Robot arm mechanism

A robot arm mechanism has a plurality of link sections. The plurality of link sections are connected by a plurality of joints. Each of the link sections is provided with a plurality of photoelectric sensors. The photoelectric sensor is constituted of a light projecting section and a light receiving section. The light projecting section is installed at one end of the link section. The light receiving section is installed at the other end of the link section. On an outside of the link section, an optical path reaching the light receiving section from the light projecting section is positioned. Approach of a worker to the link section can be detected by the optical path of any of the photoelectric sensors being cut off.

FIELD

Embodiments described herein relate generally to a robot arm mechanism.

BACKGROUND

Conventionally, an articulated robot arm mechanism is used in various fields such as an industrial robot. A polar coordinates robot is highly safe because the polar coordinates robot is not equipped with an elbow joint, but has been applied to only specific fields because the polar coordinates robot has a small movable area. The linear extension and contraction mechanism that is put to practical use by the inventors has a long extension and contraction length than the conventional linear motion mechanism and realizes a wide movable area. Thereby, it becomes possible to apply the linear extension and contraction mechanism to various fields, and an environment in which the robot and a worker cooperate with each other becomes realistic. In the cooperative environment where the robot is close to a worker, higher safety is required of the robot. Therefore, in many robots, the arm sections, the wrist sections and the like are equipped with contact sensors or proximity sensors.

In order to enhance safety, it is necessary to enlarge the sensitivity range comprehensively by disposing a number of sensors minutely, but this is not realistic because in that case, not only increase in cost but also increase in weight of the arm section and the like is unavoidable. Further, the arm section which is given an extension and contraction property by the linear extension and contraction mechanism is stored in the support column section with contraction, so that it is difficult to equip a contact sensor and a proximity sensor in a middle of the arm section, and a blind area is unavoidable.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

A purpose is to simplify a structure, enlarge a sensitivity range, and thereby realize enhancement of safety, in a robot arm mechanism.

Solution to Problem

A robot arm mechanism according to the present embodiment is formed by a link section being supported by a joint. At least one photoelectric sensor is installed on a link section or a joint in such a manner that an optical path of detection light is positioned over at least both ends of the link section, on an outside of the link section.

DETAILED DESCRIPTION

Hereinafter, a robot arm mechanism according to the present embodiment will be described with reference to the drawings. There exist a plurality of types of robot arm mechanisms.FIG. 1Aillustrates a vertical articulated robot arm mechanism,FIG. 1Billustrates a horizontal articulated robot arm mechanism (SCARA robot arm mechanism) that has two parallel rotation joints and operates within a selected plane,FIG. 1Cillustrates an orthogonal triaxial robot arm mechanism having three linear motion joints, in which these movement axes are orthogonal to each other, andFIG. 1Dillustrates a polar coordinates robot arm mechanism having two rotation joints and one linear motion joint in the arm, in which these axes constitute a polar coordinate system. Besides, there are a parallel link robot arm mechanism that has a link configuring a closed loop structure in an arm, a cylindrical coordinate robot arm mechanism having at least one rotation joint and one linear motion joint in an arm, in which these axes configure a cylindrical coordinate system, and the like. The present embodiment is not limited to a specific type, but can be applied to an arbitrary type robot arm mechanism. The present embodiment is a robot arm mechanism that is formed by at least one link (also referred to as the arm section) being supported by at least one joint.

The robot arm mechanism according to the present embodiment is provided with a simple configuration in which a single joint is installed on an installment surface such as a floor surface, a wall surface and a ceiling surface, and a single link section is rotatably or movably supported by the joint, or a general configuration in which a plurality of link sections are connected via joints.FIGS. 1A to 1Dillustrate examples of the general configuration, and the robot arm mechanism according to the present embodiment may be of any type. Here, a polar coordinates robot arm mechanism will be described as an example.

