Abstract:
An isolated force/torque sensor assembly for a force controlled robot includes an end effector for operatively attaching to an arm of the force controlled robot, the end effector having a gripping portion adapted to be gripped by a hand of a user, and a force/torque sensor adapted to be disposed between the gripping portion and the arm of the robot, the force/torque sensor having a high force end effector interface adapted to be attached to the arm of the robot, a low force end effector interface operatively attached to the gripping portion, and a transducer disposed between the high force end effector interface and the low force end effector interface for reacting to loads applied to the low force end effector interface for user controlled positioning of a surgical tool and for generating corresponding output signals, and wherein the transducer is bypassed for high loads.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of pending U.S. Provisional Patent Application No. 62/101,647, filed Jan. 9, 2015, the entire disclosure of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a force/torque sensor assembly for a force controlled robot. 
     BACKGROUND 
     Medical practitioners have found it useful to use robotic systems to assist in the performance of surgical procedures. Such robotic systems may include a force controlled robot having a moveable arm and an end effector at the end of the arm. Typically, a surgical tool is attached to the end effector. The tool is designed to be applied to a surgical site. Generally, a controller regulates movement of the arm to position the tool with a high degree of accuracy at the surgical site. Optimum control of the force controlled robot is achieved by directly sensing forces applied by a user at a location where the user interacts with the robot. This is typically at the end effector/robot arm interface or part of the end effector itself. 
     A component of many robotic systems is a force/torque sensor. The force/torque sensor is typically attached between the free end of the arm and the tool. The force/torque sensor monitors forces and torques that are applied to the tool. These may be forces and torques that are applied to the tool as a consequence of the tool pressing against tissue. These also may be forces and torques a user applies in order to set a position and/or orientation of the tool. Signals output by the force/torque sensor are received by the controller. The controller uses these signals to determine a target position for the tool. Based on the determined target position, the controller actuates the arm in order to advance the arm so that the tool is moved to the target position. 
     In order to ensure all forces and torques applied to the tool are measured, it is common practice to provide a six component force/torque sensor. This type of force/torque sensor measures forces applied to the tool along three axes and torques applied to the tool around the three axes. 
     One type of six component force/torque sensor is also known as a force/torque transducer. A typical force/torque transducer includes a pair of sensor members, one for attaching to the robot arm and one for attaching to the end effector. A plurality of beams is flexibly mounted between the sensor members and one or more strain gauges are associated with each beam. Each strain gauge generates an electrical signal proportional to a flexure of the beam with which the strain gauge is associated. The output signals from the strain gauges are input variables into an algorithm that yields the measured forces and torques. 
     One disadvantage of the above force controlled robot is that the force/torque sensor is subjected to all other forces imparted to the tool in addition to the forces presented by the user and these other forces may be in a range that is capable of exceeding the operating range of the force/torque sensor or even high enough to damage the force/torque sensor. This is especially true when the use-case of the force controlled robot is to be a manual positioner for a high impact procedure such as impacting an acetabular cup in a total hip arthroplasty. In this application, the user guides the robot into the correct position to hold the impactor using traditional force control and then manually strikes the tool with a hammer, subjecting the force/torque sensor to the impact forces. Therefore, there is a need in the art to provide a force/torque sensor for a force controlled robot that isolates the force/torque sensor such that the impacting forces are not imparted to the force/torque sensor. 
     SUMMARY 
     Accordingly, in one embodiment, the present invention provides an isolated force/torque sensor assembly for a force controlled robot including a gripping portion adapted to be gripped by a hand of a user. The gripping portion is configured to be operatively attached to an arm of the robot. The isolated force/torque sensor assembly also includes a force/torque sensor for disposing between the gripping portion and the arm of the robot. The force/torque sensor has a high force end effector interface for attaching to the arm of the robot, a low force end effector interface operatively attached to the gripping portion, and a transducer disposed between the high force end effector interface and the low force end effector interface for reacting to loads applied to the low force end effector interface for user controlled positioning of a surgical tool and for generating corresponding output signals, and wherein the transducer is bypassed for high loads. 
     In another embodiment, the present invention provides an isolated force/torque sensor assembly for a force controlled robot including a gripping portion adapted to be gripped by a hand of a user. The gripping portion is configured to be operatively attached to an arm of the robot with a shaft portion extending radially from the gripping portion. A force/torque sensor has a high force end effector interface for attaching to the arm of the robot, a low force end effector interface attached to the shaft portion, and a transducer disposed between the high force end effector interface and the low force end effector interface for reacting to loads applied to said low force end effector interface for generating corresponding output signals. 
