DK201700599A1 - Automatic tool changer for robots - Google Patents

Abstract

Automatic tool changer for robots that enables a robotic arm to connect to or from a tool alone using the robot arm's movements. The tool is connected to the robotic arm through a Kelvin ball-based coupling and the connection is maintained by a hook suspended in a crank pulling the two parts of the coupling together by means of a crossbar. A pin on the side of the hook follows a groove in the coupling housing and controls the movement of the hook so that the hook goes free of the cross-stick when the crank is turned to the open position and pulled over the cross-stick before the hook pulls the two parts of the coupling together. The crossbar is slightly tapered and can be moved longitudinally so that the traction in the hooks and cranks can be adjusted. The crank is driven by a string of balls which, through a pipe system, are pressed into a channel that encloses the crank. The separation occurs by inserting the clutch into a cutout in a rubber-hung parking plate where the clutch tool part is held by a groove around the clutch. When the robot arm turns the clutch in the parking plate, the wreath is held by the cutout in the parking plate and the wreath pushes the ball string in around the crank. The clutch is reassembled by turning the clutch opposite in the holder. The clutch has a series of switches and resistors that allow the use of output voltages from a voltage divider to read the state of the clutch and identify the connected tool

Description

Small robots for handling items or for performing simple operations typically consist of a robotic arm and a tool such as a gripper. The robot arm is controlled via a computer with a control program that can rotate the various joints so that the robot arm performs the desired movement or holds a certain position. The robot arm with control is typically a standard unit that can be used for many different types of tasks. A tool is mounted on the end of the robot arm which allows the robot arm to perform a specific task. The tool is adapted to the task and if the robot is to perform another type of task it is necessary to change the tool.

If you often need to change tools, the tool can be unscrewed by the robot arm. It is also possible to connect the tool to the robot arm with a special switching device. An operator can, with the switching device, remove one tool and mount another tool without the use of extra tools. However, pneumatic and electrical connections between the robot arm and tools must, however, be changed by the operator on the same occasion. However, some advanced manual tool switches also have special connectors so electrical and pneumatic connections are switched at the same time as the tool change.

When switching back and forth between different tools on a robot arm, it is important that each tool will sit in exactly the same position when reassembling. Otherwise, the robot will lose its precision and may have to. reprogrammed to use the tool again. Manual tool changers are therefore typically designed as precise flange couplings which are clamped together by a rotary or with a bypass. Larger robots that need to switch between different tools typically have an automatic tool changer. Here the tensioning of the flanges is carried out by means of pneumatics, hydraulics or an electric motor in the coupling.

In this automatic tool changer, the motion of the robot arm is utilized to disengage and to disengage the tool. The locking mechanism is driven by the movement of the robot arm. In Fig. 1 the two parts of the coupling are shown separated. (1) is the part of the clutch mounted on the robot arm and (2) is the part mounted on the tool.

The precision of the coupling is achieved by means of a Kelvin coupling where the two parts of the coupling engage in three points. These points of engagement form a triangle.

In FIG. 2, the two coupling parts are shown separately and one can see the balls forming the points of engagement.

In the first point of engagement, three degrees of freedom are locked by pushing a ball (3), fixed in one coupling part, down against three balls (4) fixed in the other coupling part. These three spheres are placed in a small triangle with a distance between them which makes the three points of contact between the spheres perpendicular to each other.

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In the second point of engagement, a ball is pressed down similarly between two balls. Here, too, the distance between the balls is chosen so that the two contact points are perpendicular to each other. In addition, the center line between the two balls in the second point of engagement is perpendicular to the line between the center of the three balls in the first point of engagement and the center of the two balls at the second point of engagement.

In the third point of engagement, a ball in one coupling part directly presses against a single ball in the other coupling part. Here, the contact surface between the two spheres is parallel to the plane of the coupling of the two coupling parts.

This coupling principle is similar to a Kelvin coupling where the classic tapered holes, v-grooves and flat abutments are replaced by three, two and one ball.

The Kelvin coupling is known to provide extremely high repetition accuracy and is therefore often used in optical setups. The Maxwell clutch, which is similar to the Kelvin clutch but relies on bullets resting in v-grooves, is used for precise manual mounting of instruments on robots as described in US 8,500,132 B2.

