Abstract:
A robotic tool changer with an improved safety interlock includes a master unit, a tool unit, and a coupler movable between coupled and decoupled positions and operative to couple the master and tool units. A circuit for actuating the coupler is associated with the tool unit, for connection to an interlock that closes when the tool is safely parked in a tool stand. The circuit enables the coupler to assume the decoupled position when the master and tool units are coupled and the circuit is closed. The robotic tool changer additionally includes a circuit operative to enable the coupler to assume the decoupled position when the master unit is decoupled from the tool unit.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to the field of robotics and specifically to a safety interlock provided on the tool side of a robotic tool changer. 
   Industrial robots have become an indispensable part of modem manufacturing. Whether transferring semiconductor wafers from one process chamber to another in a cleanroom or cutting and welding steel on the floor of an automobile manufacturing plant, robots perform many manufacturing tasks tirelessly, in hostile environments, and with high precision and repeatability. 
   In many robotic manufacturing applications, it is cost-effective to utilize a relatively generic robot to accomplish a variety of tasks. For example, in an automotive manufacturing application, a robot may be utilized to cut, grind, or otherwise shape metal parts during one production run, and perform a variety of spot welding tasks in another. Different welding tool geometries may be advantageously mated to a particular robot to perform welding tasks at different locations or in different orientations. In these applications, a tool changer is used to mate different tools to the robot. One half of the tool changer, called the master unit, is permanently affixed to a robot arm. The other half, called the tool unit, is affixed to each tool that the robot may utilize. When the robot arm positions the master unit adjacent the tool unit connected to a desired tool, a coupler is actuated that mechanically locks the master and tool units together, thus affixing the tool to the end of the robot arm. Utilities such as electrical current, air pressure, hydraulic fluid, cooling water, electronic or optical data signals, and the like, may be transferred through the robot changer from the master unit to the tool unit via mating terminals, valve connections, electrical connectors, and the like, making the utilities available to the selected tool. 
   Safety is of paramount concern in any industrial robotic application. To prevent possible injury or damage to the tool, it is imperative that a tool not come dislodged from a robot arm to which it is coupled until the robot arm has positioned the tool in a tool stand or similar receptacle designed to safely support and store the tool. Since the only part of the robot arm and tool assembly not typically bolted together is the coupler of the tool changer, design and control of the coupler are key concerns. The coupler of a tool changer, i.e., the mechanism that selectively couples and decouples master unit and tool units, may comprise an electromechanical, hydrologic, pneumatic, or similar construction. Tool changers and their constituent couplers are well known in the robotics arts, and are commercially available, such as from the assignee, ATI Industrial Automation of Apex, North Carolina. 
   Although it may assume a wide variety of shapes, sizes, and modes of operation, a coupler is typically designed in a fail-safe manner, with its default state being coupled. That is, if power or pneumatic pressure is interrupted or a command interface is terminated, the master and tool units remain coupled together. This may be accomplished, for example, by spring-biasing the coupler to the coupled position, and requiring the positive application of electrical power, pneumatic pressure, or the like, to move it to the decoupled position. Also, control of the coupler during operation is carefully controlled, with robot control software typically performing myriad checks such as consulting sensors, shutting down utilities, removing applied power from the tool, and the like, prior to issuing a decouple command to the tool changer. 
   Typically, commands to actuate the coupler to couple or decouple the tool changer units are generated by a controller, which is typically located in the master unit. In modern robotic tool changers, this controller may conform to the DeviceNet specification promulgated by the Open DeviceNet Vendor Association (ODVA), information on which is available from odva.org. Alternatively, the controller may comply with other bus system specifications, or may be a custom-designed unit. Regardless of the specific controller, the generation and transmission of decouple commands is typically carefully controlled so as not to be inadvertently generated, causing untimely decoupling of the tool from the robot arm. Nevertheless, due to fear of software glitches, human error, and the like, it is desirable to interpose a hardware safety interlock into the decoupling circuit. 