     In another embodiment, the present invention provides an isolated force/torque sensor assembly for a force controlled robot including a gripping portion adapted to be gripped by a hand of a user. The gripping portion is configured to be operatively attached to an arm of the robot. A force/torque sensor has a high force end effector interface for attaching to the arm of the robot and a low force end effector interface attached to one end of the gripping portion. The gripping portion floats with the low force end effector interface. The force/torque sensor also includes a transducer disposed between the high force end effector interface and the low force end effector interface for reacting to loads applied to the low force end effector interface for generating corresponding output signals. 
     In another embodiment, the present invention provides an isolated force/torque sensor assembly for a force controlled robot including a gripping portion adapted to be gripped by a hand of a user. The gripping portion is configured to be operatively attached to an arm of the robot with a shaft portion extending from the gripping portion. A force/torque sensor has a high force end effector interface for attaching to the arm of the robot, a low force end effector interface attached to the shaft portion, a plurality of beams extending between the low force end effector interface and the high force end effector interface, and a transducer disposed between the high force end effector interface and the low force end effector interface for reacting to loads applied to the low force end effector interface for generating corresponding output signals. 
     Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of an isolated force/torque sensor assembly, according to the present invention, illustrated in operational relationship with a force controlled robot. 
         FIG. 2  is a perspective view of another embodiment of an isolated force/torque sensor assembly, according to the present invention, illustrated in operational relationship with a force controlled robot. 
         FIG. 3  is a perspective view of yet another embodiment of an isolated force/torque sensor assembly, according to the present invention, illustrated in operational relationship with a force controlled robot. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings and in particular  FIG. 1 , one embodiment of an isolated torque/force sensor assembly  10 , according to the present invention, is shown in operational relationship with a robot, generally indicated at  12 . In one embodiment, the robot  12  is of a force controlled type and includes a robot arm  14  extending from a body (not shown) of the robot  12 . The robot  12  also includes a wrist joint, generally indicated at  16 , attached to an end of the robot arm  14 . In this embodiment, the wrist joint  16  includes a bracket  18  attached to the robot arm  14 . The bracket  18  is generally “U” shaped. The wrist joint  16  also includes a flange  20  pivotally connected to the bracket  18 . The flange  20  is generally rectangular in shape, but may be any suitable shape. The flange  20  is disposed in the opening of the bracket  18  and pivotally connected to the bracket  18  by a suitable mechanism such as a pin (not shown). It should be appreciated that the flange  20  pivots or rotates relative to the bracket  18 . It should also be appreciated that the flange  20  is controlled by an actuator (not shown) such as an encoder, motor, and gearbox that is grounded to the bracket  18  to pivot the flange  20 . 
     In one embodiment, the robot  12  further includes an end effector, generally indicated at  22  in the dashed lines, mounted to the wrist joint  16 . The end effector  22  includes a tool holder or guide  24 . The guide  24  includes a guide portion  26  extending axially. The guide portion  26  is generally cylindrical in shape. The guide portion  26  includes an aperture  28  extending axially therethrough to allow a tool such as a reamer or impacter (I) to extend therethrough. The guide  24  also includes a support portion  30  extending radially from the guide portion  26 . In one embodiment, the support portion  30  extends from an upper end of the guide portion  26 . The guide  24  further includes a mounting portion  32  extending from the support portion  30  for attachment to the flange  20  of the wrist joint  16 . The mounting portion  32  may be mounted to the flange  20  by a suitable mechanism such as fasteners (not shown). The guide  24  is integral, unitary, and/or one-piece to form a single rigid body. It should be appreciated that the guide  24  is used by a user (not shown) to insert the tool such as the reamer or impacter during hip replacement surgery. 
     As illustrated in  FIG. 1 , the isolated force/torque sensor assembly  10  includes a user interface, generally indicated at  34 , operatively cooperating with the guide  24 . In one embodiment, the user interface  34  includes a gripping portion  36  extending axially to allow a hand of the user to grip the user interface  34 . The gripping portion  36  is generally cylindrical in shape. The gripping portion  36  includes an aperture  38  extending axially therethrough to allow the guide portion  26  of the guide  24  to extend therethrough. The user interface  34  may also include a shaft portion  40  extending radially from the gripping portion  36 . The user interface  34  is integral, unitary, and/or one-piece to form a single rigid body. It should be appreciated that the gripping portion  36  has one hundred percent clearance around the guide portion  26  of the guide  24 . It should also be appreciated that the user interface  34  is shaped for being gripped by a hand of the user. 
     Referring to  FIG. 1 , the isolated force/torque sensor assembly  10  includes a force/torque sensor, generally indicated at  42  in phantom lines. As illustrated, the force/torque sensor  42  is provided to react to loads applied to the user interface  34 . The loads include forces and torques applied to the user interface  34  by a user when the user desires to set a position and/or orientation of the guide  24 . It should be appreciated that a robot controller (not shown) sets the position of the robot arm  14  and wrist joint  16 , and thus the guide  24 , based on the forces and torques measured by the force/torque sensor  42 . 