The two coupling parts are held together by a hook (5) in one coupling part gripping a cross bar (6) in the other coupling part. The hook is located approx. midway between the three switching points.

The hook that pulls the two coupling parts together is mounted on a crank, so that the crank can just be turned over the apex when the coupling is assembled. The crank is rotated slightly past the apex and up to a stop, thus locking in the coupled position. FIG. 3 shows a section through a slightly separated coupling where the hook (5) is in the free position. The crossbar (6) is seen in the tool part of the coupling (2). In FIG. 4, the coupling is assembled and the hook (5) engages the crossbar (6).

The crossbar is a weakly tapered pin located in a correspondingly weak tapered hole in one coupling member. The tapered hole has a slight inclination such of the side of the pin that the hook pulls in just parallel to the plan of the coupling. A section through a locked coupling is shown in FIG. 6. The hook (5) engages the tapered crosspiece (19). The hook hangs on the space pin (18) which is suspended in ball bearings.

By moving the taper pin back and forth in the taper hole, the position of the flat hook gripper can be varied. This option to vary the distance between crank (18) and cross bar (19) is used to adjust the tension in the hook and to compensate for variations from the manufacture of the coupling parts.

The movement of the hook is controlled by a pin (16) on the side of the hook. This pin follows a groove (17) in the coupling plate and together with the crank movement, it causes the tip of the hook to follow a path where the hook turns away from the cross bar (16) when the coupling is released. Similarly, the hook is turned over the crossbar when the crank begins to close

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DK 2017 00599 A1 movement. The tip of the hook is then pulled straight forward towards the cross bar and only just before the crank (18) when its top position becomes the hook free to adjust itself between the crank and the cross bar. A section through the coupling of FIG. 5 shows the hook (5) with the pin (16) following the groove (17).

The crank is actuated by a string of balls (19) pressed into a wing pump at the end of the crank. By pushing the balls into one or the other side of the channel around the crank (18), the wing (24) will rotate the crank. In FIG. 7, the crank (18) with the hook (5) is shown from the end so that one can see the annular channel with the wing (24) which forms a fixed part of the crank. A string of balls (19) is pressed into each side of the duct, thereby driving the crankshaft. When the balls are pressed into one side, the balls are simultaneously pushed back into the other side. In FIG. Figure 8 shows the same components from the other side. Here you see the end of the crank (18) and the hook (5) with the pin (16).

The balls are led into the annular duct from two pipe ducts in the coupling plate. A wreath (9) around the coupling plate can be rotated about the coupling plate, thereby pushing the balls into one or other channel of the crank wing pump. In FIG. 9, the crank mechanism with the ball strings (19) is shown together with the wreath (9).

The part of the coupler that sits on the tool (2) is provided with a groove (14) around the coupling. This groove fits with the cutout (23) in the holder (20) where the tool is placed when not in use.

There is an opening in the parking plate to the position where the tool is parked. However, this opening is slightly narrower than the diameter in the parking position. A pair of cutouts at the bottom of the groove (14) on the tool coupling plate allows the coupling to pass into the cutout in the parking plate.

When the clutch is in the parking position, the clutch can be turned so that the clutch cannot be pushed back out of the holder.

The wreath around the clutch has an elevation (15) that fits in width with the passage into the parking plate (20). When the clutch is inserted into the parking plate, this elevation is trapped in the inlet. When the coupling is turned into the parking position, the elevation will hold the wreath so that the wreath (9) will rotate around the coupling.

The parking of a tool takes place by the robot arm inserting the clutch into the parking plate (20) and rotating the clutch thereby turning the wreath (9) relative to the clutch plate with the crank. The wreath pushes the balls through the ducts and into the crank's wing pump. The crank is turned and the hook is released from the crossbar. Now the robot arm can pull the fixed part of the clutch out of the clutch tool part and the clutch is separated. The parked coupling is shown in FIG. 12

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When the robot arm is to engage on a tool, the arm with the clutch plate is inserted into the clutch plate that is in the holder with the tool.

The coupling on the robotic arm has some raised sides which form a tapered entrance down towards the surface with the Kelvin coupling. The clutch plate on the tool is similarly tapered on the outside and these two tapered surfaces help the robotic arm to hit right into the clutch.

