Fluid pressure cylinder travel time sensor

Abstract

SOLUTION: To provide a fluid pressure cylinder movement time sensor comprising: a single magnetic sensor 12, in which, a time point when magnetic flux density detected by the magnetic sensor is greater than or lower than a first threshold value, is one of a start point and a finish point, and a time point when the magnetic flux density detected by the magnetic sensor is greater rthan or lower than a second threshold value, is the other of the start point and the finish point.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a sensor that measures the time required for a piston of a fluid pressure cylinder such as an air cylinder to move a predetermined stroke. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a fluid pressure cylinder has been known that includes a sensor that detects the magnetic force of a magnet attached to a piston and detects the position of the piston.

[0003] For example, Patent Document 1 describes a position detection device for a fluid pressure cylinder in which a pair of magnets is attached to the piston and two proximity switches are arranged on the outside of the cylinder tube. This position detection device for a fluid pressure cylinder uses a pair of magnets with the same poles facing each other, thereby increasing the peak of the magnetic force to be detected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5889808 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned fluid pressure cylinder position detection device requires two proximity sensors (magnetic sensors). Generally, if there are multiple piston positions to be detected, a corresponding number of magnetic sensors are required. Therefore, to measure the time it takes for the piston to move from a predetermined first position to a predetermined second position, two magnetic sensors are required.

[0006] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0007] The fluid pressure cylinder travel time sensor according to the present invention includes a single magnetic sensor that detects the magnetic flux density of a magnet attached to a piston of a fluid pressure cylinder and measures the time required for the piston to travel a predetermined stroke. The magnet is positioned so that its magnetization direction coincides with the direction of piston movement, and the magnetic sensor can detect magnetic flux density perpendicular to the direction of piston movement. The relationship between the position of the magnet along the direction of piston movement and the magnetic flux density detected by the magnetic sensor is represented by a curve having a positive maximum value and a negative minimum value. A positive value smaller than the positive maximum value is set as a first threshold, and a negative value larger than the negative minimum value is set as a second threshold. The point in time when the magnetic flux density detected by the magnetic sensor exceeds or falls below the first threshold is set as one of the start point and the end point, and the point in time when the magnetic flux density detected by the magnetic sensor exceeds or falls below the second threshold is set as the other of the start point and the end point. The time from the start point to the end point is then measured.

[0008] According to the above-described fluid pressure cylinder movement time sensor, the magnetic flux density detected by the single single-axis magnetic sensor can be compared with a first threshold value and a second threshold value to determine the start and end points of the piston moving a predetermined stroke. [Effects of the Invention]

[0009] The fluid pressure cylinder movement time sensor according to the present invention can determine the start and end points based on the magnetic flux density detected by a single single-axis magnetic sensor, and therefore can measure the time required for the piston to move a predetermined stroke using a magnetic sensor with a simple configuration. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the basic configuration of a fluid pressure cylinder equipped with a fluid pressure cylinder movement time sensor of the present invention. [Figure 2] FIG. 2 is a diagram showing the relationship between the piston position and the detected magnetic flux density in the fluid pressure cylinder of FIG. [Figure 3]FIG. 3 is a diagram for explaining a method for determining the start point and the end point using a threshold value of the magnetic flux density. [Figure 4] FIG. 4 is a diagram for explaining a method for setting the determination conditions for the start point and the end point. [Figure 5] FIG. 5 is a diagram for explaining a first application mode of the fluid pressure cylinder movement time sensor of the present invention. [Figure 6] FIG. 6 is a diagram for explaining a second application mode of the fluid pressure cylinder movement time sensor of the present invention. [Figure 7] FIG. 7 is a diagram for explaining a third application mode of the fluid pressure cylinder movement time sensor of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The basic configuration of a fluid pressure cylinder 14 equipped with a fluid pressure cylinder travel time sensor 10 according to an embodiment of the present invention is shown in Figure 1. A permanent magnet (magnet) 18 is attached to the piston 16 of the fluid pressure cylinder 14. The magnetization direction of the permanent magnet 18 coincides with the movement direction (X direction) of the piston 16. The fluid pressure cylinder travel time sensor 10 includes a magnetic sensor 12 capable of detecting the magnetic flux density of the permanent magnet 18, and is disposed outside a cylinder tube 20 of the fluid pressure cylinder 14.

