove the influence of external light and reflected light from the light received level of the second light receiving unit. Therefore, the detection of contact becomes less susceptible to the influence of external light and reflected light from the target.

[0008] Figure 1 is an exploded perspective view of an optical force sensor according to the first embodiment. Figure 2 is a schematic side view showing the positional relationship between the output terminal of the optical waveguide 20, the second light receiving unit 25, and the light shielding unit 40A. Figure 3A is a cross-sectional view of the second light receiving unit 25, and Figure 3B is a cross-sectional view of the reference light receiving unit 28. Figure 4A is a graph showing the relationship between the light receiving level of the reference light receiving unit 28 and the displacement of the light shielding unit 40A, and Figure 4B is a graph showing the relationship between the ratio of the light receiving level of the second light receiving unit 25 to the light receiving level of the reference light receiving unit 28 and the displacement of the light shielding unit 40A. Figures 5A and 5B are cross-sectional views of the light shielding unit 40A and its vicinity of the optical force sensor according to a modified example of the first embodiment, perpendicular to the light propagation direction of the optical waveguide 20. Figures 6A and 6B are cross-sectional views of the light-shielding portion 40A and its vicinity in an optical force sensor according to another modification of the first embodiment, perpendicular to the direction of light propagation in the optical waveguide 20. Figures 7A and 7B are cross-sectional views of the light-shielding portion 40A and its vicinity in an optical force sensor according to another modification of the first embodiment, perpendicular to the direction of light propagation in the optical waveguide 20. Figure 8 is a schematic cross-sectional view of an optical force sensor according to the second embodiment. Figures 9A and 9B are cross-sectional views of the optical waveguide 20 and reference light-receiving portion 28 in an optical force sensor according to a modification of the second embodiment. Figure 10 is a schematic cross-sectional view of an optical force sensor according to the third embodiment. Figure 11 is an exploded perspective view of the substrate 30 and components mounted on the substrate 30 in an optical force sensor according to the fourth embodiment. Figure 12 is an exploded perspective view of an optical force sensor according to the fifth embodiment. Figure 13 is an exploded perspective view of an optical force sensor according to the sixth embodiment. Figure 14 is an exploded perspective view of an optical force sensor according to the seventh embodiment. Figure 15A is a schematic perspective view showing components related to the distance measuring function of an optical force sensor according to a modification of the seventh embodiment, and Figure 15B is a diagram showing an example of the positional relationship of four first light receiving units 50 and one light emitting unit 10 in a plan view. Figure 16 is a diagram showing the positional relationship and coordinate system of one first light receiving unit 50, a light emitting unit 10, and a target 60. Figure 17 is a schematic diagram showing the directional characteristics of the first light receiving unit 50 and the light emitting unit 10. Figure 18 is a flowchart showing the procedure executed by the control unit 80 (Figure 15A) of the optical force sensor according to a modification of the seventh embodiment.

[0009] [First Embodiment] An optical force sensor according to the first embodiment will be described with reference to the drawings from Figure 1 to Figure 4B. Figure 1 is an exploded perspective view of the optical force sensor according to the first embodiment. The optical force sensor according to the first embodiment includes a plurality of components mounted on a substrate 30, a displacement member 40 that displaces in response to an external force, and a first light receiving unit 50 mounted on a substrate 51.

[0010] The substrate 30 is equipped with a light-emitting unit 10, an optical waveguide 20, a branched optical waveguide 21, a second light-receiving unit 25, and a reference light-receiving unit 28. The light-emitting unit 10 includes a light-emitting element 10A and a transparent optical member 10B. As the light-emitting element 10A, for example, a surface-mount type light-emitting diode (LED), a vertical-cavity surface-emitting laser (VCSEL), a laser diode (LD), etc. The transparent optical member 10B is arranged on the substrate 30 so as to cover the light-emitting element 10A and has a lens function. The transparent optical member 10B gives directionality to the light emitted from the light-emitting element 10A and propagates the light in the direction of the direction axis 15. The direction axis 15 is, for example, perpendicular to the surface of the substrate 30. In this way, the light-emitting unit 10 outputs narrowly directional light. Preferably, the half-width of the direction angle of the narrowly directional light is, for example, ±15° or less.

[0011] Light is emitted from the light-emitting unit 10 in the direction of the directional axis 15, and a portion of the light that is diffusely reflected by the target (not shown) is received by the first light-receiving unit 50. The first light-receiving unit 50 includes, for example, a position-sensitive detector. The light-emitting unit 10 and the first light-receiving unit 50 constitute a triangulation-type distance measuring sensor.

[0012] The input end of the optical waveguide 20 is coupled to the side surface of the transparent optical member 10B. A portion of the light generated by the light-emitting unit 10 (i.e., the light emitted from the light-emitting element 10A) is incident on the input end of the optical waveguide 20 and transmitted through the optical waveguide 20. A branch optical waveguide 21 branches off from the optical waveguide 20. A portion of the light incident on the input end of the optical waveguide 20 is transmitted through the branch optical waveguide 21, and the remainder is transmitted through the optical waveguide 20 downstream of the branch. A second light-receiving unit 25 is positioned where a portion of the light output from the output end of the optical waveguide 20 is incident. The second light-receiving unit 25 is positioned at a distance from the output end of the optical waveguide 20.

[0013] A reference light receiving unit 28 is coupled to the output terminal of the branched optical waveguide 21. Light emitted from the output terminal of the branched optical waveguide 21 is received by the reference light receiving unit 28. The transparent optical member 10B, a portion of the optical waveguide 20, and the branched optical waveguide 21 function as a light propagation path (hereinafter referred to as the reference propagation path) that propagates the light generated in the light-emitting unit 10 to the reference light receiving unit 28.

