Transmission system

Abstract

A transmission system (10) includes a first piston (12), a second piston (14) and a modulator piston (16). The first piston (12) receives an input force (F.sub.IN), the second piston (14) transmits an output force (F.sub.OUT), and the modulator piston (16) transmits a modulating force (F.sub.ACT>which modulates the input force (F.sub.IN) received by the second piston (14) to implement tremor cancellation and force and/or provide variable motion scaling.

Claims

1. A hydraulic transmission system for use in a micromanipulator system, comprising: an input actuator comprising an input piston, the input piston configured to receive an input force; a control actuator comprising a modulator piston, the modulator piston operatively associated with the input piston and configured to apply a modulating force to modulate the input force; an output actuator comprising an output piston, the output piston operatively associated with the first piston and the modulator piston, the output piston configured to receive the modulated input force and output an output force from the transmission system; and a control system comprising one or more position sensor associated with the input actuator, output actuator and control actuator, wherein the control system is configured to control the control actuator according to the sensed position of the input piston, the output piston and the modulator piston to vary the ratio of the input force to the output force up or down by reconfiguring the control actuator so as to permit the effect of a tremor contained within the input force to be cancelled, mitigated or otherwise controlled within a given acceptable range.

2. The transmission system of claim 1, wherein the transmission system is configured to modulate the input force by attenuating or dampening the input force to provide a reduced output force and/or reduced displacement of the output piston.

3. The transmission system of claim 1, wherein the transmission system is configured to modulate the input force to provide an increased output force from the output piston and/or increased displacement of the output piston where required.

4. The transmission system of claim 1, wherein the transmission system is configured to modulate the input force in response to a force applied to the modulator piston.

5. The transmission system of claim 1, wherein the control actuator is reconfigurable to extend the modulator piston, extension of the modulator piston modulating the input force by decreasing the input force, thereby providing a reduced modulated input force to the output piston.

6. The transmission system of claim 1, wherein the control actuator is reconfigurable to retract the modulator piston retraction of the modulator piston modulating the input force by increasing the input force, thereby providing an increased modulated input force to the output piston.

7. The transmission system of claim 1, wherein the transmission system is configured to maintain the ratio of the input force to the output force at a given value or value range.

8. The transmission system of claim 1, wherein the transmission system comprises a drive arrangement configured to move and/or control the displacement of the modulator piston.

9. The transmission system of claim 8, wherein the drive arrangement comprises a motor.

10. An apparatus comprising the transmission system of claim 1.

11. The apparatus of claim 10, further comprising an instrument, and wherein the output piston is coupled to the instrument and is configured to transfer the output force to the instrument.

12. The apparatus of claim 11, wherein the instrument comprises a surgical instrument.

13. A method comprising: providing a transmission system according to claim 1; applying a modulating force to the modulating piston to modulate the input force received by the output piston.

14. The transmission system of any preceding claim, comprising a sealed chamber for containing substantially incompressible hydraulic fluid so as to define a sealed fluid volume, the sealed chamber configured to communicate with the input piston, the output piston and the modulator piston, such that external forces applied to the output piston are transmitted via the sealed fluid volume to the input piston so as to provide haptic feedback from the output piston at the input piston.

15. The transmission system of claim 14, comprising at least one of: one or more pressure sensors configured to measure the fluid pressure in the chamber; and one or more temperature sensors configured to measure the temperature in the chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects will now be described by way of example only with reference to the accompanying drawings, of which:

(2) FIG. 1 shows a transmission system;

(3) FIG. 2 shows a micromanipulator apparatus including the transmission system of FIG. 1;

(4) FIG. 3 is a schematic internal view of the transmission system shown in FIG. 1; and

(5) FIG. 4 shows a schematic view of a piston of the transmission system shown in FIG. 1.

