Linear motion guide unit and method for measuring the load of the linear motion guide unit

Abstract

To provide a linear guide unit capable of determining the direction of a load imposed on a casing accurately.SOLUTION: A linear guide unit includes a rail, a casing, a plurality of rolling elements, a side face strain sensor, an end surface sensor, and a pair of direction conversion members. The rail includes a pair of rail side rolling faces arranged on both sides in a width direction. The casing includes a casing body and a pair of sleeve parts connected to both sides in a width direction of the casing body. The pair of sleeve parts is formed with casing side rolling faces for forming a pair of rolling element rolling passages between the rail side rolling faces and itself. The casing is formed with a pair of return passages penetrating the casing. The pair of direction conversion members is formed with a direction conversion passage for connecting the rolling element rolling passages with the return passage. The side face strain sensor is disposed on a side face of the casing. The end surface strain sensor is disposed on a casing end surface, which is an end surface of the casing in a longitudinal direction, and detects strain in a vertical direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a linear guide unit and a method for measuring the load of a linear guide unit.

Background Art

[0002] Due to the current progress of IoT (Internet of Things), the market demand for technologies for monitoring the actual load applied to mechanical parts such as bearings and linear guide units is increasing. This type of technology is described in, for example, Patent Document 1.

[0003] Patent Document 1 describes a method for detecting the strain of a linear guide unit. This linear guide unit includes a track rail and a slider that slides along the track rail. The slider includes a casing and end caps provided at both ends in the sliding direction of the casing. This casing consists of a mounting portion that is horizontal with the upper surface of the track rail, and a pair of sleeve portions that extend downward from both ends in the width direction of the mounting portion and straddle the track rail and face each other.

[0004] In Patent Document 1, two strain detection sensors are arranged adjacent to each other on the side surface in the width direction of the casing. In this publication, the strain generated on the side surface of the casing is detected by each sensor, and by calculating the strain ratio based on the detected strain value, the direction of the load applied to the casing is determined.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Document 1, errors may occur in the strain ratio value due to measurement errors in the strain value on the side surface of the casing or individual differences in the components (casing, sensor, etc.). Therefore, Patent Document 1 has the problem that it is difficult to accurately determine the direction of the load applied to the casing.

[0007] The purpose of this disclosure is to provide a linear motion guide unit and a method for measuring the load on a linear motion guide unit that can more accurately determine the direction of the load applied to the casing. [Means for solving the problem]

[0008] A linear motion guide unit according to this disclosure comprises a rail, a casing movable along the longitudinal direction of the rail, a plurality of rolling elements arranged between the rail and the casing so as to be able to roll while in contact with the rail and the casing, a side strain sensor located on the casing, an end strain sensor located on the casing, and a pair of direction changing members located at both ends of the casing in the longitudinal direction. The rail includes a pair of rail-side rolling surfaces arranged on both sides in the width direction perpendicular to the longitudinal direction and extending in the longitudinal direction. The casing includes a casing body extending in the width direction and a pair of sleeves connected to both sides of the casing body in the width direction. The pair of sleeves have casing-side rolling surfaces that face the pair of rail-side rolling surfaces and extend in the longitudinal direction, forming a pair of rolling element rolling paths between them and the rail-side rolling surfaces. The casing has a pair of return paths, which are through holes extending along each of the pair of rail-side rolling surfaces and penetrating the casing. The pair of direction changing members have direction changing paths that connect the rolling element rolling paths and the return paths. The rolling elements circulate along an annular track formed by a rolling element track, a return track, and a direction change track. Side strain sensors are located on the side of the casing, which is the surface opposite to the side facing the rail of the sleeve in the width direction. End strain sensors are located on the end face of the casing, which is the end face of the casing in the longitudinal direction.