[0014] The transparent optical member 10B, the optical waveguide 20, and the branched optical waveguide 21 are formed from the same transparent optical material. As the transparent optical material, for example, a known polymer material for waveguides can be used. Alternatively, the walls of the optical waveguide 20, which is made of the polymer material for waveguides, may be covered with a material having a lower refractive index than the material constituting the optical waveguide 20, or a metal film may be formed on the walls of the optical waveguide 20 other than the input and output ends. As the optical waveguide 20 and the branched optical waveguide 21, optical fiber cables having a core and cladding may be used, or a light guide with reflectors on its walls to allow light to propagate through the air may be used.

[0015] The displacement member 40 is supported by a plurality of elastic members 32 so as to be displaceable perpendicular to the substrate 30. For example, coil springs are used as the elastic members 32. The displacement member 40 has sufficiently high rigidity and does not substantially deform even when an external force is applied. The displacement member 40 is made of a light-blocking material and includes a light-shielding portion 40A and a press plate 40B. The press plate 40B is supported substantially parallel to the substrate 30. An opening 40C is provided in the press plate 40B. With the displacement member 40 supported on the substrate 30 by the elastic members 32, the transparent optical member 10B of the light-emitting portion 10 is inserted into the opening 40C.

[0016] A light-shielding portion 40A protrudes from the surface of the press plate 40B facing the substrate 30. With the displacement member 40 supported on the substrate 30 by the elastic member 32, the light-shielding portion 40A is positioned between the output end of the optical waveguide 20 and the second light-receiving portion 25.

[0017] Figure 2 is a schematic side view showing the positional relationship between the output end of the optical waveguide 20, the second light-receiving unit 25, and the light-shielding unit 40A. The optical waveguide 20 and the second light-receiving unit 25 are mounted on the surface of the substrate 30. The press plate 40B of the displacement member 40 is supported by the elastic member 32 so as to be displaceable on the substrate 30. The light-shielding unit 40A, which protrudes from the press plate 40B toward the substrate 30, shields a portion of the cross-section of the light propagation path from the output end of the optical waveguide 20 toward the second light-receiving unit 25. When the displacement member 40 is displaced by an external force, the area of ​​the region shielded by the light-shielding unit 40A in the cross-section of the light propagation path from the output end of the optical waveguide 20 toward the second light-receiving unit 25 changes. As a result, the power of the light received by the second light-receiving unit 25 changes. That is, the power of the light received by the second light-receiving unit 25 changes according to the force applied to the displacement member 40.

[0018] In contrast, the reference propagation path from the light-emitting unit 10 to the reference light-receiving unit 28 is not affected by the displacement of the displacement member 40. For example, the intensity of the light received by the reference light-receiving unit 28 from the light generated by the light-emitting unit 10, i.e., the reception level, is hardly affected by the displacement of the displacement member 40.

[0019] Figure 3A is a cross-sectional view of the second light-receiving unit 25. The second light-receiving unit 25 includes a light-receiving element 25A surface-mounted on a substrate 30 and an optical waveguide 25B arranged on the surface of the substrate 30. The input end of the optical waveguide 25B faces the output end of the optical waveguide 20. The output end of the optical waveguide 25B covers the light-receiving element 25A. The upper surface near the output end of the optical waveguide 25B is inclined, and light propagating through the optical waveguide 25B is reflected by the inclined surface and incident on the light-receiving element 25A.

[0020] Figure 3B is a cross-sectional view of the reference light-receiving section 28. The reference light-receiving section 28 includes a light-receiving element 28A surface-mounted on the substrate 30 and an optical waveguide 28B arranged on the surface of the substrate 30. The branched optical waveguide 21 and the optical waveguide 28B are formed of a continuous transparent optical material. That is, the input end of the optical waveguide 28B is continuous with the output end of the branched optical waveguide 21. The output end of the optical waveguide 28B covers the light-receiving element 28A. The upper surface near the output end of the optical waveguide 28B is inclined, and light propagating through the optical waveguide 28B is reflected by the inclined surface and incident on the light-receiving element 28A.

[0021] In the example shown in Figure 3B, the branched optical waveguide 21 and the optical waveguide 28B are formed from a continuous transparent optical material, but they do not necessarily need to be continuous. Similar to the configuration shown in Figure 3A, the output end of the branched optical waveguide 21 and the input end of the optical waveguide 28B may be placed opposite each other with a gap in between. If a light-shielding section is not placed in this gap, the power of the light incident on the reference light-receiving section 28 will not be affected by the displacement of the displacement member 40.

[0022] The control unit 80 shown in Figure 1 controls the emission of light from the light-emitting unit 10. The control unit 80 takes in the measurement results (receiving level) of light intensity from the second light-receiving unit 25 and the reference light-receiving unit 28, compares the two, and calculates the force applied to the displacement member 40. Furthermore, it takes in the detection results from the first light-receiving unit 50 and calculates the distance to the target based on the principle of triangulation.

[0023] Next, with reference to Figures 4A and 4B, the results of measuring the light reception levels of the second light receiving unit 25 and the reference light receiving unit 28 (Figure 1) will be described.

[0024] Figure 4A is a graph showing the relationship between the light reception level of the reference light receiving unit 28 and the displacement of the light shielding unit 40A. The horizontal axis represents the displacement of the light shielding unit 40A in units [mm], and the vertical axis represents the light reception level of the reference light receiving unit 28 in arbitrary units. The position of the light shielding unit 40A when no external force is applied to the displacement member 40 is used as the reference, and displacement in the direction toward the substrate 30 is defined as positive. The circle and star symbols in the graph indicate the light reception level when there is external light and when there is no external light, respectively.

