Hydraulic forceps system

A hydraulic forceps system includes: robotic forceps including: a gripper, first piston coupled to the gripper, first cylinder forming first pressure chamber, filled with a hydraulic fluid, together with the first piston, second piston, second cylinder forming a second pressure chamber, filled with hydraulic fluid, together with the second piston, communication passage through which the chambers communicate, motor that drives the second piston via a linear motion mechanism; control device that controls the motor based on a command position for the first piston; and position sensor used for detecting a position of the second piston. The control device includes: an observer that derives an estimated position of the first piston based on the position of the second detected by the sensor; and a position controller that derives a target rotational speed of the motor based on a deviation between the estimated position of the first piston and the command position.

TECHNICAL FIELD

The present invention relates to a hydraulic forceps system including robotic forceps whose gripper is opened and closed by utilizing hydraulic pressure.

BACKGROUND ART

Conventionally, wire-driven robotic forceps are used in a surgery assisting robot. The gripper of the robotic forceps is opened/closed by pulling/retracting a wire. In recent years, robotic forceps whose gripper is opened and closed by utilizing pneumatic pressure have been proposed to replace wire-driven robotic forceps. For example, FIG. 9 of Patent Literature 1 shows a pneumatic actuator used in such robotic forceps.FIG. 4shows this pneumatic actuator100.

Specifically, in the pneumatic actuator100, a piston130is accommodated in a cylinder140. The piston130is coupled to a gripper110by a rod120. The cylinder140is provided with a displacement sensor150, which detects a moving amount of the piston130. The displacement sensor150is used for calculating an external force F.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the pneumatic actuator100shown inFIG. 4, in order to control the opening and closing of the gripper110, the displacement sensor150can be used also as a position sensor for detecting the position of the piston130. However, since the distal end portions of the robotic forceps are very thin, it is difficult to install such a position sensor (displacement sensor150) at the distal end portions of the robotic forceps.

In view of the above, an object of the present invention is to make it possible to control the opening and closing of the gripper without installing the position sensor at the distal end portions of the robotic forceps.

Solution to Problem

In order to solve the above-described problems, the present invention provides a hydraulic forceps system including: robotic forceps including a gripper, a first piston coupled to the gripper, a first cylinder accommodating the first piston and forming a first pressure chamber together with the first piston, the first pressure chamber being filled with a hydraulic fluid, a second piston, a second cylinder accommodating the second piston and forming a second pressure chamber together with the second piston, the second pressure chamber being filled with the hydraulic fluid, a communication passage through which the first pressure chamber and the second pressure chamber communicate with each other, and a motor that drives the second piston via a linear motion mechanism; a position sensor used for detecting a position of the second piston; and a control device that controls the motor based on a command position for the first piston. The control device includes: an observer that derives an estimated position of the first piston based on the position of the second piston detected by using the position sensor; and a position controller that derives a target rotational speed of the motor based on a deviation between the estimated position of the first piston and the command position.

According to the above configuration, since the incompressible hydraulic fluid is used, the moving amount of the first piston coupled to the gripper, i.e., the moving amount of the first piston disposed at the distal end side of the robotic forceps, is proportional to the moving amount of the second piston, almost without being affected by the external force. In addition, the second piston is driven by the motor via the linear motion mechanism. Accordingly, by controlling the motor with the control device based on the command position for the first piston, the opening and closing of the gripper can be controlled. Moreover, the control device includes the observer, which derives the estimated position of the first piston based on the position of the second piston, and the estimated position of the first piston is compared with the command position. Therefore, installation of a position sensor that detects the position of the first piston is unnecessary. That is, the control of the opening and closing of the gripper is made possible without installing the position sensor at the distal end portions of the robotic forceps.

For example, the position sensor may be a rotary encoder that detects a rotational displacement of the motor and converts the rotational displacement into the position of the second piston.

The above hydraulic forceps system may further include a pressure sensor that detects a pressure of the hydraulic fluid. The observer may derive the estimated position of the first piston based on the pressure of the hydraulic fluid detected by the pressure sensor and the position of the second piston detected by using the position sensor. According to this configuration, the precision of the estimation of the position of the first piston can be improved compared to a case where the estimated position of the first piston is derived based solely on the position of the second piston.