     As illustrated in  FIG. 1 , the force/torque sensor  42  acts between the robot arm  14  and the user interface  34 . The force/torque sensor  42  includes a high force end effector interface  44 , a transducer  45 , and a low force end effector interface  48 . The interfaces  44  and  48  support the force/torque sensor  42  for operation between the robot arm  14  and the user interface  34 . The high force end effector interface  44  may either be part of the guide  24  or end effector  22 . The low force end effector interface  48  may be part of the user interface  34 . It should be appreciated that the force/torque sensor  42  is of a six axis force transducer type. It should also be appreciated that the high force end effector interface  44  may be connected to or integral with the mounting portion  32  of the guide  24 . 
     As illustrated in  FIG. 1 , the high force end effector interface  44  is a plate mounted to the flange  20  of the robot  12  by a suitable mechanism such as fasteners (not shown). The low force end effector interface  48  is mounted to or integral with the user interface  34 . The transducer  45  is disposed between the interfaces  44  and  48 . 
     The transducer  45  includes a first sensor member  46  such as a first sensor plate fixed to the high force end effector interface  44  by a suitable mechanism such as fasteners (not shown). The transducer  44  also includes a second sensor member  47  such as a second sensor plate fixed to the low force end effector interface  48  by a suitable mechanism such as fasteners (not shown). A plurality of beams (not shown) is flexibly mounted between the first sensor member  46  and second sensor member  47 . One or more strain gauges (not shown) are associated with each beam. Each strain gauge generates an electrical signal proportional to a flexure of the beam with which the strain gauge is associated. The transducer  45  may be of a silicon strain gauge type. Such a transducer  45  is commercially available from ATI Industrial Automation of Apex, N.C. The transducer  45  is connected by cabling to a force/torque controller (not shown) or the robot controller. 
     It should be appreciated that the high force end effector interface  44  is mechanically grounded to the robot arm  14 , bypassing the transducer  45  of the force/torque sensor  42  when any forces and/or torque are applied to the guide  24 . It should also be appreciated that the low force end effector interface  48  is mechanically attached to the force/torque sensor  42  for fine motion control. It should be appreciated that the first sensor member  46  may be integrated into the high force end effector interface  44  and the second sensor member  47  may be integrated into the low force end effector interface. It should still further be appreciated that the force/torque sensor  42  may be integrated into the robot  12  and not the end effector  22 . 
     In addition, the isolated force/torque sensor assembly  10  may include a second force/torque sensor (not shown) placed on the guide  24  to measure the other forces and added to the hand force of the first force/torque sensor  42  to compute total force. In the same way, the second force/torque sensor could be placed directly at the end of the flange  20  to measure total force and be able to compute a tool force by subtracting hand force of the first force/torque sensor  42  from the total force. 
     The isolated force/torque sensor assembly  10  is considered to be in a loaded state when loads are applied to the user interface  34 . When loads (e.g., forces and/or torques) are applied to the isolated force/torque sensor assembly  10 , the interfaces  44  and  48  can engage in six types of displacement relative to each other. Three of the movements are translation, along the x-axis, arbitrarily, the horizontal axis through the interfaces  44  and  48 , along the y-axis, arbitrarily the vertical axis through the interfaces  44  and  48 , and along the z-axis, arbitrarily the axis through the center of the interfaces  44  and  48  that extends in and out of the plane of  FIG. 1 . The low force end effector interface  48  can also engage in at least some rotational movement around each of the above-identified axes. Typically as a result of the application of forces and torques to the isolated force/torque sensor assembly  10 , the low force end effector interface  48  engages in several of these movements. 
     In one application, a user (not shown) may dispose a reamer (not shown) through the aperture  28  of the guide portion  26  of the guide  24  to ream out bone (not shown) of a hip socket (not shown) of a patient (not shown) for an acetabular cup implant (not shown). Once completed, the user may place the acetabular cup implant in the hip socket. The user may then dispose a tool such as an impactor (I) through the aperture  28  of the guide portion  26  of the guide  24  and hit the impacter (I) with a hammer (not shown). The user may then use the robot  12  in a vibration mode to set the acetabular cup implant in place. When hitting the impactor (I) with the hammer, high forces may be imparted to the guide  24 . These high forces are grounded by virtue of the high force end effector interface  44 . These forces also bypass the transducer  45  owing to the clearance between the guide portion  26  and the gripping portion  36 . 
