ARM USING A TWO-JOINT MODULE
A robotic arm includes at least two two-joint modules and at least a first link. Each two-joint module includes a housing, a pair of hollow rotary actuator assemblies and a pair of motor drives. Each actuator assembly has an axis and a hollow shaft and the axes are arranged at an angle to each other. The pair of hollow rotary actuator assemblies are arranged such that a back end of the actuator assemblies is inside the housing and a front end of the actuator assemblies extends outwardly of the housing, and attached to the housing such that cables can be fed from the outside of one of the actuator assemblies to the inside thereof and to the inside of the other actuator assemblies to the outside thereof. The pair of motor drives are operably attached to the actuator assemblies and the motor drives are outside the housing.
This disclosure relates to robotic arms and in particular an arm using a two joint module having two degrees of freedom and having a generally L-shape.
BACKGROUNDTwo degree-of-freedom (2-DOF) joint modules used in robotic arms are becoming more common due to several advantages such as: compact size, light weight and lower cost. Joint modules are designed to meet certain requirements and constraints and these are transformed into the design specifications. For industrial applications, the requirements of payload range, speed, accuracy, reliability, lifetime, safety, ease of assembly and maintenance are very important.
There is a type of 2-DOF joint module, called Powerball ERB™ designed by Schunk GmbH & Co. KG. This joint module is housed in a ball shape enclosure that contains all the components needed to control the joint: servo motor, encoder, motor drive, harmonic drive, holding brake and hollow shaft for internal cabling. The joint module is not sealed as ventilation is needed to dissipate heat generated by the electronic components such as motor, motor drive and brake. The module is light weight, compact and is highly integrated. However, this design has limitations.
First, the Powerball ERB™ joint module consists of many mechanical and electronic components and this increases the complexity of the structure while also creates a heat dissipation problem. Since all electrical and control components are integrated in the module housing, the heat generated by these components requires a relatively large space to dissipate. However, since this joint is designed to be a compact joint, the power consumed by the electronic components is constrained by the heat that is generated. This in turn limits the output power of the joint module. Hence, the application of this type of joint module in terms of payload range is limited.
Second, to solve the issue of heat dissipation, openings or slots are made on the housing. This limits the applications of the joint module under certain harsh industrial environments such as dusty, humid, and explosive environments. These joints could not be used in robot arms for painting, coating and welding. For example; the explosive gases and sparks that may be present in such industrial applications could get into the joint module and cause explosions.
Third, the Powerball ERB™ can be used to build a robotic arm, LWA-4P™. The LWA-4P arm comprises three Powerball joint modules and two links. Since the joint modules have limitations on heat dissipation and power capped issues, the arm cannot work under some harsh industrial environments and the payload of the arm is limited.
There is another 2-DOF joint module, designed by Engineering Services Inc. (ESI) with patent number U.S. Pat. No. 9,044,865. This joint module is designed for large torque and low speed applications. The joint module includes a module housing and two joints. Also, one of joints has a hollow shaft gearhead, an off-axis drive, a servo motor, and internal cables extending through the hollow shaft gearhead. Since the joint module is designed to connect with a link, it has an active side and a passive side with electronic connectors. The active side is mechanically connected to the link and the electronic connectors of the passive side are operably connected to the link cables. The joint is used to build a robotic arm. There are limitations with this design as discussed below.
First, since all the components needed to control the motion of the joint are integrated into the module, it has the same heat dissipation problem mentioned in the Powerball EBR™.
Second, the cable routing inside the module is complicated because of the internal structure of the joint module. One of joints uses a non-hollow shafted motor and gearhead for providing the torque. Because of the internal structure of the joint, the cables go into one end of the module and inside the module turn 90 degrees and go out the other side of the module. In this case, the cables will be squeezed inside the housing. This may cause large torsional forces on the cables.
There is another type of 2-DOF joint module, designed by Fanuc Robotics North America as shown in a patent U.S. Pat. No. 5,293,107. Each module housing accommodates two hollow shafted rotary actuators, other electronic components and internal cables. The joint is used to build a robotic arm. However, this design also has limitations.
First, the installation process of rotary actuators and electronic components is complicated because it requires too many assembly steps. The two actuator sets are installed inside the housing, with their output shaft facing outside and the motor facing inside of the housing. The two actuators will be fixed to the housing wall by bolts and screws. To mount the two actuators in the housing, the two actuators cannot be put in from outside to inside of the housing. Instead, the actuators must be installed from the inside. So, the entire housing must be dissembled. Once the actuators are installed the housing is reassembled as one piece with screws and bolts. Therefore, the installation process is complicated.
Second, the joint module housing of Fanuc is not made of one piece. The housing box is made of several pieces and these pieces are fixed by screws and bolts to form the housing. So, the structure of the housing is not as strong as the one-piece housing.
Third, the maintenance process of the joint module is complicated. To access the actuators and other electronic components, a user needs to dissemble the housing case, conduct the maintenance, and resemble the housing once the maintenance is finished.
All of the aforementioned approaches to modular joints have limitations for industrial applications. It would be advantageous to design a new type of 2-DOF joint module which will have features such as compact, low heat generation, sealed and rigid housing, large payloads, ease of installation and maintenance process and assembly.
