ROBOTIC SNAKE-LIKE MOVEMENT DEVICE
The invention relates to robotic arms, particularly, to snake-like arms comprising a plurality of sequentially rotatably connected modules.
There are known different designs of the robotic snake-like movement devices used in industry, human surgery, nuclear reactors and many other fields.
There is known a two-rotation freedom degree active wrist mechanism used for mechanical arm or snake shaped robot (patent CN 100560307 C) which is characterized by the following: fixing motor in two motor cylinders and two fixing caps; connecting two bevel gears and two big gears with output shaft of motor; gearing two big gears and two small gears fixed on the output shaft of potentiometers; fixing two conical gears at the sector end surfaces with two shafts of cross-shaped coupling shaft; gearing the conical wheel and the conical gear at the sector end surface; fixing four racks on two upper and lower fixing end caps symmetrically; connecting the corrugation pipe with two fixing end lids to form a complete sealing mechanism. The main drawback of the known device is that the necessary power to move on load in each degree of freedom is being achieved by corresponding power of motor resulting in necessity using powerful motors, which are usually bulky and heavy. This has an impact on the weight and size of the device. Moreover there is a gear backdrive reducing static stability of the wrist mechanism.
There is known a joint assembly for moving a free end relative to a reference end like a human arm (patent application US 4683406) having angular double swivel joint as a subassembly. To prevent any relative twist between the two bays the known device utilizes a heavy and bulky joint. Besides that this joint is relatively difficult to control.
There is known joint assembly (patent US 6871563, Fig. 21a and 21b) comprising link members provided with worm gears adapted to transfer drive torque from the motors mounted in the link members to the tooth-wheel being geared with the segment of the bigger tooth- wheel fixed on the joint, thereby allowing rotation of the link members one relative to the other. The disadvantage of the known device is also the necessity using powerful motors in each link member, which negatively impacts the weight and size of the
whole device. Moreover there is a problem of gear backdrive in the device reducing its static stability.
There is known a link assembly for a snake like robot arm (International patent application WO02100608) comprising a first and a second link members each adapted for limited movement one with respect to the other and resilient elastomer means disposed between said first and second members and bonded or keyed thereto whereby movement between the first and second member results in shear movement within the elastomer means disposed therebetween. The control means comprise three wires each extending from one end of the segment to the other whereby changing the tension in the wires one relative to the other causes or allows the links to flex thereby controlling movement of the segment. The main drawback of the known device is that the number of the link members of the snake like robot arm is limited by possible number of wire sets. Moreover when number of elements rise to achieve more curved snake form the wires tension control becomes more complicate.
There is known a flexible robot arm (patent application US 5174168) provided with a large number of elements disposed in a line so that both surfaces of each element which are curved projectingly become contact surfaces, and with a plurality of wire-like operation members for curving the line consisting of the group of these elements in a desired direction. The known robot arm includes two driving units each interconnected to each base end of each of pairs of operation members facing each other on the diagonal among the plurality of operation members and driven through rotary members each being rotated both clockwise and counter-clockwise by one motor. The number of the elements of the flexible robot arm is limited by maximum four wire sets. Besides wire tension control also becomes complicate when number of elements rise to achieve more curved robot arm's form.
There is known a robotic arm (International patent application WO2009141635) having a plurality of sequentially arranged articulated links, and at least one group of operating cables extending from a proximal end of the arm to terminate at a control link, for controlling the position of that link, the cables each having a path comprising a passage in each successive more proximal link for closely receiving the cable, wherein the arm is configured such that, in the path of at least one cable, at least one pair of adjacent links have passages whose axes are not aligned with each other, such that the cable bears against a predetermined portion of the passages in use of the arm. The main disadvantage of the
known device is that the number of the articulated links is limited by the number of operating cables. Besides, stability of the device is based on friction forces and changes when load changes. That requires a complicated control. Disclosure of Invention
The objective of the invention is to eliminate the drawbacks of the prior art and to provide a relatively low cost light weight robotic snake-like movement device having improved accuracy, a high ability of movement and easy control.
The set objective is achieved by offering a robotic snake-like movement device comprising a plurality of sequentially rotatably connected modules, each module containing one or more light motors (preferably two) each being operably connected with one worm being geared with a worm gear fixed on the worm gear's axle, where each subsequent module is being fixedly mounted on the worm gear's axle of the previous module such that upon rotation of the worm gear, the subsequent module is being able to be turned relative to the previous module, hereto, the chain of sequentially rotatably connected modules is being provided with (i) two or more drives fixed at the end two of the said chain of modules, and with (ii) two or more drive wires being fixed on the last module in the said chain of modules and operably connected with the drives such that operation of the drives would allow changing tension in the drive wires one relative to the other causing or allowing the modules to turn. Since rotation movement cannot be transfered from the wormgear to the worm, notwithstanding one or more drive wires being tensioned by the drives are forcing the chain of modules to bend, the modules can bend and turn one relative to the other only if the worm gear is being turned to the respective direction, hereto the modules would bend and/or turn as much, as much the worm gear is being turned. Thereby the necessary turn force for all the modules according to the offered design is being provided only via the tensioned drive wires drives, while the worm- wormgear pairs serve as controllable anti-turning or locking elements.