In the present embodiment, a photoelectric sensor40is adopted to detect approach of a worker or the like to link sections constituting various types of robot arm mechanisms. The photoelectric sensor40may be of either a transmission type or a reflective type. When the photoelectric sensor40is of a transmission type, the photoelectric sensor40has a light projecting section41and a light receiving section42. When the photoelectric sensor40is of a reflective type, the photoelectric sensor40has a light projecting/receiving section and a reflection section. Here, a transmission type of photoelectric sensor will be described as an example. The light projecting section41is installed in a position that is at one end side of a link section61, and on an outside with respect to a perpendicular direction from a center axis of the link section61. The light receiving section42is installed in a position that is at the other end side of the link section61and on an outside with respect to a perpendicular direction from the center axis of the link section61. Thereby, an optical path of detection light reaching the light receiving section42from the light projecting section41extends substantially parallel with the center axis from the one end to the other end, on an outside of the link section61. As a matter of course, the optical path of the detection light is not limited to a range from the one end to the other end of the link section61, but may exceed the range. Thereby, no blind section exists along a length direction of the link section61, and an entire area thereof can be made a detection area, so that safety can be enhanced. By arranging four of the photoelectric sensors40on four sides, an up, down, left and right to the link section61, the four optical paths of detection light can surround the link section61from the four sides, and even when approach is made to the link section61from any of the four directions, the approach is detected, so that safety can be more enhanced. Safety can be more enhanced by installing an area sensor in which a larger number of photoelectric sensors40are minutely arranged in a circular ring shape or an angular ring shape.

Hereinafter, the present embodiment will be described in detail with a polar coordinates robot arm mechanism taken as an example. First, a basic structure of the polar coordinates robot arm mechanism will be described.FIG. 2illustrates an external appearance of the polar coordinates robot arm mechanism according to the present embodiment,FIG. 3illustrates a side view of the robot arm mechanism, andFIG. 4illustrates an internal structure of the robot arm mechanism. The robot arm mechanism includes a base1, a turning section2, a rising and lowering section4, an arm section (link section)5and a wrist section6in order from the base1. A plurality of joints J1, J2, J3, J4, J5and J6are arranged in order from the base1. The turning section2forming a cylindrical body is typically installed vertically on the base1. The turning section2stores the first joint J1as a turning rotation joint. The first joint J1includes an axis of rotation RA1. The axis of rotation RA1is parallel with a vertical direction. The turning section2has a lower frame (link section)21and an upper frame (link section)22. The lower frame21and the upper frame22are connected at the first joint J1. The frames21and22are respectively covered with cylindrical housings31and32. The upper frame22axially rotates with rotation of the first joint J1, and thereby the arm section5turns horizontally. In an internal hollow of the turning section2forming a cylindrical body, a first and second piece strings51and52of the third joint J3as a linear extension and contraction mechanism that will be described later are stored.

On the upper frame22, the second joint J2as a rising and lowering rotation joint is installed. The second joint J2is a rotation joint. An axis of rotation RA2of the second joint J2is a horizontal axis. A pair of side frames23that constitute the second joint J2are covered with a cover33in a saddle shape. A cylindrical body24that is also used as a motor housing is supported by the pair of side frames23to be axially rotatable. A motor (actuator) is fixed to an inside of the cylindrical body24. A rotating shaft of the motor is fixed to the side frames23. The cylindrical body24axially rotates with rotation of the motor. A feeding mechanism25of the third joint J3is fixed to an outer circumferential surface of the cylindrical body24. The feeding mechanism25is covered with a cover34. A gap between the covers33and34is covered with a U-shaped bellows cover14that is U-shaped in section. The U-shaped bellows cover14extends and contracts by following a rising and lowering motion of the second joint J2. The feeding mechanism25is formed by a drive gear56, a guide roller57and a roller unit58being supported by a box-shaped frame60. The feeding mechanism25supports the arm section5movably back and forth. The feeding mechanism25rotates with axial rotation of the cylindrical body24, and the arm section5rises and lowers vertically.

The third joint J3is provided by the linear extension and contraction mechanism. The linear extension and contraction mechanism includes a structure which is newly developed by the inventors, and is clearly distinguished from a so-called conventional linear motion joint from a viewpoint of a movable range. The arm section5of the third joint J3is bendable, but is restricted from bending when the arm section5is fed forward from the feeding mechanism25at a root of the arm section5along a center axis (center axis of extension and contraction RA3) and has linear rigidity ensured to configure the link section. When the arm section5is pulled backward, bending is restored. The arm section5has the first piece string51and the second piece string52. The first piece string51is constituted of a plurality of first pieces53that are bendably connected. The first piece53is formed into a substantially flat plate shape, for example. The first pieces53are bendably connected at hinge portions at end spots. The second piece string52is constituted of a plurality of second pieces54. The second piece54is formed into a cylindrical body U-shaped in section or rectangular in section, with one surface opened, for example. The second pieces54are bendably connected at hinge portions at bottom plate end spots. Bend of the second piece string52is restricted in a position where end surfaces of side plates of the second pieces54abut on each other. In that position, the second piece string52is linearly arranged. The leading first piece53of the first piece string51and the leading second piece54of the second piece string52are connected by a head piece55.