DETAILED DESCRIPTION

(6) Referring to FIG. 1 of the accompanying drawings, a transmission system 10 includes a first piston 12, a second piston 14 and a modulator piston 16. The three pistons act as actuators to transmit forces. The first piston 12 transmits an input force F.sub.IN, the second piston 14 transmits an output force F.sub.OUT, and the modulator piston 16 transmits a modulating force F.sub.ACT, as shown in FIG. 1. The transmission system can implement tremor cancellation and motion scaling by enhancing the input force F.sub.IN using the modulating force F.sub.ACT, resulting in the output force F.sub.OUT. The input force F.sub.IN is enhanced by actuation of the modulator piston (16) to control the modulating force F.sub.ACT.

(7) As shown in FIG. 2, the input force F.sub.IN transmitted by the first piston 12 can be generated by a user 18 such as a surgeon. The transmission system 10 can be utilised to control a tool 20 such as a surgical instrument, in some cases the surgical instrument may be an instrument for minimally invasive or laparoscopic surgery. The ability to eliminate tremor from the surgeon's hands whilst scaling the motion and/or force of the output piston offers significant improvements in the accuracy and safety of such surgical procedures.

(8) The modulating force F.sub.IN transmitted by the modulator piston 16 is controlled by an actuator 22. The actuator 22 should provide sufficient force and displacement to the modulator piston 16, according to the equations derived below for different working modes of the system.

(9) The actuator 22 is driven by a motor 28. For safety reason, the motor 28 should be a non-back-drivable mechanism. Thus, in the event that the motor 28 stops working and the modulator piston 16 can no longer be actuated, the transmission system 10 will become a traditional mechanical hydraulic interface, working to transmit the input force F.sub.IN to an output force F.sub.OUT without any modulation.

(10) Referring to FIG. 3 of the accompanying drawings, between each of the pistons is a sealed fluid volume 24. The output force F.sub.OUT transmitted by the second piston 14 is generated by the first piston 12 and the modulator piston 16 transmitting forces to the sealed fluid volume 24. The transmission system 10 can operate in different working modes. In a basic working mode, the modulator piston 16 is “off” and remains in a fixed position; therefore the input force F.sub.IN produced by the user 18 is directly transmitted to the output force F.sub.OUT. If both the input force F.sub.IN and the modulating force F.sub.ACT are applied to the sealed fluid volume 24 by the first piston 12 and modulator piston 16 respectively, the output force F.sub.OUT will be a resultant force the depends on the enhancement of the input force F.sub.OUT by the modulating force F.sub.ACT. In a tremor cancellation working mode, the modulator piston 16 is actuated to apply the modulating force F.sub.ACT such that any tremor produced by the user 18 in generating the input force F.sub.IN is cancelled or mitigated in the output force F.sub.OUT. In a motion scale working mode, the modulator piston 16 is actuated to apply a force F.sub.ACT to the sealed fluid volume 24 such that the input force F.sub.IN generated by the user 18 is variably scaled to the output force F.sub.OUT. In a motion scale and tremor cancellation working mode, the modulator piston 16 is actuated to apply the modulating force F.sub.ACT to the sealed fluid volume 24 such that the input force F.sub.IN is modulated to both cancel tremor and scale motion.

(11) Sensors can be used to monitor the output force F.sub.OUT, thereby allowing improved control precision. The modulation of the input force F.sub.IN can be controlled according to the sensed output force F.sub.OUT to avoid any excess forces resulting in damage to the tool 20 connected to the second piston 14.

(12) The position of each piston is measured to implement the control of the modulator piston 16. Equations for the control of the modulator piston 16 in the previously described working modes are derived below. Embedded position sensors 26 would be suitable for measuring the position of each piston. For example each sensor may be, a magnetic sensor, or a linear encoder. Sensors can also be provided to measure the pressure and temperature of the working fluid can also improve the performance of the control, due to the relationship of the parameters to the fluid viscosity.

(13) If external forces are applied to the second piston 14 and transmitted to the sealed fluid volume, a force corresponding to those external forces will be transmitted through the first piston 12. As a result of this, the user 24 will “feel” any external forces applied to the second piston, F.sub.OUT, and adjust the input force, F.sub.IN, accordingly. The transmission system is a cheap alternative solution to an expensive master slave manipulator. The transmission system can sense external forces and provide haptic feedback without the use of any complex systems of sensors and actuators.