   One example of such a safety interlock known in the art comprises physically breaking the connection that energizes the decoupling circuit upon command by the controller, and bringing the open circuit to external contacts on the tool changer. These contacts may then be connected to a switch located on the exterior of the tool unit or the tool itself, in such a position and manner that the switch contacts are closed by the tool stand when the tool is placed in the tool stand and securely supported. This closes the circuit, allowing the decouple signal generated by the controller to pass through the closed switch and reach the coupler, decoupling the master and tool units and removing the tool from the robot arm. When the tool is in any position other than safely stowed in its tool stand, the switch contacts remain open, and any decouple signal generated by the controller cannot reach the coupler to effect the decouple operation. 
   Prior art implementations located these switch contacts on the exterior of the master unit (which typically houses both the coupler and the controller), with a switch attached that extended to the vicinity of the tool, to be closed by the tool stand. In practice, this has been found to be a deficient solution. For example, it has been proven difficult to design and implement a switch on the master unit that is operative with a variety of tools, due to the different geometries that each tool presents. It has been discovered that in many applications, personnel simply connect a short-circuit connector to the contacts, thus thwarting the safety benefit of the interlock. 
   Moving the interlock contacts to the tool unit (by, for example, passing the unlock signal path between the master and tool units via inter-tool-changer utility connections) alleviates the necessity of a universal tool interlock switch design. Since each tool unit is typically permanently attached to a particular tool, a switch that fits the geometry of the tool may easily be designed and attached to the tool unit or to the tool itself. However, such a relocation introduces a problem: when the master and tool units are decoupled, as described above, the default position of the coupler is the coupled position. The coupler must move to the decoupled position to be able to mate the master unit with a tool unit. Yet the circuit to actuate the coupler is broken, and, regardless of the position of the tool-mounted switch, the circuit cannot be closed until the master and tool units are mated together and the utility contacts complete the circuit from the controller in the master unit, through the switch mounted on the tool, back to the coupler in the master unit. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a robotic tool changer with an improved safety interlock. The tool changer includes a master unit, a tool unit, and a coupler movable between coupled and decoupled positions and operative to couple the master and tool units. The tool changer also includes a,circuit for actuating the coupler, including contacts associated with the tool unit and operative to enable the coupler to assume the decoupled position when the contacts are connected, and a switch operative to enable the coupler to assume the decoupled position only when the master unit is decoupled from the tool unit. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a functional block diagram of a tool changer, with the master and tool units coupled and the tool removed from the tool stand. 
       FIG. 2  is a functional block diagram of a tool changer, with the tool mounted in a tool stand and the master and tool units decoupled. 
       FIG. 3  is a functional block diagram of a tool changer, depicting an interlock having status feedback signals. 
       FIG. 4  is a functional block diagram of a tool changer according to the present invention, implemented with pneumatic circuits. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention relates to a robotic tool changer with an inventive tool safety interlock circuit.  FIGS. 1 and 2  both depict, in functional block diagram form, one implementation of the tool changer of the present invention, in different configurations. Like parts are numbered consistently between the figures, and both figures should be referred throughout the following discussion. It should be noted that the tool safety interlock depicted in  FIGS. 1 and 2  comprises electrical circuits. The present invention is not, however, limited to this embodiment, and, as described below, may be implemented in a variety of ways. 
   The tool changer according to the present invention, indicated generally by the numeral  10 , comprises master unit  20  and tool unit  50 . The tool changer  10  provides a standard interface for physically coupling a robot arm  12  with a robotic tool  14 . The tool changer  10  selectively physically couples the master unit  20  to the tool unit  50 , and additionally supplies various utilities from the robot arm  12  to the tool  14 , such as high-voltage electricity, pneumatic pressure, fluids, electrical signals, and the like, through mating connections (not shown) between the master unit  20  and the tool unit  50 . Details of the tool changer  10  are not presented herein because such details are not per se material to the present invention, and further, tool changers are well known in the art. 