[0025] When there is no external light, even if the light-shielding portion 40A is displaced, there is almost no change in the light-receiving level. The slight change in the light-receiving level is due to the influence of reflected light from the push plate 40B (Figure 1). When there is external light, the external light passes through the opening 40C (Figure 1) and enters the transparent optical member 10B, and is received by the reference light-receiving portion 28 after passing through the optical waveguide 20 and the branched optical waveguide 21. For this reason, the light-receiving level is higher compared to when there is no external light. In the example shown in Figure 4A, the light-receiving level is about 30% higher due to the presence of external light.

[0026] Figure 4B is a graph showing the relationship between the ratio of the light reception level of the second light reception unit 25 to the light reception level of the reference light reception unit 28 and the displacement amount of the light shielding unit 40A. The horizontal axis represents the displacement amount of the light shielding unit 40A in the unit of [mm], and the vertical axis represents the ratio of the light reception level of the second light reception unit 25 to the light reception level of the reference light reception unit 28. The circle symbols and star symbols in the graph indicate the ratios of the light reception levels when there is external light and when there is no external light, respectively. The intensity of the external light is the same as the intensity when there is external light shown in FIG. 4A.

[0027] As shown in FIG. 4A, even when the light reception level is increased by about 30% due to the presence of external light, it can be seen that the ratio of the light reception level of the second light reception unit 25 to the light reception level of the reference light reception unit 28 is hardly affected by the external light. Therefore, regardless of the presence or absence of external light, the displacement amount of the light shielding unit 40A can be determined from the ratio of the light reception levels. The force applied to the displacement member 40 can be obtained from the displacement amount of the light shielding unit 40A.

[0028] Next, the excellent effects of the first embodiment will be described. In the first embodiment, a contact sensor for detecting the contact of the target and a force sensor for measuring the force applied in the vertical direction to the displacement member 40 (FIG. 1) are realized by the light emitting unit 10, the optical waveguide 20, the branched optical waveguide 21, the second light reception unit 25, and the reference light reception unit 28. Further, a triangulation type distance measuring sensor is realized by the light emitting unit 10 and the first light reception unit 50 (FIG. 1).

[0029] Since the light emitting unit 10 is shared by the force sensor and the distance measuring sensor, it is possible to achieve miniaturization and cost reduction. When the light emitting unit 10 is shared, in order to measure the distance to the target, the light emitted from the light emitting unit 10 must be guided to the outside. If a configuration for guiding the light emitted from the light emitting unit 10 to the outside is adopted, the incidence of external light and return light to the light emitting unit 10 cannot be avoided. In the first embodiment, as described with reference to FIG. 4B, by arranging the reference light reception unit 28, the influence of external light and return light can be reduced, contact can be detected with high accuracy, and the force applied in the vertical direction can be calculated.

[0030] The displacement member 40 (Fig. 1) is not in contact with the optical systems such as the light emitting unit 10, the first light receiving unit 50, the second light receiving unit 25, the reference light receiving unit 28, the optical waveguide 20, and the branching optical waveguide 21. Therefore, even if an external force is applied to the displacement member 40, no stress is applied to the optical system, and no strain occurs.

[0031] Due to the reaction force from the elastic member 32, stress may be applied to the substrate 30, and strain may occur in the substrate 30, which may indirectly apply stress to the optical system. However, by increasing the rigidity of the substrate 30, the stress applied to the optical system and the strain generated in the optical system can be reduced to a level that can be substantially ignored. To increase the rigidity of the substrate 30, the substrate 30 may be made thicker or the substrate 30 may be backfilled with metal. In addition, it is also effective to make the location where the elastic member 32 is fixed separate from the substrate 30. For example, the substrate 30 may be fixed to a housing with high rigidity, and the elastic member 32 may be fixed to the same housing.

[0032] Next, an optical force sensor according to a modification of the first embodiment will be described with reference to the drawings from Fig. 5A to Fig. 7B.

[0033] The drawings from Fig. 5A to Fig. 7B are cross-sectional views perpendicular to the light propagation direction of the optical waveguide 20 of the light shielding portion 40A of the optical force sensor according to a modification of the first embodiment and its vicinity. In the modification shown in Fig. 5A, a leaf spring is used instead of the coil spring as the elastic member 32, and an elastomer foam is used in the modification shown in Fig. 5B. Thus, other elastic members other than the coil spring may be used as the elastic member 32.

[0034] In the first embodiment (Figs. 1 and 2), the light shielding portion 40A is displaced in the direction perpendicular (vertical direction) to the surface of the substrate 30. In contrast, in the modifications shown in the drawings from Fig. 6A to Fig. 7B, the light shielding portion 40A is displaced in the direction parallel (horizontal direction) to the surface of the substrate 30.

[0035] In the modified configuration shown in Figures 6A and 6B, the press plate 40B is connected to the light-shielding portion 40A via a link 40L. The link 40L is connected to the side of the light-shielding portion 40A that is farther away from the light propagation path of the light output from the output end of the optical waveguide 20. The link 40L has the function of converting the vertical displacement of the press plate 40B into the lateral displacement of the light-shielding portion 40A. Figure 6A shows a state in which the light-shielding portion 40A does not intersect with the light propagation path, and Figure 6B shows a state in which the light-shielding portion 40A intersects with a part of the light propagation path.

