SICK Ladar Rotational Mechanism

Transcription

1 SICK Ladar Rotational Mechanism EML 2023 Michael Larkin 10/25/2013

2 A. Introduction The SICK Ladar is a high-tech device that uses an internal mirror to project a laser that rotates 180 degrees in front of the device. This laser beam comes in contact with objects in in front of the device and reflects back to the internal mirror in less than one second. The Ladar then evaluates the information received and creates images and maps of the area it scans. The laser, however, scans only in the XY plane, and without a mechanism to rotate the Ladar as a whole in the z-direction, there is significant potential that the laser fails to detect objects below or above its field of vision. Complex robots that use the Ladar to detect obstacles could be damaged when failing to maneuver around them. In this way, the directional limitation of its field of vision could be cause for significant financial liabilities. The objective of this project is to design a mechanism that will rotate a SICK Ladar in the z- direction about the axis pictured in Figure 1. Figure 1: SICK Ladar Page 1 of 24

3 B. Design Specifications This design must adhere to the following performance requirements and design constraints: The weight of the device must not exceed 100 lbs. The device must fit within a 36 x24 x24 volume The average angle at which the device stops rotating should be within.5 degrees of the desired angle. Angular velocity of rotation should be constant throughout the motion to ensure symmetrical, clear imaging. The mechanism must not restrict the laser beam from scanning a full 180 degrees in the XY plane. Any actuators must be either the 135 RPM 12 VDC Buehler Gearmotor or the Denso DC Motor. Every actuator will have a Honeywell / Clarostat CBL Optical Encoder so that closed loop feedback control can be used. Every actuator must have a homing switch. Every actuator must have motion limit switches if there are limits to the actuator's rotation. The design must include one Device Craft Motor Driver for each motor. The design must include one National Instruments (NI) 6009 DAQ for each motor. The cost of building one prototype device must be identified (not including the NI DAQ). Page 2 of 24

4 C. Background The SICK Ladar is used for a variety of different purposes in the technological world. While its ability to create high resolution images is useful in fields including geology, archaeology, meteorology, and space exploration, its applications in robotics and the military most closely relate to this project. Robots and some military tanks use this technology to analyze and avoid potential obstacles, as well as identify targets and landmines. Alternative mechanisms to rotate the SICK Ladar in the z-direction would clearly be necessary to detect mines in the ground. A patent exists for a design that allows the Ladar to map in three dimensions. It features a turntable that allows a Ladar mounted on it and oriented approximately 45 degrees below the horizontal to rotate 360 degrees around, creating a three dimensional map. Page 3 of 24

5 D. Design Concepts The first of three design concepts, pictured in Figure 2, features a mechanism that attaches to the Ladar at two points on each side. One, located at or near the center of mass in the z direction, will remain stationary and serve as a pivot point for which the Ladar to rotate about. The second will be at the very top of the Ladar and will be extendable and retractable from inside the device. It will have teeth on the side that mesh with gears rotated by a DC motor. When the motor runs, the gears will turn and extend the arms, causing the Ladar to rotate downward. The switch on the motor will then cause the gears to rotate in the opposite direction, causing the arms to retract, rotating the Ladar upward. Figure 2: Two arm rotating mechanism The second design, pictured in Figure 3, is based on an attached conveyor belt on the rear side of the Ladar. The conveyor belt will be powered by a DC motor. There will be teeth on the sides of the conveyor belt that will mesh with fixed gears attached to the sides of the Ladar. The conveyor belt will run in one direction, rotating the Ladar to the desired angle, and then running in the opposite direction until the desired degree of rotation is achieved. Figure 3: Conveyor Belt Concept Page 4 of 24