[0009] The load measurement method for a linear motion guide unit according to this disclosure is a method for measuring the load applied to the casing of the linear motion guide unit. In this method, the magnitude of the load applied to the casing is determined based on the output of the side strain sensor, and the direction of the load applied to the casing is determined based on the output of the end face strain sensor. [Effects of the Invention]

[0010] This disclosure provides a linear motion guide unit and a method for measuring the load on a linear motion guide unit that can more accurately determine the direction of the load applied to the casing. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing the overall configuration of a linear motion guide unit according to an embodiment. [Figure 2] Figure 2 is a front view showing the casing end face of a linear motion guide unit according to an embodiment. [Figure 3] Figure 3 is a block diagram showing the configuration of the strain detection device for a linear motion guide unit according to an embodiment. [Figure 4] Figure 4 is a graph showing the relationship between the load applied to the casing and the strain at the casing end face. [Figure 5] Figure 5 is a graph showing the relationship between the load applied to the casing and the strain on the side surface of the casing. [Modes for carrying out the invention]

[0012] [Summary of the Embodiment] A linear motion guide unit according to this disclosure comprises a rail, a casing movable along the longitudinal direction of the rail, a plurality of rolling elements arranged between the rail and the casing so as to be able to roll while in contact with the rail and the casing, a side strain sensor located on the casing, an end strain sensor located on the casing, and a pair of direction changing members located at both ends of the casing in the longitudinal direction. The rail includes a pair of rail-side rolling surfaces arranged on both sides in the width direction perpendicular to the longitudinal direction and extending in the longitudinal direction. The casing includes a casing body extending in the width direction and a pair of sleeves connected to both sides of the casing body in the width direction. The pair of sleeves have casing-side rolling surfaces that face the pair of rail-side rolling surfaces and extend in the longitudinal direction, forming a pair of rolling element rolling paths between them and the rail-side rolling surfaces. The casing has a pair of return paths, which are through holes extending along each of the pair of rail-side rolling surfaces and penetrating the casing. The pair of direction changing members have direction changing paths that connect the rolling element rolling paths and the return paths. The rolling elements circulate along an annular track formed by a rolling element track, a return track, and a direction change track. Side strain sensors are located on the side of the casing, which is the surface opposite to the side facing the rail of the sleeve in the width direction. End strain sensors are located on the end face of the casing, which is the end face of the casing in the longitudinal direction.

[0013] Intensive research was conducted to determine how to accurately determine the direction of the load applied to the casing of the linear motion guide unit. As a result, it was found that at the casing end face, the strain value becomes negative when a vertical compressive load (downward load) is applied to the casing, while the strain value becomes positive when a vertical tensile load (upward load) is applied to the casing.

[0014] This disclosure is based on the above-mentioned perspective. Specifically, in the linear motion guide unit according to this disclosure, a strain sensor (end face strain sensor) is arranged on the casing end face, so that it is possible to determine whether the load applied to the casing in the vertical direction is a compressive load or a tensile load based on the positive or negative value detected by the end face strain sensor. Therefore, the linear motion guide unit of this disclosure makes it possible to determine the direction of the load applied to the casing more accurately.

[0015] Furthermore, in the linear motion guide unit according to this disclosure, strain sensors are also arranged on the side of the casing in addition to the end face strain sensors (side strain sensors). This makes it possible to avoid adjacent placement of strain sensors. Consequently, the size constraints of the strain sensors are relaxed, and multiple strain sensors can be easily arranged even in a small casing.

[0016] In the linear motion guide unit described above, an opening may be formed at the end face of the casing, which is the end of the return path. The casing body may include a rail-facing surface, which is the surface facing the rail, and an upper surface located on the opposite side of the rail-facing surface in the vertical direction perpendicular to the longitudinal and width directions. The end face strain sensor may be positioned on the end face closer to the upper surface than the opening. This configuration allows for more sensitive detection of strain occurring at the casing end face.

[0017] In the linear motion guide unit described above, an opening may be formed at the end face of the casing, which is the end of the return path. The end face strain sensor may be positioned in the width direction at a location on the end face that is closer to the casing side than to the rail-side running surface and closer to the rail-side running surface than to the opening. This configuration allows for even more sensitive detection of strain occurring at the casing end face.