[0036] In the modified examples shown in Figures 7A and 7B, a shape-changing member 40E (for example, an air bladder, elastomer, etc.) that changes its shape due to external force is sandwiched between the press plate 40B and the substrate 30. When the shape-changing member 40E is compressed in the vertical direction, it expands in the horizontal direction, and as a result, the light-shielding portion 40A is displaced in the horizontal direction. Figure 7A shows a state in which the light-shielding portion 40A does not intersect with the light propagation path, while Figure 7B shows a state in which the shape-changing member 40E is compressed and the light-shielding portion 40A intersects with a part of the light propagation path.

[0037] As shown in the modified examples from Figures 6A to 7B, the light-shielding portion 40A may be displaced in a direction parallel to the surface of the substrate 30.

[0038] Next, other modifications of the first embodiment will be described. In the first embodiment, the light-emitting unit 10 and the first light-receiving unit 50 constitute a distance measuring sensor, but it is also possible to configure various other sensors. For example, a light-receiving element with a wide field of view may be placed in addition to the first light-receiving unit 50 to configure a light intensity type proximity sensor. In addition, a human body information detection sensor such as pulse wave, blood glucose level, and oxygen saturation may be configured.

[0039] [Second Embodiment] Next, with reference to Figure 8, an optical force sensor according to the second embodiment will be described. Hereinafter, the configuration common to the optical force sensor according to the first embodiment, which was described with reference to Figures 1 to 4B, will not be explained.

[0040] Figure 8 is a schematic cross-sectional view of an optical force sensor according to the second embodiment. In the first embodiment (Figure 1), a reference light receiving unit 28 is located at the tip of a branched optical waveguide 21 that branches off from the optical waveguide 20. In contrast, in the second embodiment, the reference light receiving unit 28 is located in the middle of the optical waveguide 20. The reference light receiving unit 28 is, for example, a surface-mount type light receiving element, and the optical waveguide 20 covers the reference light receiving unit 28. No optical waveguides branching off from the optical waveguide 20 are provided.

[0041] Light propagating through the optical waveguide 20 has a component that propagates in the vertical direction because it is reflected by the upper surface of the optical waveguide 20. The reference light receiving unit 28 receives the component of the propagating light that propagates in the vertical direction. The light propagation path from the light emitting unit 10 to the reference light receiving unit 28 (reference propagation path) is not affected by the displacement of the displacement member 40. Therefore, as in the first embodiment, the light reception level of the reference light receiving unit 28 can be used as information to eliminate the influence of external light.

[0042] Next, the excellent effects of the second embodiment will be described. In the second embodiment, as in the first embodiment, the displacement amount of the displacement member 40 is calculated based on the ratio of the light-receiving level of the second light-receiving unit 25 to the light-receiving level of the reference light-receiving unit 28. This reduces the influence of external light and reflected light, allows for high-precision contact detection, and enables the calculation of the force applied in the vertical direction.

[0043] Next, an optical force sensor according to a modification of the second embodiment will be described with reference to Figures 9A and 9B. Figures 9A and 9B are cross-sectional views of the optical waveguide 20 and reference light receiving section 28 of the optical force sensor according to a modification of the second embodiment. In the modification shown in Figure 9A, a notch 20A is formed on the upper surface of the optical waveguide 20 at a location corresponding to the reference light receiving section 28. In the modification shown in Figure 9B, a diffuse reflection surface 20B is formed on the upper surface of the optical waveguide 20 at a location corresponding to the reference light receiving section 28.

[0044] Providing a notch 20A or a diffuse reflection surface 20B on the upper surface of the optical waveguide 20 increases the power of the light incident on the reference light receiving unit 28. If the light reception level of the reference light receiving unit 28 is too low, it becomes susceptible to noise. By providing a notch 20A or a diffuse reflection surface 20B on the upper surface of the optical waveguide 20 and increasing the light reception level of the reference light receiving unit 28, the excellent effect of becoming less susceptible to noise is obtained.

[0045] [Third Embodiment] Next, with reference to Figure 10, an optical force sensor according to the third embodiment will be described. Hereinafter, the configuration common to the optical force sensor according to the second embodiment, described with reference to Figure 8, will be omitted from the explanation.

[0046] Figure 10 is a schematic cross-sectional view of an optical force sensor according to the third embodiment. In the second embodiment (Figure 8), the reference light receiving unit 28 is located in the middle of the optical waveguide 20. In contrast, in the third embodiment, the reference light receiving unit 28 is covered by the transparent optical member 10b of the light-emitting unit 10 together with the light-emitting element 10a. A portion of the light generated by the light-emitting unit 10 (light emitted from the light-emitting element 10a) propagates through the transparent optical member 10B and enters the reference light receiving unit 28. The reference transmission path from the light-emitting element 10A to the reference light receiving unit 28 is not affected by the displacement of the displacement member 40, as in the second embodiment.

[0047] Next, the excellent effects of the third embodiment will be described. In the third embodiment, as in the second embodiment, the displacement amount of the displacement member 40 is calculated based on the ratio of the light-receiving level of the second light-receiving unit 25 to the light-receiving level of the reference light-receiving unit 28. This reduces the influence of external light and reflected light, allows for high-precision contact detection, and enables the calculation of the force applied in the vertical direction.

[0048] [Fourth Embodiment] Next, an optical force sensor according to the fourth embodiment will be described with reference to Figure 11. The following description will omit details of the components common to the optical force sensor according to the first embodiment, which was described with reference to Figures 1 to 4B.