[0012] The magnetic sensor 12 is a one-axis magnetic sensor composed of a Hall IC or the like. The magnetic sensor 12 detects magnetic flux density in a direction perpendicular to the movement direction of the piston 16 (Y direction), but does not detect magnetic flux density in the movement direction of the piston 16. The fluid pressure cylinder movement time sensor 10 including the magnetic sensor 12 is attached to the cylinder tube 20 in a state where its position can be adjusted along the longitudinal direction (X direction) of the cylinder tube 20. The fluid pressure cylinder movement time sensor 10 is equipped with a control unit, a calculation unit, a memory unit, etc., which are composed of a circuit board (not shown).

[0013] The relationship between the position of the permanent magnet 18 along the movement direction of the piston 16 and the magnetic flux density detected by the magnetic sensor 12 is shown in Figure 2. Hereinafter, the position of the permanent magnet 18 along the movement direction of the piston 16 will be referred to as the "piston position." Also, the magnetic flux density detected by the magnetic sensor 12 will be referred to as the "detected magnetic flux density." The piston position when the detected magnetic flux density is zero is taken to be zero.

[0014] In the negative region of the piston position, as the piston 16 moves from a position far away from the origin toward the origin, the detected magnetic flux density gradually increases within the positive value range, reaches a maximum value M1, and then decreases approximately linearly to zero. In the positive region of the piston position, as the piston 16 moves from a position far away from the origin toward the origin, the detected magnetic flux density gradually decreases within the negative value range, reaches a minimum value M2, and then increases approximately linearly to zero.

[0015] The detected magnetic flux density varies approximately linearly between the vicinity of the maximum value and the vicinity of the minimum value. For convenience, in the present invention, the relationship between the piston position and the detected magnetic flux density is represented by a curve, including this linearly varying portion. The curve representing the relationship between the piston position and the detected magnetic flux density is symmetrical with respect to the origin. In FIG. 2 , the detected magnetic flux density is positive in the negative piston position region and negative in the positive piston position region. When the magnetic pole orientation of the permanent magnet 18 is reversed, the detected magnetic flux density is negative in the negative piston position region and positive in the positive piston position region. The following description will be based on the curve shown in FIG. 2 , but the same applies when the magnetic pole orientation of the permanent magnet 18 is reversed.

[0016] The present invention is a sensor that measures the time required for the piston 16 to move a predetermined stroke (hereinafter referred to as the "movement time of the piston 16"). It is important to determine the start and end points on the time axis when the piston 16 moves a predetermined stroke. Below, with reference to Figure 3, we will explain how to determine these start and end points using two threshold values ​​related to magnetic flux density.

[0017] Figure 3 shows the relationship between piston position and detected magnetic flux density along with specific numerical values, as well as two threshold values ​​for magnetic flux density. In the example in Figure 3, when the piston position is -7 mm (millimeters), the detected magnetic flux density reaches a maximum, with a maximum value M1 of 5 mT (millitesla). When the piston position is 7 mm, the detected magnetic flux density reaches a minimum, with a minimum value M2 of -5 mT. The absolute value of minimum value M2 is equal to the absolute value of maximum value M1.

[0018] A positive value smaller than the maximum value M1 is set as the first threshold T1, and a negative value larger than the minimum value M2 is set as the second threshold T2. The absolute value of the second threshold T2 may be the same as or different from the absolute value of the first threshold T1. In the example of FIG. 3, the first threshold T1 is 3.5 mT, the second threshold T2 is −3.5 mT, and the absolute value of the second threshold T2 is equal to the absolute value of the first threshold T1.

[0019] The detected magnetic flux density is equal to the first threshold value T1 around the piston position where the detected magnetic flux density is maximum. That is, when the piston position is the first position P1 and the second position P2, the detected magnetic flux density is equal to the first threshold value T1. Also, the detected magnetic flux density is equal to the second threshold value T2 around the piston position where the detected magnetic flux density is minimum. That is, when the piston position is the third position P3 and the fourth position P4, the detected magnetic flux density is equal to the second threshold value T2. In the example of FIG. 3, the first position P1 is -11 mm, the second position P2 is -3 mm, the third position P3 is 3 mm, and the fourth position P4 is 11 mm.

