JP5251651B2 - Wheel travel device resistant to sensor failure - Google Patents

Description

  The present invention relates to a wheel traveling device that realizes fail-safe against failure of a sensor that senses a speed and an inclination angle.

  In a wheel traveling device that travels on a wheel by driving a power device such as a motor, a rotary encoder that is a position sensor that converts a mechanical displacement amount in a rotational direction into a digital amount is generally used for measuring a road surface inclination angle. Each acceleration sensor is used. When the wheel traveling device performs automatic traveling such as a robot, a control unit that controls traveling performs various controls on the driving unit based on signals input from these sensors. For example, control is performed such that the motor output is stopped when the speed is exceeded or the tilt angle is exceeded.

  When a sensor breaks down in the wheel traveling device, appropriate control of the drive unit by the control unit does not work, and obstacles such as a collision due to excessive speed and a fall due to inability to detect the tilt occur. Along with this, the vehicle traveling device may cause a serious accident. Therefore, there is a demand for a technique (fail safe) that ensures the safety of the vehicle travel device by appropriately controlling the drive unit when these sensors fail.

  As a prior art, when a malfunction occurs in a vehicle due to an accident or the like, there is an invention in which measures are taken to avoid a secondary accident by detecting the malfunction state by some sensor and limiting the traveling function of the vehicle (patent) References 1 to 3).

JP 2001-350516 A JP 2002-200952 JP JP 2002-274295 A

  When the sensor fails, it is necessary to stop the motor output from the fail-safe concept. However, such fail safe is not realized in the prior art. For example, when the rotary encoder breaks down, the input signal from the rotary encoder to the control unit remains zero (a single line without pulses), so the control unit cannot distinguish from the case where the speed is zero. For this reason, the motor output is not stopped, and it is not fail-safe against sensor failure. As described in the above-mentioned patent document, even if a redundant sensor or another sensor for detecting a sensor failure is provided, this problem cannot be solved.

  In the disclosed technology, a wheel traveling device that is used to control a wheel traveling device in response to an excessive speed or an excessive tilt angle and that is fail-safe even when a sensor that senses the speed and the tilt angle has failed is disclosed. The challenge is to achieve this.

  A viscous fluid is sealed inside the rotating unit that rotates coaxially with the wheel, and the sensor detects that the fluid has not reached a predetermined distance from the road surface, and the sensor does not reach the control unit. When the input indicating this (hereinafter referred to as unachieved input) is not performed, the control unit stops the drive unit.

  According to the disclosed wheel traveling device, the viscous fluid reaches the predetermined distance from the road surface by the frictional force when the speed is exceeded and by the slope when the inclination angle is exceeded, while the viscous fluid is normally accumulated in the direction of gravity. . Therefore, when the speed is exceeded and the tilt angle is exceeded, the unreached input is not performed to the control unit. On the other hand, when the sensor fails, the unreached input is not performed to the control unit. That is, the appearance from the control unit is the same when the speed exceeds or the inclination angle exceeds and when the sensor fails. Thereby, when a sensor breaks down, a control part can stop a drive part, and the above-mentioned subject can be solved.

1 is a perspective view of a wheel traveling device according to a first embodiment. It is a side view of the wheel traveling device concerning a 1st embodiment. 1 is a front view of a wheel traveling device according to a first embodiment. It is a top view of the wheel traveling device concerning a 1st embodiment. It is a figure which shows the structure of the drive wheel for a detection. It is a figure which shows the behavior of the opaque viscous fluid at the time of driving | running | working and inclination of a wheel traveling apparatus. It is a figure explaining the dynamic consideration with respect to a wheel traveling apparatus. It is a figure which shows the structure of the wheel traveling apparatus which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 show an example of an overall view of a wheel traveling device according to a first embodiment of the present invention. 1 is a perspective view, FIG. 2 is a side view, FIG. 3 is a front view, and FIG. 4 is a top view. In each figure, the same number is attached | subjected about the corresponding part.