[0049] Figure 11 is an exploded perspective view of the substrate 30 and several components mounted on the substrate 30 of the optical force sensor according to the fourth embodiment. In Figure 11, the first light receiving unit 50 and the substrate 51 (Figure 1) are omitted from the description. In the first embodiment (Figure 1), the light receiving level of the second light receiving unit 25 is changed according to the displacement of the light receiving unit 40A by blocking a part of the light propagation path from the output terminal of the optical waveguide 20 to the second light receiving unit 25. In contrast, in the fourth embodiment, the light output from the output terminal of the optical waveguide 20 is reflected by the reflecting unit 40R, and a part of the reflected light is incident on the second light receiving unit 25. The reflecting unit 40R is fixed to the press plate 40B and is displaced together with the press plate 40B. As the reflecting unit 40R is displaced, the power of the light received by the second light receiving unit 25 changes. The reflection by the reflecting unit 40R may be specular reflection or diffuse reflection.

[0050] The reference light receiving unit 28 is located near the tip of the branch optical waveguide 21 that branches off from the optical waveguide 20, similar to the first embodiment (Figure 1).

[0051] Next, the superior effects of the fourth embodiment will be described. In the fourth embodiment, as in the first embodiment, the placement of the reference light receiving unit 28 reduces the influence of external light and reflected light, enabling high-precision contact detection and calculation of the force applied in the vertical direction. In the first embodiment (Figure 1), the second light receiving unit 25 is placed on the extension line of the output end of the optical waveguide 20, but in the fourth embodiment, the second light receiving unit 25 can be placed to the side of the optical waveguide 20. As a result, the dimensions of the substrate 30 in the longitudinal direction of the optical waveguide 20 can be reduced.

[0052] [Fifth Embodiment] Next, an optical force sensor according to the fifth embodiment will be described with reference to Figure 12. The following description will omit the explanation of components common to the optical force sensor according to the first embodiment, which was described with reference to Figures 1 to 4B.

[0053] Figure 12 is an exploded perspective view of an optical force sensor according to the fifth embodiment. In the first embodiment (Figure 1), a triangulation-type distance measuring sensor is configured by a light-emitting unit 10 and a first light-receiving unit 50. In contrast, in the fifth embodiment, a TOF (Time of Flight) module 11 has the functions of both the light-emitting unit 10 and the first light-receiving unit 50. The TOF module 11 includes a vertical-cavity surface-emitting laser (VCSEL) as the light-emitting unit 10 and a photodiode, phototransistor, etc. as the first light-receiving unit 50, thereby configuring a TOF-type distance measuring sensor.

[0054] Because the VCSEL outputs a narrowly directional laser beam, it may not be necessary to place an external lens. In this case, a lens to focus the laser beam output from the VCSEL is unnecessary. The laser beam output from the VCSEL propagates to the outside through the opening 40C provided in the displacement member 40. Distance measurement can be performed by the TOF control unit 12 controlling the TOF module 11.

[0055] The configurations of the optical waveguide 20, the second light receiving unit 25, the branched optical waveguide 21, the reference light receiving unit 28, and the displacement member 40 are the same as those of the optical force sensor according to the first embodiment (Figure 1). The vicinity of the input end of the optical waveguide 20 covers the TOF module 11. The laser beam output from the VCSEL has narrow directivity, but some components also propagate in a direction parallel to the surface of the substrate 30 and are incident on the optical waveguide 20 from its input end. Notches or diffuse reflection surfaces, as shown in Figures 9A and 9B, may be provided on the upper surface of the optical waveguide 20 in an area that overlaps with a portion of the path of the laser beam output from the VCSEL and does not affect the distance measurement performance of the TOF module 11. Providing notches or diffuse reflection surfaces allows the laser beam output from the VCSEL to propagate efficiently into the optical waveguide 20.

[0056] Next, the excellent effects of the fifth embodiment will be described. In the fifth embodiment, as in the first embodiment, the reference light receiving unit 28 is arranged to reduce the influence of external light and reflected light, enabling high-precision contact detection and calculation of the force applied in the vertical direction.

[0057] Instead of the TOF module 11, the LiDAR sensor may be configured using the light-emitting unit 10 and the first light-receiving unit 50.

[0058] [Sixth Embodiment] Next, an optical force sensor according to the sixth embodiment will be described with reference to Figure 13. Hereinafter, the configuration common to the optical force sensor according to the first embodiment, described with reference to Figures 1 to 4B, will be omitted from the explanation.

[0059] Figure 13 is an exploded perspective view of an optical force sensor according to the sixth embodiment. In the first embodiment (Figure 1), only one first light-receiving unit 50 is provided, but in the sixth embodiment, multiple first light-receiving units 50 are provided. For example, four first light-receiving units 50 are arranged in a point-symmetric relationship with respect to the light-emitting unit 10.

[0060] Each of the four first light-receiving units 50 has a different directional characteristic. When the distance from the light-emitting unit 10 to the target changes, the light-receiving level of each first light-receiving unit 50 changes. Because each of the first light-receiving units 50 has a different directional characteristic, the manner in which the light-receiving level changes also differs. For example, if the ratio of the light-receiving levels of two first light-receiving units 50 changes monotonically in accordance with the change in distance to the target, the distance to the target can be calculated from the ratio of the light-receiving levels.

[0061] Next, the excellent effects of the sixth embodiment will be described. In the sixth embodiment, as in the first embodiment, the placement of the reference light receiving unit 28 reduces the influence of external light and reflected light, enabling high-precision contact detection and calculation of the force applied in the vertical direction. Furthermore, by arranging multiple first light receiving units 50 with different directional characteristics, the distance to the target can be calculated. Note that if only one first light receiving unit 50 is used, it can be operated as a sensor that detects the proximity of a target without performing distance measurement.