(14) For the purpose of deriving the control equations, the sealed fluid volume 24 is considered to be incompressible. This is a valid assumption due to the small amount of fluid.

(15) FIG. 4 shows parameters for a piston. The system design requirements are the displacement I.sub.i and force F.sub.i provided to the sealed fluid volume by the piston. The static behaviour of the system is described by the following equations:

(16) $\begin{array}{cc}{S}_i=\frac{\pi }{4}{d}_i^2& \left(2.1\right)\\ P_i=\frac{F_i}{S_i}& \left(2.2\right)\end{array}$
where S.sub.i is the cross-section area of the piston, P.sub.i is the pressure of the sealed fluid volume, F.sub.i is the force applied, d.sub.i is the diameter, and I.sub.i is the displacement of the piston.

(17) The volume of fluid moved by a piston is as follows:
V.sub.i=S.sub.il.sub.i  (2.3)
Assuming the sealed fluid volume remains constant, the system can be described by the following equation:
Σ.sub.n=1.sup.3V.sub.i=V.sub.IN+V.sub.OUT+V.sub.ACT=0  (2.4)
By using equations 2.1 and 2.3, equation 2.4 becomes:

(18) $\begin{array}{cc}{.Math.}_{n=1}^3{V}_i={.Math.}_{n=1}^3{S}_i{l}_i={.Math.}_{n=1}^3\frac{\pi }{4}{d}_i^2{l}_i=0& \left(2.5\right)\\ d_{\mathrm{IN}}^2{l}_{\mathrm{IN}}+d_{ACT}^2{l}_{ACT}+d_{OUT}^2{l}_{OUT}=0& \left(2.6\right)\\ -l_{OUT}=\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}{l}_{\mathrm{IN}}+\frac{d_{ACT}^2}{d_{\mathrm{OUT}}^2}{l}_{ACT}& \left(2.7\right)\end{array}$

(19) The displacement, I.sub.OUT, of the second piston 14 is the sum of the displacements I.sub.IN of the first piston 12 and the displacement I.sub.ACT of the modulator piston 16 multiplied by the ratio of the diameter of the pistons.

(20) When the modulator piston 16 is off, the transmission system functions as a standard hydraulic system. The input force F.sub.IN applied by the user 18 is transmitted to the second piston 14.

(21) $\begin{array}{cc}-l_{OUT}=\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}{l}_{\mathrm{IN}}& \left(2.8\right)\\ F_{OUT}=\frac{d_{\mathrm{OUT}}^2}{d_{\mathrm{IN}}^2}& \left(2.9\right)\end{array}$

(22) The relation between the displacement I.sub.OUT of the second piston 14 and the displacement I.sub.IN of the first piston 12 is described by equation 2.8 and the relation between the forces F.sub.OUT and F.sub.IN is described by equation 2.9.

(23) When the modulator piston 16 is on, the transmission system can enhance the output force F.sub.OUT and therefore cancel tremors in the displacement I.sub.OUT of the second piston 14 produced by an uneven force F.sub.IN. Equation 2.7 describes the relation between the displacement provided by both the first piston 12 and the modulator piston 16, to the output piston. The pressure P.sub.ACT provided by the modulator piston 16 has to be equal to the pressure provided by both the first piston 12 and second piston 14:
P.sub.ACT=P.sub.IN+P.sub.OUT  (2.10)
combining equations 2.10 and 2.2 gives:

(24) $\begin{array}{cc}\frac{F_{ACT}}{S_{ACT}}=\frac{F_{\mathrm{IN}}}{S_{\mathrm{IN}}}+\frac{F_{OUT}}{S_{OUT}}& \left(2.11\right)\end{array}$
The force F.sub.ACT provided by the modulator piston 16 is as follows:

