Patent Description:
The end effectors of the robotic surgical system are positioned at the end of robotic arms. Each end effector is manipulated by an Instrument Drive Unit (IDU). The IDU includes a drive motor that is associated with the end effector to move the end effector about a respective axis or to perform a particular function of the end effector (e.g., approximate, pivot, etc. jaws of the end effector). The IDU can include a plurality of drive motors with each drive motor being associated with a respective degree of freedom or function of the end effector.

There is a need for precisely and accurately measuring the force applied by the drive motors in order to anticipate and predict a life expectancy of the drive motors. In addition, there is a continuing need for reduced feedback signal response time for providing real-time haptic feedback to a user.

<CIT> discloses a torque detection apparatus including a base portion, a drive portion, and a detection portion. The drive portion includes a rotor having a main axis in a direction of a first axis, and a stator configured to rotate the rotor around the main axis. The detection portion includes a strain body and a detection element. The strain body includes a first end portion to be fixed to the base portion and a second end portion to be fixed to the rotor, and is arranged concentrically with the rotor. The detection element is provided to the strain body so as to detect a strain of the strain body around the first axis with respect to the base portion.

According to the invention there is provided a torque transducer as recited in the independent claim with preferred features as set forth in the dependent claims. In an aspect of the present disclosure, a torque transducer for mounting a motor includes a motor plate, a mounting plate, a flex ring, and a strain gauge. The motor plate is configured to be fixed to the motor and the mounting plate is configured to be fixed to fixed structure. The flex ring is positioned between the motor plate and the mounting plate. The flex ring includes a body having first and second ends that are moveable relative to one another. The first end of the body is fixed to the motor plate and the second end of the body is fixed to the mounting plate. The body is configured to flex in response to the first and second ends moving with respect to one another. The strain gauge is positioned on the body of the flex ring to measure flexation of the body.

In aspects, the torque transducer includes a bearing that has an inner surface positioned over the motor plate and an outer surface positioned within the mounting plate. The motor plate may include a bearing stem that extends towards the mounting plate. The inner surface of the bearing may be fixed to the bearing stem. The mounting plate may include a bearing cylinder that extends towards the motor plate. The outer surface of the bearing may be fixed to an inner surface of the bearing cylinder. The flex ring may be positioned over an outer surface of the bearing cylinder and/or the bearing.

In some aspects, the motor plate includes a radially extending motor flange and the mounting plate includes a radially extending mounting flange. The flex ring may include a radially extending first flange at the first end of the body and a radially extending second flange at the second end of the body. The first flange may be fixed to the motor flange and the second flange may be fixed to the mounting flange.

In certain aspects, the body of the flex ring includes a low strain member and a high strain member that each have a first end fixed to the motor ring and a second end fixed to the mounting ring. Each of the low and high strain members are parallel to a longitudinal axis that is defined between centers of the motor and mounting rings. The mounting ring may define recesses that clock the mounting ring to the fixed structure.

In particular aspects, the body of the flex ring has inner and outer diameters that determine a stiffness of the body. The strain gauge may be positioned halfway between the first and second end of the body of the flex ring.

In another aspect of the present disclosure, a drive unit includes a fixed structure, a first motor, and a first torque transducer. The first motor has a drive shaft that passes through the fixed structure. The first torque transducer is positioned between the fixed structure and the first motor about the drive shaft of the first motor to mount the first motor to the fixed structure. The first torque transducer includes a motor plate, a mounting plate, a flex ring, and a strain gauge. The motor plate is positioned about the drive shaft of the first motor and is fixed to the first motor. The mounting plate is positioned about the drive shaft of the first motor and is fixed to the fixed structure. The flex ring is positioned between the motor plate and the mounting plate and about the drive shaft of the first motor. The flex ring includes a body that has first and second ends that are moveable relative to one another. The first end of the body is fixed to the motor plate and the second end of the body is fixed to the mounting plate. The body is configured to flex in response to the first and second ends moving with respect to one another. The strain gauge is positioned on the body of the flex ring to measure flexation of the body.