[0062] [Seventh Embodiment] Next, with reference to Figure 14, an optical force sensor according to the seventh embodiment will be described. Hereinafter, the configuration common to the optical force sensor according to the first embodiment, which was described with reference to Figures 1 to 4B, will be omitted from the explanation.

[0063] Figure 14 is an exploded perspective view of an optical force sensor according to the seventh embodiment. In the first embodiment (Figure 1), one optical waveguide 20 is coupled to the transparent optical member 10B of the light-emitting part 10. In contrast, in the seventh embodiment, four optical waveguides 20 are coupled to the transparent optical member 10B. The four optical waveguides 20 are arranged radially on the surface of the substrate 30 with the light-emitting part 10 as the center. Specifically, the four optical waveguides 20 are positioned to be four rotationally symmetrical with respect to the light-emitting part 10.

[0064] The lengths of the four optical waveguides 20 are equal. That is, the output ends of the four optical waveguides 20 are located on a single circle centered on the light-emitting unit 10. Four second light-receiving units 25 are arranged opposite each output end of the four optical waveguides 20 at intervals.

[0065] The reference light receiving unit 28 is coupled to the side surface of the transparent optical member 10B. Specifically, the input end of the optical waveguide 28B of the reference light receiving unit 28 is coupled to the side surface of the transparent optical member 10B, and the vicinity of the output end of the optical waveguide 28B covers the light receiving element 28A mounted on the substrate 30. One reference light receiving unit 28 can be used as a reference light receiving level for each of the light receiving levels of the four second light receiving units 25.

[0066] Four first light-receiving units 50 are mounted on the surface of the substrate 30. Each of the four first light-receiving units 50 is positioned between two adjacent second light-receiving units 25 in the circumferential direction centered on the light-emitting unit 10.

[0067] Eight elastic members 32 are arranged along the circumference centered on the light-emitting unit 10, in positions that do not interfere with the second light-receiving unit 25 and the first light-receiving unit 50. A displacement member 40 is supported so as to be displaceable relative to the substrate 30 via the elastic members 32. The displacement member 40 includes a press plate 40B and a light-shielding portion 40A that protrudes from the press plate 40B toward the substrate 30. The press plate 40B is provided with an opening 40C into which the transparent optical member 10B of the light-emitting unit 10 is inserted, and four openings 40D into which each of the four first light-receiving units 50 is inserted.

[0068] The light-shielding section 40A has a ring-shaped form centered on the light-emitting section 10 and is positioned between each output end of the four optical waveguides 20 and the second light-receiving section 25 facing them.

[0069] When the displacement member 40 is displaced perpendicular to the substrate 30 while maintaining a position parallel to the substrate 30, the light reception levels of the four second light receiving units 25 change uniformly. The ratio of the light reception levels of the four second light receiving units 25 to the light reception level of the reference light receiving unit 28 also changes uniformly. Based on this change, the force applied to the displacement member 40 can be calculated.

[0070] Furthermore, when the displacement member 40 is tilted relative to the substrate 30, the light-receiving levels of each of the four second light-receiving units 25 change unevenly with respect to the light-receiving level of the reference light-receiving unit 28. This makes it possible to calculate the displacement of the light-shielding unit 40A located between each output end of the four optical waveguides 20 and the second light-receiving unit 25. From these displacement amounts, the tilt angle and tilt direction of the press plate 40B can be determined. From this tilt angle and tilt direction, the moment of force applied to the displacement member 40 can be calculated.

[0071] Next, the excellent effects of the seventh embodiment will be described. In the seventh embodiment, as described above, in addition to the vertical force applied to the displacement member 40, the moment of force applied to the displacement member 40 can be calculated. Furthermore, in the seventh embodiment, by having the narrowly directional light output from the light-emitting unit 10 reflected by the target and the reflected light received by the four first light-receiving units 50, sensors with various functions can be realized. For example, as in the first embodiment, it is also possible to realize a triangulation type distance measuring sensor.

[0072] In addition, the direction from which the target is approaching can be detected by simply detecting the amount of reflected light with the four first light-receiving units 50. By changing the directivity and position of each first light-receiving unit 50, it is also possible to realize a distance measuring sensor, similar to the sixth embodiment (Figure 13).

[0073] In the seventh embodiment, four optical waveguides 20 and four second light receiving units 25 are arranged, but three of each may be arranged, or five or more of each may be arranged.

[0074] Next, with reference to Figures 15A to 18, an optical force sensor according to a modification of the seventh embodiment will be described. In this modification, the distance to the target and the orientation of the target can be calculated by receiving reflected light from the target with four first light receiving units 50.

[0075] Figure 15A is a schematic perspective view showing components related to the distance measuring function of an optical force sensor according to a modification of the seventh embodiment. Four first light receiving units 50 and one light emitting unit 10 are mounted on a substrate 30. A control unit 80 controls the light emitting unit 10 and the first light receiving units 50. For example, a photodiode, phototransistor, CdS cell, etc., can be used as the first light receiving unit 50. For example, an LED, VCSEL, etc., can be used as the light emitting unit 10.

[0076] Four first light-receiving units 50 and one light-emitting unit 10 are arranged on the surface of the substrate 30. The optical force sensor detects a target 60 located on the directional axis 15 of the light-emitting unit 10. The directional axis 15 is perpendicular to the surface of the substrate 30.