SUMMARYThe present disclosure relates to a two joint module. The two joint module includes a housing and a pair of hollow rotary actuator assemblies. Each actuator assembly has an axis and a hollow shaft and the axes are arranged at an angle to each other. The pair of hollow rotary actuator assemblies are arranged back to back and attached to the housing such that cables can be fed from the outside of one of the pair of hollow rotary actuator assemblies to the inside thereof and to the inside of the other of the pair of hollow rotary actuator assemblies to the outside thereof.
The axes of the pair of hollow rotary actuator assemblies may be arranged orthogonally.
Each hollow rotary actuator assembly may include a brushless DC servo motor having a hollow central portion, an encoder having a hollow central portion, a brake having a hollow central portion and an encoder having a hollow central portion. Each hollow rotary actuator assembly may be a combo actuator.
The housing may include a housing body and a housing cover releasably attachable to the housing body. The housing body may include a pair of generally cylindrical compartments for housing the pair of hollow rotary actuator assemblies. The housing body may further include a center compartment between the two generally cylindrical compartments.
The axes of the pair of hollow rotary actuator assemblies may be arranged at an obtuse angle therebetween.
The power, speed and torque of the pair of the hollow rotary actuator assemblies may be the same. Alternatively, the power, speed and torque of the pair of the hollow rotary actuator assemblies may be different.
The two joint module may include a pair of motor drives operably attached to the pair of hollow rotary actuator assemblies and the motor drives are outside the housing.
The disclosure also relates to a robotic arm. The robotic includes at least two two joint modules wherein each two joint module is as described above and at least a first link.
The robotic arm may include a third two joint module and a second link, wherein the two joint modules are a shoulder module, an elbow module and a wrist module. The shoulder module and the elbow module are operably attached to opposing ends of the first link and the elbow module and the wrist module are attached to opposing ends of the second link.
The first link may be a shoulder link. The shoulder link may include a body and a hollow cover and having a first port and a second port. The first port and the second port of the shoulder link are generally in the same plane.
The second link may be a wrist link. The wrist link may have a first and second port that are generally orthogonal to each other.
The robotic arm may include a motor drive operably attached to each of the hollow rotary actuator assemblies and the motor drives being outside the housing.
Further features will be described or will become apparent in the course of the following detailed description.
The embodiments will now be described by way of example only, with reference to the accompanying drawings, in which:
and
Referring to
As best seen in
Referring to
Holes 52 are used for connecting the joint module 10 to a robot arm link 102 as described below in relation to
In addition, as shown in
As shown in
An internal cable bundle 66 goes in to the arm 100 and is electronically connected to the electronic box 114. The cable bundle 116 passes through the following components: the turret seat 112, the turret-shoulder module 104, the shoulder link 102, the elbow-wrist module 106, the elbow link 110 and the wrist module 108 as shown in
Referring to
Referring to
By using the combo actuators and placing motor drives 124 outside joint module, the 2-DOF joint module 10 is more compact and light weight.
Also, since the motor drives 124 are outside joint module 10, the influence of heat from the motor in the motor drive is external to the joint module and this allows the joint module to be designed in compact manner. These features enable the new joint modules to be used by robot arms working in industrial environments. This design overcomes the aforementioned heat dissipation problem in the prior art joints discussed above and specifically the Powerball ERB™ and U.S. Pat. No. 9,044,865B2.
It will be appreciated by those skilled in the art that to achieve larger power, torque and higher speed of the joints, the size of the joint module increases proportionally for the different purposes, such as accommodation of bigger components and heat dissipation. However, once the heat generation inside the joint module housing is reduced, within the original module space, each joint can be designed to achieve larger power, torque and higher speed. As shown in Table 1, each joint of L-shaped 2 DOF joint module 10 described herein is designed with larger motor power, torque and higher speed in comparison to SCHUNK's POWERBALL™ joint.
In addition the joint modules 10 may be sized for the particular purpose. As shown herein the turret-shoulder 104, elbow 106, and wrist 108 modules are sized for their particular purpose. For example the wrist module 108 has a smaller payload so the wrist module may be smaller. As well, the power, speed and torque of the hollow rotary actuator assemblies may be chosen for the specific purpose. The power, speed and torque characteristics may be different in one of the two degree of freedom joint module 10. As shown in Table 1 in the turret-shoulder module 104 the power, speed and torque of the hollow rotary actuator assemblies 14 for the turret joint and the shoulder joint are the same. In contrast in the elbow module 106 the power, speed and torque of the hollow rotary actuator assemblies 14 are different. As can be seen in
The two degree of freedom joint module 10 may be varied by changing the angle between the two hollow rotary actuator assemblies 14 as shown in
As discussed above the lengths of the links may vary depending on the needs of the user. An example of this is shown in
In the configuration shown in
The structure of the new joint module is of “L-Shape”, which is not seen in the prior art. The “L-Shape” two joint module 10, consisting of two cylindrical tubes with their central axes orthogonal to each other is manufactured in one piece so its mechanical structure is very sturdy. As discussed the size of the cylindrical tubes may be the same or vary depending on the combo actuators 14 sized to be used therein.