The first and second piece strings51and52are brought into contact with each other by being pressed to each other by rollers59when passing through the roller unit58of the feeding mechanism25. Thereby, the first and second piece strings51and52exhibit linear rigidity and configure the columnar arm section (link section)5. The arm section5exits from a flange65in an angular ring shape of the frame60of the feeding mechanism25. The drive gear56is disposed with the guide roller57behind the roller unit58. The drive gear56is connected to a motor unit not illustrated. The motor unit generates power for rotating the drive gear56. Though not illustrated, a linear gear is formed along a connecting direction in a width center of an inside surface of the first piece53, in other words, a surface on a side contacting the second piece54. When the plurality of first pieces53are lined up linearly, adjacent linear gears are connected linearly, and configures an integral long linear gear. The linear gear of the first piece53is meshed with the drive gear56by being pressed by the guide roller57. The linear gears which are connected linearly configure a rack and pinion mechanism with the drive gear56. When the drive gear56rotates forward, the first and second piece strings51and52are fed forward from the roller unit58. When the drive gear56rotates reversely, the first and second piece strings51and52are pulled backward of the roller unit58. The first and second piece strings51and52which are pulled back are separated between the roller unit58and the drive gear56. The first and second piece strings51and52which are separated respectively return to a bendable state. The first and second piece strings51and52which return to the bendable state both bend in a same direction (inward), and are vertically stored inside the turning section2. At this time, the first piece string51is stored in a state substantially aligned in substantially parallel with the second piece string52.

The wrist section6is attached to a tip end of the arm section5. The wrist section6is equipped with the fourth to sixth joints J4to J6. The fourth to sixth joints J4to J6respectively include axes of rotation RA4to RA6which are orthogonal three axes. The fourth joint J4is a rotation joint rotating on the fourth axis of rotation RA4that substantially corresponds to the center axis of extension and contraction RA3, and the end effector is swingably rotated by rotation of the fourth joint J4. The fifth joint J5is a rotation joint rotating on the fifth axis of rotation RA5which is disposed perpendicular to the fourth axis of rotation RA4, and the end effector is tilted and rotated back and forth by rotation of the fifth joint J5. The sixth joint J6is a rotation joint rotating on the sixth axis of rotation RA6which is disposed perpendicularly to the fourth axis of rotation RA4and the fifth axis of rotation RA5, and the end effector is axially rotated by rotation of the sixth joint J6.

The end effector (end effector) not illustrated is attached to an adapter7that is provided at a lower part of a rotating section of the sixth joint J6of the wrist section6. The end effector is a portion for the robot to have a function of directly working on an object to be worked (work), and various tools exist in accordance with tasks, such as a grasping section, a vacuum suction section, a nut fastening tool, a welding gun, and a spray gun, for example. The end effector is moved to an arbitrary position by the first, second and third joints J1, J2and J3, and is disposed in an arbitrary posture by the fourth, fifth and sixth joints J4, J5and J6. In particular, a length of an extension and contraction distance of the arm section5of the third joint J3enables the end effector to reach objects in a wide range from a proximity position to a remote position of the base1. The third joint J3is clearly distinguished from the conventional linear motion mechanism from a viewpoint of the linear extension and contraction motion and the length of the extension and contraction distance which are realized by the linear extension and contraction mechanism that configures the third joint J3.

As illustrated inFIG. 5, at one end side of the arm section5, for example, a rear end side, the light projecting section41constituting the photoelectric sensor40is installed, and at the other end side, for example, a front end side, the light receiving section42constituting the photoelectric sensor40is installed. Note that the light projecting section41may be installed at the front end side of the arm section5, and the light receiving section42may be installed at the rear end side. The photoelectric sensor40may be of either a transmission type or a reflective type as described above, but is described as a transmission type herein. In the case of the reflective type, the light projecting section shall be read as a light projecting/receiving section, and the light receiving section shall be read as a reflection section respectively.