[0018] In the linear guide unit, the casing body may include a rail facing surface that is a surface facing the rail, and an upper surface that is located on the opposite side of the rail facing surface in the vertical direction perpendicular to the longitudinal direction and the width direction. The end face strain sensor may be disposed at a position closer to the upper surface than the side face strain sensor. According to this configuration, the strain generated on the casing end face can be detected with higher sensitivity.

[0019] In the linear guide unit, the surface roughness of the sensor mounting region on the end face of the casing where the end face strain sensor is mounted may be greater than that of the region other than the sensor mounting region on the end face. According to this configuration, the end face strain sensor can be easily attached to the casing end face.

[0020] The linear guide unit may further include an end face strain detection unit that detects the output of the end face strain sensor, an end face strain determination unit that determines the positive or negative of the output of the end face strain sensor, and a load direction determination unit that determines the direction of the load applied to the casing based on the determination result of the end face strain determination unit. According to this configuration, the direction of the load applied to the casing can be automatically and accurately determined. Note that the end face strain detection unit, the end face strain determination unit, and the load direction determination unit may be partially or entirely integrally configured.

[0021] The load measurement method of the linear guide unit according to the present disclosure is a method for measuring the load applied to the casing in the linear guide unit. In this method, the magnitude of the load applied to the casing is determined based on the output of the side face strain sensor, and the direction of the load applied to the casing is determined based on the output of the end face strain sensor. According to this method, the direction of the load applied to the casing can be more accurately determined based on the strain value of the casing end face.

[0022] In the load measurement method for the linear motion guide unit described above, it may be determined that a tensile load is being applied to the casing when the output of the end face strain sensor is a positive value. It may also be determined that a compressive load is being applied to the casing when the output of the end face strain sensor is a negative value. This method allows for easy and accurate determination of the direction of the load applied to the casing.

[0023] [Specific examples of embodiments] Next, an example of a specific embodiment of the linear motion guide unit and the load measurement method for the linear motion guide unit of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0024] First, the configuration of the linear motion guide unit 1 according to this embodiment will be described based on Figures 1 to 3. Figure 1 is a perspective view showing the overall configuration of the linear motion guide unit 1. Figure 2 is a front view of the linear motion guide unit 1 as seen from the longitudinal direction D1 of the rail 10, with the first end cap 22 removed from the casing 21. Figure 3 is a block diagram showing the configuration of the strain detection device 70 of the linear motion guide unit 1.

[0025] Referring to Figure 1, the linear motion guide unit 1 mainly comprises a rail 10 and a slider 20. The rail 10 extends linearly in the longitudinal direction D1. The slider 20 is attached to the rail 10 so as to sandwich it from both sides in the width direction D2 (a direction perpendicular to the longitudinal direction D1), and is movable along the longitudinal direction D1. The slider 20 includes a casing 21 and a first end cap 22 and a second end cap 23 (a pair of direction changing members). As shown in Figure 1, the first end cap 22 and the second end cap 23 are located at both ends of the casing 21 in the longitudinal direction D1.

[0026] Referring to Figure 2, the rail 10 includes a rail upper surface 15, a rail lower surface 16 opposite to the rail upper surface 15 in the vertical direction D3 (a direction perpendicular to the longitudinal direction D1 and the width direction D2), and a pair of rail-side turning surfaces (first rail-side turning surface 11 and second rail-side turning surface 12) located on both sides in the width direction D2. The rail upper surface 15, the rail lower surface 16, the first rail-side turning surface 11, and the second rail-side turning surface 12 extend in the longitudinal direction D1 (the depth direction of the paper in Figure 2). The first rail-side turning surface 11 and the second rail-side turning surface 12 are formed in pairs side by side in the vertical direction D3.