For example, the observer may: derive an estimated position of the second piston and an estimated pressure of the hydraulic fluid; calculate an estimated error based on a deviation between the pressure of the hydraulic fluid detected by the pressure sensor and the estimated pressure of the hydraulic fluid and a deviation between the position of the second piston detected by using the position sensor and the estimated position of the second piston; and feed back the calculated estimated error to the deriving of the estimated position of the first piston.

Advantageous Effects of Invention

The present invention makes it possible to control the opening and closing of the gripper without installing the position sensor at the distal ends of the robotic forceps.

DESCRIPTION OF EMBODIMENTS

FIG. 1shows a hydraulic forceps system1according to one embodiment of the present invention. The hydraulic forceps system1includes robotic forceps2and a control device7.

For example, in a case where the hydraulic forceps system1is used in a surgery assisting robot, a doctor operates the robotic forceps2by remote control using a master device, while the robotic forceps2are attached to a slave device. In this case, the control device7may be mounted in the master device or in the slave device. Alternatively, the control device7may be incorporated in a drive unit21of the robotic forceps2. The drive unit21will be described below.

The robotic forceps2include a gripper24, which is opened and closed by utilizing the hydraulic pressure of a hydraulic fluid20. The hydraulic fluid20is not limited to a particular type of fluid, but may be a saline solution or oil, for example.

Specifically, the robotic forceps2include: the drive unit21; an insertion shaft22extending from the drive unit21and inserted in the body of a patient; and the gripper24provided at the distal end of the insertion shaft22and formed by a pair of tips25. Although not illustrated, a mechanism that slides the insertion shaft22in its axial direction, and a mechanism that rotates the insertion shaft22about its central axis, may be incorporated in the drive unit21. The insertion shaft22may be configured such that the distal end portion thereof is swingable, and a mechanism that swings the distal end portion of the insertion shaft22may be incorporated in the drive unit21.

In the present embodiment, the insertion shaft22is a straight tube with high rigidity. However, as an alternative, the insertion shaft22may be a flexible tube.

A first cylinder31is disposed in the distal end portion of the insertion shaft22. In the present embodiment, the central axis of the first cylinder31coincides with the central axis of the insertion shaft22. The first cylinder31includes: a tubular portion; a front wall that blocks the inside of the tubular portion from the gripper24side; and a rear wall that blocks the inside of the tubular portion from the side opposite to the gripper24side.

A first piston32is accommodated in the first cylinder31. A first pressure chamber3A is formed between the first piston32and the rear wall of the first cylinder31, and a back pressure chamber3B is formed between the first piston32and the front wall of the first cylinder31. The inside of the first pressure chamber3A is filled with the hydraulic fluid20, and the inside of the back pressure chamber3B is open to the atmosphere. In the present embodiment, a spring34, which urges the first piston32, is disposed in the back pressure chamber3B.

The first piston32is coupled to the gripper24by a rod33via a link mechanism23. The rod33penetrates the front wall of the first cylinder31. The link mechanism23converts linear motion of the rod33into opening/closing motion of the gripper24.

A second cylinder41, which is connected to the first cylinder31by a communication passage26, is disposed in the drive unit21. In the present embodiment, the axial direction of the second cylinder41is parallel to the axial direction of the insertion shaft22. However, the axial direction of the second cylinder41is not particularly limited. The second cylinder41includes: a tubular portion; a front wall that blocks the inside of the tubular portion from the insertion shaft22side; and a rear wall that blocks the inside of the tubular portion from the side opposite to the insertion shaft22side.

A second piston42is accommodated in the second cylinder41. A second pressure chamber4A is formed between the second piston42and the front wall of the second cylinder41, and a back pressure chamber4B is formed between the second piston42and the rear wall of the second cylinder41. The inside of the second pressure chamber4A is filled with the hydraulic fluid20, and the inside of the back pressure chamber4B is open to the atmosphere.