  The wheel traveling device includes a body 101, driving wheels 102, driven wheels 103, a photo interrupter 104 including a light emitting unit 1041 and a light receiving unit 1042, a motor 105, a frame 106, and a control unit (not shown). .

  The body 101 has a total of four frames 106 extending from the bottom to the front and rear, one on each side. Motors 105 are fixed to the left and right pairs in front of the frames 106, and driving wheels 102 are attached to the shafts of the motors 105, respectively. In addition, driven wheels 103 are pivotally supported by a pair of left and right rear of the frame 106 so as to be vertically rotatable.

  An opaque viscous fluid 1021 is sealed in any one of the pair of left and right drive wheels 102 (hereinafter referred to as a detection drive wheel 102a). The structure of the detection driving wheel 102a is shown in FIG. 5 (in this figure, the opaque viscous fluid 1021 is not shown for convenience). The detection drive wheel 102a is made of a material such as an acrylic resin having transparency and a certain degree of impact resistance, and a donut-shaped cavity 1023 that makes a round of the axle bearing 1022 is provided therein. The inner periphery and the outer periphery of the donut-shaped cavity 1023 are two concentric circles having different diameters, and the width in the axle direction is constant. A predetermined amount of opaque viscous fluid 1021 such as lubricating oil is sealed in the cavity, and the fluid is sealed so that the fluid does not leak outside the detection driving wheel 102a. Since the detection driving wheel 102a has permeability, the enclosed opaque viscous fluid 1021 can be observed from the outside. As a result, the photo interrupter 104 installed outside the detection driving wheel 102a can detect excess speed or excess tilt angle based on the behavior of the opaque viscous fluid 1021. The detailed configuration of the detection drive wheel 102a will be described later.

  The photo interrupter 104 includes a light emitting unit 1041 and a light receiving unit 1042, and when there is no light shielding material between the light emitting unit 1041 and the light receiving unit 1042 (during transmission), the output current becomes a specified value or more, and the light emitting unit 1041 receives light. It has a property that the output current becomes less than a specified value when a light shielding object is inserted between the portion 1042 (when light shielding). In the vehicle traveling device, the photo interrupter 104 is fixed to the body 101 at a predetermined position where the detection driving wheel 102a is sandwiched between the light emitting unit 1041 and the light receiving unit 1042. The predetermined position is a position where a portion at a predetermined distance from the road surface can be monitored in the cavity provided in the detection driving wheel 102a. Details of the predetermined distance will be described later. The photo interrupter 104 is preferably arranged at each position where the rear and front of the detection driving wheel 102a can be monitored so that both forward and backward movement of the wheel traveling device can be detected. If the detection is sufficient, it may be arranged only on the rear side of the detection drive wheel 102a.

  The motor 105 is a servo motor, is electrically connected to the control unit, and rotates the shaft according to a pulse in an input signal from the control unit. The motor stops rotating when no pulse is input. As a result, the driving wheel 102 fixed to the shaft rotates or stops.

  The control unit stops outputting the pulse signal to the motor 105 when the output current from the photo interrupter 104 is less than the specified value. By configuring the control unit in this way, the motor 105 is stopped when the photo interrupter 104 is shielded from light. The control unit is realized by a program executed by a CPU (not shown), or is realized by hardware based on wired logic.

  Based on FIG.6 and FIG.7, the method in which the wheel traveling apparatus which concerns on 1st Embodiment senses a speed and an inclination angle, and the method of implement | achieving fail safe are demonstrated.