[0027] The casing 21 includes a casing body 24 and a pair of sleeves (a first sleeve 25 and a second sleeve 26). As shown in Figure 2, the casing body 24 extends in the width direction D2 when viewed from the longitudinal direction D1. The casing body 24 includes a first end 24A located outside the rail 10 in the width direction D2, and a second end 24B located outside the rail 10 in the width direction D2 and on the opposite side of the first end 24A. The pair of sleeves are connected to both sides of the casing body 24 in the width direction D2. The first sleeve 25 extends vertically D3 from the first end 24A of the casing body 24 toward the lower surface 16 of the rail. The second sleeve 26 extends vertically D3 from the second end 24B of the casing body 24 toward the lower surface 16 of the rail.

[0028] The casing body 24 includes a rail-facing surface 36 that faces the rail upper surface 15, and a casing upper surface 35 (upper surface) located on the opposite side of the rail-facing surface 36 in the vertical direction D3. A pair of casing-side running surfaces (first casing-side running surface 31 and second casing-side running surface 32) are formed on a pair of sleeve portions that face a pair of rail-side running surfaces. The first casing-side running surface 31 is parallel to the first rail-side running surface 11 and extends in the longitudinal direction D1. The second casing-side running surface 32 is parallel to the second rail-side running surface 12 and extends in the longitudinal direction D1. As shown in Figure 2, the first casing-side running surface 31 and the second casing-side running surface 32 are formed in pairs, side by side in the vertical direction D3.

[0029] The casing 21 includes a casing end face 37, which is the end face of the casing 21 in the longitudinal direction D1. The first end cap 22 and the second end cap 23 (Figure 1) are positioned on this casing end face 37, respectively. The first sleeve portion 25 includes a first casing side surface 38, which is the surface opposite to the side facing the rail 10 in the width direction D2. The second sleeve portion 26 includes a second casing side surface 39, which is the surface opposite to the side facing the rail 10 in the width direction D2.

[0030] Referring to Figure 2, the linear motion guide unit 1 includes a plurality of rolling elements (first rolling elements 41 and second rolling elements 42) arranged between the rail 10 and the casing 21 so as to be able to roll while in contact with the rail 10 and the casing 21. The first casing-side rolling surface 31 forms a first rolling element transfer path (one of a pair of rolling element transfer paths) between itself and the first rail-side rolling surface 11, and the first rolling element 41 is arranged in this first rolling element transfer path. The first rolling element 41 is in contact with the first rail-side rolling surface 11 and the first casing-side rolling surface 31. The second casing-side rolling surface 32 forms a second rolling element transfer path (the other of a pair of rolling element transfer paths) between itself and the second rail-side rolling surface 12, and the second rolling element 42 is arranged in this second rolling element transfer path. The second rolling element 42 is in contact with the second rail-side running surface 12 and the second casing-side running surface 32. The first rolling element 41 and the second rolling element 42 are, for example, cylindrical rollers, but are not limited to these.

[0031] The casing 21 has a pair of return paths (first return path 51 and second return path 52) which are through holes extending along each of the pair of rail-side running surfaces and penetrating the casing 21 in the longitudinal direction D1. As shown in Figure 2, the first return path 51 is a circular through hole when viewed from the longitudinal direction D1 and penetrates the first sleeve portion 25 in the longitudinal direction D1 from one casing end face 37 to the other casing end face 37. Two first return paths 51 are formed in the first sleeve portion 25 side by side in the vertical direction D3. The second return path 52 is a circular through hole when viewed from the longitudinal direction D1, similar to the first return path 51. The second return path 52 penetrates the second sleeve portion 26 in the longitudinal direction D1 from one casing end face 37 to the other casing end face 37. Two second return paths 52 are formed in the second sleeve portion 26 side by side in the vertical direction D3. An opening is formed at the end face of the first sleeve portion 25 in the longitudinal direction D1, which is the end of the first return path 51 in the longitudinal direction D1, and an opening is formed at the end face of the second sleeve portion 26 in the longitudinal direction D1, which is the end of the second return path 52 in the longitudinal direction D1.

