DESC:F O R M 2
THE PATENTS ACT, 1970
(39 of 1970)
The Patent Rule, 2003

COMPLETE SPECIFICATION
(See section 10 and rule 13)

“Underwater Linear Actuator for Observational Class ROVs”
By
Planys Technologies Private Limited
An Indian company
03 - A2, 3rd Floor, IITM Incubation cell, Madras Research Park, Kanagam Road Tharamani, Chennai 600113

The following specification particularly describes the invention and the manner in which it is to be performed
FIELD OF THE INVENTION
The present invention relates generally to a linear motion drive, in particular to linear actuator for generating a linear motion from a rotary motion for actuating tools.
BACKGROUND OF THE INVENTION
A submersible ROV remotely operated vehicle, commonly referred to as an ROV, is a tethered underwater vehicle. ROVs are highly manoeuvrable and operated by a crew aboard a vessel. The applications of submersible ROVs include observational tasks such as visual and/or sensory inspection of platforms, structures and pipelines, intervention tasks like construction and repair of inter-oceanic pipelines and structures as well as object location and recovery tasks including detection of underwater mines and so on. For observational class ROVs, survey and inspection of underwater surfaces and structures form a major part of their applications. These are done by using various sensors to test the required surface or structure underwater. The sensors are often operated by manipulator tools which allow the ROV operator to orient the sensor in the required position. The most basic manipulator tool is 1 degree of freedom (DoF) actuator. This actuator provides either a linear motion or actuates a gripper and other 1 DoF tools.
Conventionally, an actuator comprises an output shaft which, in use, effects an axial movement, and drive means therefor. In particular the output shaft is intended to effect a controlled, slow moving, extending or retracting axial movement for operating an associated mechanism.
In most existing designs of actuators of the type referred to above, the axial movement of the output shaft is obtained by arranging for a power source to drive the worm of a worm and worm wheel set to effect a single stage reduction in speed, varying typically between 15 to 1 to 80 to 1. The worm wheel rotates a drive nut which is threaded on to the valve spindle so that rotation of the drive nut extends or retracts the output shaft.
There are applications where this type of actuator introduces installation and operating problems. Firstly, there are applications where the plan area for the equipment is restricted to a relatively small diameter. This occurs in under-sea equipment where the gear box and motor has to be encased in chambers subjected to high external pressures. Secondly, there are applications where the equipment must be of the fail safe type in the case of a valve, the spindle must move under spring force to one or other terminal position upon failure of the power supply. The conventional actuator is not, normally, suitable for this duty as the drive nut will not normally "back drive" when a force is applied to the spindle.
Thus there is need for, an underwater linear actuator which can overcome the aforesaid drawbacks and provides a robust closed loop feedback control for precise control of the motion of the end effector operating at deep depths of sea water.
OBJECTIVE OF THE INVENTION
These objectives are provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This objective are not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
An important objective of the invention aims at providing a multipurpose underwater actuator based on a linear actuation mechanism.
Another objective of the invention is to provide a robust closed loop feedback control for precise control of the motion of the end effector or tool.
Further objective of the invention is to safeguard the motor from taking in excess current.
Yet another objective of the invention is to employ sealing for the system against the high pressure of 300m of sea water.
An underwater linear actuator according to the invention which is mounted on ROV through ROV mounts has a central hull cylinder which houses all the components. The hull cylinder is sealed from both sides using end caps viz. rear end cap and front end cap which have orings to provide a lateral seal.
These objectives are achieved according to the invention an underwater linear actuator mounted on ROV through ROV mounts has a central hull cylinder housing a rotary motion producing means and a linear motion producing means, wherein said linear motion producing means coupled with said rotary motion producing means converting said rotary motion to linear motion, said linear motion producing means comprises a threaded shaft and nut arrangement. Further, the actuator comprises an actuator shaft movable linearly by said linear motion producing means between a first position and a second position, said actuator shaft being coupled to one of said threaded shaft and nut arrangement through a shaft coupler. A linear bearing supporting the actuator shaft supports a sensor system for detecting linear extension. The linear motion producing means in activated condition converts rotary motion to linear motion enabling the actuator shaft to be reversibly moved between said first and said second positions enabling the tool to perform the function with preferred degree of freedom (DoF).
Object of the present invention is not limited to the above mentioned problem. Other technical problems that are not mentioned will become apparent to those skilled in the art from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to an embodiment which is illustrated in the drawing figures:
Figure 1 shows pictorial view of linear actuator according to an embodiment of the present invention; and
Figure 2 shows perspective view of sensor system mounted on linear bearing of a linear actuator, according to an embodiment of the present invention.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
In the claims, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," and the like are to be understood to be open- ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of," respectively, shall be closed or semi-closed transitional phrases.
To facilitate the understanding of this invention, a number of terms may be defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as "a", "an", and "the" are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the disclosed system or method, except as may be outlined in the claims.
The use of directional description such as linear, rectilinear, and to and fro has been contemplated only for purposes of describing the drawing figures. Therefore, as the directional description is merely relative, depending upon how the actual present linear drive is positioned or mounted, the present invention is not to be confined to the directional description set forth herein.
Figure 1 shows pictorial view of linear actuator according to an embodiment of the present invention. An underwater linear actuator 100 according to the present invention mounted on ROV through ROV mounts 102 has a central hull cylinder 104 housing all the components. The ends of hull cylinder 104 are sealed by end caps viz. rear end cap 106 and front end cap 108 which have orings to provide a lateral seal. The hull cylinder 104 houses a rotary motion producing means 112 mounted on a motor mount 110 near to the rear end cap 106. Said rotary motion producing means 112 can be an electric motor. A linear motion producing means 118, 120 coupled with said rotary motion producing means 112 converts said rotary motion to linear motion, said linear motion producing means 118, 120 comprising of a threaded shaft 118 and a nut arrangement 120. The rotary producing means 112 and the linear motion producing means 118, 120 are connected by a flexible coupler 116, the coupler 116 transfers torque from the rotary producing means 112 to the linear motion producing means 118, 120. Also said flexible coupler 116 connected to the rotary motion producing means 112 accounts for any angular misalignment and it dampens the effect of backlash of the electric motor 112.
Further the hull cylinder 104 houses an actuator shaft 124 movable linearly by said linear motion producing means 118, 120 between a first position and a second position, the actuator shaft 124 is coupled to one of said threaded shaft 118 and nut 120 arrangement through a shaft coupler 122 at one end and to an end effector (not shown in figure) at the second end. The actuator shaft 124 passes through a linear bearing 126 which supports a sensor system 130 for detecting linear extension. The sensor system 130 comprises a potentiometer 134 and a wheel 136, wherein the wheel 136 mounted against the actuator shaft 124 rotates along the linear motion of the actuator shaft 124 converting linear motion of the actuator shaft 124 to rotation of the knob of the potentiometer. The corresponding figure 2 shows perspective view of sensor system mounted on linear bearing of a linear actuator, according to an embodiment of the present invention.
A set of limit switches are mounted at the ends safeguarding the rotary motion producing means. The limit switches includes a trip switch 140 mounted on the potentiometer housing 138 for safely limiting the extension of the linear actuator 124 at the second position and the rear limit switch 114 mounted on motor mount 110 at the first position. Thus, said limit switches coupled with said rotary producing means provides a robust closed loop feedback control for precise control of the motion of an end effector.
The end effector also called as tool is mounted on the actuator shaft to perform the preferred function. The tool can be a 1 DoF tool, such as a 2 claw planar gripper, a 3 claw spatial gripper or even an underwater cable cutting tool. Alternatively, the tool can also be used to handle sophisticated sensors which need to be safely and accurately positioned using precise steps than provided by the motion of the ROV.
At both ends, additional sealing provisions are provided for sealing the electrical wires entering the hull 104 from the rear end cap 106 and the actuator shaft 124 which passes through a set of hydraulic seals mounted in the front end cap 108. The hydraulic seals consist of a rod seal and wiper seal set, where the rod seal is primarily responsible for sealing the interior of the hull against the high pressure seawater and the wiper seal is used to prevent entry of contaminants and dirt thus enhancing the performance of the rod seal.
The linear motion producing means 118, 120 in an activated condition converts rotary motion to linear motion enabling the actuator shaft 124 to be reversibly moved between said first and said second positions, wherein the coupler 116 transfers the torque from the motor shaft (not shown in figure) to the threaded shaft 118 which coupled with its corresponding nut 120, converts the rotational motion of the motor shaft into linear motion of the actuator shaft 124. The linear extension between the positions is detected by the sensor system 130 and the corresponding first and second positions are sensed by the limit switches as safety and redundancy to safeguard the rotary motion producing means from taking in excess current confronted with a stop at the ends.
The linear actuator is capable of operating at over 300m of seawater depth. Further said actuator runs on an electric motor and employs a lead screw mechanism to convert the rotary motion of the motor to linear motion of the tool with an actuation length upto 8cm.
While the preferred embodiment of the invention has been illustrated and described herein, it is to be understood that the invention is not limited to the precise construction herein disclosed, and the right is reserved to all changes and modifications coming within the scope of the invention.
Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims.