  FIG. 6A shows an example in which the wheel traveling device stops traveling when the speed exceeds a certain reference speed, and FIG. 6B shows the wheel traveling device when the inclination angle exceeds a certain reference angle. Represents the case where the vehicle stops traveling. The photo interrupter 104 is shielded from light by the opaque viscous fluid 1021 in the detection drive wheel. As shown in FIG. 7A, when the vehicle travels at a low speed on a flat road surface, the opaque viscous fluid 1021 in the detection drive wheel remains below the body (in the direction of gravity), and the photo interrupter 104 is not shielded from light. However, as shown in FIG. 7B, as the speed increases, the opaque viscous fluid 1021 moves in the rotation direction of the detection drive wheel by its own frictional force, and the photo interrupter 104 is shielded from light. Similarly, as the inclination angle increases, the opaque viscous fluid 1021 moves in the rotation direction of the detection driving wheel due to the inclination of the wheel traveling device, and the photo interrupter 104 is shielded from light. When the photo interrupter 104 is shielded from light, its output current becomes less than the specified value, so that the motor is stopped by the control unit, and the wheel traveling device stops traveling. Even when the vehicle traveling apparatus rolls over or rolls over, the opaque viscous fluid 1021 remains at the position where the photo interrupter 104 is shielded from light, and thus the motor output is stopped.

  According to the present embodiment, even when the photo interrupter 104, which is a sensor that senses the speed and the inclination angle, fails, the wheel traveling device stops traveling. This is because when the photo interrupter 104 fails, the output current becomes zero, the motor is stopped by the control unit, and the wheel traveling device stops traveling. This realizes fail-safe against failure of the sensor (photo interrupter).

Based on FIG. 7, parameters such as the size of each part of the detection drive wheel 102a and the predetermined distance from the road surface for fixing the photo interrupter 104 will be described. As described above, in order for the wheel traveling device to stop when the speed is exceeded or the inclination angle is exceeded, these parameters need to satisfy a predetermined condition from a mechanical consideration. As a precondition, a reference speed that is a reference for excess speed is set as U _max , and a reference angle that is a reference for excess inclination angle is set as θ _max .

First, consider a case where the wheel traveling device is traveling at a speed U _max . In this case, the opaque viscous fluid 1021 moves in the rotational direction of the detection driving wheel 102a by a frictional force generated between the opaque viscous fluid 1021 and the contact surface of the wheel. Then, the frictional force F ₁ and the gravity F ₂ remain in balance. Here, the frictional force F ₁ can be calculated by Newton's law of viscosity. According to Newton's law of viscosity, when two flat plates of area A sandwiched between fluids of thickness h (viscosity is μ) move at a relative speed U, the force F ₁ generated between the liquid and the plate is: It is represented by Formula 1).

F ₁ = μAU / h (Formula 1)
In this embodiment, for the sake of simplicity, the amount of the opaque viscous fluid 1021 is set to a height that is half the wheel diameter of the detection driving wheel 102a. At this time, A = t (D-2b) π / 2. Where t is the liquid width, D is the wheel diameter, b is the difference between the wheel diameter and the outer diameter of the cavity, and π is the circumference. Next, in this embodiment, U corresponds to the speed of the outer periphery of the cavity. When the wheel travel device travels at a speed U _max , the speed of the outer periphery of the detection drive wheel 102a is also U _max , so the speed of the outer periphery of the cavity is U = U _max (D−2b) / D. Further, in this embodiment, the opaque viscous fluid 1021 is applied with a force not only from the outer periphery of the cavity but also from the inner periphery, so the force applied between the fluid and the outer periphery is half the actual liquid thickness of the fluid. Therefore, h = a / 2. Substituting these A, U, and h into (Expression 1) leads to the following (Expression 2).

F ₁ = μ · t (D-2b) π / 2 · U _max (D-2b) / D / (a / 2) (Formula 2)
Further, the gravity F ₂ applied to the opaque viscous fluid 1021 during traveling of the wheel traveling device has a difference in height of 2 (H−D / 2) between the rising side and the falling side of the fluid. The following (Formula 3) is derived.

F ₂ = ρ · 2 (H−D / 2) at · g (Formula 3)
Here, ρ is the viscosity of the liquid, H is the distance from the road surface of the photo interrupter, a is the liquid thickness (difference between the outer diameter and the inner diameter of the cavity), and g is the acceleration of gravity.

Since F ₁ and F ₂ are balanced, the following (Expression 4) is established from (Expression 2) and (Expression 3).