[0032] The first end cap 22 has a first direction change path that connects the first rolling element track (the space between the first rail-side track surface 11 and the first casing-side track surface 31) and the first return track 51. More specifically, the first rolling element track closer to the casing top surface 35 of the two first rolling element tracks and the first return track 51 further from the casing top surface 35 of the two first return tracks 51 are connected by the first direction change path. Also, the first rolling element track further from the casing top surface 35 of the two first rolling element tracks and the first return track 51 closer to the casing top surface 35 of the two first return tracks 51 are connected by the first direction change path. The second end cap 23 also has a first direction change path formed in the same way as the first end cap 22. As the slider 20 (Figure 1) moves linearly along the longitudinal direction D1 of the rail 10, the first rolling element 41 (Figure 2) circulates along a ring-shaped track formed by the first rolling element track, the first return track 51, and the first direction change track.

[0033] Although not shown in the diagram, the first end cap 22 and the second end cap 23 have a second direction change path connecting the second rolling element track and the second return path 52 (Figure 2), similar to the first direction change path. Therefore, as the slider 20 moves linearly, the second rolling element 42 (Figure 2) circulates along the annular track formed by the second rolling element track, the second return path 52, and the second direction change path.

[0034] The linear motion guide unit 1 includes a side strain sensor 61 and an end face strain sensor 62 located on the casing 21. As shown in Figure 1, in this embodiment, two side strain sensors 61 are arranged side by side in the longitudinal direction D1 on the first casing side 38. Similarly, two side strain sensors 61 are also arranged side by side in the longitudinal direction D1 on the second casing side 39 (Figure 2). The side strain sensors 61 detect strain in the vertical direction D3 occurring on the first casing side 38 and the second casing side 39. The side strain sensors 61 are strain gauges and are attached to the first casing side 38 and the second casing side 39, respectively, by adhesive, for example.

[0035] Referring to Figure 2, two end face strain sensors 62 are arranged side by side in the width direction D2 on the casing end face 37. More specifically, in the vertical direction D3, the end face strain sensors 62 are positioned closer to the casing top surface 35 than the openings of the first return path 51 and the second return path 52 on the casing end face 37. That is, the end face strain sensors 62 are located on the casing top surface 35 side of the dashed line L1 in Figure 2. Also, as shown in Figure 2, the end face strain sensors 62 are positioned closer to the casing top surface 35 than the side strain sensors 61. The end face strain sensors 62 detect the strain in the vertical direction D3 that occurs on the casing end face 37. The end face strain sensors 62 are strain gauges and are attached to the casing end face 37, for example, by adhesive. Although Figure 2 shows the end face strain sensor 62 positioned on one casing end face 37, two end face strain sensors 62 are similarly positioned on the other casing end face 37.

[0036] One end face strain sensor 62 (the right end face strain sensor 62 in Figure 2) is positioned in the width direction D2 on the casing end face 37 at a location closer to the first casing side surface 38 than to the first rail-side running surface 11, and also closer to the first rail-side running surface 11 than to the opening of the first return path 51. That is, this one end face strain sensor 62 is located on the first casing side surface 38 side of the dashed line L2 in Figure 2, and on the first rail-side running surface 11 side of the dashed line L3. Similarly, the other end face strain sensor 62 (the left end face strain sensor 62 in Figure 2) is positioned in the width direction D2 on the casing end face 37 at a location closer to the second casing side surface 39 than to the second rail-side running surface 12, and also closer to the second rail-side running surface 12 than to the opening of the second return path 52. In other words, the other end face strain sensor 62 is located on the second casing side surface 39 side of the dashed line L4 in Figure 2, and on the second rail side running surface 12 side of the dashed line L5.

[0037] In this embodiment, the sensor mounting area of ​​the casing end face 37 to which the end face strain sensor 62 is attached has a rougher surface than the area of ​​the casing end face 37 other than the sensor mounting area. However, the linear motion guide unit of this disclosure is not limited to this, and the surface roughness of the casing end face 37 may be uniform.

[0038] Referring to Figure 3, the linear motion guide unit 1 further includes a strain detection device 70. As shown in Figure 3, the strain detection device 70 includes an end face strain detection unit 71, a side face strain detection unit 72, an end face strain determination unit 73, a load estimation unit 74, and a load direction determination unit 75.