I/we claim,
1. A linear actuator for a ROV, comprising:
a hull cylinder enclosed by a front end cap and a rear end cap, housing;
a rotary motion producing means and a linear motion producing means, wherein said linear motion producing means coupled with said rotary motion producing means for converting said rotary motion to linear motion, said linear motion producing means comprising a threaded shaft and nut arrangement;
an actuator shaft movable linearly by said linear motion producing means between a first position and a second position, said actuator shaft being coupled to one of said threaded shaft and nut arrangement through a shaft coupler at one end and to an end effector at second end;
a linear bearing supporting the actuator shaft for smooth linear motion adapted to support a sensor system for detecting linear extension; and
a set of limit switch at ends safeguarding the rotary motion producing means;
characterized in that:
said linear motion producing means in an activated condition converts rotary motion to linear motion enabling the actuator shaft to be reversibly moved between said first and said second positions, the linear extension between the positions is detected by the sensor system and the corresponding first and second positions are sensed by the limit switches as safety and redundancy to safeguard the rotary motion producing means from taking in excess current confronted with stop at the ends.
2. The linear actuator according to claim 1, wherein said sensor system further comprises a potentiometer and a wheel, the wheel mounted against the actuator shaft rotates along the linear motion of the actuator shaft converting linear motion of the actuator shaft to rotation of the knob of the potentiometer.
3. The linear actuator according to claim 2, wherein the sensor system further comprises a trip switch mounted on the potentiometer safely limiting the extension of the linear actuator at the second position.
4. The linear actuator according to claim 1, wherein said limit switches coupled with said rotary producing means provides a robust closed loop feedback control for precise control of the motion of an end effector.
5. The linear actuator according to claim 1, wherein said rotary producing means is mounted on a motor mount near to the rear end cap.
6. The linear actuator according to claim 1 or 5 wherein said rotary motion producing means is an electric motor.
7. The linear actuator according to claim 1, wherein the motor mount supports the rear limit switch at the first position.
8. The linear actuator according to claim 1, wherein the rotary producing means and the linear motion producing means are connected by a flexible coupler, the coupler transfers torque from the rotary producing means to the linear motion producing means.
9. The linear actuator according to claim 1, capable of operating upto 300m of water depth.
10. The linear actuator according to claim 1, has high actuation length upto 8cm.