In addition, the tapered sides have some pins (8) and grooves (7) that only allow the coupling to be assembled if the two coupling parts are turned correctly in relation to each other.

The parking plate (20) with the tool is flexibly suspended (22) and allows a small movement if the robot arm does not hit quite right or if it moves a little too far. When the robot arm clutch plate comes so far into the tool clutch plate that the balls in the Kelvin clutch make contact, the balls will rotate the two parts in the correct position relative to each other. When the Kelvin clutch is held together, there will be no contact between the two tapered insertion sides of the clutch plates.

In this situation, the elevation (15) of the wreath on the robot arm coupling plate will be located in the parking plate inlet. As the robot arm rotates the clutch around, the parking plate (20) holds back the wreath (9) and the wreath will push the balls round in the circuit, thereby activating the crank (18) and the hook (5). Eventually in this pivotal motion, the crank will pass the apex and the hook will retain the tool clutch plate. The robot arm can now move the arm with the interlocked clutch and tool out of the holder (20).

Between the spheres of the Kelvin coupling, a set of contact units, (10) and (11) are arranged in Figs. 2, which transmits electricity and signals between the robot arm and the tool. Furthermore, there is also a set of pneumatic couplings terminating two pneumatic connections when the coupling is locked, (12) and (13) in Figs. 2nd

The electrical contacts in both parts of the coupling are made as standalone units that can be replaced or completely replaced. Similarly, the pneumatic clutch is an independent unit that can be replaced or omitted.

The coupling on the robot arm has three built-in electrical contacts that are activated during the coupling. The first contact (S1) is activated by a pin between the group of three spheres in the Kelvin clutch. When the ball in the opposite coupling part pushes up against the three balls, this contact (S1) is activated. The other two contacts are actuated by the hook, respectively, when the hook is free of the transverse pin (S3) and when the crank is passed over vertices and the hook is therefore in a locked position (S2).

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The three contacts are in a circuit with some electrical resistors. From the outside, this circuit can be applied to a supply voltage (Power as well as GND) and the resistors will form a voltage divider. Measuring voltage (M) from the voltage divider will depend on the resistances in the circuit and on which resistors the three contacts have switched on or off the circuit.

A diagram of the circuit is shown in FIG. 13th

By reading this measurement voltage one can distinguish between three states of the coupling. The coupling can be with the hook in the open position and with no tools mounted ie. that the clutch is ready to engage on a tool.

Tension may also indicate that the clutch is in an intermediate position where the hook is actuated and a clutch assembly is running. In the third mode, the voltage indicates that the robot arm coupling is connected to a tool and that the hook is in the locked position.

If there is an electrical coupler mounted in the tool coupler and this electrical coupler is equipped with a suitable resistor (Rid), this resistor will also be coupled into the voltage divider. In FIG. 13, the connection to the coupling tool part is shown as an electrical coupling with Pogo pins.

Connecting a resistor from the tool part (Rid) to the circuit will give a voltage at the output of the voltage divider (M) which is dependent on this resistance (Rid). By reading the measuring voltage in this situation you can not only find that the coupling is closed and locked, but you can also identify the tool based on the current voltage.

If there is no resistance in the tool's electrical coupling unit, you will simply get a voltage indicating that the coupling is closed and locked but you will not have any identification of the tool.

The voltage divider has an additional resistor (R3) whose purpose is to limit the current in the event of a fault condition where several contacts are activated at the same time. In addition, there is a rectifier (D1) in the input of the resistor from the tool. This rectifier prevents the current from flowing the wrong way through the circuit e.g. during the coupling of the spring-influenced contact pins (Pogo Pin).