[0039] The end face strain detection unit 71 detects the output of the end face strain sensor 62. The side strain detection unit 72 detects the output of the side strain sensor 61. The end face strain detection unit 71 and the side strain detection unit 72 constitute a receiving unit that receives data from the end face strain sensor 62 and the side strain sensor 61. The end face strain determination unit 73 determines whether the output of the end face strain sensor 62 is positive or negative. The load estimation unit 74 estimates the magnitude of the load applied to the casing 21 based on the output of the side strain sensor 61. The load direction determination unit 75 determines the direction of the load applied to the casing 21 based on the determination result of the end face strain determination unit 73. The end face strain determination unit 73, the load estimation unit 74, and the load direction determination unit 75 constitute a calculation unit. The load estimation unit 74 and the load direction determination unit 75 are connected to a display unit 80, such as a display, so that the estimated load value and the load direction are displayed on the display unit 80. The load measurement of the casing 21 performed using the strain detection device 70 will be described below.

[0040] A method for measuring the load of a linear motion guide unit according to this embodiment will be described. In this method, the load applied to the casing 21 in the linear motion guide unit 1 is measured as follows.

[0041] First, the side strain sensor 61 detects vertical strain D3 occurring on the first casing side 38 and the second casing side 39, while the end face strain sensor 62 detects vertical strain D3 occurring on the casing end face 37. This detection data is transmitted to the side strain detection unit 72 and the end face strain detection unit 71, respectively.

[0042] Next, the strain detection device 70 determines the magnitude of the load applied to the casing 21 based on the output of the side strain sensor 61, and also determines the direction of the load applied to the casing 21 based on the output of the end face strain sensor 62. First, the determination of the direction of the load applied to the casing 21 will be explained.

[0043] Figure 4 shows the relationship between the magnitude of the load applied to the casing 21 (horizontal axis) and the strain of the casing end face 37 (vertical axis). In Figure 4, (1) is the data when a tensile load (upward load) of D3 in the vertical direction is applied to the casing 21, and (2) is the data when a compressive load (downward load) of D3 in the vertical direction is applied to the casing 21. As shown in Figure 4, the inventors have found that when a tensile load is applied to the casing 21, the strain generated in the casing end face 37 is a positive value, while when a compressive load is applied to the casing 21, the strain generated in the casing end face 37 is a negative value.

[0044] The end face strain determination unit 73 determines whether the strain on the casing end face 37 detected by the end face strain detection unit 71 is positive or negative. Based on this determination result, the load direction determination unit 75 determines the direction of the load applied to the casing 21. That is, the load direction determination unit 75 determines that a tensile load is applied to the casing 21 when the output of the end face strain sensor 62 is a positive value, and determines that a compressive load is applied to the casing 21 when the output of the end face strain sensor 62 is a negative value.

[0045] Next, we will explain how to determine the magnitude of the load applied to the casing 21. Figure 5 shows the relationship between the magnitude of the load applied to the casing 21 (horizontal axis) and the strain on the side surface of the casing (vertical axis). In Figure 5, (1) shows the data when a tensile load (upward load) of D3 in the vertical direction is applied to the casing 21, and (2) shows the data when a compressive load (downward load) of D3 in the vertical direction is applied to the casing 21. This correlation data is acquired in advance and stored in the memory.

[0046] The load estimation unit 74 calculates the magnitude of the load applied to the casing 21 (horizontal axis value in Figure 5) based on the strain detected by the side strain detection unit 72 and the correlation data in Figure 5. The direction of the load applied to the casing 21 is determined by the method described above. When a tensile load is applied to the casing 21, the correlation data in (1) in Figure 5 is used, while when a compressive load is applied to the casing 21, the correlation data in (2) in Figure 5 is used. That is, by using the strain on the side of the casing as the vertical axis value in the correlation data in (1) or (2) in Figure 5, an estimated value of the load applied to the casing 21 is obtained as the horizontal axis value.