μ ・ t (D-2b) π / 2 ・ U _max (D-2b) / D / (a / 2) = ρ ・ 2 (H−D / 2) at ・ g (Formula 4)
Next, consider a case where the wheel travel device has an inclination angle θ _max . At this time, the following (formula 5) is established.

tanθ _max = (H−D / 2) / (D / 2−b−a / 2) (Formula 5)
From the above, the vehicle running in which the parameters of μ, t, D, b, a, ρ, and H are set so as to satisfy (Equation 4) and (Equation 5) with respect to U _max and θ _max as preconditions. What is necessary is just to comprise an apparatus. Specifically, for example, in addition to the preconditions U _max = 2 m / s, θ _max = 10 °, μ = 0.5 Pa · s (equivalent to lubricating oil), t = 0.03 m, D = 0.25 m, b = When 0.01 m and ρ = 900 kg / m ³ are specified in advance, H = 0.143 m and a = 0.030 m are automatically determined. In this way, when the wheel travel device reaches the reference speed U _max or the reference angle θ _max , the opaque viscous fluid 1021 rises to the height of the photo interrupter 104 and the photo interrupter 104 is shielded from light. Thus, when the wheel traveling device reaches the reference speed U _max or the reference angle θ _max , the wheel traveling device behaves to stop.

  As described above, according to the first embodiment of the present invention, the viscous fluid is normally accumulated in the direction of gravity while the viscous fluid is caused by the frictional force when the speed is exceeded and by the slope when the inclination angle is exceeded. Reaches a predetermined distance from the road surface. Therefore, when the speed is exceeded and the tilt angle is exceeded, the current input to the control unit becomes zero. On the other hand, even when the photo interrupter fails, the current input to the control unit becomes zero. That is, the appearance from the control system is the same when the speed exceeds or the inclination angle exceeds and when the sensor fails. Thereby, when a sensor fails, a control part can stop a motor output, and it can implement | achieve fail safe with respect to a sensor failure.

  FIG. 8 shows an example of a vehicle travel device according to the second embodiment of the present invention. Basically, the configuration of the first embodiment is followed, but the following points are different.

  In the first embodiment, a material having permeability is used as the material for the detection drive wheel 102a, whereas in the second embodiment, any material may be used for the detection drive wheel 102a. . Instead, this is an example in which a disk-shaped case 107 that moves in conjunction with an arbitrary one of the drive wheels 102 is provided.

  In addition to the drive wheels 102, a disk-shaped case 107 is attached to the motor shaft. In FIG. 8, the disk-shaped case 107 is attached between the motor 105 and the drive wheel 102, but it may be attached outside the drive wheel 102. The disc-shaped case 107 is made of a permeable material, and an opaque viscous fluid is sealed in an internal cavity so that the fluid is not leaked to the outside of the detection driving wheel. Then, the photo interrupter 104 is fixed to the body 101 at a predetermined position where the disc-like case 106 is sandwiched. With the above configuration, the detection drive wheel 102a and its surrounding configuration in the first embodiment are realized in the disk-like case 107 and its surroundings.

  According to 2nd Embodiment, there exists the same effect | action and effect as 1st Embodiment. That is, since the motor output can be stopped not only when the speed is exceeded and when the tilt angle is exceeded, but also when the photo interrupter is broken, fail-safe against sensor failure can be realized. Furthermore, in the second embodiment, as a material for the detection drive wheel, a metal such as an aluminum alloy or stainless steel, or any other material having strength stronger than an acrylic resin can be used. Therefore, according to the second embodiment, there is a specific effect that the strength of the detection drive wheel can be increased. Further, the second embodiment does not require a detection drive wheel having a special configuration, and the drive wheel and the disk-like case are separate parts. Therefore, according to the second embodiment, there is also a specific effect that the manufacturability and maintainability of the drive wheel and the disk-like case, and thus the wheel traveling device are improved.

  As mentioned above, although embodiment of the wheel traveling apparatus which concerns on this invention was described, this invention is not limited to the said embodiment, A various design change is possible within the range of the technical idea.