In aspects, the drive unit includes a first drive cable that is operably associated with the drive shaft and is configured to manipulate a tool in response to rotation of the drive shaft. The drive unit may include a converter that is coupled to the drive shaft of the motor to convert rotation of the drive shaft into linear movement of the first drive cable.

In some aspects, the first motor is configured to manipulate a tool in a first degree of freedom. The drive unit may include a second motor that is configured to manipulate the tool in a second degree of freedom different from the first degree of freedom. The second motor may be mounted to the fixed structure by a second torque transducer.

In certain aspects, the fixed structure is an end of an arm of a robotic system.

Various aspects of the present disclosure are described hereinbelow with reference to the drawings, which are incorporated in and constitute a part of this specification, wherein:.

Embodiments of the present disclosure are now described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein, the term "clinician" refers to a doctor, a nurse, or any other care provider and may include support personnel. Throughout this description, the term "proximal" refers to the portion of the device or component thereof that is closest to the clinician and the term "distal" refers to the portion of the device or component thereof that is farthest from the clinician.

The present disclosure generally relates to a torque transducer that measures the reaction torque of a motor of an instrument drive unit (IDU) to determine the forces being applied to an end effector of a robotic surgical system. The torque transducer is positioned between the motor and a fixed plate of the IDU to secure the motor within the IDU. The measured reaction torque may be used to control the end effector and/or provide feedback to the user of the robotic surgical system.

Referring to <FIG>, a robotic surgical system <NUM> is shown generally as a robotic system <NUM>, a processing unit <NUM>, and a user interface <NUM>. The robotic system <NUM> generally includes linkages <NUM> and a robot base <NUM>. The linkages <NUM> moveably support an end effector or tool <NUM> which is configured to act on tissue. The linkages <NUM> may be in the form of arms each having a plurality of members <NUM>. A member 13a of the plurality of members <NUM> has an end <NUM> that supports an end effector or tool <NUM> which is configured to act on tissue. In addition, the end <NUM> of the member 13a may include an imaging device <NUM> for imaging a surgical site "S". Each of the plurality of members <NUM> of the linkages <NUM> may be connected to one another about joints <NUM>. The user interface <NUM> is in communication with robot base <NUM> through the processing unit <NUM>.

The user interface <NUM> includes a display device <NUM> which is configured to display three-dimensional images. The display device <NUM> displays three-dimensional images of the surgical site "S" which may include data captured by imaging devices <NUM> positioned on the end <NUM> of the member 13a and/or include data captured by imaging devices that are positioned about the surgical theater (e.g., an imaging device positioned within the surgical site "S", an imaging device positioned adjacent the patient "P", imaging device <NUM> positioned at a distal end of an imaging arm <NUM>). The imaging devices (e.g., imaging devices <NUM>, <NUM>) may capture visual images, infra-red images, ultrasound images, X-ray images, thermal images, and/or any other known real-time images of the surgical site "S". The imaging devices transmit captured imaging data to the processing unit <NUM> which creates three-dimensional images of the surgical site "S" in real-time from the imaging data and transmits the three-dimensional images to the display device <NUM> for display.

The user interface <NUM> also includes input handles <NUM> which allow a clinician to manipulate the robotic system <NUM> (e.g., move the linkages <NUM>, the ends <NUM> of the linkages <NUM>, and/or the tools <NUM>). Each of the input handles <NUM> is in communication with the processing unit <NUM> to transmit control signals thereto and to receive feedback signals therefrom. Each of the input handles <NUM> may include input devices which allow the surgeon to manipulate (e.g., clamp, grasp, fire, open, close, rotate, thrust, slice, etc.) the tools <NUM> supported at the end <NUM> of the member 13a.

For a detailed discussion of the construction and operation of a robotic surgical system <NUM>, reference may be made to <CIT>, entitled "Medical Workstation".