[0077] Figure 15B shows an example of the positional relationship of the four first light-receiving units 50 and the one light-emitting unit 10 in a plan view. The four first light-receiving units 50 are not arranged on a common straight line passing through the light-emitting unit 10, nor are they arranged on a common circumference centered on the light-emitting unit 10. That is, when a straight line SL is drawn passing through the light-emitting unit 10 and one first light-receiving unit 50, at least one of the other three first light-receiving units 50 is positioned outside the straight line SL. In the example shown in Figure 15B, two of the first light-receiving units 50 are positioned outside the straight line SL. Also, when a circumference C is drawn centered on the light-emitting unit 10 and passing through one first light-receiving unit 50, at least one of the other three first light-receiving units 50 is positioned outside the circumference C. In the example shown in Figure 15B, two of the first light-receiving units 50 are positioned outside the circumference C.

[0078] Due to such an arrangement, the distance between at least one first light-receiving unit 50 and the light-emitting unit 10 is different from the distances between the other three first light-receiving units 50 and the light-emitting unit 10. A total of four light-receiving and light-emitting pairs are formed by each of the four first light-receiving units 50 and one light-emitting unit 10.

[0079] Next, referring to FIG. 16, the definition of the coordinate system and various parameters will be described. FIG. 16 is a diagram showing the positional relationship between one first light-receiving unit 50, the light-emitting unit 10, and the target 60, and the coordinate system. The xy plane of the xyz orthogonal coordinate system corresponds to the surface of the substrate 30, and the light-emitting unit 10 is arranged at the origin O. The z-axis corresponds to the pointing axis 15. Note that a left-handed system is adopted as the xyz orthogonal coordinate system.

[0080] When the four first light-receiving units 50 are numbered in order from 1, the i-th first light-receiving unit 50 is denoted as 50i. The x-coordinate and y-coordinate of the first light-receiving unit 50i are denoted as a ｘｉ , a ｙｉ respectively, and the distance from the origin O to the first light-receiving unit 50i is denoted as r ｉ . The azimuth angle of the position of the first light-receiving unit 50i with respect to the x-axis as the reference direction is denoted as θ ｒｉ .

[0081] The intersection point of the surface of the target 60 facing the origin O and the pointing axis 15 (hereinafter referred to as the representative point of the target 60) is denoted as P. The distance from the origin O (light-emitting unit 10) to the representative point P of the target 60 is denoted as z. The distance z from the light-emitting unit 10 to the representative point P of the target 60 may sometimes be simply referred to as the distance z from the light-emitting unit 10 to the target 60. The unit vector from the representative point P of the target 60 to the first light-receiving unit 50i is denoted as n ｉ . The angle formed by the unit vector n ｉ and the pointing axis 15 is denoted as θ ｉ .

[0082] The unit normal vector of the surface of the target 60 at the position of the representative point P is denoted as n ｓ . The angle formed by the unit normal vector n ｓ and the pointing axis 15 is denoted as φ ｚ . The angle φ ｚ is referred to as the inclination angle of the target 60, and the unit normal vector nｓ The angle between the perpendicular projection of the image onto the xy-plane and the x-axis is φ. ｘ This is how it is indicated. Angle φ ｘ This is called the inclination azimuth angle of the surface of target 60.

[0083] Figure 17 is a schematic diagram showing the directional characteristics of the first light-receiving unit 50 and the light-emitting unit 10. The directional characteristics DC1 of the first light-receiving unit 50 and DC2 of the light-emitting unit 10 are shown in graph form. The tilt angle from the positive z-axis is denoted as θ. In the first light-receiving unit 50, the light-receiving sensitivity is maximum at θ = 0° (forward direction), and the light-receiving sensitivity decreases as the tilt angle θ increases. The tilt angle θ at which the light-receiving sensitivity becomes half of the light-receiving sensitivity in the forward direction is called the half-angle at half maximum (HMAX) θ. １／２ In the light-emitting section 10, the light intensity is maximum at θ = 0° (forward direction), and as the inclination angle θ increases, the light intensity decreases. The inclination angle θ at which the light intensity becomes half of the light intensity in the forward direction is called the half-angle at half maximum θ. １／２ That's what they say.

[0084] The first light-receiving unit 50 has a wider angle of view than the light-emitting unit 10. For example, it has a wide-angle directional characteristic that allows it to receive reflected light from a target 60 (Figure 15A) located on the directional axis 15 with sufficient sensitivity. The light-emitting unit 10 has a sharp directional characteristic that reduces the light intensity incident on an object located far off the directional axis 15 to a sufficiently small level. For example, the half-angle θ of the directional characteristic of the light-emitting unit 10. １／２ The angle is preferably 15° or less, more preferably 10° or less, and most preferably 5° or less.

[0085] If the directional characteristics of the first light-receiving unit 50 do not depend on the azimuth angle, the directional characteristics LD(θ) of the first light-receiving unit 50 can generally be approximated by the following formula. Here, n is a parameter determined by the directional characteristics of the first light-receiving unit 50. The larger n is, the sharper the directional characteristics become.

[0086] The light receiving sensitivity of the i-th first light receiving unit 50i in the front direction is C ｉThe light emission intensity of the light-emitting unit 10 is denoted as G. The reflectance of the surface of the target 60 is denoted as α. The directional characteristics LD(θ) of the four first light-receiving units 50 are the same.

[0087] The intensity of light detected by the first light-receiving unit 50i, that is, the luminance Li of the representative point P when the representative point P is viewed from the first light-receiving unit 50i as a new light source, is expressed by the following formula.

