Encoder for joint motor rotation angle measurement

Abstract

The invention discloses an encoder for joint motor rotation angle measurement. The encoder comprises an excitation unit, a PCB, a turn number detection module and an angle detection module. The turn number detection module and the angle detection module are both mounted on the PCB, and the excitation unit is mounted on a rotating shaft of the joint motor and is suitable for being matched with the turn number detection module and the angle detection module; the turn number detection module is suitable for being in a standby state when the joint motor is powered down, and the turn number detection module is suitable for being triggered when the rotating shaft rotates so as to detect the rotating direction and the turn number of the rotating shaft; the angle detection module is suitable for detecting the rotating angle of the rotating shaft in the single circle. The device has the beneficial effects that the turn number detection module responds to the rotation of the rotating shaft of the joint motor to trigger turn number calculation, so that the turn number detection module can be in a standby state when the joint motor is powered down, and the power consumption can be effectively reduced.

Description

Technical Field

[0001] The present application relates to the technical field of joint motor angle measurement, and in particular to an encoder for joint motor angle measurement. Background Art

[0002] Robots in many scenarios of industrial automation require the use of joint motors. In the actual working process, since both mechanical positioning and servo motor drivers need to know the angle of the joint motor shaft when implementing the FOC algorithm, an angle measurement system needs to be set up for the joint motor to collect its angle data.

[0003] There are many specific solutions for the existing angle measurement system. The common solution is to use a two-channel code disk, and use the slight deviation of the main channel and the vernier channel to measure the absolute value of the shaft angle within a single turn; the number of turns is measured by setting a multi-point magnetic field strength measurement chip on the main channel and the vernier channel, and measuring the magnetic field strength at multiple points on the main channel and the vernier channel at the same time to form a characteristic magnetic image to identify the number of turns. However, this solution has the following disadvantages: the production cost of the code disk and the multi-point magnetic field strength measurement chip is relatively high; since it is necessary to continuously measure the characteristic magnetic image to determine the number of turns in the case of power failure, it is not conducive to low-power design and easily shortens the service life of the backup battery of the angle measurement system. Summary of the invention

[0004] One of the objects of the present application is to provide an encoder for measuring the rotation angle of a joint motor which can solve at least one of the defects in the above-mentioned background technology.

[0005] In order to achieve at least one of the above-mentioned purposes, the technical solution adopted in the present application is: an encoder for measuring the rotation angle of a joint motor, comprising an excitation unit, a PCB board, a number of turns detection module and an angle detection module; the number of turns detection module and the angle detection module are both installed on the PCB board, the excitation unit is installed on the rotating shaft of the joint motor and is suitable for cooperating with the number of turns detection module and the angle detection module; the number of turns detection module is suitable for being in a standby state when the joint motor loses power, and the number of turns detection module is suitable for being triggered when the rotating shaft rotates, thereby detecting the direction and number of turns of the rotating shaft; the angle detection module is suitable for detecting the rotation angle of the rotating shaft within a single turn.

[0006] Preferably, the number of turns detection module includes multiple first trigger units and an MCU unit; the first trigger unit is suitable for cooperating with the excitation unit to output a working level, and the MUC unit is suitable for being electrically connected to the first trigger unit to receive the working level output by the first trigger unit; when the working level state of the output of the first trigger unit changes according to the rotation of the shaft, the MCU unit is awakened; and then the MCU unit compares the current working level state of all the first trigger units with the working level state recorded at the previous moment, and obtains the rotation direction and number of turns of the shaft according to the comparison result.

[0007] Preferably, the calculation of the number of rotations of the rotating shaft includes the following process: defining the positive and negative directions of rotation of the rotating shaft; determining the rotation direction of the rotating shaft according to the position of the first trigger unit being triggered; if the rotation direction of the rotating shaft is positive, then each time the first trigger unit is triggered, the encoding value is increased by one, thereby obtaining a positive number of triggering times n of the first trigger unit; if the rotation direction of the rotating shaft is negative, then each time the first trigger unit is triggered, the encoding value is reduced by one, thereby obtaining a negative number of triggering times n of the first trigger unit; and the ratio of the number of triggering times n to the total number N of the first trigger units is rounded to obtain the number of rotations of the rotating shaft.

[0008] Preferably, the excitation unit is a magnetic ring, the first trigger unit is a switch-type Hall sensor, and a plurality of the first trigger units are arranged around the magnetic ring.