Referring also to <FIG>, an instrument drive unit (IDU) <NUM> is disposed within or supported on the member 13a adjacent the end <NUM>. The IDU <NUM> is operatively associated to a tool <NUM> coupled to the end <NUM> to manipulate the tool <NUM> in response to control signals transmitted from the processing unit <NUM>. The IDU <NUM> includes at least one motor <NUM>, a respective converter <NUM>, a respective drive cable <NUM>, and a respective torque transducer <NUM>. The motor <NUM> rotates a drive shaft <NUM> that extends through the torque transducer <NUM> in response to energy being supplied to the motor <NUM>. The converter <NUM> converts rotation of the drive shaft <NUM> of the motor <NUM> to linear movement of the drive cable <NUM> as indicated by arrow "T". The converter <NUM> may be secured to a fixed plate <NUM> of the IDU <NUM>.

The drive cable <NUM> extends from the converter <NUM> to the end effector <NUM>. As shown in <FIG>, the drive cable <NUM> is associated with effecting a rotation of the end effector <NUM> about a pulley <NUM>. It will be appreciated each IDU <NUM> may include a plurality of motors <NUM> with a drive cable <NUM> associated with each of the plurality of motors <NUM> such that each drive cable <NUM> is associated with a different degree of freedom of the end effector <NUM> or a function of the end effector <NUM>.

With reference to <FIG>, the torque transducer <NUM> is provided in accordance with the present disclosure and is a reaction torque transducer that measures motor torque applied by the motor <NUM> to the converter <NUM> and thus, measures force applied to the end effector <NUM> by the cable <NUM>. The torque transducer <NUM> is positioned about the drive shaft <NUM> of the motor <NUM> and secures the motor <NUM> to the fixed plate <NUM> of the IDU <NUM>. The torque transducer <NUM> includes a motor plate <NUM>, a mounting plate <NUM>, a bearing <NUM>, a flex ring <NUM>, and a strain gauge <NUM> (<FIG>).

The motor plate <NUM> is rotatably supported on the motor <NUM> about the drive shaft <NUM>. The motor plate <NUM> includes a cylindrical body <NUM> that defines a recess or bore <NUM> facing the motor <NUM> which is dimensioned to receive a protrusion 62a of the motor <NUM> extending about the drive shaft <NUM>. The motor plate <NUM> is press-fit over the protrusion 62a of the motor <NUM> such that the protrusion 62a of the motor <NUM> is received within the recess <NUM> in an interference fit. In embodiments, the protrusion 62a of the motor <NUM> may have a geometric shape (e.g., square, pentagonal, etc.) and that the recess <NUM> of the motor plate <NUM> may have a complimentary geometric shape to receive the protrusion <NUM> to rotatably fix the motor plate <NUM> to the motor <NUM>. In such embodiments, a press-fit between the body <NUM> of the motor plate and the protrusion 62a of the motor is not required. The body <NUM> of the motor plate <NUM> includes a bearing stem <NUM> that extends from a face of the body <NUM> facing away from the motor <NUM>. The bearing stem <NUM> includes an outer surface 76a that is configured to support an inner race or surface 88a of the bearing <NUM>. The inner surface 88a of the bearing <NUM> may be press-fit over the bearing stem <NUM> of the motor plate <NUM>. The motor plate <NUM> also includes a flange or ear <NUM> that extends radially from an outer surface of the body <NUM>.

The mounting plate <NUM> is positioned between the motor plate <NUM> and the fixed plate <NUM> of the IDU <NUM> (<FIG>). The mounting plate <NUM> includes a body <NUM> that is secured to the fixed plate <NUM> to rotatably and longitudinally fix the mounting plate <NUM> relative to the fixed plate <NUM>. It is contemplated that the mounting plate <NUM> may be integrally formed with the fixed plate <NUM>, welded to the fixed plate <NUM>, affixed to the fixed plate <NUM>, or any combination thereof. The body <NUM> includes a bearing cylinder <NUM> that extends towards the motor plate <NUM>. The bearing cylinder <NUM> includes an inner surface 84a that is dimensioned to receive an outer race or surface 88b of the bearing <NUM>. The outer race 88b of the bearing <NUM> may be press-fit into the bearing cylinder <NUM>. The bearing <NUM> has a length along a longitudinal axis of the drive shaft <NUM> such that the bearing <NUM> is disposed within the bearing cylinder <NUM> of the mounting plate <NUM> and over the bearing stem <NUM> of the motor plate <NUM>. The mounting plate <NUM> also includes a flange or ear <NUM> extending radially from the body <NUM>.

