WO2009110842A1

WO2009110842A1 - A robot for seizing obj ects

Info

Publication number: WO2009110842A1
Application number: PCT/SE2009/050208
Authority: WO
Inventors: Anders Reyier
Original assignee: Binar Aktiebolag
Priority date: 2008-03-04
Filing date: 2009-02-26
Publication date: 2009-09-11
Also published as: TW200938345A; SE532222C2; SE0800509L; DE112009000506T5

Abstract

The invention relates to a robot (1) for seizing objects (2) which robot (1) comprises a movable robot arm with a gripper (4) and on which movable robot arm (3) a sensor (5) is arranged which sensor is connected to a control unit (6) for controlling the robot arm. The sensor (5) comprises a line laser (8) and an optical receiver (9) arranged to receive reflected laser light. The invention also relates to a handling system that comprises such a robot and to a method for seizing objects.

Description

A robot for seizing objects

FIELD OF THE INVENTION

The invention relates to a robot for seizing objects which robot comprises a movable robot arm with a gripper and a sensor arranged on the robot arm. The invention also relates to a handling system for objects to be handled in an industrial process and to a method for seizing objects.

BACKGROUND OF THE INVENTION

To handle objects in an industrial process, robots are used that are provided with gripping devices for seizing, holding and moving such objects. The objects to be handled may be, for example, objects that are to be processed, e.g. machined, and/or mounted. In US patent No. 5617335, it has been suggested that a robot may be provided with a camera. Objects to be handled are marked and the camera follows the marking that has been applied to the object in question. Data obtained by the camera are then used to control the robot. It is an object of the present invention to provide an improved robot for seizing objects, an improved system for handling objects and an improved method for seizing objects.

DESCRIPTION OF THE INVENTION

The invention relates to a robot for seizing objects which robot comprises a movable robot arm with a gripper. On the movable arm, a sensor is arranged. The sensor is connected to a control unit which is arranged to control the robot arm. The sensor comprises a line laser and an optical receiver arranged to receive reflected laser light.

The sensor may be arranged to be fixed in relation to the gripper.

The line laser and the optical receiver may be arranged in an angle relative to one another which is between 10° and 65°.

The invention also relates to a handling system for handling objects in an industrial process. The inventive handling system comprises a conveyor on which the objects may be carried forwards. A robot is located in connection to the conveyor and arranged to seize/grip the objects. The robot comprises a movable robot arm with a gripper and a sensor is arranged on the movable robot arm. The sensor is connected to a control unit for controlling the robot arm and the sensor comprises a line laser and an optical receiver is arranged to receive reflected laser light.

The invention further also relates to a method for seizing objects that are being handled in an industrial process. The method comprises the use of a robot which robot has a movable robot arm with a gripper and on which movable robot arm a sensor is arranged. The sensor is connected to a control unit for controlling the movable robot arm. The sensor comprises a line laser and an optical receiver arranged to receive reflected laser light. The method comprises illumination of the object to be seized with laser light from the line laser of the sensor and reception in the optical receiver of the laser light that has been reflected from the object to be seized. The method further comprises comparison of the reflected laser light with a reflection defined in advance (a previously defined reflection) and displacement of the robot arm until the reflected laser light matches (coincides with) the reflection that has been defined in advance. Finally, the method comprises seizing of the object when the reflected laser light matches (coincides with) the reflection that has been defined in advance.

The object or objects to be seized may be in a state of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows, schematically, a robot and a handling system.

Figure 2 shows, from another perspective, a sensor mounted on a robot arm 3.

Figure 3 shows a sensor which is intended for use in the present invention.

Figure 4 shows, schematically, how an industrial robot seizes/grips an object.

Figure 5 shows, schematically, how a sensor mounted on a movable robot arm detects an object to be seized.

Figure 6 is an enlargement of the area VI in Figure 5.