[0047] Next, the method for calculating the internal load in the casing 21 will be explained. First, the value detected by the side strain sensor 61 is substituted as the vertical axis value in a straight line (showing the relationship between load and side strain when a lateral load D2 in the width direction is applied to the casing 21) that has a slope between the slope of straight line (1) and the slope of straight line (2) in the graph of Figure 5. This gives an estimated value of the load applied to the casing 21.

[0048] Next, as shown in Figure 4, based on the estimated load A applied to the casing 21, the theoretical value B1 of the end face strain in the case of tensile load (straight line (1)) and the theoretical value B2 of the end face strain in the case of compressive load (straight line (2)) are calculated. In the case of tensile load, the load ratio on the upper and lower pair of first and second casing-side rolling surfaces 31, 32 (Figure 2) is 100% on the upper side and 0% on the lower side. On the other hand, in the case of compressive load, the load ratio is 0% on the upper side and 100% on the lower side.

[0049] The difference between the theoretical values ​​of end face strain in the case of tensile load and the case of compressive load is B1-B2. Here, the rate of change of the above load ratio with respect to the change in end face strain is calculated by 100 / (B1-B2). Using this rate of change, the actual load ratio on the upper and lower pair of first and second casing-side rolling surfaces 31,32 (Figure 2) can be calculated as follows. That is, the difference between the measured value of end face strain detected by the end face strain sensor 62 and the theoretical value B2 of end face strain in the case of compressive load is found, and this difference is multiplied by the above rate of change. This calculates the amount of deviation of the load ratio from the case of a perfect compressive load (upper load ratio is 0% and lower load ratio is 100%). Note that when the load ratio of the upper and lower pair of first and second casing-side rolling surfaces 31,32 (Figure 2) is 50% each, it is the case when a lateral load in the width direction D2 is applied to the casing 21.

[0050] Next, the estimation of the load on the casing 21 as a whole will be explained. As shown in Figure 1, the casing 21 can be divided into four regions (regions 1 to 4 R1 to R4) with the center C1 in the longitudinal direction D1 and width direction D2 as the origin. In this embodiment, one set of side strain sensors 61 and end face strain sensors 62 is placed in each of the first to fourth regions R1 to R4.

[0051] In the first region R1, the force F applied to the upper and lower casing-side rolling surfaces is calculated by multiplying the estimated load by the load ratio described above. The cross product of this force F vector and the vector from the center C1 toward the casing-side rolling surfaces gives the moment M due to force F with center C1 as the origin. This moment M is similarly calculated for the upper and lower casing-side rolling surfaces in the second to fourth regions R2 to R4, and by summing these up, the total load applied to the casing 21 can be estimated.

[0052] As described above, with the linear motion guide unit 1 according to this embodiment, since the end face strain sensor 62 is arranged on the casing end face 37, it is possible to determine whether the load applied to the casing 21 is a compressive load or a tensile load based on the positive or negative value detected by the end face strain sensor 62. Therefore, the direction of the load applied to the casing 21 can be determined easily and accurately.

[0053] Other embodiments will now be described.

[0054] The position of the end face strain sensor 62 on the casing end face 37 is not limited to the position shown in Figure 2. For example, the end face strain sensor 62 may be located closer to the rail bottom surface 16 than the dashed line L1 in Figure 2, or closer to the casing side surface than the dashed lines L3 and L5 in Figure 2, or between the dashed lines L2 and L4 in Figure 2. Also, the side strain sensor 61 may be located closer to the casing top surface 35 than the end face strain sensor 62.