[0009] Preferably, the magnetic ring is provided with adjacent N-pole and S-pole regions along the circumferential direction; the magnetic induction sensitive direction of the first trigger unit is parallel to the tangent direction of the magnetic ring; when the magnetic flux passing through the magnetic induction sensitive direction of the first trigger unit crosses a preset flipping threshold, the working level output by the first trigger unit will change from high to low.

[0010] Preferably, the number of the first trigger units is at least three.

[0011] Preferably, the encoder for joint motor angle measurement also includes a backup battery, and the backup battery is suitable for supplying power to the MCU unit.

[0012] Preferably, the angle detection module includes a plurality of second trigger units, and the second trigger units are suitable for cooperating with the excitation unit through magnetic induction to output an output voltage with a sine / cosine distribution; and the rotation angle of the rotating shaft within a single turn is obtained by interpolation based on the obtained output voltage.

[0013] Preferably, the number of the second trigger units is four, and the four second trigger units are equally spaced in a circle; in a clockwise or counterclockwise order, the voltage output by each second trigger unit is U a , U b , U c and U d , then the rotation angle of the shaft in a single circle is .

[0014] Preferably, the excitation unit adopts a magnetic ring, and the magnetic ring is provided with adjacent N-pole and S-pole regions along the circumferential direction; the second trigger unit adopts a Hall sensor, and the magnetic induction sensitive direction of the second trigger unit is along the radial direction of the magnetic ring.

[0015] Compared with the prior art, the beneficial effects of this application are: The number of turns detection module responds to the rotation of the shaft of the joint motor to trigger the number of turns calculation. In this way, when the joint motor loses power, the number of turns detection module can also be in standby mode, thereby effectively reducing power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural schematic diagram of the anti-fall device of the present application installed on a climbing ladder.

[0017] In the figure: a PCB board 100, a first trigger unit 200, a second trigger unit 300, an excitation unit 400, and a rotating shaft 500. DETAILED DESCRIPTION

[0018] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0019] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of the present application.

[0020] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0021] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be connected, detachably connected, or integrated; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0023] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0024] One of the preferred embodiments of the present application is as follows: Figure 1As shown, an encoder for measuring the rotation angle of a joint motor includes an excitation unit 400, a PCB board 100, a number of turns detection module and an angle detection module. The PCB board 100 can be fixedly connected to the housing of the joint motor so that the number of turns detection module and the angle detection module installed on the PCB board 100 can be in a stationary state relative to the joint motor. The excitation unit 400 is installed on the rotating shaft 500 of the joint motor and can cooperate with the number of turns detection module and the angle detection module. When the joint motor is in a power-off state, the number of turns detection module and the angle detection module can both be in a standby state to reduce power consumption. When the joint motor rotates the rotating shaft 500 due to an accidental touch, the number of turns detection module can be triggered; at this time, the number of turns detection module can detect the rotation direction and number of turns of the rotating shaft 500. Taking into account that the joint motor may be accidentally touched before starting, the rotation angle of the shaft 500 within a single circle needs to be detected each time it is started to determine whether it is deflected before starting. If deflection occurs, the current rotation angle data of the shaft 500 can be updated.

[0025] It is understandable that when the joint motor is in a power-off state, its rotating shaft 500 can still be driven manually, which may cause the rotating shaft 500 to rotate due to human error when the joint motor is powered off and shut down. When the joint motor is subsequently started, the mechanical positioning may change, causing inaccurate calculation of the FOC algorithm, thereby affecting the control accuracy of the joint motor. Therefore, it is necessary to know the rotation angle of the joint motor during the entire working process of the joint motor.

[0026] The traditional method of measuring the rotation angle of the joint motor is to detect the rotation angle of the joint motor shaft 500 in a single circle in real time through two code disks, and use a multi-point magnetic field strength detection chip to detect the number of rotations of the shaft 500 in real time. That is, whether the joint motor is in normal working state or power-off state, the traditional angle measurement method will detect the number of rotations and the single-circle rotation angle of the shaft 500, which may cause the multi-point magnetic field strength detection chip to fail to work properly when the joint motor is in the power-off state, or the multi-point magnetic field strength detection chip is powered by a backup battery, causing the backup battery to be quickly consumed, thereby causing other electrical equipment to fail to operate normally.