6 The third concept, pictured in Figure 4, features two gears placed on either side of the axis of rotation that will be fixed and immovable. The Ladar will be suspended on a shaft at this axis and free to rotate about it. Another gear behind the fixed gear will mesh with it and be rotated by a DC motor, thus rotating the entire Ladar. This mechanism will work identically on each side of the Ladar. E. Selection of Design Approach Figure 4: Dual Gear and Shaft Concept Given that there are infinite possibilities of how to rotate the Ladar about the given axis, there are several functionalities that will determine the efficiency of each design. The first of these criteria is the physical feasibility of each design. It is imperative that the chosen design distributes the weight of the Ladar to components of the design that withstand that weight. A design that wouldn t withstand its weight would equal costly expenditures, and therefore, this factor will be weighted heavily in the selection of the optimal design concept. The constraints section states that the design must not exceed 100 lbs. Therefore, the design that would weigh the least would carry the most value. The third factor that will determine the efficiency of each design is the range in the XY plane that the design leaves undisturbed for the laser to scan. For example, two of the designs impede some of that range with gears, while the third leaves the entire range available. The following decision table, pictured in Figure 5, shows the numerical grade that verifies the dual gear and shaft design as the most efficient of the three. Figure 5: Decision Table Page 5 of 24

7 F. Design Description There are several subassemblies that make up the entirety of this design. At its finish, the design, minus the Ladar, motor drivers and NI DAQ s, weighs pounds. The first of these is the Ladar subassembly (CAD-MA-0001), shown in Figures 6 and 7. This consists of a manufactured bracket (CAD-MP-0002) that fits exactly around the given SICK Ladar (CAD-MP-0001), and two 24-pitch 48-tooth gears (CAD-MP-0003) welded to shafts extending from either side of the Ladar that are fixed in place and unable to rotate about the bracket. These shafts are located in a way that they pinpoint the desired axis of rotation given by the instructor. This bracket was attached to the Ladar with two screws on each side (CAD-MP-0004) and four on the rear face (CAD-MP-0005). Figure 6: Ladar Subassembly Exploded Page 6 of 24

8 Figure 7: Ladar Subassembly Collapsed Page 7 of 24

9 The next subassembly (CAD-MA-0002) consists of the base (CAD-MP-0006) and the suspension shaft (CAD-MP-0007) from which the Ladar will be suspended in the air. This base is pictured in Figure 8. All the other components of this design, including the motor, switches, optical encoder, NI DAQ, and motor driver will all be attached to this base in one of various ways. The motor subassembly will be gone into more detail later, but holes have been drilled into the base in order to attach this subassembly. Holes have also been drilled for a shaft that has been manufactured to suspend the Ladar subassembly in air. The shaft will be welded to the base on one end, and the other end will slide through the gear and meet the extension from the Ladar bracket so that the Ladar subassembly may rotate about this shaft. The shaft itself is pictured in Figure 9, and the manner in which is attached is in Figure 10. Figure 8: Base Page 8 of 24

10 Figure 9: Suspension shaft Figure 10: Suspension shaft in design Page 9 of 24

11 The third subassembly of this design is the motor subassembly (CAD-MA-0003). This consists of the DC motor (CAD-MP-0008) and all of its attachments. These will be specified in order that they appear, starting from closest to the motor. The shaft of the motor was connected to an adaptor (CAD-MP-0009) that was then secured to a rigid coupler (CAD-MP-0010). Connecting to the other side of the coupler was a very basic, straight manufactured shaft (CAD-MP-0011). A 24-pitch 15-tooth gear (CAD-MP-0012) is slid over this shaft and welded in place. On the other side of this gear is another rigid coupler for the attachment of the optical encoder to monitor the rotations of the DC motor. The securing of this encoder will be discussed later. Once fully assembled, two of these subassemblies will be attached to either side of the base with screws (CAD-MP-0013). Figures 11 and 12 show exploded and collapsed views of the motor subassembly, respectively. Figure 13 shows the motor subassembly attached to the base. Figure 11: Motor subassembly exploded view Figure 12: Motor subassembly collapsed Page 10 of 24

12 Figure 13: Motor subassembly attached The next subassembly (CAD-MA-0004) supports the optical encoder (CAD-MP-0014) where it aligns with the positioning of the motor attached to the base. The encoder is held in place by a hold (CAD-MP- 0015) manufactured to the dimensions of the encoder. Because there are two motors, this subassembly will be positioned symmetrically on each side of the Ladar. Its position on one side of the device is pictured in Figure 14. Figure 14: Encoder Hold Page 11 of 24