The aforementioned communication passage26extends through the inside of the insertion shaft22, and the first pressure chamber3A and the second pressure chamber4A communicate with each other through the communication passage26. The inside of the communication passage26is also filled with the hydraulic fluid20. For example, the communication passage26is formed by a metal tube or a flexible resin tube.

The second piston42is coupled to a linear motion mechanism51by a rod43, which penetrates the rear wall of the second cylinder41. The linear motion mechanism51is coupled also to an output shaft53of a motor52. The linear motion mechanism51converts rotational motion of the output shaft53of the motor52into linear motion of the rod43. That is, the motor52drives the second piston42via the linear motion mechanism51and the rod43. The motor52is, for example, a servomotor.

When the second piston42moves forward as a result of the motor52rotating in one direction, the hydraulic fluid20is supplied from the second pressure chamber4A to the first pressure chamber3A, and thereby the first piston32moves forward against the urging force of the spring34. On the other hand, when the second piston42moves rearward as a result of the motor52rotating in the reverse direction, the urging force of the spring34causes the first piston32to move rearward, and thereby the hydraulic fluid20is discharged from the first pressure chamber3A to the second pressure chamber4A. That is, the second cylinder41, the second piston42, the linear motion mechanism51, and the motor52form a hydraulic fluid supply/discharge mechanism that supplies and discharges the hydraulic fluid to and from the first pressure chamber3A.

The control device7receives, for example, an input of a command position tx1for the first piston32from the aforementioned master device. Alternatively, the control device7may receive an input of an opening degree command for the gripper24, and the control device7may include a command position calculator that calculates the command position tx1for the first piston32based on the opening degree command.

The control device7controls the motor52based on the command position tx1for the first piston32. The control device7includes, for example, a CPU and memories such as a ROM and RAM. The CPU executes a program stored in the ROM. Specifically, the control device7includes a position controller71, a speed controller72, an inverter73, a differentiator75, and an observer8. The control device7may be a single device, or may be divided into a plurality of devices.

In the present embodiment, the control device7is electrically connected to a pressure sensor61and a position sensor62. The pressure sensor61detects the pressure P of the hydraulic fluid20. The position sensor62is used for detecting the position x2of the second piston42.

In the present embodiment, the position sensor62is a rotary encoder provided on the motor52. The position sensor62detects the rotational displacement of the motor52, and converts the rotational displacement into the position x2of the second piston42. Alternatively, the position sensor62may be a linear encoder provided on the linear motion mechanism51. Further alternatively, the position sensor62may be provided on the second cylinder41, and may directly detect the position x2of the second piston42.

The observer8derives an estimated position ex1of the first piston32based on the pressure P of the hydraulic fluid20detected by the pressure sensor61and the position x2of the second piston42detected by using the position sensor62. It should be noted that the function of the observer8will be described below in detail.

The position controller71derives a target rotational speed Vt of the motor52based on a deviation Δx1(=tx1−ex1) between the estimated position ex1of the first piston32and the command position tx1for the first piston32. The relationship between the deviation Δx1and the target rotational speed Vt is preset.

The differentiator75calculates the current rotational speed V of the motor52by performing differentiation on the position x2of the second piston42, which is detected by using the position sensor62. The speed controller72derives a target electric current Ct of the motor52based on a deviation ΔV (=Vt−V) between the target rotational speed Vt and the current rotational speed V of the motor52. The relationship between the deviation ΔV and the target electric current Ct is preset.

A current sensor74is provided on an electric power line between the inverter73and the motor52. The inverter73supplies an electric current to the motor52, such that a deviation between an electric current Cn detected by the current sensor74and the target electric current Ct is small.

Next, the function of the observer8is described in detail with reference toFIG. 2. The observer8is the modeling of a moving amount of the second piston42and a moving amount of the first piston32when a force F is applied to the second piston42. The observer8can be represented by a state equation 1 and an output equation 2 shown below. It should be noted that, in the description below, a dot symbol that should be placed above a parameter according to Newton's notation is placed on the upper right of the parameter.
X·=AX+BF(1)
Y=CX(2)X·, X, Y: state parameters represented by matrixes shown inFIG. 3x1: position of the first pistonx2: position of the second pistonP: pressure of the hydraulic fluidF: force applied to the second pistonA, B: matrixes each representing a coefficient in the state equation 1C: matrix representing a coefficient in the output equation 2

The matrixes A and B are obtained from, for example, a state equation relating to the first piston32and a state equation relating to the second piston42.