[0020] First, consider the case where the piston 16 moves from the negative region toward the positive region of the piston position. As described above, the detected magnetic flux density becomes equal to the first threshold value T1 at two piston positions, the first position P1 and the second position P2. The position at which the detected magnetic flux density becomes equal to the first threshold value T1 can be determined by monitoring changes in the detected magnetic flux density. That is, when the detected magnetic flux density changes from being smaller than the first threshold value T1 to being larger than it, it can be determined that the piston 16 has passed the first position P1. When the detected magnetic flux density changes from being larger than the first threshold value T1 to being smaller than it, it can be determined that the piston 16 has passed the second position P2.

[0021] The detected magnetic flux density is equal to the second threshold value T2 at two piston positions, the third position P3 and the fourth position P4. The position at which the detected magnetic flux density is equal to the second threshold value T2 can be determined by monitoring changes in the detected magnetic flux density. That is, when the detected magnetic flux density changes from being greater than the second threshold value T2 to being less than the second threshold value T2, it can be determined that the piston 16 has passed the third position P3. When the detected magnetic flux density changes from being less than the second threshold value T2 to being greater than the second threshold value T2, it can be determined that the piston 16 has passed the fourth position P4.

[0022] Since the piston 16 moves from the negative region toward the positive region, the start point is determined to be the point when the piston 16 passes through the first position P1 or the second position P2. The end point is determined to be the point when the piston 16 passes through the third position P3 or the fourth position P4. Then, by measuring the time from the start point to the end point, the movement time of the piston 16 can be measured.

[0023] There are four possible combinations of the two starting points and the two end points. Among the four combinations, when the first position P1 is the starting point and the fourth position P4 is the end point, the distance between the piston position at the starting point and the piston position at the end point is the maximum. Furthermore, among the four combinations, when the second position P2 is the starting point and the third position P3 is the end point, the distance between the piston position at the starting point and the piston position at the end point is the minimum. Hereinafter, the piston position at the starting point will be referred to as the "starting point position," and the piston position at the end point will be referred to as the "end point position."

[0024] Next, consider the case where the piston 16 moves from the positive region toward the negative region of the piston position. The detected magnetic flux density becomes equal to the second threshold value T2 at two piston positions, the fourth position P4 and the third position P3. The position at which the detected magnetic flux density becomes equal to the second threshold value T2 can be determined by monitoring changes in the detected magnetic flux density. That is, when the detected magnetic flux density changes from being greater than the second threshold value T2 to being less than the second threshold value T2, it can be determined that the piston 16 has passed the fourth position P4. When the detected magnetic flux density changes from being less than the second threshold value T2 to being greater than the second threshold value T2, it can be determined that the piston 16 has passed the third position P3.

[0025] The detected magnetic flux density is equal to the first threshold value T1 at two piston positions, the second position P2 and the first position P1, and the position at which the detected magnetic flux density is equal to the first threshold value T1 can be determined by monitoring changes in the detected magnetic flux density. That is, when the detected magnetic flux density changes from being smaller than the first threshold value T1 to being larger than it, it can be determined that the piston 16 has passed the second position P2. When the detected magnetic flux density changes from being larger than the first threshold value T1 to being smaller than it, it can be determined that the piston 16 has passed the first position P1.

[0026] Since the piston 16 moves from the positive region toward the negative region, the start point is determined to be the point when the piston 16 passes through the fourth position P4 or the third position P3. The end point is determined to be the point when the piston 16 passes through the second position P2 or the first position P1. Then, by measuring the time from the start point to the end point, the movement time of the piston 16 can be measured.

[0027] The combinations of the two start points and the two end points are arbitrary, and there are a total of four combinations. Among the four combinations, when the fourth position P4 is the start point and the first position P1 is the end point, the distance between the start point and the end point is the longest. Furthermore, among the four combinations, when the third position P3 is the start point and the second position P2 is the end point, the distance between the start point and the end point is the shortest.