[0027] In the technical solution of the present application, by installing the excitation unit 400 on the rotating shaft 500 of the joint motor, both the number of turns detection module and the angle detection module need to be excited by the excitation unit 400, so when the joint motor is in power-off but no action, since the excitation unit 400 does not change the relative position, the number of turns detection module and the angle detection module will not be triggered and are in standby state, thereby effectively reducing energy consumption. Only when the rotating shaft 500 of the joint motor rotates, the number of turns detection module will be triggered; and the angle detection module will only respond when the joint motor needs to be started, so that the energy loss of the joint motor when power is off can be further reduced, and the calculation accuracy of the FOC algorithm after the joint motor is started can also be guaranteed. Compared with the traditional angle measurement method, the present application can realize the low-power design of the angle measurement of the joint motor, thereby realizing cost saving, and can also simplify the data calculation amount of the angle measurement process to improve the response speed of the angle measurement.

[0028] In this embodiment, there are multiple specific structures of the turn detection module. For the sake of easy understanding, one of the structures will be described in detail below. Figure 1 As shown, the lap detection module includes a plurality of first trigger units 200 and an MCU unit (not shown). The first trigger unit 200 can cooperate with the excitation unit 400 to output a working level, and the MUC unit can be electrically connected to the first trigger unit 200 to receive the working level output by the first trigger unit 200.

[0029] When the joint motor rotates in the power-off state, the position of the excitation unit 400 installed on the shaft 500 relative to the first trigger unit 200 changes, which will cause the state of the working level output by the first trigger unit 200 to change. At this time, the MCU unit is awakened when the working level output by the first trigger unit 200 changes. After the MUC unit is awakened, the MCU unit can compare the current working level state of all the first trigger units 200 with the working level state recorded at the last moment, and determine the rotation direction of the shaft 500 of the joint motor according to the position of the first trigger unit 200 whose working level has changed. At the same time, it can also determine the number of rotations of the shaft 500 according to the number of times the current working level state of the first trigger unit 200 has changed.

[0030] It is understandable that the specific structure and working principle of the MCU unit are well-known technologies for those skilled in the art, so they are not elaborated in detail here. The MCU unit and multiple first trigger units 200 can form a low-resolution encoder that works continuously. When working normally, the MCU unit continuously monitors the working level state of multiple first trigger units 200 outputs to count. In the power-off state of the encoder, the first trigger unit 200 and the MCU unit will be powered by the backup battery, and the MCU unit can enter the power-off mode for standby. When the joint motor rotates under the action of an external force, the working level output by the encoder changes, and the MCU unit is awakened by connecting the wake-up pin of the MCU unit to the first trigger unit 200. The MCU unit compares the working level state of the current first trigger unit 200 with the working level state stored last time, and performs addition and subtraction operations on the encoding value. Since the encoder has a sleep wake-up function, the MCU unit can be in the power-off standby mode for most of the time, so this scheme is very easy to achieve extremely low power consumption, and is suitable for being powered by a backup battery in the power-off mode.

[0031] In this embodiment, the calculation of the number of rotations of the rotating shaft 500 includes the following process: defining the positive direction and negative direction of rotation of the rotating shaft 500, and determining the rotation direction of the rotating shaft 500 according to the position of the triggered first trigger unit 200. If the rotation direction of the rotating shaft 500 is positive, the encoding value is increased by one each time the first trigger unit 200 is triggered, thereby obtaining the positive number of triggers n of the first trigger unit 200. If the rotation direction of the rotating shaft 500 is negative, the encoding value is reduced by one each time the first trigger unit 200 is triggered, thereby obtaining the negative number of triggers n of the first trigger unit 200. The ratio of the trigger number n to the total number N of the first trigger units 200 is rounded to obtain the number of rotations of the rotating shaft 500.

[0032] It should be known that in order to accurately determine the rotation direction of the rotating shaft 500, the number of the first trigger units 200 is at least two, preferably at least three; for example Figure 1 As shown, the number of the first triggering units 200 is preferably four. For ease of understanding, the specific determination process of the number of rotations of the rotating shaft 500 will be described in detail below.

[0033] Specifically, the rotation of the rotating shaft 500 in the clockwise direction is defined as positive, and the rotation of the rotating shaft 500 in the counterclockwise direction is defined as negative; the four first trigger units 200 can be marked as trigger units #1 to trigger units #4, and trigger units #1 to trigger units #4 are arranged in a clockwise direction. Assume that the excitation unit 400 recorded at the beginning of the joint motor power failure is located between trigger units #2 and trigger units #3; if trigger unit #2 is triggered during the power failure of the joint motor, it means that the rotating shaft 500 of the joint motor has rotated counterclockwise; if trigger unit #3 is triggered during the power failure of the joint motor, it means that the rotating shaft 500 of the joint motor has rotated clockwise. If not all of the four first trigger units 200 are triggered, it means that the rotation number of the rotating shaft 500 of the joint motor has not reached one circle. At this time, the counting of the rotation number of the rotating shaft 500 of the joint motor is still based on the historical record data; if all of the four first trigger units 200 are triggered, and the triggering times of some or all of the first trigger units 200 are greater than 1; for example, all of the first trigger units 200 are triggered 6 times in total, it means that the rotating shaft 500 has rotated more than one circle but less than two circles.