[0055] The embodiments disclosed herein should be understood in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0056] 1 Linear guide unit, 10 Rail, 11 First rail side running surface, 12 Second rail side running surface, 15 Rail top surface, 16 Rail bottom surface, 20 Slider, 21 Casing, 22 First end cap, 23 Second end cap, 24 Casing body, 24A First end, 24B Second end, 25 First sleeve, 26 Second sleeve, 31 First casing side running surface, 32 Second casing side running surface, 35 Casing top surface (top surface), 36 Rail opposing surface, 37 Casing end surface, 38 First casing side surface, 39 Second casing side surface, 41 First rolling element, 42 Second rolling element, 51 First return path, 52 Second return path, 61 Side strain sensor, 62 End face strain sensor, 70 Strain detection device, 71 End face strain detection unit, 72 Side strain detection unit, 73 End face strain determination unit, 74 Load estimation unit, 75 Load direction determination unit, 80 Display unit, D1 Longitudinal direction, D2 Width direction, D3 Vertical direction

Claims

1. Rails and A casing that is movable along the longitudinal direction of the rail, A plurality of rolling elements are arranged between the rail and the casing so as to be able to roll while in contact with the rail and the casing, A side strain sensor is arranged in the casing, An end face strain sensor is placed in the casing, The casing comprises a pair of direction changing members positioned at both ends in the longitudinal direction of the casing, The rail is arranged on both sides in the width direction perpendicular to the longitudinal direction and includes a pair of rail-side running surfaces extending in the longitudinal direction. The aforementioned casing is The casing body extending in the width direction, The casing body includes a pair of sleeve portions connected to both sides in the width direction, The pair of sleeve portions have casing-side running surfaces that face the pair of rail-side running surfaces, extend in the longitudinal direction, and form a pair of rolling element running paths between them and the rail-side running surfaces. The casing has a pair of return paths formed therein, which are through holes that extend along each of the pair of rail-side running surfaces and penetrate the casing. The pair of direction-changing members have a direction-changing path formed therein that connects the rolling element track and the return path. The rolling element circulates along an annular track formed by the rolling element track, the return track, and the direction change track. The side strain sensor is positioned on the side of the casing, which is the surface opposite to the side of the sleeve portion facing the rail in the width direction. The end face strain sensor is a linear motion guide unit that is positioned on the casing end face, which is the end face of the casing in the longitudinal direction, and detects strain in the vertical direction.

2. An opening, which is the end of the return path, is formed at the end face of the casing. The casing body is, The rail-facing surface is the surface facing the rail, In the vertical direction perpendicular to the longitudinal direction and the width direction, the upper surface located on the opposite side from the rail-facing surface includes, The linear motion guide unit according to claim 1, wherein the end face strain sensor is positioned on the end face closer to the upper surface than the opening.

3. An opening, which is the end of the return path, is formed at the end face of the casing. The linear motion guide unit according to claim 1 or 2, wherein the end face strain sensor is positioned in the width direction at a location on the end face that is closer to the casing side than the rail-side running surface and closer to the rail-side running surface than the opening.

4. The casing body is, The rail-facing surface is the surface facing the rail, In the vertical direction perpendicular to the longitudinal direction and the width direction, the upper surface located on the opposite side from the rail-facing surface includes, The linear motion guide unit according to any one of claims 1 to 3, wherein the end face strain sensor is positioned closer to the upper surface than the side face strain sensor.

5. The linear motion guide unit according to any one of claims 1 to 4, wherein the sensor mounting area of ​​the end face to which the end face strain sensor is attached has a greater surface roughness than the area of ​​the end face other than the sensor mounting area.

6. An end face strain detection unit that detects the output of the end face strain sensor, An end face strain determination unit that determines whether the output of the end face strain sensor is positive or negative, A linear motion guide unit according to any one of claims 1 to 5, further comprising: a load direction determination unit that determines the direction of the load applied to the casing based on the determination result of the end face strain determination unit.

7. A method for measuring the load applied to the casing in a linear motion guide unit according to any one of claims 1 to 6, A method for measuring the load of a linear motion guide unit, comprising determining the magnitude of the load applied to the casing based on the output of the side strain sensor, and determining the direction of the load applied to the casing based on the output of the end face strain sensor.

8. When the output of the end face strain sensor is a positive value, it is determined that a tensile load is being applied to the casing. A method for measuring the load of a linear motion guide unit according to claim 7, wherein it is determined that a compressive load is applied to the casing when the output of the end face strain sensor is a negative value.

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