[0028] Next, a method for setting the determination conditions for the start and end points, including the first threshold T1 and the second threshold T2, when the start and end points are specified, will be described. It is assumed that the magnetic sensor 12 is disposed between the specified start and end points.

[0029] The fluid pressure cylinder 14 is driven to actually move the piston 16 from a specified start position to a specified end position, and the detected magnetic flux density is monitored. Note that the start position and end position relate to the piston position, but it is easier to understand if, instead of the piston position, for example, the position of the end of the piston rod 22 extending outward from the cylinder tube 20 is considered.

[0030] The sign of the detected magnetic flux density at the specified end point is different from the sign of the detected magnetic flux density at the specified start point. Below, we will explain two cases: when the detected magnetic flux density at the former is a positive value and the detected magnetic flux density at the latter is a negative value, and when the detected magnetic flux density at the former is a negative value and the detected magnetic flux density at the latter is a positive value.

[0031] If the detected magnetic flux density at the specified start position is a positive value and the detected magnetic flux density at the specified end position is a negative value, the former is set as the first threshold value T1 and the latter is set as the second threshold value T2. If the detected magnetic flux density increases immediately after the piston 16 leaves the specified start position, the start point determination condition is set as "the detected magnetic flux density exceeds the first threshold value T1." If the detected magnetic flux density decreases immediately after the piston 16 leaves the specified start position, the start point determination condition is set as "the detected magnetic flux density falls below the first threshold value T1."

[0032] Furthermore, if the piston 16 reaches the designated end position while the detected magnetic flux density is decreasing, the condition for determining the end point is set to "the detected magnetic flux density being below the second threshold value T2." If the piston 16 reaches the designated end position while the detected magnetic flux density is increasing, the condition for determining the end point is set to "the detected magnetic flux density being above the second threshold value T2."

[0033] On the other hand, if the detected magnetic flux density at the specified start position is a negative value and the detected magnetic flux density at the specified end position is a positive value, the former is set as the second threshold T2 and the latter is set as the first threshold T1. If the detected magnetic flux density decreases immediately after the piston 16 leaves the specified start position, the start point determination condition is set as "the detected magnetic flux density falling below the second threshold T2." If the detected magnetic flux density increases immediately after the piston 16 leaves the specified start position, the start point determination condition is set as "the detected magnetic flux density exceeding the second threshold T2."

[0034] Furthermore, if the piston 16 reaches the designated end position while the detected magnetic flux density is increasing, the condition for determining the end point is set to "the detected magnetic flux density exceeds the first threshold value T1." If the piston 16 reaches the designated end position while the detected magnetic flux density is decreasing, the condition for determining the end point is set to "the detected magnetic flux density falls below the first threshold value T1."

[0035] In this way, by actually moving the piston 16 from a specified start position to a specified end position and monitoring the detected magnetic flux density, it is possible to determine the conditions for determining the start and end points. These conditions for determining the start and end points, including the first threshold value T1 and the second threshold value T2, are stored in the memory unit or control unit of the fluid pressure cylinder movement time sensor 10. Thereby, the calculation unit of the fluid pressure cylinder movement time sensor 10 can easily calculate the movement time of the piston 16 thereafter.

[0036] A specific example of setting the start point and end point determination conditions according to the above method will be described with reference to FIG. 4. As the start point, the user specifies P1' (-12 mm), which corresponds to the above-mentioned P1. As the end point, the user specifies P3' (3 mm), which corresponds to the above-mentioned P3. When specifying P1' and P3', the user does not need to be aware of these numerical values; for example, the user can simply specify the positions of two ends of the piston rod 22. However, the magnetic sensor 12 must be positioned at least between P1' and P3'.

[0037] The piston 16 was actually moved from P1' to P3', and the detected magnetic flux density was monitored. The detected magnetic flux density was 3 mT when the piston was at P1', and it was monitored that the detected magnetic flux density exceeded 3 mT immediately after the piston 16 moved away from P1'. In this case, the first threshold T1 was set to 3 mT, and the criterion for determining the start point was set to "the detected magnetic flux density exceeds the first threshold T1." Furthermore, the detected magnetic flux density was -4 mT when the piston was at P3', and it was monitored that the detected magnetic flux density decreased as the piston 16 reached P3'. In this case, the second threshold T2 was set to -4 mT, and the criterion for determining the end point was set to "the detected magnetic flux density falls below the second threshold T2."