[0034] In this embodiment, there are many specific structures of the excitation unit 400 and the first trigger unit 200 that can cooperate with each other to generate the working level. The commonly used method is to use the method of magnetoelectricity. Figure 1 As shown, the excitation unit 400 adopts a magnetic ring, the first trigger unit 200 adopts a switch-type Hall sensor, and a plurality of first trigger units 200 are arranged around the magnetic ring.

[0035] It should be known that the specific structure and working principle of the switch type Hall sensor are well-known technologies to those skilled in the art, so they will not be elaborated in detail here; the switch type Hall sensor has relatively low power consumption and is often used in electronic products, mainly for sensing whether there is a magnet outside to realize the wake-up operation of the device. Specifically, the switch type Hall sensor is provided with a certain magnetic induction sensitive direction. When the magnetic flux passing through its sensitive direction crosses the internal preset flip threshold, the first trigger unit 200 can output a high and low changing working level signal, and the MCU unit realizes wake-up according to the high and low changes of the working level.

[0036] In this embodiment, the arrangement of the magnetic induction sensitive direction of the first trigger unit 200 is related to the magnetic field distribution on the magnetic ring; Figure 1 As shown, the magnetic ring is provided with adjacent N-pole and S-pole regions along the circumferential direction; the magnetic induction sensitive direction of the first trigger unit 200 is parallel to the tangent direction of the magnetic ring. Therefore, when the magnetic flux passing through the magnetic induction sensitive direction of the first trigger unit 200 crosses the preset flip threshold, the working level output by the first trigger unit 200 will change from high to low.

[0037] It can be understood that, based on the distribution of the N pole and the S pole, there is a critical reversal position of the N pole and the S pole on the magnetic ring; when the magnetic ring corresponds to the first trigger unit 200 through the N pole or the S pole, the magnetic flux passing through the magnetic induction sensitive direction of the first trigger unit 200 remains consistent, and then the first trigger unit 200 will output a low-level working level; and when the magnetic ring corresponds to the first trigger unit 200 through the critical reversal position, the magnetic flux passing through the magnetic induction sensitive direction of the first trigger unit 200 will be reversed, and then the first trigger unit 200 will output a high-level working level.

[0038] In this embodiment, there are multiple specific structures of the angle detection module that can realize the single-turn angle measurement of the rotating shaft 500. For the sake of easy understanding, the following will be described in detail using one of the structures. Figure 1 As shown, the angle detection module includes multiple second trigger units 300, which can cooperate with the excitation unit 400 for magnetic induction to output an output voltage with a sine / cosine distribution; the rotation angle of the rotating shaft 500 in a single circle is obtained by interpolation based on the obtained output voltage.

[0039] It should be known that each second trigger unit 300 and the excitation unit 400 can cooperate to form an output voltage with a sine / cosine distribution, and the output voltages formed by different second trigger units 300 have a phase difference according to the installation position, and then the rotation angle of the shaft 500 in a single circle can be obtained by combining the output voltage formulas of the second trigger units 300. For ease of understanding, the rotation angle of the shaft 500 in a single circle is The derivation process is described in detail.

[0040] Specifically, the number of the second trigger units 300 is at least two. In this embodiment, four second trigger units 300 are preferably used. The four second trigger units 300 are equally spaced around the excitation unit 400. In a clockwise or counterclockwise order, the voltage output by each second trigger unit 300 is U a , U b , U c and U d The maximum magnetic flux between the excitation unit 400 and the second trigger unit 300 can be set to B m When the magnetic flux is 0, the bias voltage output by the second trigger unit 300 is U0.

[0041] Define the output voltage as U a The position corresponding to the second trigger unit 300 is the initial position of the rotating shaft 500, then: .

[0042] .

[0043] .

[0044] .

[0045] Combining the above formulas, we get .

[0046] Then, the rotation angle of the rotating shaft 500 in a single circle can be obtained. .