Referring to <FIG>, the flex ring <NUM> is an open ring positioned between the motor plate <NUM> and the mounting plate <NUM> over the bearing cylinder <NUM> of the mounting plate <NUM>. The flex ring <NUM> includes a body <NUM> that has an inner diameter DI larger than the bearing cylinder <NUM> of the mounting plate <NUM> such that the body <NUM> does not contact the bearing cylinder <NUM>. The body <NUM> of the flex ring <NUM> has first and second ends 92a, 92b that are moveable relative to one another in a plane transverse to the longitudinal axis of the drive shaft <NUM> or substantially tangentially to the longitudinal axis of the drive shaft <NUM>. The first end 92a of the body <NUM> includes a motor flange <NUM> and the second end 92b of the body <NUM> includes a mounting flange <NUM> that define a gap "G" therebetween. The flanges <NUM>, <NUM> extend radially from the body <NUM> of the flex ring <NUM> and have a length or thickness along the longitudinal axis of the drive shaft <NUM> that is less than the length or thickness of the body <NUM>.

The motor flange <NUM> is aligned with a surface of the body <NUM> facing the motor plate <NUM> such that the surface of the body <NUM> facing the motor plate <NUM> is continuous with the motor flange <NUM>. The mounting flange <NUM> is aligned with a surface of the body <NUM> facing the mounting plate <NUM> such that the surface of the body <NUM> facing mounting plate <NUM> is continuous with the mounting flange <NUM>. The first end 92a of the body <NUM> may form a notch with the motor flange <NUM> that engages a corresponding notch of the mounting plate <NUM> to limit the movement of the motor flange <NUM> towards the mounting flange <NUM>, as shown in <FIG>. Similarly the second end 92b of the body <NUM> may form a notch with the mounting flange <NUM> that engages a corresponding notch of the motor plate <NUM> to limit movement of the motor flange <NUM> towards the mounting flange <NUM>.

With particular reference to <FIG>, a first fastener 99a passes through the motor flange <NUM> of the flex ring <NUM> and the flange <NUM> of the motor plate <NUM> to rotatably fix the motor flange <NUM>, and thus the first end 92a of the body <NUM>, to the motor <NUM>. A second fastener 99b passes through the mounting flange <NUM> of the flex ring <NUM> and the flange <NUM> of the mounting plate <NUM> to rotatably fix the mounting flange <NUM>, and thus the second end 92b of the body <NUM>, to the fixed plate <NUM>. The fastener 99b may pass through the flange <NUM> of the mounting plate <NUM> and into the fixed plate <NUM>.

Briefly referring back to <FIG>, when the motor <NUM> is energized to rotate the drive shaft <NUM> in a first direction as indicated by arrow R, the motor <NUM> is subject to a reactive torque from the drive shaft <NUM> in a second direction opposite the first direction. This reactive torque passes through the torque transducer <NUM> which secures the motor <NUM> to the fixed plate <NUM>. As the reactive torque passes through the torque transducer <NUM>, the body <NUM> of the flex ring <NUM> flexes such that the first and second ends 92a, 92b move relative to one another. The flex of the body <NUM> is measured by a strain gauge <NUM> (<FIG>) positioned on an inner surface of the body <NUM> opposite of the gap G. The configuration of the motor plate <NUM>, the mounting plate <NUM>, the bearing <NUM>, and the flex ring <NUM> isolate the body <NUM> of the flex ring <NUM> from flexing in a direction other than the opening or closing the gap G. As detailed below, the gap G opens and closes in response to the reaction torque of the motor <NUM>.