Figure 7 shows, schematically and in principle, a part of a control sequence when an object is seized by the inventive robot. DETAILED DESCRIPTION OF THE INVENTION

With reference to Figure 1 and Figure 4, the invention comprises a robot 1 for seizing objects 2. The robot 1 may suitably be an industrial robot with at least two degrees of freedom. For example, the robot 1 may be an industrial robot with 6 axes. The robot arm 3 and/or its gripper 4 can turn about these axes or be linearly displaced along one or several of these axes in a way known per se. As indicated in Figure 1, the objects 2 may be objects that are transported by a conveyor 11.

The robot 1 comprises a movable robot arm 3 that has a gripper 4. On the movable robot arm 3, a sensor 5 is arranged. The sensor 5 is connected to a control unit 6 for controlling the robot arm. As best seen in Figure 3, the sensor 5 comprises a line laser 8 and an optical receiver 9 arranged to receive reflected laser light. As can be seen from Figure 3, the line laser 8 and the optical receiver 9 may be arranged inside an exterior shell 7 that protects the line laser 8 and the optical receiver 9. An example of a line laser 8 suitable in this context may be a Las iris™ SNF laser having a wave length of 635 to 1550 nm but other components may also be used.

Figure 2 shows a possible embodiment where the sensor 5 is arranged at the end of the robot arm 3. The gripper 4 may also be arranged at the end of the robot arm 3 such that the gripper 4 is fixed in relation to the gripper 4. The gripper 4 will then move together with the sensor 5 such that the sensor 5 will always be in exactly the same position in relation to the gripper 4. The gripper 4 may be, for example, a gripper with mechanical fingers but there are also other ways of realizing the gripper 4. For example, the gripper 4 may be provided with suction cups or magnets. In Figure 2, the robot arm 3 is showed without its gripper 4 but it should be understood that a gripper may be arranged on the mounting flange 13 in Figure 2.

The line laser 8 and the optical receiver 9 can be arranged/directed in different ways in relation to each other. In some embodiments, the line laser 8 and the optical receiver may be arranged in an angle relative to one another which is between 10° and 65°.

Through practical trials, the inventor has found that the reliability of the measurements tends to decrease of the angle is less than 10° while the sensor becomes unnecessarily bulky and unwieldy if the angle is larger than 65°. However, embodiments are conceivable where the angle is larger than 65°. For example, the angle may lie in the range of 10° to 90°. With reference to Figure 1 , the invention can also be understood in terms of a handling system for objects 2 to be handled in an industrial process. The handling system comprises the above described robot and a conveyor 11. However, it should be understood that the conveyor may take other forms. For example, the conveyor 11 may be a conveyor belt. In Figure 1, a conveyor 11 is showed in which suspended objects 2 are carried forwards in the direction of the arrow. The robot 1 is placed in connection with the conveyor 11 and arranged to seize the objects 2 that are carried forwards by the conveyor 11.