Claims (10)

patent claims 1. Coupling for attaching a tool to a robot arm in such a way that, by performing a series of motions, the robot arm can engage and disengage the tool, characterized in that the contact surface between the robot arm and tool is constituted by a Kelvin coupling wherein three 5 contact elements arranged on the contact surface to form a triangle consisting of a contact element where a ball on one half of the coupling contacts three balls on the other half of the coupling such that the triangular faces are perpendicular to each other and a contact element where a ball contacts two balls such that the two interfaces are 10 perpendicular to each other while the axis between the two spheres of this contact element is perpendicular to the axis between this contact element and three-sphere contact element, in addition, the third contact element consists of two spheres where the contact surface is parallel to the contact surface of the coupling Coupling according to claim 1, characterized in that a hook placed between the three contact elements can pull the two parts of the coupling together with the same. 20 a force large enough to hold the contact at all contact points while the coupling is subjected to stresses from the robot arm and the tool 25 Clutch according to Claim 1 and Claim 2, characterized in that the hook holding the two coupling parts together is suspended on a crank so that the crank can, in a pivotal movement one way, release the hook from its engagement with the opposite clutch part and a pivot the other road can pull the opposite coupling part to get full 30 contacts in all of the Kelvin clutch contacts Coupling according to claim 1, claim 2 and claim 3, characterized in The crank moving the hook is driven by a string of balls being pressed into a channel around the crank and here pressing against the crank by a wing or pin which is part of the crank and which can also drive the crank in the opposite direction of rotation by a string of bullets is pressed into the duct from the other side 40 at the same time as the wing or pin pushes the balls out of the channel in the opposite side Page 6/17 DK 2017 00599 A1 Coupling according to Claim 1, Claim 2, Claim 3 and Claim 4, characterized in that the two strings of balls driving the crank are advanced to the channels around the crank through two channels or tubes, both of which terminate in a groove enclosing the coupling part. which holds the crank and the balls are held in this groove by a pivotal wreath having two end stops limiting the movement of the balls in such a way that a rotation of the wreath will push the balls forward through one or the other channel, depending on which direction the wreath is rotated, however. the balls in the last section of the groove towards the end stop may be replaced by a coil or a flexible rod Coupling according to Claim 1, Claim 2, Claim 3, Claim 4 and Claim 5, characterized in that the movement of the hook which, when turning the crank, retains or releases the opposite coupling part is controlled by a pin on the side of the hook which is passed through a groove. along the side of the hook and thereby controlling the movement of the hook such that the tip of the hook is turned away from the point of engagement when the crank is turned to the position where the hook releases the coupling fashion part and correspondingly the tip of the hook leads over the point of attack when the crank is turned toward the position where the hook also engages the coupling counterpart, the groove for the pin of the crank allows the hook greater freedom of movement on the last piece of crank movement where the hook engages with the counterpart and where the movement of the hook is therefore controlled by the contact at the point of engagement and crank movement. Coupling according to Claim 1, Claim 2, Claim 3, Claim 5, Claim 5 and Claim 6, characterized in that the hook holding the two parts of the clutch engages a light conical cross bar inserted into a corresponding light conical hole of across the coupling member such that it has a slight inclination to the surface between the two coupling members and such that the flat hook engages a tangent parallel to the surface between the two coupling members while restricting the cross bar in the longitudinal axis of an adjustable stop at each end of the crossbar Coupling according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6 and claim 7, characterized in that the plate tool part of the coupling is inserted into and retained when the tool is disconnected is suspended in spring elements of preferably rubber on a such that they allow the plate to both move and rotate slightly to allow the robotic arm to squeeze the plate slightly out of position during entry and exit as well as during locking and release of the locking function Page 7/17 DK 2017 00599 A1 Coupling according to Claim 1, Claim 2, Claim 3, Claim 4, Claim 5, Claim 6, Claim 7 and Claim 8, characterized in that the clutch is provided with a switch which is actuated when the two coupling elements are assembled and a series of switches therein. actuated by the hook's movements or the crank's rotation in such a way that these switches are included in an electrical circuit but a series of resistors in such a way that the resistors form a voltage divider where an output voltage can be measured when the circuit is connected between an 0 conductor and a voltage supply, however, so that the different switches can switch on and off parts of circuits, thereby changing the output voltage after which the switch is activated. Coupling according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8 and claim 9, characterized in that the resistance circuit can be connected by means of an electrical connection between the coupling parts a resistor located in the tool part of couplings and where this resistance is selected such that the output voltage of the voltage divider assumes a preselected value which can thus be used to identify the tool, however, so that the current through the resistance in the tool part passes through a diode which prevents the current from running through the circuit in an inappropriate way. way during connection or disconnection Page 8/17