   To effect selective coupling and decoupling of the master unit  20  and tool unit  50 , the master unit  20  includes a coupler  22  (in other embodiments, the coupler  22  may be located on the tool unit  50 ). In the functional block diagrams of  FIGS. 1 and 2 , coupler  22  protrudes from the master unit  20 , and mates into a corresponding recess  52  in the tool unit  50 . When the coupler  22  is located in recess  52 , coupling may be achieved by extending retractable protrusions  24  of the coupler  22  into corresponding receptacles  54  formed in the recess  52  of the tool unit  50 . The extendable protrusions  24  may, for example, be located radially around the circumference of a circular coupler  22 , providing a plurality of generally evenly spaced locking points.  FIG. 1  depicts the master unit  20  and tool unit  50  coupled together, with the coupler  22  residing in recess  52 , and the extendable protrusions  24  extended into corresponding receptacles  54 . 
   To decouple the master unit  20  from the tool unit  50 , such as for example to connect a different tool  14  to the robot arm  12 , the extendable protrusions  24  may be retracted into the coupler  22 , as depicted by the motion arrows of  FIG. 2 , allowing the coupler  22  to exit the recess  52 . 
   It should be noted that the coupler  22  of  FIGS. 1 and 2  is a functional block diagram, for explanatory purposes only. In practice, tool changer couplers may comprise intricate and complex electro-mechanical or pneumatic systems, and may include a plurality of locking elements, such as ball bearings, cylindrical rollers, or the like, as are known in the robotic arts. Regardless of the complexity of any given implementation of a coupler  22 , however, the coupler  22  is typically actuated with one or two command signals. For example, the coupler  22  depicted in  FIGS. 1 and 2  assumes a coupled state by default, and assumes a decoupled state upon assertion of an unlock signal from a controller  21  (located, in this example, in or on the master unit  20 ), That is, the extendable protrusions  24  are spring-loaded or otherwise biased to the extended position, as depicted In both  FIGS. 1 and 2 . The protrusions  24  only assume the retracted position during the assertion of an unlock signal at the uncouple input  23  of the coupler  22 . The unlock signal may, for example, be generated by the controller  21  (denoted “UL”). Such a coupler  22  may, for example, be implemented with the use of electrical solenoids for retractable protrusions  24 , as is well known in the art. The solenoids  24  are retracted into the coupler  22  upon application of electrical power, i.e., for the duration of the assertion of the unlock signal. When power is removed, i.e., when the unlock signal is deasserted, the solenoids  24  extend to their protruding positions, as depicted in  FIGS. 1 and 2 . In other implementations, the coupler  22  may require a separate lock signal from the controller  21  to actuate the coupler  22  into the coupled position. In fact, a wide variety of additional signals may be implemented in any given implementation of a coupler  22 ; however, where some signal or combination of signals is applied to the coupler  22  to decouple the master unit  20  from the tool unit  50 , the tool safety interlock of the present invention is applicable. 
   The master unit  20  includes controller  21 , in wired or wireless communication with a robot control system (not shown). In an exemplary embodiment, controller  21  comprises a DeviceNet controller. In other embodiments, controller  21  may comprise a different standard bus interface, a microprocessor and associated circuits, a custom integrated circuit such as an ASIC or FPGA, or the like. To decouple the master unit  20  from the tool unit  50 , controller  21  generates an unlock command signal at its unlock output  26 . For a safety interlock, rather than route the unlock command directly to the decouple input  23  of the coupler  22 , the unlock output  26  is routed across the master/tool interface, and through the tool unit  50  to an external contact  60 . Another external contact  62  on the tool unit  50  carries the return signal through the tool unit, across the master/tool interface, and routes it to the decouple input  23  of the coupler  22 . The external contacts  60  and  62  of tool unit  50  may be integrated in a common connector, possibly along with additional signals, as is well known in the art. 