Referring to <FIG>, the strain gauge <NUM> is positioned opposite the gap "G" between the first and second ends 92a, 92b at a point of maximum flexation of the body <NUM>. The flex ring <NUM> is tuned to the application of the motor <NUM> to provide adequate stiffness to prevent excessive displacement or flexation of the body <NUM> and to provide enough flexation of the body <NUM> for a measurable response from the strain gauge <NUM>. Excessive flexation of the flex ring <NUM> may result in lost motion of the end effector <NUM>. However, insufficient flexation of the body <NUM> will result in an undetectable flexation of the body <NUM> (i.e., the noise of the system may be greater than the measureable flexation).

The flexation of the body <NUM> of the flex ring <NUM> is tuned to a particular application of the motor <NUM> by varying the inner diameter "DI" and an outer diameter "DO" of the body <NUM> to increase or decrease a thickness "T" of the body <NUM>. It will be appreciated that as the thickness "T" of the body <NUM> of the flex ring <NUM> is increased, the stiffness of the body <NUM> is increased and the flexation is decreased when the body <NUM> is subjected to the same torque. Likewise, as the thickness "T" of the body <NUM> of the flex ring <NUM> is decreased, the stiffness of the body <NUM> is decreased and the flexation is increased when the body <NUM> is subjected to the same torque. The flex ring <NUM> may also be tuned by varying the material of the flex ring <NUM> (e.g., steel, aluminum, plastic, etc.). Further, it will be appreciated that as the inner diameter "DI" and the outer diameter "DO" of the body <NUM> are increased, with the thickness "T" remaining constant, the stiffness of the body <NUM> is increased.

Referring to <FIG>, the strain gauge <NUM> includes an active strain sensor <NUM> and a calibration strain sensor <NUM>. The active strain sensor <NUM> is aligned with a direction of the flexation of the body <NUM>, e.g., in a direction transverse to the longitudinal axis of the drive shaft <NUM> (<FIG>). The active strain sensor <NUM> measures the strain of the body <NUM> of the flex ring <NUM> as the body <NUM> flexes in response to reactive torque of the motor <NUM>. The calibration strain sensor <NUM> is aligned with the longitudinal axis of the drive shaft <NUM> and is orthogonal to the active strain sensor <NUM>. The calibration strain sensor <NUM> measures strain of the body <NUM> of the flex ring <NUM> due to factors other than the flexation of the body <NUM> in response to reactive torque of the motor <NUM> (e.g., thermal expansion of the body <NUM>).

With reference to <FIG>, a measurement circuit <NUM> determines the reaction torque of the motor <NUM> from the measured flexation from the strain gauge <NUM>. The measurement circuit <NUM> includes the strain gauge <NUM>, a voltage source <NUM>, a filter <NUM>, an amplifier <NUM>, and a controller <NUM>. The strain gauge <NUM> includes the active strain sensor <NUM> and the calibration strain sensor <NUM> as part of a bridge circuit including two resistors R<NUM>, R<NUM>. Strain of the body <NUM> of the flex ring <NUM> is measured as a voltage change of the strain gauge <NUM> whereby the resistance of each of the strain sensors <NUM>, <NUM> varies in response to flexation of the body <NUM>. The measured voltage is passed from strain gauge <NUM> to a filter <NUM>. As shown, the measured voltage accounts for factors other than the flexation of the body <NUM> as a result of positioning the calibration strain sensor <NUM> adjacent and orthogonal to the active strain sensor <NUM>. The filter <NUM> is a low pass filter to remove noise from the measured voltage. The filter <NUM> transmits the filtered voltage to an amplifier <NUM> which transmits the amplified voltage to a controller <NUM>. The controller <NUM> detects changes in the amplified voltage and calculates a strain of the body <NUM> of the flex ring <NUM>. From the strain of the body <NUM> of the flex ring <NUM>, the controller <NUM> calculates the flexation of the body <NUM>. The controller <NUM> calculates reaction torque of the motor <NUM> from the flexation of the body <NUM> of the flex ring <NUM> in view of the known properties and dimensions of the body <NUM>. The controller <NUM> transmits the calculated reaction torque of the motor <NUM> to the processor <NUM> (<FIG>).