The function of the inventive robot 1 is as follows. As indicated in Figure 1, objects 2 are carried forwards by the conveyor 11. The objects 2 that are transported forwards on the conveyor 2 may be, for example, cam shafts that are to be mounted in an engine. However, the invention can, of course, be applied to in principle any objects. When an object 2 to be seized passes the robot 1, the object 2 is illuminated by the line laser 8 of the sensor 5 as showed in for example Figure 5 and Figure 6. When the line laser 8 illuminates the object 2, the laser light will form a curve B on the object 2 as can be seen in Figure 6. The laser light is reflected and received by the optical receiver 9 of the sensor 5. The optical receiver will then read a signal that corresponds to the curve B. The optical receiver is connected to a control unit that comprises software defining a virtual "sight" 12. A reference curve C is programmed into the control unit 6 that may comprise a computer. The reference curve C corresponds to an expected shape of the curve B. A pre-defined point on the reference curve C is located at the centre of the sight 12 (in the middle of the cross-hairs in Figure 1). When the gripper 4 is in a correct position to seize an object 2, a pre-defined point of the read/detected curve B should also be at the centre of the sight 12. In other words, the curve B and the reference curve C shall coincide. The predefined point may be, for example, a maximum or a minimum on the curve B or the middle point of a curve that is constituted by a straight line. The position of the object 2 is transformed into a signal that is compared to the set value/nominal value according to the reference curve C. When the object 2 is in a correct position in relation to the gripper 4, the position of the read curve B shall coincide with the position for reference curve C. In Figure 1, the lateral deviation in a two-dimensional coordinate system is showed as δx. Since a laser is used, it is also possible to measure the distance between the object 2 and the object 2 and the sensor 5. A deviation from the correct distance is registered as δy in Figure 1. The control unit 6 converts the deviations δx, δy from the set value into a signal to the robot 1 to change the position of the robot arm 3 in such a way that the deviations are eliminated or reduced to a value that is below a threshold value. The reflected laser light is thus compared to a pre-defined reflection and the robot arm 3 is moved/displaced until the reflected laser light matches (coincides with) the pre-defined reflection. A predefined reflection in the form of a reference curve C is thus programmed into the control unit 6 and the control unit 6 is adapted/programmed/arranged to compare laser light that has been reflected from the object to be seized to the predefined reflection. The robot arm 3 is then controlled to move until the reflected laser light matches (coincides with) the predefined reflection. The control unit 6 may comprise an amplifier 14 for amplifying the signal that goes to the robot 1 for controlling the robot 1.

As explained above, the control unit 6 is programmed to determine a deviation (a distance) in depth and a lateral deviation from the object 2 to be seized and to correct the position of the robot arm 3 such that the deviations are eliminated or reduced below a threshold value. Thereafter, the object is seized.

As showed in Figure 1, the objects 2 that are to be seized may be in a state of movement. For example, the objects 2 may be suspended from a moving conveyor 11. Alternatively, the conveyor 11 can halt its movement in front of the robot 1 and allow the robot 1 to seize an object while the object is swinging which is also schematically indicated in Figure 1.

When a moving object is to be seized, the settling time to correct position must be short. In Figure 7, a contemplated case is showed where a swinging object is to be seized. The curve F represents the pendulum movement of the object to be seized while the curve R represents the movement of the robot arm 3 with its gripper 4. As can be seen in Figure 7, one will quickly approach a condition where the robot arm follows the object 2 such that it can seize the object in its movement. It should be understood that, in this context, the "correct position" is the position of the object 2 which is to be seized and which may be in a state of movement.

If the object 2 which is to be seized is in a state of movement, the movement is registered by the control unit 6 that directs the robot arm 3 to simply follow the object which is to be seized.

The inventive robot can also be used for other purposes than seizing different objects. When the robot 1 has seized an object, it may be suitable to let the robot place the object 2 that has been seized in a box or on a predetermined support (not showed in the figures) where objects 2 are to be packaged or placed in intermediate storage. When the robot has put down an object 2 on such a place, the sensor 5 may be used to make a reading of the position of the object 2. If one it is then established that an object 2 has been incorrectly placed, this can be taken into consideration when the next object is to be placed beside the incorrectly placed object.

Assume, for example, that three objects 2A, 2B and 2C are to be placed next to each other in a box or on a support. It is assumed that a first object 2A has already been placed in its position. The robot 1 now lays a second object 2B next to the first object 2A. Following this, the sensor 5 is activated to check the position of the second object 2B. If it is then found that the second object 2B lies in a correct position, the operation is continued in that the third object 2C is placed a correct position. However, if it is found that the second object 2B is laterally displaced in relation to the first object 2 A, it is possible to compensate for this by laying the third object 2C on the place originally intended for the second object 2B. The inventive robot can thus be used to place a plurality of objects next to each other and, by using the sensor 5, check the position of every object that has been so placed. Based on the position of previously laid down objects 2, it can then be determined where the next object to be laid down shall be placed.