     FIG. 1  depicts the master unit  20  and tool unit  50  coupled together, which connects the tool  14  to the robot arm  12 . To prevent inadvertent decoupling of the master unit  20  from the tool unit  50  (possibly causing the robot arm  12  to drop the tool  14 ), an interlock switch  70  is mounted on the tool  14 , and its switch contacts connected to a circuit in the tool unit  50  comprising external contacts  60  and  62 . This circuit connects to the unlock output  26  of the controller  21  and the decouple input  23  of the coupler  22  on the master unit  20 , when the master unit  20  and tool unit  50  are coupled together. Interlock switch  70  comprises normally-open electrical contacts  72  and plunger  74 , biased to the extended position. As depicted in  FIG. 1 , during normal operation of the robot, the tool  14  cannot inadvertently be decoupled from the robot arm  12 . Even in the event that a software glitch, communications error, erroneous manual input, or the like, causes the controller  21  to erroneously issue an unlock command  26 , the corresponding electrical signal will travel across the master/tool interface, to the external contact  60 , and to the interlock switch  70 . As the interlock switch contacts  72  are maintained in an open-circuit condition, the unlock signal  26  is unable to traverse the return path (i.e., to external contact  62 , across the master/tool interface, and to the coupler unlock input  23 ). 
   Also depicted in  FIG. 1  is a tool stand  80 , shaped and configured so as to receive and securely hold the tool  14 , when the tool  14  is decoupled from the robot arm  12  by the tool changer  10 . As used herein, the term “tool stand” denotes a broad array of tool storage locations. In practice, the tool stand  80  may comprise any appropriate receptacle or holding mechanism for the tool  14 , such as a stand, rack, hook or other suspension device, or the like. In the functional diagram depicted in  FIG. 1 , tool stand  80  includes an actuating surface  82  positioned so as to engage and actuate the interlock switch  70  when the tool  14  is placed in the tool stand  80 . As depicted in  FIG. 2 , the actuating surface  82  depresses the plunger  74 , closing electrical contacts  72 . This completes the electrical circuit between unlock signal  26  at the controller  21  and the unlock signal  23  at the coupler  22 . With the safety interlock switch  70  closed, an unlock command generated by the controller  21  will reach the coupler  22 , retracting the plungers  24  and allowing the master unit  20  to decouple from the tool unit  50 . 
   Note that the interlock switch  70  is a functional block diagram only. In practice, the interlock switch  70  may comprise an electromechanical switch as shown, or alternatively may comprise a proximity-operated relay, or any of a broad array of sensors and switches as known in the art, such as for example, ultrasonic, magnetic, optical, radio frequency, capacitive, or other proximity sensors. 
   Locating the external contacts  60 ,  62  on the tool unit allows for an interlock switch  70  designed to the geometry of a particular tool  14 . The interlock switch  70  may be located on the tool  14 , as shown, or alternatively may be located on the tool unit  50 , such as directly connecting to external contacts  60 ,  62 , with an appropriate extension placing the plunger  74  or other actuating element in a position to be engaged by surface  82  of the tool stand  80  when the tool  14  is securely housed in the tool stand  80 . 
   Locating the connectors  60 ,  62  on the tool unit  50  introduces a problem. Referring to  FIG. 2 , when the tool  14  is secured in the tool stand  80 , and the master unit  20  has decoupled from the tool unit  50 , the electrical connectivity between the unlock signal  26  at controller  21  and the unlock signal  23  at coupler  22  (established through the interlock switch  70 ) is broken. As the coupler  22  is of a fail-safe design, whose default position is the coupled position, this causes the retractable plungers  24  to extend to the coupled position. As the robot arm  12  maneuvers to attach to another tool  14 , the coupler  22  cannot mate with the recess  52  of the desired tool unit  50 , without energizing the unlock signal  23  to actuate the coupler  22  to retract the plungers  24 , assuming the decoupled position. To provide an alternate path for the unlock signal  26 , the master unit  20  according to the present invention includes a switch  30 , depicted in  FIGS. 1 and 2  as a relay. In the normally-closed position, which the switch  30  assumes when the master unit  20  and tool unit  50  are decoupled, as depicted in  FIG. 2 , the relay  30  connects the unlock signal  26  from the controller  21  with the unlock input  23  of the coupler  22 . This allows the coupler  22  to assume the decoupled position whenever an unlock command is generated by the controller  21 , so long as the master unit  20  and tool unit  50  are decoupled. 