[0088] The z in the denominator of the right-hand side of equation (2) β The term indicates that as the distance z increases, the field of view of the light-emitting unit 10 widens, and the contribution of brightness per unit area of ​​the surface of the target 60 (Figure 1A) decreases. When light is irradiated onto a part of the surface of the target 60, and the surface of the target 60 is larger than the irradiation area of ​​the light-emitting unit 10, the irradiation area of ​​the light-emitting unit 10 will remain inside the surface of the target 60 even as the distance z increases. In such cases, z β The influence of this term becomes smaller. The shape and size of the target 60 and the half-angle at half maximum θ of the directional characteristics of the light-emitting part 10. １／２ Depending on the magnitude of the factor, β in equation (2) will actually take on a value within the range of 0 to 2.

[0089] The parameter C on the right-hand side of equation (2) ｉ αG / z β Since this is common among the four first light-receiving units 50, in equation (2), the unknown is parameter C. ｉ αG / z β , distance z, tilt azimuth φ ｘ , inclination angle φ ｚ These are the four units, and four equations (2) are generated with i = 1, 2, 3, and 4. Since the four first light-receiving units 50 are not arranged on a single common straight line passing through the light-emitting unit 10, nor are they arranged on a single common circle centered on the light-emitting unit 10, the four equations are linearly independent. For this reason, the control unit 80 solves this system of four equations to determine the parameter C ｉ αG / z β , distance z, tilt azimuth φ ｘ , inclination angle φ ｚ It is possible to find this.

[0090] Next, with reference to Figure 18, a method for detecting the target 60 (Figure 16) using an optical force sensor according to a modification of the seventh embodiment will be described. Figure 18 is a flowchart showing the procedure executed by the control unit 80 (Figure 15A) of the optical force sensor according to a modification of the seventh embodiment.

[0091] The control unit 80 (Figure 15A) causes the light-emitting unit 10 to emit light and measures the intensity of the light received by each of the four first light-receiving units 50 (step SA1). Substituting each of the four measured values ​​from the first light-receiving units 50 into equation (2) generates a system of four linear equations, and by solving the system of four linear equations, the distance z and the tilt azimuth angle φ are obtained. ｘ , inclination angle φ ｚ We seek (Step SA2).

[0092] The optical force sensor according to the seventh embodiment, as described with reference to Figures 15A to 18, can determine not only the distance to the target 60 (Figure 15A), but also the tilt azimuth and tilt angle of the target 60.

[0093] The embodiments described above are illustrative, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. Similar effects and benefits from similar configurations in multiple embodiments will not be mentioned sequentially for each embodiment. Furthermore, the present invention is not limited to the embodiments described above. For example, it will be obvious to those skilled in the art that various modifications, improvements, and combinations are possible.

[0094] 10 Light-emitting section 10A Light-emitting element 10B Transparent optical member 11 TOF module 12 TOF control unit 15 Directional axis 20 Optical waveguide 20A Notch 20B Irregular reflection surface 21 Branch optical waveguide 25 Second light-receiving section 25A Light-receiving element 25B Optical waveguide 28 Reference light-receiving section 28A Light-receiving element 28B Optical waveguide 30 Substrate 31 Virtual plane 32 Elastic member 40 Displacement member 40A Light-shielding section 40B Pressing plate 40C, 40D Opening 40E Shape-changing member 40L Link 40R Reflecting section 50 First light-receiving section 51 Substrate 60 Target 80 Control unit

Claims

1. An optical force sensor comprising: a light-emitting unit that emits light in the direction of a directional axis; a first light-receiving unit that receives a portion of the light diffusely reflected by a target intersecting the directional axis; at least one optical waveguide having an input terminal at a position into which a portion of the light generated by the light-emitting unit is incident; a second light-receiving unit positioned at a position into which a portion of the light output from the output terminal of the optical waveguide is incident; a displacement member that changes the power of the light output from the output terminal of the optical waveguide and received by the second light-receiving unit by being displaced by an external force; and a reference light-receiving unit positioned at a position into which a portion of the light generated by the light-emitting unit is incident after propagating through a reference propagation path that is not affected by the displacement of the displacement member.

2. The optical force sensor according to claim 1, further comprising a substrate on which the light-emitting unit, the optical waveguide, the second light-receiving unit, and the reference light-receiving unit are fixed, and an elastic member that supports the displacement member so as to be displaceable relative to the substrate.

3. The optical force sensor according to claim 2, wherein the light-emitting portion includes a light-emitting element that generates light and a transparent optical member disposed on the substrate so as to cover the light-emitting element and functioning as a lens, and the input end of the optical waveguide is coupled to the side surface of the transparent optical member.

4. The optical force sensor according to any one of claims 1 to 3, wherein the displacement member includes a light-shielding portion that shields a portion of the cross-section of the light propagation path from the output end of the optical waveguide to the second light-receiving portion, and the power of the light received by the second light-receiving portion changes as the position of the light-shielding portion changes.

5. The optical force sensor according to any one of claims 1 to 3, wherein the displacement member includes a reflecting portion that reflects a portion of the light output from the output end of the optical waveguide toward the second light receiving portion, and the power of the light received by the second light receiving portion changes as the position of the reflecting portion changes.

6. The optical force sensor according to any one of claims 1 to 5, wherein at least three optical waveguides are arranged so as to extend radially from the light-emitting portion along a plane perpendicular to the directional axis, and the second light-receiving portion is arranged for each of the optical waveguides.

7. The optical force sensor according to any one of claims 1 to 6, wherein the light-emitting unit and the first light-receiving unit constitute a light intensity type proximity sensor, a triangulation type distance measuring sensor, a TOF type distance measuring sensor, a LiDAR sensor, or a bio-information detection sensor.

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