To be more specific, the observer8first uses the matrixes A and B to obtain an estimated state parameter eX·, and then integrates the estimated state parameter eX·to calculate an estimated state parameter X·. That is, the observer8derives not only the estimated position ex1of the first piston32, but also an estimated position ex2of the second piston42and an estimated pressure eP of the hydraulic fluid20. The derived estimated position ex1of the first piston32is, as mentioned above, compared with the command position tx1for the first piston32.

Further, the observer8uses the matrix C to extract the estimated position ex2of the second piston42and the estimated pressure eP of the hydraulic fluid20, and compares them with the position x2of the second piston42detected by using the position sensor62and the pressure P of the hydraulic fluid20detected by the pressure sensor61. Then, the observer8uses a matrix K to calculate estimated errors for all the elements of the state parameter X·based on a deviation Δx2(=x2−ex2) between the detected position x2and the estimated position ex2of the second piston42and a deviation ΔP (=P−eP) between the detected pressure P and the estimated pressure eP of the hydraulic fluid20. Thereafter, the observer8feeds back the calculated estimated errors to the calculation of the estimated state parameter eX·. In other words, the estimated errors are fed back to the deriving of the estimated position ex1of the first piston32.

As described above, in the hydraulic forceps system1of the present embodiment, since the incompressible hydraulic fluid20is used, the moving amount of the first piston32coupled to the gripper24, i.e., the moving amount of the first piston32disposed at the distal end side of the robotic forceps2, is proportional to the moving amount of the second piston42, almost without being affected by the external force. In addition, the second piston42is driven by the motor52via the linear motion mechanism51. Accordingly, by controlling the motor52with the control device7based on the command position tx1for the first piston32, the opening and closing of the gripper24can be controlled. Moreover, the control device7includes the observer8, which derives the estimated position ex1of the first piston32based on the position x2of the second piston42, and the estimated position ex1of the first piston32is compared with the command position tx1. Therefore, installation of a position sensor that detects the position of the first piston32is unnecessary. That is, the control of the opening and closing of the gripper24is made possible without installing the position sensor at the distal end portions of the robotic forceps2.

The present invention is not limited to the above-described embodiment. Various modifications can be made without departing from the spirit of the present invention.

As one example, the pressure sensor61may be eliminated, and the observer8may derive the estimated position ex1of the first piston32based solely on the position x2of the second piston42detected by using the position sensor62. However, if the estimated position ex1of the first piston32is derived based on the position x2of the second piston42detected by using the position sensor62and the pressure P of the hydraulic fluid20detected by the pressure sensor61as in the above-described embodiment, the precision of the estimation of the position of the first piston32can be improved compared to a case where the estimated position ex1of the first piston32is derived based solely on the position x2of the second piston42.

In the above-described embodiment, the first piston32is moved rearward by the urging force of the spring34. However, as an alternative, another hydraulic fluid supply/discharge mechanism including the second cylinder41, the second piston42, the linear motion mechanism51, and the motor52may be installed; the second pressure chamber4A of this other hydraulic fluid supply/discharge mechanism may be connected to the back pressure chamber3B formed between the front wall of the first cylinder31and the first piston32; and the first piston32may be moved rearward by the hydraulic pressure of the hydraulic fluid supplied to the back pressure chamber3B. As another alternative, one end of a wire may be fixed to the first piston32, and the first piston32may be moved rearward by pulling the wire.

As another example, there may be additionally provided means that make it possible to perform correction on the observer8in accordance with the state of the first piston32and/or the second piston42, load conditions, individual differences of the robotic forceps2, surrounding environment, etc.

REFERENCE SIGNS LIST

3A first pressure chamber

4A second pressure chamber

51linear motion mechanism