[0047] In this embodiment, Figure 1 As shown, it can be known from the above content that the excitation unit 400 adopts a magnetic ring, and the magnetic ring is provided with adjacent N-pole and S-pole regions along the circumferential direction; in order to facilitate the excitation unit 400 to simultaneously cooperate with the first trigger unit 200 and the second trigger unit 300 for magnetic induction, the second trigger unit 300 also adopts a Hall sensor. According to the form of the output voltage of the second trigger unit 300, the magnetic induction sensitive direction of the second trigger unit 300 is along the radial direction of the magnetic ring, and then in the process of the magnetic ring rotating with the rotating shaft 500, different magnetic ring positions pass through different magnetic fluxes in the sensitive direction of the same second trigger unit 300, thereby forming an output voltage in the form of sine / cosine.

[0048] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. An encoder for measuring the rotation angle of a joint motor, characterized in that: It includes an excitation unit, a PCB board, a circle number detection module and an angle detection module; The number of turns detection module and the angle detection module are both installed on the PCB board, and the excitation unit is installed on the rotating shaft of the joint motor and is suitable for cooperating with the number of turns detection module and the angle detection module; The number of turns detection module is adapted to be in a standby state when the joint motor is powered off, and the number of turns detection module is adapted to be triggered when the shaft rotates, thereby detecting the direction and number of turns of the shaft; The angle detection module is suitable for detecting the rotation angle of the rotating shaft within a single circle.

2. The encoder for measuring the rotation angle of a joint motor according to claim 1, characterized in that: The lap detection module includes a plurality of first trigger units and an MCU unit; The first trigger unit is suitable for cooperating with the excitation unit to output a working level, and the MUC unit is suitable for being electrically connected to the first trigger unit to receive the working level output by the first trigger unit; When the first trigger unit causes the output working level state to change according to the rotation of the shaft, the MCU unit is awakened; The MCU unit compares the current working level status of all the first trigger units with the working level status recorded at the last moment, and obtains the rotation direction and number of revolutions of the rotating shaft according to the comparison result.

3. The encoder for measuring the rotation angle of a joint motor as claimed in claim 2, characterized in that: The calculation of the number of rotations of the rotating shaft includes the following process: defining a positive direction and a negative direction of rotation of the rotating shaft, and determining the rotation direction of the rotating shaft according to the position of the first triggering unit being triggered; If the rotation direction of the rotating shaft is positive, the encoding value is increased by one each time the first trigger unit is triggered, thereby obtaining a positive triggering number n of the first trigger unit; If the rotation direction of the rotating shaft is negative, the encoding value is reduced by one each time the first trigger unit is triggered, thereby obtaining a negative triggering number n of the first trigger unit; The number of rotations of the rotating shaft is obtained by rounding the ratio of the triggering times n to the total number N of the first triggering units.

4. The encoder for measuring the rotation angle of a joint motor as claimed in claim 2, characterized in that: The excitation unit adopts a magnetic ring, the first trigger unit adopts a switch-type Hall sensor, and a plurality of the first trigger units are arranged around the magnetic ring.

5. The encoder for measuring the rotation angle of a joint motor as claimed in claim 4, characterized in that: The magnetic ring is provided with adjacent N-pole and S-pole regions along the circumferential direction; the magnetic induction sensitive direction of the first trigger unit is parallel to the tangent direction of the magnetic ring; When the magnetic flux in the magnetic induction sensitive direction passing through the first trigger unit crosses a preset flip threshold, the working level output by the first trigger unit will change from high to low.

6. The encoder for measuring the rotation angle of a joint motor according to claim 5, characterized in that: The number of the first trigger units is at least three.

7. The encoder for measuring the rotation angle of a joint motor according to any one of claims 2 to 6, characterized in that: The encoder for joint motor angle measurement also includes a backup battery, which is suitable for supplying power to the MCU unit.

8. The encoder for joint motor angle measurement according to claim 1, characterized in that: The angle detection module includes a plurality of second trigger units, which are suitable for cooperating with the excitation unit through magnetic induction to output an output voltage with a sine / cosine distribution; and the rotation angle of the rotating shaft within a single turn is obtained by interpolation based on the obtained output voltage.

9. The encoder for measuring the rotation angle of a joint motor according to claim 8, characterized in that: The number of the second trigger units is four, and the four second trigger units are distributed at equal intervals around the circumference; In clockwise or counterclockwise order, the voltage output by each of the second trigger units is U a , U b , U c and U d , then the rotation angle of the shaft in a single circle is .

10. The encoder for measuring the rotation angle of a joint motor according to claim 8, characterized in that: The excitation unit adopts a magnetic ring, and the magnetic ring is provided with adjacent N-pole and S-pole regions along the circumferential direction; The second trigger unit adopts a Hall sensor, and the magnetic induction sensitive direction of the second trigger unit is along the radial direction of the magnetic ring.

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