13 The final subassembly (CAD-MA-0005) will collectively refer to three manufactured blocks to which three switches (CAD-MP-0016) are attached with appropriate screws (CAD-MP-0017). The first of the three is the bottom kill switch mount (CAD-MP-0018) this will be welded on the bottom of the base at a position where, when the Ladar is pointed at 45 degrees above the horizontal, the bottom rear edge of the bracket will strike the kill switch, limiting its motion to 45 degrees both ways. The top kill switch mount (CAD-MP-0019) will be welded in a very similar manner on the ceiling of the base, which the bracket will strike when rotated 45 degrees below the horizontal. The third mount (CAD-MP-0020) is for the homing switch, and will be welded near the bottom kill switch in a position that the Ladar bracket will strike the switch once each time it completes the 90 degree range of rotation. An exploded view of the bottom kill switch is pictured in Figure 15. The other two switches are not pictured because they are attached in an identical manner. The position of the bottom kill switch is pictured in the left of Figure 16 and the homing switch to the right in that same figure. The top kill switch is pictured in Figure 17. Figure 15: Bottom kill switch mount exploded view Page 12 of 24

14 Figure 16: Bottom kill switch (left) and homing switch (right) Figure 17: Top kill switch attached Page 13 of 24

15 A picture of the fully assembled mechanism is shown in Figure 18. For further clarification on its operation, the Ladar will be rotated by the smaller of the two meshing gears that is attached to the motor subassembly. The larger gear on the Ladar bracket is fixed and will cause the entire Ladar to be rotated. A closer view of the motor subassembly and the rotational portion is pictured in Figure 19. As seen in the full view, the NI DAQ (CAD-MP-0021) and motor driver (CAD-MP-0022) for each motor have been placed on either side of the base, close to the motor for easy access. Figure 18: Dimetric view of fully assembled mechanism Page 14 of 24

16 Figure 19: Close view of rotational devices G. Cost Analysis The final cost of constructing this mechanism is $ , not including the given parts. The manufacturing costs were not included, but instead were included as the cost of multipurpose aluminum blocks from McMaster-Carr. The Bills of Materials is shown in Figure 20 below. Figure 20: Bill of Materials Page 15 of 24

17 Appendix Table of Contents Cover Page 0 A. Introduction.1 B. Design Specifications...2 C. Background..3 D. Design Concepts..4 Two Arm Design..4 Conveyor Belt Concept 4 Dual Gear and Shaft Design.5 E. Selection of Design Approach.5 F. Design Description...6 Ladar Subassembly...6 Base Subassembly 8 Motor Subassembly..10 Encoder Subassembly..11 Switch Subassembly 12 Full Assembly.14 G. Cost Analysis.15 Appendix 16 GDT Drawing of Bracket...17 GDT Drawing of Base 18 GDT Drawing of Suspension Shaft...19 GDT Drawing of Straight Shaft.20 GDT Drawing of Encoder Hold.21 GDT Drawing of Bottom Kill Switch Mount 22 GDT Drawing of Top Kill Switch Mount..23 GDT Drawing of Homing Switch Mount..24 Page 16 of 24

18 GDT Drawing of Ladar Bracket (CAD-MP-0002) Page 17 of 24

19 GDT Drawing of Base (CAD-MP-0006) Page 18 of 24

20 GDT Drawing of Suspension Shaft (CAD-MP-0007) Page 19 of 24

21 GDT Drawing of Straight Shaft (CAD-MP-0011) Page 20 of 24

22 GDT Drawing of Encoder Hold (CAD-MP-0015) Page 21 of 24

23 GDT Drawing of Bottom Kill Switch Mount (CAD-MP-0018) Page 22 of 24

24 GDT Drawing of Top Kill Switch Mount (CAD-MP-0019) Page 23 of 24

25 GDT Drawing of Homing Switch Mount (CAD-MP-0020) Page 24 of 24