(25) $\begin{array}{cc}{F}_{ACT}=\frac{S_{\mathrm{ACT}}}{S_{\mathrm{IN}}}{F}_{\mathrm{IN}}+\frac{S_{\mathrm{ACT}}}{F_{OUT}}{F}_{OUT}=\frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{IN}}^2}{F}_{\mathrm{IN}}+\frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{OUT}}^2}{F}_{OUT}=d_{ACT}^2\left(\frac{F_{\mathrm{IN}}}{d_{\mathrm{IN}}^2}+\frac{F_{\mathrm{OUT}}}{d_{\mathrm{OUT}}^2}\right)& \left(2.12\right)\end{array}$

(26) Equation 2.12 describes the relation between the force provided by the first piston 12 and the second piston 14 to the modulator piston 16. In order to cancel tremor, the displacement, I.sub.IN, of the first piston 12 can be described by using a Fourier transformation:

(27) $\begin{array}{cc}{l}_{\mathrm{IN}}=\underset{k=0}{\overset{\infty }{.Math.}}{l}_{{\mathrm{INke}}^{j2\pi f_{0}t}}=l_{\mathrm{IN}0}+\underset{k=1}{\overset{\infty }{.Math.}}{l}_{{\mathrm{INke}}^{j2\pi {\mathrm{kf}}_{0}t}}=l_{\mathrm{IN}0}+l_{\mathrm{INTR}}& \left(2.13\right)\end{array}$

(28) Where I.sub.IN0 is the continuous component of the displacement I.sub.IN of the first piston 12, the tremor component of the displacement I.sub.IN of the first piston 12 is:

(29) $\begin{array}{cc}{l}_{\mathrm{INTR}}=\underset{k=1}{\overset{\infty }{.Math.}}{l}_{{\mathrm{INke}}^{j2\pi {\mathrm{kf}}_{0}t}}& \left(2.14\right)\end{array}$

(30) From a consideration of equation (2.12), the modulator piston 16 needs to provide an opposite displacement to the one provided by the tremor component I.sub.INTR of the displacement I.sub.IN of the first piston 12, in order to avoid transmittal of the tremor to the second piston 14. By combining equations 2.7 and 2.14, the displacement I.sub.OUT of the second piston 14 is described by the following equation:

(31) $\begin{array}{cc}-l_{OUT}=\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}\left(l_{\mathrm{IN}0}+l_{\mathrm{INTR}}\right)+\frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{OUT}}^2}{l}_{ACT}& \left(2.15\right)\end{array}$

(32) The modulator piston 16 needs to cancel the tremor component I.sub.INTR of the displacement I.sub.IN of the first piston 12, which is described by the following equation:

(33) $\begin{array}{cc}\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}{l}_{\mathrm{INTR}}+\frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{OUT}}^2}{l}_{ACT}=0& \left(2.16\right)\\ \frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{OUT}}^2}{l}_{ACT}=-\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}{l}_{\mathrm{INTR}}& \left(2.17\right)\\ l_{ACT}=-\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{ACT}}^2}{l}_{\mathrm{INTR}}& \left(2.18\right)\end{array}$

(34) Equations 2.12 and 2.18 describe a compromise in the choice of the diameter d.sub.ACT of the modulator piston 16. The modulating force F.sub.ACT is directly proportional to the diameter d.sub.ACT of the modulator piston 16, although the displacement I.sub.ACT of the modulator piston 16 is inversely proportional to diameter d.sub.ACT of the modulator piston 16. The tremor component, I.sub.INTR, of the displacement I.sub.IN of the first piston 12 is the second of the continuous component I.sub.IN0 of the displacement I.sub.IN of the first piston 12 which implies that the displacement I.sub.ACT of the modulator piston 16 necessary to cancel the tremor is less that the total displacement I.sub.IN of the first piston 12.