By using a sensor with a line laser, it is possible to obtain a measurement of the distance to the details which is not possible through traditional two-dimensional technology. A 2-D camera can achieve detection in a plane (laterally and vertically) while, according to the present invention, it is possible to detect both a vertical deviation and a deviation in depth from a correct position for seizing/gripping. Thereby, it is possible to effectively direct the gripper 4 of the robot arm to a correct position for seizing the object which is to be seized. Seizure is possible also when the object to be seized is in a state of movement.

Since the sensor 5 is arranged on the robot arm 3 itself, the control can be substantially simplified. The control unit does not need to know the exact position for either the robot arm 3 or the object 2. It is sufficient that the position of the robot arm 3 in relation to the object 2 can be established, i.e. their relative position vis-a-vis each other. The industrial robot is thus arranged/programmed to be controlled such that the robot arm 3 and its gripper 4 reaches a predetermined position in relation to the position of the object to be seized, also when the object 2 is moving. This results in a fast and reliable control which is especially important when moving objects are to be seized. It should be understood that the predetermined (relative) position of the robot arm 3 may be a zone where the deviation from an ideal position lies below a threshold value. While the invention has been described above with reference to a robot for seizing objects, a handling system for objects and a method for seizing objects, it should be understood that these categories only reflect different aspects of one and the same invention. Thus, the robot and the handling system are adapted to perform the inventive method and the handling system comprises a robot according to the invention.

Claims

1. An industrial robot (1) for seizing objects (2) which robot (1) comprises a movable robot arm (3) with a gripper (4) and a sensor (5) arranged on the movable robot arm (3), the sensor being connected to a control unit (6) for controlling the robot arm, characterized in that the sensor (5) comprises a line laser (8) and an optical receiver (9) arranged to receive reflected laser light.

2. A robot according to claim 1, characterized in that the sensor (5) is arranged to be fixed in relation to the gripper (4).

3. A robot according to claim 1, characterized in that the line laser (8) and the optical receiver (9) are arranged in an angle relative to one another which is between 10° and 65°.

4. A robot according to any of claims 1 - 3, characterized in that a predefined reflection in the shape of a reference curve (C) is programmed into the control unit (6) and in that the control unit (6) is programmed to compare laser light that has been reflected from an object (2) to be seized to the predefined reflection and control the robot arm (3) to move until the reflected laser light matches the predefined reflection.

5. A handling system for objects (2) which are to be handled in an industrial process, the handling system comprising a conveyor (11) on which objects (2) can be carried forwards and a robot (1) arranged in connection to the conveyor and arranged to seize objects (2) that are carried forwards by the conveyor (11), the robot (1) comprising a movable robot arm (3) with a gripper (4), characterized in that a sensor (5) is arranged on the movable robot arm (3) which sensor is connected to a control unit (6) for controlling the robot arm (3) and in that the sensor (5) comprises a line laser (8) and an optical receiver (9) arranged to receive reflected laser light.

6. A handling system according to claim 5, characterized in that a predefined reflection in the shape of a reference curve (C) is programmed into the control unit (6) and in that the control unit (6) is programmed to compare light that has been reflected from an object (2) to be seized to the predefined reflection and control the robot arm (3) to move until the reflected laser light matches the predefined reflection.

7. A method for seizing objects (2) that are being handled in an industrial process, the method comprising use of a robot (1) which robot (1) has a movable robot arm (3) with a gripper (4) and on which movable robot arm (3) a sensor (5) is arranged, the sensor (5) being connected to a control unit (6) for controlling the movable robot arm (3), characterized in that the sensor (5) comprises a line laser (8) and an optical receiver (9) arranged to receive reflected laser light, in that the method comprises illumination of an object (2) to be seized with laser light from the line laser (8) of the sensor (5); receiving in the optical receiver (9) laser light that has been reflected from the object to be seized; comparing the reflected laser light to a pre-defined reflection; moving the robot arm (3) until the reflected laser light matches the pre-defined reflection; and seizing the object (2) when the reflected laser light matches with the pre-defined reflection.

8. A method according to claim 7, characterized in that the object (2) which is to be seized is in a state of movement.