1. Introduction
Students from the University of Johannesburg submitted an entry that combines pneumatic and linear drive systems with a predictive laser system to automate and improve the training of taking shots on goal (adaptable for other ball sports), with an additional interesting suggestion to use the proposed machine to promote interest in science and engineering.
Click here to download a summary of the design.
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Competing Students - Adrian Levy; Stephen Rose; Milan Isvarlal; John Taylor.
Email us for more information about these entrants or the Automated Goalkeeper with Ball Return Function.
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2. Design Breakdown
Two laser distance sensors (for the x and y axes respectively) are positioned just after where the ball is to be kicked from. The laser distance sensors are available from Festo and are found in the SOEL family of sensors. When the ball is kicked through the laser grid, its x, and y intersection is logged. Then, by means of using the method of similar triangles (in the x and y planes respectively), the final position of the ball at the goalmouth, is predicted. This predicted position is then sent to the controllers for the main translational system and the vertical translational system.
The main translational system providing horizontal motion uses two electrical linear motors (positioned on either side of the horizontal bars of the goalmouth, working in unison). These linear motors are to be used in conjunction with the DGE linear axis (Festo) and the CMMS controller (Festo).
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Automated Goalkeeper with Ball Return Function
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Schematic of Ball Position System
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Schematic of Horizontal Translational Motion System
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The vertical subsystem essentially provides vertical motion using a large pneumatic cylinder. This cylinder rests on the top portion of the horizontal translational system defined above. The cylinder to be used for this application is from the DNC family (Festo) and has a maximum stroke of two metres to cover the entire goalmouth.
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Schematic of Vertical Motion System
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The last major subsystem is the ball-catch-return system. This system effectively catches the ball by means of a mild steel cage that is designed to slow the ball to a stop and keep it constrained. In conjunction with the rest of the system (pneumatic actuator, and linear motors) the box is returned to the zero position. This position is defined as the half way point of the horizontal and vertical crossbars of the goals. Upon reaching this point, the ball is returned to the player.
This return feature is facilitated by making use of the swivel module (DSMI) from Festo. The swivel module is connected (by a mild steel rod from the rotational axis) to a plastic return basket. When activated (from the zero position) the DSMI swivel module propels the ball, with a predetermined amount of torque that will “shoot” the ball the required distance so that the player can retrieve the ball quickly, with turnaround time being optimised.
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Ball Retrieval and Return System
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3. Maintenance of System
System maintenance considerations are always of importance when designing a system. This is because any increase in service life of a product or system is desirable. Possible system maintenance procedures and suggestions were documented in the project.
4. Product Design Specification
• Used to train for sporting activities
• Cost effective
• Utilises a maximum of a 2.2 KW compressor for pneumatics
• Entire system must fit into a 3 x 2m goalmouth
• Travel time between horizontal posts must be less than 3 seconds
• Travel time between vertical posts must be less than 3 seconds
• Maximum weight of ball 3kg
• Energy efficient
• High life cycle (1 x 108)
• Steel for frame use (low carbon)
• Weight of system less than 200Kg
• Pressure of operational system may not exceed 600KPa
• Maintainable
• Reliable
• Pneumatically and motor driven
• Pneumatic tubing must be moisture resistant
• Dust filters must be present in the design
• Eco-friendly
• Ecologically sound
• Safe for rigorous use
• For use with all age groups
• Indoor use
• Easy to assemble, on site
• Must conform to safety standards
• Single phase, A.C. 50Hz, 220V
• Kill switch
• Warning system when system is live
• Operation at ambient temperatures (0 - 40°C)
• Co-efficient of expansion of selected steel must be small
• General service guarantee
• Ball Mass 0.45kg
• Ball Speed 30m/s
• Maximum cost of system R300 000.00
5. Reviewing Design Concepts and Principles
A number of concepts and principles had to be calculated and considered:
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• Calculations of the Linear Drive By inputting the variables according to the design, a force of 1683 N was calculated for the linear piston.
• Allowable Distance of Free-Kick Spot Due to idle and reaction time of the linear motors and actuators, there exists a limitation of the minimum distance between the free-kick spot and the goals. It was calculated that the greatest reaction time for the automated goal-keeper to save any shot is 1.56 seconds (time taken to move furthest distance away from neutral position plus idle time).
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• Position of Goals, Laser Grid and Free-Kick Spot If a ball is shot and no interference with the pre-planned grid occurs, it implies that the bottom of the ball after a meter of travel is at a height greater than 0.125m as thus given a straight shot without dipping due to gravity will go over the cross-bar, i.e. will miss. The computer which analyses the interference must therefore be programmed to neglect values greater than 0.125m and not cause any reaction of the motors and actuators. The same process must occur for the horizontal projection.
• Control Processes The control processes for the Automated Goalkeeper with Return Function are relatively complex, requiring programming by an appropriate individual. Therefore, in pursuit of an effective and completely functional system, the control processes and automisation of the pneumatic and linear drives, as well as the electronic system interfaces between the above and the laser ball prediction system will be outsourced to qualified personnel.
6. Environmental, Ecological, Ergonomic and Safety Considerations
• Environmental The environmental impact of this system is minimal. The operation of the system does not cause any environmental harm. The pneumatic system utilises air, rather than harmful gases. Also, as far as possible, recyclable materials are used in the construction of the system. The device will also be energy efficient as energy consumption will be calculated and minimized as far as possible.
• Ecological As this system is intended to be used in an indoor environment, interaction with the surrounding ecology is almost non-existent. Therefore, this system will produce no ecological harm or affect the ecological system at all.
• Ergonomics The system is designed to be used in conjunction with standardised indoor football goals. This essentially means that it will conform to ergonomic specifications set out by the Indoor Football governing bodies. Also, the placement of the ball prior to kicking, is subject to specifications set out by the Indoor Football governing bodies.
• Safety A vast array of safety features were incorporated into the design, such as; warning lights and a kill switch and it was designed to be safe for use with all ages (parental supervision is required for children under the age of twelve). In addition to these basic safety requirements the proposal also stipulated that it conforms to: ASTM F1749 – 09 (referring to Standard Specification for Fitness Equipment and Fitness Facility Safety Signage and Labels), as well as the Safety at Sports and Recreational Events Bill (2005) in the South African Legislature which would ensure the safety of spectators.
7. Components Used
The following table details the parts required for the system:
Festo Components
Vertical Motion System
Festo Cylinder DNG-80-1500-PPV-A-S2
Festo Valve CPE-24-M3H-5LS-3/8
Festo Silencer U-3/8
Festo Flow Control Valve GRLA-3/8-B
Festo Tubing PUN-16x2.5-BL
Festo Fittings QS-3/8-16
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SEW Eurodrive Components
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Horizontal Motion System
Festo Linear Drive DGE-63-3000-ZR-LH-RH-KG
Festo Axial Unit EAMM-A-F62-1206
Festo Motor EMMS-AS-100-M-RS
Festo Gearbox (5:1) EMGA-120-P-G3-SAS-100
Festo Controller CMMP-AS-C5-11A-P3
Ball Retrieval and Return System
Festo Swivel Module DSMI-40-270
Festo Positioning Module CPX-CMAX-C1-1
Miscellaneous
Festo PLC Controller FEC-FC600-FST
Festo Laser Distance Sensor SOEG-RTD-Q20-PP-K-2L-TI
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