     FIG. 1  depicts the relay  30  when the master unit  20  is coupled to the tool unit  50 . The relay  30  is energized by a “tool present” signal from detector  28 . Detector  28  is a proximity detector that may respond for example to a proximity indicator  58  located on the tool unit  50 . The proximity detector  28  (and optionally the proximity indicator  58 ) may comprise any proximity sensor system as well known in the art, for example a magnet  58  and read switch or Hall Effect sensor  28 ; an optical emitter  58  and receiver  28 ; a high-density element  58  and ultrasonic range finder  28 ; or the like. Upon detecting the presence of the tool unit  50  (indicating that master unit  20  and tool unit  50  are coupled together), the proximity detector  28  energizes the relay  30 . This causes the relay  30  to switch to its normally-open position, opening the circuit between the unlock output  26  of the controller  21  and the decouple input  23  of the coupler  22 . In this state, no unlock signal generated by the controller  21  can actuate the coupler  22  without passing through the interlock switch  70 , which is only closed when the tool  14  is securely positioned within the tool stand  80 . 
   When the master unit  20  and tool unit  50  are coupled together, and the relay  30  is energized by the proximity detector  28 , not only is the electrical path from the controller  21  to the coupler  22  open-circuited, but the coupler decouple input  23  is additionally routed back to the controller  21  via the normally-open contact of the relay  30 . This provides a feedback signal to the controller  21  for verifying the operation of both the relay  30  and the coupler  22 . Similarly, and referring to  FIG. 2 , when the master unit  20  and tool unit  50  are decoupled, the controller  21  will not sense the state of the decouple input  23 . In this manner, the controller  21  may monitor the state of the relay  30 , and by comparison with other sensors, may verify its proper operation (for example, the proximity sensor  28  may additionally send the “tool connected” signal to the controller  21 ; the coupler  22  may send status signals to the controller  21 , and the like, none of which are depicted in  FIG. 1  or  2 ). 
   The interlock switch  70  may, in an exemplary embodiment, be implemented as a double pole switch, relay, pneumatic valve or other circuit that provides one or more additional feedback signals. This is depicted in  FIG. 3 , wherein the interlock circuits are shown as electrical signals.  FIG. 3  additionally depicts the interlock switch  70  mounted to the tool unit  50  rather than the tool  14 . In the double-pole switch  70 , the plunger  74  or other actuator is activated by the surface  82  of the tool stand  80  when the tool  14  is securely stowed in the tool stand  80 . The plunger  74  simultaneously closes switch contacts  72  and switch status indicator  71 . Switch contacts  72  route the controller  21  unlock output  26  to the coupler  22  decouple input  23 , as describe above and with reference to  FIGS. 1 and 2 . The contacts of switch status indicator  71  are routed through external switch status contacts  64 ,  66  (which may for example be co-located with contacts  60 ,  62 ), through the master/tool interface, and to additional feedback inputs of the controller  21 . In this manner, the controller  21  may monitor the status of the interlock switch  70  independently of its effect in enabling the coupler  22 . Monitoring the status of both the relay  30  and the safety interlock switch  70  is desirable due to the critical safety function performed by the interlock circuits. If switch  30  or  70  were to fail in the short-circuit position, the interlock circuit&#39;s essential function would be defeated. In this situation, the controller  21 , or a system robotic controller or master program in communication with controller  21 , should detect the condition and initiate a shut-down, trigger a safety-critical equipment failure flag, or take other action as appropriate. 