Due to the “L-Shape” structure of the module housing, the installation method of joints for each module is simpler than that of the prior art. The installation method is shown in
There are at least two advantages of this installation method. First, when installing the combo actuators 14 to the housing 12, the entire housing is not taken apart and the module remains in one piece. The firmness and stability of the structure, therefore, will remain. This feature overcomes the shortcoming of Fanuc design described above, whose actuators are installed from inside to outside and the entire joint is has to be taken apart for installation or maintenance. Second, since the two actuators 14 are back-to-back, the hollow shaft structure allows for simple cable routing and cable management. As shown in
Due to the structure of the module housing 12 and the simple installation method of joint module 10, the maintenance process of the joint and arm is relatively easy. As shown in
Robotic arm 100 has a different structure from the robot arms the prior art robotic arms that use single joint modules or 2 DOF joint modules. Robotic arm 100 is configured such that the rotation axis of elbow-roll of the elbow joint 104 is not aligned or is offset with the rotation axis of wrist-twist of the wrist joint 108 as shown in
In addition the manufacturing and assembly processes of robotic arm 100 are greatly simplified. The arm uses same type of joint modules, the assembly between joint modules and links can be done in few steps. The number of components is lower than other robot arms using modular joints.
Generally speaking, the systems described herein are directed to 2-DOF joint modules and robotic arms that use same. Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.
As used herein, the terms, “comprises” and “comprising” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms, “comprises” and “comprising” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.
As used herein the “operably connected” or “operably attached” means that the two elements are connected or attached either directly or indirectly. Accordingly the items need not be directly connected or attached but may have other items connected or attached therebetween.
Claims
1. A robotic arm comprising:
- at least two two-joint modules wherein each two-joint module includes: a housing; a pair of hollow rotary actuator assemblies each having an axis and a hollow shaft and the axes being arranged at an angle to each other and the pair of hollow rotary actuator assemblies being arranged such that a back end of each of the hollow rotary actuator assemblies is inside the housing and a front end of each of the hollow rotary actuator assemblies extends outwardly of the housing, and attached to the housing body such that the cables can be fed from the outside of one of the pair of hollow rotary actuator assemblies to the inside thereof and to the inside of the other of the pair of hollow rotary actuator assemblies to the outside thereof; and a pair of motor drives operably attached to the pair of hollow rotary actuator assemblies and the motor drives being outside the housing; and
- at least a first link.
2. The robotic arm of claim 1 further including a third two-joint module and a second link, and the two-joint modules are a shoulder module, an elbow module and a wrist module and shoulder module and the elbow module are operably attached to opposing ends of the first link and the elbow module and the wrist module are attached to opposing ends of the second link.
3. The robotic arm of claim 1 wherein each the axes of the pair of hollow rotary actuator assemblies are arranged orthogonally.
4. The robotic arm of claim 3 wherein each hollow rotary actuator assembly is a combo actuator.
5. The robotic arm of claim 4 wherein each hollow rotary actuator assembly includes a brushless DC servo motor having a hollow central portion, an encoder having a hollow central portion, a brake having a hollow central portion and an encoder having a hollow central portion.
6. The robotic arm of claim 1 wherein housing of each two-joint module includes a housing body and a housing cover releasably attachable to the housing body.
7. The robotic arm of claim 6 wherein each housing body includes a pair of generally cylindrical compartments for housing the pair of hollow rotary actuator assemblies.
8. The robotic arm of claim 7 wherein each housing body further includes center compartment between the two generally cylindrical compartments.
9. The robotic arm of claim 1 wherein the axes of the pair of hollow rotary actuator assemblies are arranged at an obtuse angle therebetween.
10. The robotic arm of claim 1 wherein the power, speed and torque of the pair of the hollow rotary actuator assemblies is the same.
11. The robotic arm of claim 1 wherein the power, speed and torque of the pair of the hollow rotary actuator assemblies is different.
12. The robotic arm of claim 1 wherein the first link is a shoulder link.
13. The robotic arm of claim 12 wherein the shoulder link includes a body and a hollow cover and having a first port and a second port.
14. The robotic arm of claim 13 wherein the first port and the second port of the shoulder link are generally in the same plane.
15. The robotic arm of claim 14 wherein the at least two two-joint modules are three two-joint modules being a shoulder module, an elbow module and a wrist module and further including a second link being a wrist link and wherein the shoulder module is attached at one end of the shoulder link and the elbow module is attached at the other end thereof and the elbow module is attached a one end of the wrist link and the wrist module is attached at the other end thereof.
16. The robotic arm of claim 15 where in the wrist link has a first and second port that are generally orthogonal to each other.
17. The robotic arm of claim 1 further a motor drive operably attached to each of the hollow rotary actuator assemblies and the motor drives being outside the housing.
Type: Application
Filed: Jul 13, 2018
Publication Date: Nov 8, 2018
Inventors: Xiaojia He (Toronto), Ziren LU (Thornhill), Andrew A. GOLDENBERG (Toronto)
Application Number: 16/035,182