A wavelength band used for the photoelectric sensor40may be of either near-infrared light or visible light, or beam light or laser light. Adoption of visible light has an advantage that the worker or the like can visually recognize detection light around the arm section5. The light projecting section41typically includes a light emitting diode as a light source, but the light source is not limited to a light emitting diode. Further, the photoelectric sensor40may be of a so-called amplifier separation type in which the light projecting section41and the light receiving section42are separated from a unit of a light projecting circuit, a light receiving circuit, a determination circuit, an output circuit and a control circuit that will be described later, or may be of a so-called amplifier incorporated type in which the light projecting section41is configured integrally with the light projecting circuit, and the light receiving section42is configured integrally with the light receiving circuit, the determination circuit and the output circuit.

In the present embodiment, the four photoelectric sensors40are typically equipped. As illustrated inFIG. 6, the four light projecting sections41are attached to the flange65of the feeding mechanism25, for example, at the rear end side of the arm section5. As a matter of course, an attaching position of the light projecting section41is not limited to the flange65, but the light projecting section41may be fitted to a surface of the cover34, for example. The four light projecting sections41are typically staggered by 90 degrees from each other around a conduction hole66of the arm section5, and are disposed by being dispersed vertically and laterally. The four light receiving sections42are attached to positions respectively facing the four light projecting sections41, on a flange of the fourth joint J4of the wrist section6or a cover surface thereof. An optical path of detection light from the light projecting section41to the light receiving section42extends on outside of the link section61in a direction of a length thereof from one end of the link section61to the other end. Typically, an optical axis of the detection light is parallel with a center axis of the link section61. The four optical paths of the four photoelectric sensors40surround the link section61from four sides, an up, down, left and right.

The light projecting section41and the light receiving section42are positioned to each other so that a spot center C2of beam-shaped detection light, for example, emitted from the light projecting section41corresponds to a center C1of a light receiving area of the light receiving section42paired with the light projecting section41. However, as illustrated inFIG. 7, the light projecting section41and the light receiving section42may be positioned to each other so that the spot center C2of the detection light emitted from the light projecting section41in a reference posture in which the arm section5is most contracted shifts slightly in a direction of gravity from the center C1of the light receiving area of the light receiving section42. In a situation where the arm section5is extended, and grasps a work as a relatively heavy matter, the arm section5is assumed to bend somewhat in the direction of gravity and also vibrate, but even in that case, occurrence of the situation where the beam light is out of the light receiving area of the light receiving section42can be reduced.

FIG. 8illustrates a configuration of an entire robot device including the robot arm mechanism according to the present embodiment. A robot device100has a system control section121. An upper, lower, left and right photoelectric sensors40-1to40-4are connected to the system control section121via a control/data bus. Further, a task program storage section125that stores a data file of a task program, an operation control section123that generates joint angles (command values) of the respective joints by using the task program read from the storage section125, transmits the generated command values to motor drivers133of the respective joints, and transmits a stop signal for stopping the motor drivers133in that position to the motor drivers133of all the joints when a signal expressing that detection light is cut off by a worker or the like is outputted from at least one of the photoelectric sensors40-1to40-4, a command value for energizing in the case of a stepping motor, an indicator103that indicates an operation state of the robot device100by distinguishing a stopping state and a normal operation state by a lamp, sound or the like, and an operation section101equipped with a button for cancelling the operation stoppage and restarting the operation are connected to the system control section121via the control/data bus. Operation stop cancel buttons are preferably installed on the rising and lowering section4and the wrist section6. A motor (actuator)132of the joint is preferably constituted of a stepping motor. The motor driver133supplies pulse power to the motor132in accordance with the command value from the operation control section123. To a drive shaft of the motor or a rotating shaft of the joint, an encoder (rotary encoder)131for measuring a rotation angle thereof is attached.

The photoelectric sensor40-1is constituted of a light projecting circuit43that drives the light projecting section41in accordance with control of a control circuit45, a light receiving circuit44that converts a current output of the light receiving section42into a voltage signal, amplifies the voltage signal and converts the voltage signal into a digital signal in accordance with control of the control circuit45, a determination circuit46that compares the output signal of the light receiving circuit44with a threshold, and an output circuit47that alternatively outputs two kinds of signals (codes) expressing two states in accordance with a comparison result, in addition to the light projecting section41and the light receiving section42. When the detection light from the light projecting section41is directly received by the light receiving section42, a first signal (on signal) expressing a first state in which a light receiving amount thereof exceeds a threshold, and nothing is interposed between the light projecting section41and the light receiving section42is outputted. When a worker or the like approaches the arm section5and is interposed between the light projecting section41and the light receiving section42to cut off the detection light, the light receiving amount of the light receiving section42falls below the threshold. Thereby, a second signal (off signal) expressing a second state in which a worker or the like is interposed between the light projecting section41and the light receiving section42is outputted. By the output of the second signal, the operation control section123realizes approach of the worker or the like to the arm section5, and can stop movement of the arm section5before the worker or the like contacts the arm section5. That is, the operation control section123can stop the movement of the arm section5when outputting the second signal expressing the state in which the light receiving amount of even one of the photoelectric sensors40-1to40-4is below the threshold, and further can recognize an approaching direction of the worker or the like from the output signals of the four photoelectric sensors40-1to40-4, so that the operation control section123also can retreat the arm section5in a same direction as the approaching direction.