[0038] If there are multiple pairs of designated start and end positions, the start and end point judgment conditions are set for each pair. For example, there may be a case where you want to measure not only the time required for the piston 16 to move a predetermined stroke in one direction, but also the time required for the piston 16 to move the same stroke in the opposite direction.

[0039] The piston speed (average value of piston speed) can also be calculated based on the movement time of the piston 16. That is, the reciprocal of the movement time of the piston 16 can be multiplied by a constant corresponding to the distance from the start position to the end position. The piston speed can be calculated using this method in the calculation unit of the fluid pressure cylinder movement time sensor 10. Furthermore, if the piston speed is calculated for multiple consecutive sections, changes in the piston speed can be detected.

[0040] Next, a first application of the fluid pressure cylinder travel time sensor 10 according to the present invention will be described with reference to Fig. 5. The first application is to determine whether the cushioning action of the shock absorber 24 that decelerates the piston 16 is appropriate. In Fig. 5, members that are the same as or equivalent to the members in the basic configuration of Fig. 1 are given the same reference numerals.

[0041] In the example shown in Figure 5, the shock absorber 24 is a fluid shock absorber that provides a buffering effect near the stroke end of the piston 16 when the piston rod 22 is retracted. The magnetic sensor 12 is positioned so that it can effectively detect changes in the magnetic flux density of the permanent magnet 18 attached to the piston 16 near the stroke end. The conditions for determining the start and end points are set appropriately, and the travel time of the piston 16 is measured. Reference numeral 26 denotes an end plate 26 fixed to the end of the piston rod 22.

[0042] When the shock absorber 24 provides an appropriate buffering effect, the movement time of the piston 16 falls within a reference time range defined by predetermined upper and lower limits. On the other hand, when the buffering effect of the shock absorber 24 is too strong, the movement time of the piston 16 will be longer than the upper limit. On the other hand, when the buffering effect of the shock absorber 24 is too weak, the movement time of the piston 16 will be shorter than the lower limit. When the movement time of the piston 16 falls outside the reference time, it can be determined that the buffering effect of the shock absorber 24 is too strong or too weak. The user is then notified that adjustment of the shock absorber 24 is necessary.

[0043] Next, a second application of the fluid pressure cylinder travel time sensor 10 according to the present invention will be described with reference to Fig. 6. In the second application, the piston speed is calculated based on the travel time of the piston 16, and the sensor is used by the user to adjust the speed controller 28 provided in the fluid pressure cylinder 14. In Fig. 6, members that are the same as or equivalent to the members in the basic configuration in Fig. 1 are denoted by the same reference numerals.

[0044] 6, the speed controller 28 is a meter-out variable throttle valve that throttles the flow rate of air discharged when the piston rod 22 of the fluid pressure cylinder 14 is pushed out. The speed controller 28 is disposed at the discharge port (not shown) of the fluid pressure cylinder 14. The magnetic sensor 12 is disposed at a position where it can detect a change in the magnetic flux density of the permanent magnet 18 attached to the piston 16 when the piston rod 22 is pushed out. The conditions for determining the start and end points are set appropriately, and the travel time of the piston 16 is measured.

[0045] The movement time of the piston 16 is converted into a piston speed using a constant corresponding to the distance from the start position to the end position, and the piston speed is displayed on a display (not shown). The user looks at the displayed piston speed, and if the piston speed is not within a desired value, the user manually operates the speed controller 28 to adjust the air flow area.

[0046] Next, a third application of the fluid pressure cylinder travel time sensor 10 according to the present invention will be described with reference to Fig. 7. The third application is an application for detecting that the elastic body 30 has been clamped in a fluid pressure cylinder 14 that clamps the elastic body 30 while compressing it. In Fig. 7, members that are the same as or equivalent to the members in the basic configuration of Fig. 1 are given the same reference numerals.