The processor <NUM> analyzes the reaction torque of the motor <NUM> to determine the force applied to the end effector <NUM> by the IDU <NUM>. The processor <NUM> may adjust energy supplied to the motor <NUM> in response to the force applied to the end effector <NUM>. Additionally or alternatively, the processor <NUM> may provide feedback to a user through the user interface <NUM> in response to the reaction torque of the motor <NUM>. The feedback may be visual, audible, or haptic.

It is also contemplated that the robot system <NUM> may include a drive unit <NUM> (<FIG>) positioned in the robot base <NUM> that is operatively associated with the linkages <NUM> to move the plurality of members <NUM> about the joints <NUM> in response to input from a user. The drive unit <NUM> may include a torque transducer (not shown) similar to torque transducer <NUM> to measure torque applied to the linkages <NUM> by the drive unit <NUM>.

Referring now to <FIG>, a torque transducer <NUM> is provided in accordance with the present disclosure and includes a motor ring or plate <NUM>, a mounting ring or plate <NUM>, and a flex ring <NUM> positioned between the motor and mounting rings <NUM>, <NUM>. The torque transducer <NUM> is positioned over a drive shaft of a motor (e.g., drive shaft <NUM> of a motor <NUM> (<FIG>)) and supports the motor <NUM> to a fixed plate (e.g., fixed plate <NUM> (<FIG>)) of an IDU. The motor ring <NUM> is secured to a motor <NUM> by flanges <NUM> to rotatably fix the motor <NUM> to the motor ring <NUM>. The mounting ring <NUM> is secured to a fixed plate or structural member (not shown). The mounting ring <NUM> defines clocking recesses <NUM> that are configured to engage the fixed plate to rotatably fix the mounting ring <NUM> to the fixed plate.

The flex ring <NUM> includes low strain members <NUM> and a high strain member <NUM> extending between the motor and mounting rings <NUM>, <NUM>. The low and high strain members <NUM>, <NUM> are parallel to the longitudinal axis of a driveshaft of a motor (e.g., drive shaft <NUM> of motor <NUM> (<FIG>)) with a first end of each of the low and high strain members <NUM>, <NUM> fixed to the motor ring <NUM> and a second end of each of the low and high strain members <NUM>, <NUM> fixed to the mounting ring <NUM>. The strain gauge <NUM> is disposed on the high strain member <NUM> with the active strain sensor <NUM> positioned on a portion of the high strain member <NUM> subject to a maximum flexation as the torque transducer <NUM> is torqued. The calibration strain sensor <NUM> is positioned on a portion of the high strain member <NUM> that is subject to no or minimum flexation as the torque transducer <NUM><NUM> is torqued. As shown, the active strain sensor <NUM> is positioned on the high strain member <NUM> halfway between the motor and mounting rings <NUM>, <NUM> and orientated in perpendicular to the longitudinal axis of the driveshaft of the motor. The calibration strain sensor <NUM> is positioned adjacent the mounting ring <NUM> and orientated parallel to the longitudinal axis of the drive shaft of the motor. It will be appreciated that the calibration strain sensor <NUM> is orientated orthogonal to the active strain sensor <NUM>.

The flex ring <NUM> functions in a manner similar to flex ring <NUM> in response to the reaction torque of the motor and the strain gauge <NUM> measures the flexation of the high strain member <NUM> of the flex ring <NUM> to calculate the reaction torque of the motor in a similar manner.

Claim 1:
A torque transducer (<NUM>) for mounting a motor (<NUM>), comprising:
a motor plate (<NUM>) configured to be fixed to the motor;
a mounting plate (<NUM>) configured to be fixed to fixed structure (<NUM>);
a flex ring (<NUM>) positioned between the motor plate and the mounting plate, the flex ring being an open ring and including a body (<NUM>) having a first end (92a) and a second end (92b) that are moveable relative to one another, the first end of the body fixed to the motor plate and the second end of the body fixed to the mounting plate, the body configured to flex in response to the first and second ends moving with respect to one another; and
a strain gauge (<NUM>) positioned on the body of the flex ring to measure flexation of the body.