     Referring to  FIG. 2 , another embodiment, according to the present invention, of the isolated force/torque sensor assembly  10  is shown. Like parts of the isolated force/torque sensor assembly  10  have like reference numerals increased by one hundred (100). In this embodiment, the isolated force/torque sensor assembly  110  includes the force/torque sensor  142  integrated into the user interface  134 . The end effector  122  includes the guide  124  having the guide portion  126  with the aperture  128 , support portion  130 , and mounting portion  132 . The user interface  134  includes the gripping portion  136  disposed about the guide portion  126  of the guide  124 . There is one hundred percent (100%) clearance between the guide portion  126  and the gripping portion  136 . The force/torque sensor  142  includes the high force end effector interface  144 , transducer  145 , and the low force end effector interface  148 . In this embodiment, the guide  124  is part of the high force end effector interface  144  mounted to the flange  20  and the low force end effector interface  148  is at an end of the gripping portion  136 . The transducer  145  is generally circular in shape and has an aperture  150  extending therethrough to allow the guide portion  126  of the guide  124  to extend therethrough. The transducer  145  includes a first sensor member  146  such as a first sensor plate fixed to the guide portion  126  by a suitable mechanism and a second sensor member  147  such as a second sensor plate fixed to the gripping portion  136  by a suitable mechanism. A plurality of beams (not shown) is flexibly mounted between the first sensor member  146  and second sensor member  147 . One or more strain gauges (not shown) are associated with each beam. Each strain gauge generates an electrical signal proportional to a flexure of the beam with which the strain gauge is associated. The low force end effector interface  148  of the force/torque sensor  142  is disposed about the guide portion  126  of the guide  124 . The transducer  145  is connected by cabling to a force/torque controller (not shown) or the robot controller. It should be appreciated that the high force end effector interface  144  is mechanically grounded to the robot arm  14 , bypassing the transducer  145  of the force/torque sensor  142  when any forces and/or torque are applied to the guide  124 . It should be appreciated that the gripping portion  136  floats about the guide portion  126  when connected to the transducer  145  of the force/torque sensor  142 . 
     It should be appreciated that the high force end effector interface  144  is mechanically grounded to the robot arm  14 . It should also be appreciated that the low force end effector interface  148  is mechanically fixed to the gripping portion  136  and is connected by the transducer  145  to the high force end effector interface  144  for fine motion control. It should further be appreciated that the operation of the isolated force/torque sensor assembly  110  is similar to the isolated force/torque sensor assembly  10 . 
     Referring to  FIG. 3 , yet another embodiment, according to the present invention, of the isolated force/torque sensor assembly  10  is shown. Like parts of the isolated force/torque sensor assembly  10  have like reference numerals increased by two hundred (200). In this embodiment, the isolated force/torque sensor assembly  210  includes the user interface  234  bridged across the force/torque sensor  242 . In one embodiment, the user interface  234  includes a gripping portion  236  extending axially to allow a hand of the user to grip the user interface  234 . The gripping portion  236  is generally cylindrical in shape. The gripping portion  236  includes an aperture  238  extending axially therethrough for receiving tools such as the reamer or impactor (I). The user interface  234  may also include a shaft portion  240  extending radially from the gripping portion  236 . The user interface  234  is integral, unitary, and/or one-piece to form a single rigid body. It should be appreciated that, in this embodiment, the end effector  232  may be solely the user interface  234  or the user interface  234  and force/torque sensor  242  combined. 
     As illustrated in  FIG. 3 , the force/torque sensor  242  includes a high force end effector interface  244 , a transducer  245 , and a low force end effector interface  248 . The low force end effector interface  248  has attachments such as flexible beams  252  for high force use that bridge across the sensitive transducer  245  that increase the overload capacity of the isolated force/torque sensor assembly  210 , but still allow the force/torque signal to be generated. The beams  252  are generally rectangular in shape, but may be any suitable shape. The beams  252  are disposed circumferentially about the low force end effector interface  248  and have one end connected by a suitable mechanism such as welding to the low force end effector interface  248 . 
     The beams  252  have another end spaced a predetermined distance from the high force end effector interface  244 . The beams  252  may be machined or otherwise arranged to contact the high force end effector interface  244  upon application of larger loads to prevent overload of the transducer  245 . The beams  252  may be calibrated so that the beams  252  contact the high force end effector interface  244  at a predetermined load. Thus, the beams  252  may act as stops to contact the high force end effector interface  244  when larger loads, such as the predetermined load, are applied to the user interface  232 . In one embodiment, strain gauges  246  may be disposed on the beams  252 . Thus, force and/or torque measurements could continue to be made once the beams  252  contact the high force end effector interface  244  albeit at a lower sensitivity/resolution. It should further be appreciated that the operation of the isolated force/torque sensor assembly  210  is similar to the isolated force/torque sensor assembly  10 . 
     The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, the present invention may be practiced other than as specifically described.