   The present invention has been described above by reference to various embodiments that implement the interlock function via electrical circuits. The present invention, however, is not limited to an electrical circuit implementation. The interlock circuits could be pneumatic, via mechanical linkages, or in a variety of other ways, all of which fall within the scope of the present invention as claimed herein. For example,  FIG. 4  depicts an embodiment wherein the interlock circuits of the present invention are implemented as pneumatic pressure lines. In general, as used herein, a “circuit” is broadly defined as an instrumentality or aggregate of instrumentalities that effect a transfer of operative control of an uncouple command from a controller  21  to a coupler  22 . According to the present invention, a circuit associated with the tool unit  50  provides a tool interlock functionality such that any unlock command generated by the controller  21  is effectively conveyed to the coupler  22  when the master unit  20  and tool unit  50  are decoupled, and only if the tool  14  is stored in a tool stand  80  when the master unit  20  and tool unit  50  are coupled together. 
   With reference to  FIG. 4 , master unit  20  includes air inlet  90  connected to a source of pneumatic pressure (not shown). Pneumatic pressure at the pneumatic circuit  93  actuates a cam  94 , which in turn causes the coupler  22  to assume a decoupled position. The coupler  22  is biased to a coupled position, which it assumes in the absence of pneumatic pressure at the cam  94 . The application of pneumatic pressure to the cam  94  is controlled by a valve  92  connected to the air input  90 . The valve  92  operates under the control of the controller  22  (which may be via an electrical signal, or other means as appropriate). The pneumatic circuit  93  exits the master unit  20  at normally-closed valve switch  96 . Valve switch  96  is biased to a closed position, in which pneumatic pressure is not transferred across it. Valve switch  96  is operated by an actuator  97 , biased to an extended position. When the actuator  97  is moved to a retracted position, such as by contact with the tool unit  50 , the valve switch  96  opens, allowing pneumatic pressure to flow across the switch  96  and into the pneumatic circuit  68  of tool unit  50 . Pneumatic pressure is carried by circuit  68  associated with the tool unit  50 , and through a safety interlock  70 . Disposed on mating surface  82  of the tool stand  80  is a plug  83 , positioned to mate with the pneumatic circuit in the interlock switch  70 . 
   In operation, when the master unit  20  and tool unit  50  are uncoupled, the coupler  22  may assume the uncoupled position upon command by the controller  21 . Pneumatic pressure supplied by air input  90  and passing through valve  92  is trapped at the closed valve switch  96 , proving pressure to actuate the cam  94  and uncouple the coupler  22  in preparation for mating with a tool unit  50 . 
   Once the master unit  20  and tool unit  50  are coupled together, however, the valve switch  96  is forced open by the actuator  97  moving to the retracted position due to contact with the tool unit  50 . This bleeds off all pneumatic pressure in the pneumatic circuit  93  and prevents actuation of the cam  94 , hence preventing the coupler  22  from assuming the uncoupled position (even if the controller  21  opens the valve  92  to uncouple the coupler  22 ). Only when the tool  14  is securely mated in the tool stand  80 , and the plug  83  mated to the interlock switch  70 , is the pneumatic circuit  68  of tool unit  50  closed, allowing pressure in the pneumatic circuit  93  of master unit  20  to build up and actuate the cam  94  to uncouple the coupler  22 . The various elements of the pneumatic interlock circuits of the embodiment of the present invention depicted in  FIG. 4  may, in practice, include various sensors and monitors as necessary or desired to provide appropriate feedback to the controller  21  or external controller or master program as prudent safety concerns may dictate. Note that the elements depicted in FIG.  4  and described herein are idealized schematic/functional block, and are not intended to represent an actual implementation. 
   Although the present invention has been described herein with respect to particular features, aspects and embodiments thereof, it will be apparent that numerous variations, modifications, and other embodiments are possible within the broad scope of the present invention, and accordingly, all variations, modifications and embodiments are to be regarded as being within the scope of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.