Further, substance of the invention and its various embodiments are described by way of examples with references to the drawings.
Brief Description of Drawings
Fig. 1 is a schematic top view of two rotatably connected modules,
Fig. 2 is a schematic top view of the module showing forces applied and deviation angles of the subsequent module,
Fig. 3 is a schematic top view of the first preferred embodiment of the chain of rotatably connected modules,
Fig. 4A and 4B are illustrating preferred division of spaces between worm' s and worm gear's teeth,
Fig. 5 A and 5B are illustrating division of spaces between worm' s and worm gear's teeth, as well as preventing backdrive in the preferred embodiment with two worms,
Fig. 5C is illustrating difference of applied forces to worm gear AF, rotation of each motor and worm gear,
Fig. 6 is a perspective view of the module according to the second preferred embodiment, Fig. 7 is illustrating connection of a worm drive to stepper motors according to the second preferred embodiment,
Fig. 8 is a perspective view of two rotatably connected modules according to the second preferred embodiment; the modules being connected such that they are turned around the longitudinal axis of symmetry of the robotic snake-like movement device at 90° each to the other.
The offered snake-like arm comprises a plurality of sequentially rotatably connected modules 1 (Fig 1 - Fig. 3), forming a chain of modules. The modules 1 may be connected such that they are axially turned relative to the longitudinal axis of symmetry of the snakelike arm at different angles, typically at 0° or 90°.
Each module 1 contains a drive 2, comprising a motor 3, preferably electrical motor, and optionally a gearbox with gears 4 (ztl ...ztN); the motor 3 being operably connected with a worm 5 and a worm gear 6 preferably via the gearbox with gears 4, for transferring drive torque from the motor 3 to the worm gear 6, wherein each subsequent module 1 is being fixedly mounted on the worm gear' s 6 axle 7 of the previous module 1 such that upon rotation of the worm gear 6, each module 1 is able to be turned relative to the previous module 1.
It is known that worm - wormgear pair have space δ between the worm 5 and the wormgear 6 teeth (Fig.4A). In some worm' s 5 and worm gear' s 6 positions, space δι may be divided into spaces δ2 and δ3 on both sides of the teeth (Fig. 4B). Such division of space is preferable, because only a small force should be applied to overcome friction force in worm drives in such positions. Applying small rotation force in appopriate direction to the
worm 5 in sync with the wormwgear's 6 turn caused by the force FL or FR allows to turn the wormwgear 6 in direction corresponding to FL or FR at an angle -a or +a (Fig. 2). With some exceptions, rotation movement cannot be transfered from the wormgear 6 to the worm 5 (if the worm 5 is not being turned) thus force FL or FR cannot change the position of the wormgear 6 if the worm 5 does not turn.
To achieve higher stability and operation efficiency of the chain of modules 1 extra worm 5 (hereinafter jointly or separately referred to as the worm 5 or worms 5), being geared with the same worm gear 6 and operably connected with the extra motor 3 (hereinafter jointly or separately referred to as the motor 3 or motors 3) may be provided. Thus each module 1 may contain two worms 5 being geared with one worm gear 6 and two motors 3, each being operably connected with the respective worm 5, preferably via the own gearbox 2 with gears 4.
To significantly reduce weight and size of each drive 2, as well as to increase stability and accuracy of the snake-like arm, the chain of sequentially rotatably connected modules 1 having two ends - one and two, is being provided with: (i) drives 8, 9, fixed at the end two of the said chain of modules 1, and (ii) drive wires 10, 11, each having two ends - one and two, wherein the ends one of the drive wires 10, 11 are being fixed at the opposite sides of the last module 1 at the end one of the said chain of modules 1, where the ends two of the drive wires 10, 11 are being operably connected with the drives 8, 9, such that operation of the drives 8, 9 would allow changing the tension in the drive wires 10, 11 one relative to the other causing or allowing the modules 1 to turn thereby controlling movement of the chain of modules 1 (Fig. 3). Drive wires 10, 11 are preferably being put through guides 12 being operably mounted on modules 1. According to the invention, the task of the motors 3 (drives 2) is to rotate the worms 5 without load and/or to serve as electrically operable lock preventing rotation of the worm gear 6. The necessary force for turning each and all the modules 1 is being provided by the drives 8, 9 via the drive wires 10, 11, while the drives 2 are turned into anti-turning or locking elements instead of power elements thus allowing to control the direction and degree of rotation of each and all the modules 1 relative to one another. This embodiment allows to significantly reduce the weight and size of each module 1, as well as power necessary for operation of the whole chain of modules 1. All motors used are preferably computer controlled to achieve the necessary shape of the chain of modules 1 and snake-like movement speed.