[0047] 7, when the piston 16 is driven a predetermined amount in the direction of pushing out the piston rod 22, the end plate 32 fixed to the end of the piston rod 22 comes into contact with the elastic body 30. When the piston rod 22 comes into contact with the elastic body 30, the piston rod 22 receives a reaction force from the elastic body 30, and the piston speed decreases. The magnetic sensor 12 is disposed in a position where it can detect a change in the magnetic flux density of the permanent magnet 18 attached to the piston 16, in a range that includes at least the position where the piston rod 22 comes into contact with the elastic body 30.

[0048] In order to determine the piston speed in multiple consecutive sections, judgment conditions are set for multiple sets of start and end points, and the time required for the piston 16 to move through each section is measured. Then, using a constant corresponding to the distance of each section, the time required for the piston 16 to move through each section is converted into the piston speed. When the piston speed decreases significantly between adjacent sections, it can be determined that the elastic body 30 has been clamped by the fluid pressure cylinder 14.

[0049] The fluid pressure cylinder travel time sensor 10 according to the present invention can be used in various other ways in addition to the first to third ways described above. For example, it can be used to compare the travel time of the piston 16 with a reference time, and when the travel time of the piston 16 deviates from the reference time, notify the user that some kind of abnormality has occurred. The cause of the abnormality can be assumed depending on the way the fluid pressure cylinder 14 is used. For example, when conveying using the fluid pressure cylinder 14, there is a high probability that the abnormality will be caused by foreign matter getting caught or the conveyed object falling, so it is sufficient to notify the user of this.

[0050] Also, it is conceivable to count the number of times the movement time of the piston 16 is measured, and when the cumulative number exceeds a predetermined value, to prompt the user to perform necessary maintenance. Generally, the life of the fluid pressure cylinder 14 is often affected by the sliding parts made up of sealing materials etc., so it is sufficient to prompt the user to perform maintenance on the sliding parts.

[0051] The present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0052] 10...Fluid pressure cylinder movement time sensor 12...Magnetic sensor 14...Fluid pressure cylinder 16...Piston 18...Permanent magnet (magnet)

Claims

1. A fluid pressure cylinder movement time sensor comprising a single magnetic sensor that detects a magnetic flux density of a magnet attached to a piston of a fluid pressure cylinder, and that measures a time required for the piston to move a predetermined stroke, the magnet is arranged so that its magnetization direction coincides with the movement direction of the piston, and the magnetic sensor is capable of detecting a magnetic flux density in a direction perpendicular to the movement direction of the piston; a fluid pressure cylinder movement time sensor in which the relationship between the position of the magnet along the movement direction of the piston and the magnetic flux density detected by the magnetic sensor is represented by a curve having a positive maximum value and a negative minimum value, a positive value smaller than the positive maximum value is a first threshold value and a negative value larger than the negative minimum value is a second threshold value, a point in time when the magnetic flux density detected by the magnetic sensor exceeds or falls below the first threshold value is set to one of a start point and an end point, and a point in time when the magnetic flux density detected by the magnetic sensor exceeds or falls below the second threshold value is set to the other of the start point and the end point, and the sensor measures the time from the start point to the end point.

2. 2. The fluid pressure cylinder travel time sensor according to claim 1, a fluid pressure cylinder movement time sensor that moves the piston from a designated start position to a designated end position, sets the magnetic flux density detected at the designated start position as one of the first threshold value and the second threshold value, and sets the magnetic flux density detected at the designated end position as the other of the first threshold value and the second threshold value, and sets a determination condition for the start point depending on whether the magnetic flux density increases or decreases immediately after the piston moves away from the designated start position, and sets the determination condition for the end point depending on whether the piston reaches the designated end position while the magnetic flux density is increasing or while the magnetic flux density is decreasing.

3. 2. The fluid pressure cylinder travel time sensor according to claim 1, A fluid pressure cylinder movement time sensor that calculates a piston speed by multiplying the reciprocal of the measured time from the start point to the end point by a constant corresponding to the distance from the start point position to the end point position.

4. 4. The fluid pressure cylinder travel time sensor according to claim 3, A hydraulic cylinder travel time sensor that calculates the piston velocity over a number of consecutive intervals.

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