Dated this the 17th day of October, 2017

ABSTRACT
Title: Underwater Linear Actuator for Observational Class ROVs
The present invention relates to linear actuator for generating a linear motion from a rotary motion for actuating tools. An underwater linear actuator mounted on ROV has a central hull cylinder housing a rotary motion producing means and a linear motion producing means, wherein said linear motion producing means coupled with said rotary motion producing means converting said rotary motion to linear motion, said linear motion producing means comprises a threaded shaft and nut arrangement. Further, the actuator comprises an actuator shaft movable linearly by said linear motion producing means between a first position and a second position, said actuator shaft being coupled to one of said threaded shaft and nut arrangement through a shaft coupler. A linear bearing supporting the actuator shaft supports a sensor system for detecting linear extension. The linear motion producing means in activated condition converts rotary motion to linear motion enabling the actuator shaft to be reversibly moved between said first and said second positions enabling the tool to perform the function with preferred DoF.
Figure 1 (for publication)
,CLAIMS:I/we claim,
1. A linear actuator for a ROV, comprising:
a hull cylinder enclosed by a front end cap and a rear end cap, housing;
a rotary motion producing means and a linear motion producing means, wherein said linear motion producing means coupled with said rotary motion producing means for converting said rotary motion to linear motion, said linear motion producing means comprising a threaded shaft and nut arrangement;
an actuator shaft movable linearly by said linear motion producing means between a first position and a second position, said actuator shaft being coupled to one of said threaded shaft and nut arrangement through a shaft coupler at one end and to an end effector at second end;
a linear bearing supporting the actuator shaft for smooth linear motion adapted to support a sensor system for detecting linear extension; and
a set of limit switch at ends safeguarding the rotary motion producing means;
characterized in that:
said linear motion producing means in an activated condition converts rotary motion to linear motion enabling the actuator shaft to be reversibly moved between said first and said second positions, the linear extension between the positions is detected by the sensor system and the corresponding first and second positions are sensed by the limit switches as safety and redundancy to safeguard the rotary motion producing means from taking in excess current confronted with stop at the ends.
2. The linear actuator according to claim 1, wherein said sensor system further comprises a potentiometer and a wheel, the wheel mounted against the actuator shaft rotates along the linear motion of the actuator shaft converting linear motion of the actuator shaft to rotation of the knob of the potentiometer.
3. The linear actuator according to claim 2, wherein the sensor system further comprises a trip switch mounted on the potentiometer safely limiting the extension of the linear actuator at the second position.
4. The linear actuator according to claim 1, wherein said limit switches coupled with said rotary producing means provides a robust closed loop feedback control for precise control of the motion of an end effector.
5. The linear actuator according to claim 1, wherein said rotary producing means is mounted on a motor mount near to the rear end cap.
6. The linear actuator according to claim 1 or 5 wherein said rotary motion producing means is an electric motor.
7. The linear actuator according to claim 1, wherein the motor mount supports the rear limit switch at the first position.
8. The linear actuator according to claim 1, wherein the rotary producing means and the linear motion producing means are connected by a flexible coupler, the coupler transfers torque from the rotary producing means to the linear motion producing means.
9. The linear actuator according to claim 1, capable of operating upto 300m of water depth.
10. The linear actuator according to claim 1, has high actuation length upto 8cm.