  For example, the wheel traveling device can be incorporated in a moving body such as a store guidance robot. In such an embodiment, the present invention is particularly effective. This is because the robot travels at a low speed (about the walking speed of humans) and almost at the same speed, so that the opaque viscous fluid does not behave irregularly due to a rapid change in speed, so stable control of travel stop is realized. Because it can.

  In addition to the acrylic resin, the transparent material includes PE (polyethylene), PP (polypropylene), PA (polyamide), vinyl chloride resin, ABS, PET (polyethylene terephthalate), urethane resin, glass Polycarbonate or the like may be used.

  As the opaque viscous fluid, in addition to the lubricating oil, grease, a humectant, or the like may be used. Further, instead of fluid, a substance such as powder that is not fluid but has fluidity may be used. In the case of powder, a certain frictional force is generated between particles unlike a liquid, so that it does not need to be particularly viscous.

  As the sensor, in addition to the photo interrupter, a reflection type photo sensor may be used. In this case, the illustrated opaque viscous fluid can be used. Unlike the photo interrupter, the reflective photo sensor can monitor the behavior of the opaque viscous fluid from one side of the wheel. Therefore, the reflective photosensor may be attached at the same position as either the light emitting part or the light receiving part of the photo interrupter.

  Instead of the motor, an external combustion engine such as a steam engine or an internal combustion engine such as a gasoline engine can be used as a power unit.

  Moreover, although the said embodiment demonstrated the four-wheel wheel travel apparatus, the number of wheels does not need to be four. In the above embodiment, the driving wheel is the front side and the driven wheel is the rear side. However, the driving wheel may be the rear side and the driven wheel may be the front side. Furthermore, although the photo interrupter etc. are installed in the drive wheel in the said embodiment, you may install a photo interrupter etc. in a driven wheel.

DESCRIPTION OF SYMBOLS 101 Body 102 Drive wheel 102a Detection drive wheel 1021 Opaque viscous fluid 1022 Axle bearing 1023 Donut-shaped cavity 103 Driven wheel 104 Photo interrupter 1041 Light emitting part 1042 Light receiving part 105 Motor 106 Frame 107 Disc-shaped case

Claims (6)

Driving wheels driven by a power unit;
A rotating part that rotates coaxially with the drive wheel and encloses a fluid or powder having viscosity therein;
It is installed in the vicinity of the rotating part and senses whether or not the fluid or powder in the rotating part has reached a predetermined distance from the installation point of the drive wheel and the road surface, and outputs when it reaches the predetermined distance A sensor to stop
When the output from the sensor is stopped, a control unit that stops the power unit that drives the drive wheels;
A wheel travel device comprising: Driving wheels driven by a power unit;
A driven wheel not driven by the power unit;
A rotating part that rotates coaxially with the driven wheel and encloses a viscous fluid or powder inside;
It is installed in the vicinity of the rotating part and senses whether or not the fluid or powder in the rotating part has reached a predetermined distance from the installation point of the driven wheel and the road surface. A sensor to stop
When the output from the sensor is stopped, a control unit that stops the power unit that drives the drive wheels;
A wheel travel device comprising: The sensor is a photo interrupter having a light emitting part and a light receiving part, and is configured such that the light emitting part and the light receiving part sandwich the rotating part,
The rotating unit is configured to have transparency to light used in the photo interrupter,
The wheel traveling device according to claim 1 or 2, wherein the fluid or the powder is configured to be impermeable to light used in the photo interrupter. 4. The wheel travel device according to claim 1, wherein the rotating part is fixed around an axle of the driving wheel or the driven wheel, and the fluid or powder is enclosed in a donut-shaped space inside the rotating part. The wheel traveling device according to claim 1, wherein the rotating unit is a driving wheel or a driven wheel. 6. The wheel travel device according to claim 1, wherein the rotating portion is configured by a case that is installed outside the driving wheel or the driven wheel and rotates together with the driving wheel or the driven wheel.

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