The threshold of the determination circuit46may be also changed dynamically under control of the control circuit45. There is a possibility that a light amount of disturbance light that is incident on the light receiving section42varies due to the extension and contraction movement, rising and lowering movement and turning movement of the arm section5. The control circuit45dynamically changes the threshold of the determination circuit46in response to a combination of an extension and contraction length, a rising and lowering angle and a turning angle which are received at fixed periods from the operation control section123. Thereby, an erroneous operation of not recognizing cutoff of the detection light by the worker due to an influence of the disturbance light, in particular, because of the light amount of the disturbance light being large, can be suppressed. As a matter of course, it is necessary to measure the light amount change of the disturbance light by the extension and contraction movement, the rising and lowering movement and the turning movement of the arm section5in advance. In order to eliminate a working burden of the previous measurement, the determination circuit46acquires the light receiving amount of the light receiving section42at the fixed period, but when the light receiving amount at a present period is compared with a light receiving amount at immediately preceding period or several periods ago, and when a change of the light receiving amount is within a predetermined range, a state transition is not performed, whereas when the change is out of the predetermined range, the state transition is performed. When the light reception amount at the present period is greatly reduced from the light reception amount at the immediately preceding period, the state is caused to transition to a state where the worker or the like is interposed between the light projecting section41and the light receiving section42from the state where no worker or the like is interposed between the light projecting section41and the light receiving section42, and the output is converted into the second signal from the first signal. When the light reception amount at the present period increases greatly from the light reception amount at the immediately preceding period, the state is caused to transition to the state where no worker or the like is interposed between the light projecting section41and the light receiving section42from the state where the worker or the like is interposed between the light projecting section41and the light receiving section42, and the output is converted into the first signal from the second signal. When the light reception amount hardly changes, the state at the immediately preceding period is kept and the first signal or the second signal is continuously outputted.

Either in the case of adopting a transmission type as the photoelectric sensor40, or in the case of adopting a reflective type, a pulse modulated light method that repeats light projection at fixed periods is adopted to suppress influence of disturbance light. Further, even when the transmission type is adopted as the photoelectric sensor40, in the case of adopting a reflective type, only reflection light in the reflection section may be detected by disposing polarizing filters different in polarization direction (a longitudinal wave, a transverse wave) are disposed in a light projecting window and a light receiving window of the light projecting/receiving section, and installing a corner tube on a reflection surface of the reflection section, in order to avoid an erroneous operation of a returning light after reflected on an object to be detected such as a worker or the like, being incident on the light projecting/receiving section to be brought into a same state as the state where the object to be detected does not exist.

Further, a time difference between a generation time of optical pulse and a light reception time is compared with a time corresponding to twice the distance between the light projecting/receiving section and the reflection section, and reflection by the reflection section and reflection by the object to be detected such as a worker or the like, that is, presence and absence of interposition of a matter in the optical path may be distinguished in response to the comparison result.

As illustrated inFIG. 9, an area sensor constituted of a light projecting ring48in which a large number of light projecting sections41are minutely arranged in a circular ring shape or an angular ring shape, and a light receiving ring49in which a large number of light receiving sections42are minutely arranged in a circular ring shape or an angular ring shape may be used. As a matter of course, inside diameters or inside dimensions of the light projecting ring48and the light receiving ring49are longer than an outside diameter or an outside dimension of the arm section5. A gap in the optical path of the detection light can be eliminated or decreased, a situation where a finger or the like of a worker is inserted in the gap of the optical path of the detection light and approach of the finger or the like cannot be detected can be avoided, and further enhancement in safety can be expected.

REFERENCE SIGNS LIST