According to the second preferred embodiment (Fig. 6 - Fig. 8), each module 1 comprises: part one PI and part two P2 being fixed each to other at their end walls. The parts PI and P2 may be connected at different angles each to other (turned relative to the longitudinal axis of symmetry of the robotic snake-like movement device) to ensure more degree of freedom for the snake-like arm. In Fig. 8 a 90° connection of modules 1 is shown. Part one PI comprising two plates 13, the plates 13 being directed to the side opposite to the side, where the part two P2 is located (Fig. 6). The plates 13 are preferably being provided with guides 12 adapted to guide drive wires 10, 11. The guides 12 can be in the form of discs rotatably mounted on the axles 14 on the outer surface of the plates 13, preferably two discs on the outer surface of both plates 13 being symmetrically mounted such, that the force being applied to the module 1 by tensioning the drive wires 10, 11 is being applied to the worm gear 6 via the guides 12 (Fig. 8). Each part two P2 in the chain of modules 1 being accommodated between the plates 13 of the previous module 1. The part P2 comprising: one or two stepper motors 3 each containing two radially magnetized permanent magnets 15 each being rotatably mounted between coils 16; one or two worms 5 each being rotatably fixed between the pair of magnets 15, worm gear 6 being geared with one or two worms 5 and fixed on the axle 7 in turn being rotatably fixed between the plates 13, such that operation of the said one or two stepper motors and thereby transferring drive torque from the stepper motors to the worms 5 would allow modules 1 to turn one relative to the other. The powertrain as in the first preferred embodiment is designed such that worms 5 can be rotated both clockwise and anticlockwise. Instead of stepper motors the device may contain homopolar motors, DC motors, AC motors, geared DC or AC motors, or any other known type electrically powered motors. Like in the embodiment described above, the chain of sequentially rotatably connected modules 1 is being provided with drives 8, 9, fixed at the end two of the said chain of modules 1, and two or more drive wires 10, 11. The ends one of the drive wires 10, 11 are being fixed on the module 1 at the end one of the said chain of modules 1, where the ends two of the drive wires 10, 11 are being operably connected with the drives 8, 9, such that operation of the drives 8, 9 would allow changing tension in the drive wires 10, 11 one relative to the other causing or allowing the modules 1 to turn, thereby controlling movement of the chain of modules 1 both by rotation or non-rotation of the worm gears 6 in one or more modules 1 and changing tension in the drive wires 10, 11 one relative to the other.
Thus notwithstanding one or more drive wires being tensioned by the drives 8, 9, are forcing the chain of modules 1 to bend, the modules 1 can turn one relative to the other only if the worm gear 6 is being turned to the respective direction, hereto the modules 1 would turn as much, as much the worm gear 6 is being turned.
The offered device operates as follows. The drives 8, 9 are being actuated thereby tensioning the drive wires 10, 11 and creating the forces FL, FR. Depending on the required trajectory of movement of the robotic snake-like movement device, one or more motors 3 in one or more modules 1 are being sequentially actuated. As a result, and under the force FL of the drive wire 10 and/or force FR of the drive wire 11 one or more worm gears 6 are being turned at an angle -a or +a. The respective module or modules 1 are being turned at the same angle -a or +a.
Forces FL and FR must be equal before starting turning the worm gear 6 clockwise - start phase (Fig. 5C). The motors 3 must provide turn moment sufficient to overcome static friction force between the worm 5 and the worm gear 6 tooth and start turning the worms 5.
While forces FL = FR and AF(FL-FR)=0 or at least close to 0, the worm 5 can turn only if its turning direction is not being blocked by the worm gear 6, in turn being blocked by the second worm 5 engaged, or if the worm's 5 turning direction is not being blocked by the force FL, FR having the opposite direction. The worm 5 can travel by the space 5A or δβ. After traveling by the space 5A or δβ, both motors 3 stop due to the insufficient power, regardless that they are still connected to a power source.
Increasing the AF value so that the worm gear 6 can turn due to the space created between the worm 5 and the worm gear 6 teeth, worms 5 are released and they turn until again are being stopped due to insufficient motor power.
The motors 3 are choosen such that they ensure the worm's 5 rotating velocity higher than the worm gear's 6 rotating velocity, so that the worm's 5 tooth follows the worm gear's 6 tooth and rotation of the worm gear's 6 to a desired angle is possible.
The motors 3 stop when necessary angle +a of the module 1 turn is achieved - stop phase (Fig. 5A and 5B). The motor 3 operably connected with worm 5 one is being forced to try to rotate in opposite direction until the worm's one tooth would contact tooth of the worm gear 6 and stop. Thus space 5A 1S being converted to the space 5c (practically 5C=6A). The worm gear 6 is being fixed between the worms 5 one and two and no worm gear 6 back drive is possible.
The motors 3 and the drives 8, 9 are under computer controll. The offered device can be pre-programmed or tele-operated.