(35) Motion scale increases user dexterity so that operations can be performed in small scale. The motion is scaled by a factor K, which is represented by the following equation:

(36) 0$\begin{array}{cc}K=\frac{l_{sc}}{l_{\mathrm{IN}}}& \left(2.19\right)\end{array}$

(37) I.sub.SC is the scaled input displacement. When K=1, the motion is not scaled, and when K=0.5, the motion is scaled by a ratio 1:2. The ratio between the diameter d.sub.IN of the first piston 12 and the diameter d.sub.OUT of the second piston 14 represents a motion scaling which is typical in any hydraulic system. The following equation describes the motion scaled by factor K.

(38) $\begin{array}{cc}-l_{OUT}=K\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}{l}_{\mathrm{IN}}& \left(2.20\right)\end{array}$

(39) Adding and removing the displacement I.sub.IN of the first piston 12, the equation remains invariant:

(40) $\begin{array}{cc}-l_{OUT}=\left(l_{\mathrm{IN}}-l_{\mathrm{IN}}+K{l}_{\mathrm{IN}}\right)\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}& \left(2.21\right)\\ -l_{OUT}=l_{\mathrm{IN}}\left(K-1\right)\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}+l_{\mathrm{IN}}\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}& \left(2.22\right)\end{array}$

(41) By multiplying and dividing for the same quantity,

(42) $\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2},$
the equation becomes:

(43) $\begin{array}{cc}-l_{OUT}=l_{\mathrm{IN}}\left(K-1\right)\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{ACT}}^2}\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}\frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{IN}}^2}+l_{\mathrm{IN}}\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}& \left(2.23\right)\\ -l_{OUT}=l_{\mathrm{IN}}\left(K-1\right)\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{ACT}}^2}\frac{d_{\mathrm{ACT}}^2}{d_{\mathrm{OUT}}^2}+l_{\mathrm{IN}}\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}& \left(2.24\right)\end{array}$

(44) From equations 2.7 and 2.24 it is evident that the displacement I.sub.ACT of the modulator piston 16 is described by the following additional equation:

(45) $\begin{array}{cc}{l}_{ACT}=l_{\mathrm{IN}}\left(K-1\right)\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{ACT}}^2}{l}_{\mathrm{IN}}& \left(2.25\right)\end{array}$

(46) The equations 2.24 and 2.25, describe the relation between the displacement I.sub.ACT of the modulator piston 16 and the scale factor K. When K=1, the motion is not scaled, and the equation becomes:

(47) $\begin{array}{cc}-l_{OUT}=l_{\mathrm{IN}}\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{OUT}}^2}& \left(2.26\right)\end{array}$
which describes a normal system with only two pistons.

(48) Both the tremor cancelation and motion scale modalities can be active together. From equations 2.13, 2.18 and 2.25 the equation of the displacement I.sub.ACT of the modulator piston 16 is:

(49) $\begin{array}{cc}{l}_{ACT}=\left(l_{\mathrm{IN}0}\left(K-1\right)-l_{\mathrm{INTR}}\right)\frac{d_{\mathrm{IN}}^2}{d_{\mathrm{ACT}}^2}& \left(2.27\right)\end{array}$

(50) This equation shows that the displacement I.sub.ACT of the modulator piston 16 in the combined modality when the motion is scaled and tremor is cancelled, is higher than its displacement I.sub.ACT in the modality where only the tremor is cancelled.

(51) The transmission system 10 is a compact and simple system composed of a minimum of three pistons and position sensors. More pistons and/or sensors may be included in the transmission system.

(52) It will be recognised that embodiments of the transmission system thus provide a number of benefits over conventional systems.

(53) Embodiments of the transmission system beneficially permit the ratio of the input force to the output force and the resulting relative motion of the input piston and the output piston to be scaled, whilst also cancelling or at least mitigating the effect of a tremor applied to the input piston or otherwise contained in the input force applied to the input piston. Embodiments of the transmission system thus provide significant improvements in the accuracy and safety of surgical procedures, and may permit surgical procedures to be carried out where such procedures were previously not possible due to the effects of tremors.

(54) Moreover, the system may provide a cheap alternative solution to conventional master slave manipulators. The transmission system can sense the output force and provide haptic feedback without the use of a complex system of sensors and actuators.

(55) Various modifications may be made without departing from the scope of the claims.