Sweepbot 1

A Floor Sweeping Autonomous Robot

Updated 7/4/11
THE TASK: Sweepbot will once a day spend a predetermined amount of time sweeping this bathroom floor keeping it litter free.

Update - July 2011

See this page for the new vacuum module installed in July.


   This new robot is a second round on the engineering of a simplified floor cleaning drone, the first was Vacbot completed a few years back. Unlike that robot, which was built from a modified commercial floor sweeper, SweepBot is completely custom built from the ground up. The task of this new robot is simple: Perform a daily short period clean sweep of the bathroom tile floor, to keep litter that has escaped from the cats litter box at bay. The robot must be autonomous, with little maintenance other than an occasional emptying the dust bin from an operator.

Mode of Operation:

The robot consists of two separate sections, the “Carrier Robot” and the “Mechanical Sweeper” assemblies. By separating the two this allows simplified sweep section maintenance, or replacement if needed. The sweeper section is nested inside the carrier, and floats on the tile surface held up by a spring suspension. The carrier and sweeper each have their own rechargeable batteries connected to one charging board.

The Carrier Robot:

   The Sweepbot carrier robot is almost completely finished. Here, the robot is connected to its IR Beacon/Battery Charger hoops which was developed in the PICbot series of projects. The robot can see the beacon on the charger from about 3 to 4 feet away (this is adjustable) and will drive to the charger when done sweeping for the day. The charger contacts contains 15vdc at 1 amp and a small charging board on the robot limits the charging on the gel cell.

This is where the primary movement and intelligence is located. The base consists of a two deck lexan construction, driven by two dc motors under the base level.Also on the base level is the 12v gel cell battery, microcontroller PCB, and touch sensors (bumpers). The top deck carries the LCD display and the IR docking fine guidance sensor bubble. The robots primary circuit board is our first home designed printed circuit board, and is designed to be a universal robot board as well complete with motor drivers and sub processors.

Sweeper Section:

   I actually built this section first, because I wasn’t sure how big it was going to be to do the job. Also constructed of heavy lexan, this motorized brush section has a small dust tray that can be dumped by releasing a magnetic door. A small circuit board on the side carries both the 4v NMh batteries for independently running the motor, and a buffered relay for simplified on/off operation with the microcontroller on the main robot. Since I am running the motor at half the voltage, it is relatively quiet and needs a smaller battery pack. It will run up to 30 minutes on an overnight charge if needed.

The Docking Station:

   The docking technology in this base was used from the best performing design on the Picbot 5 project – “Docking Logic”. Two brass hoops with a lexan separator are connected to a 15v 1A commercial power supply plugged into the wall outlet. This will trickle charge the batteries when the robot is docked. The power supply also operates the internal circuit board which consists of a 38.5 KHz oscillator connected to the IR beacon LED. This projects a narrow beam over three feet to allow the robot to home in on the charging base.

New Technologies

While the artificial intelligence of this robot was heavily based on the techniques developed in the PICbot series, several new technologies were used for the first time on SweepBot. Here is a list detailing these developments:

   - New impact bumper design – Using four touch contact type micro switches sandwiched between two lexan plates was a new and very reliable concept that was plenty sensitive and had great flexibility in the morphology.

   - New universal robot PCB – For the first time, a PCB was designed in Express PCB design software, and several boards were made. The board is intended to be universal, containing a large 16F874a processor several Texas instruments motor driver chips, and two additional slave PIC 8 pin processors for servo control. About half the board was filled here, only what was used in this design.
   - New larger robot test arena – The 14 inch size of Sweepbot made it essential that the testing arena had to be larger. Two white fiber board sheets combine to make a 48 inch square arena, with three inch sides all around. In the future, this larger size will make working with smaller robots seem like a whole new huge universe!
   - New docking contact design – The dual hoop design used here was developed in the PICbot 5 project to be the most flexible and reliable contact arrangement for robot docking and charging. The contacts can compress about a half an inch to accommodate the incoming robot which has dual plates mounted on the center bumper to mate up with the hoops. It works very well in this larger robot and Is fully scalable for future bots as well.

System Operation:

The robot is programmed with PIC Basic to run a “Finite State Machine” (FSM) type of program, which provides the framework for the artificial intelligence of the system. There are many caveats and error conditions that can occur in a robot that is designed for full time 24 hour a day operation! It took me the better part of six months to craft the software to run the robot autonomously. The basic operation of the Sweepbot is to awaken on the charger at the first light of day. Next, after it confirms the sun is really rising, and its getting brighter for a half hour or so, it undocks from the charging base, and starts the sweep mode. The robot moves about the room, using the bumpers to avoid walls and obstacles. The AI for this was fully developed in the PICbot I program. The power is applied to the sweeper at this time. After running for about 10 minutes, the robot starts looking for its charger and turns off the sweeper. When it finds the charger, it docks with the charger which is located in a tight space between the bathtub and toilet. It then confirms the presence of a charging voltage, then shuts down and waits the rest of the day for the onset of night. Once night is found when its getting dark after sunset, it changes modes and searches again for the sunrise. Then it will live its life again, over and over, day after day keeping the floor cleared of bits of cat litter.

Testing and Evaluation:

Months of extensive testing lasting sometimes for weeks on end were performed on this robot while it was in four foot square “robot arena”. There, every condition conceivable that it might encounter in real life was simulated and programmed for. Uncooked rice was used for faux cat litter for simplified testing of cleaning action, and the development of the docking, and charging systems. Once the robot performed a given period of time with any new changes, we would move on to the next phase. Then there would be few surprises when the robot was moved to its final cleaning destination upstairs.

Final Summary

This will be a long term on going project. While I don’t see too many issues with the carrier robot, how long the sweeper section will hold up remains to be seen. Because it is modular, replacing the sweep section with a new design is relatively straight forward. In six months, Ill post an update here – stay tuned!

Photo Gallery

 My inspriration, when I started this project 1 year & 4 months ago, I saw this parking lot sweeper behind the circle K in town. It works by pushing it and the back wheels drive the brush to push the trash FORWARDS into the catch bin via a rubber ramp. The rear wheel also drives a side brush to sweep stuff in the curbs in front of the sweeper intake. The robots side brushes do this very same task.
 Docked on a rice sweeping test run. The side brushes can be seen well here, and were cut with a bandsaw from a plasterers spreading brush. It is one row of six that were on the brush.
 Bottom sweeper side view. The rotating brush pushes the dirt forward up the polycarbonate ramp into the catch bin. Note the three white round slides the sweeper runs on.
 Rear veiw showing the battery and position of the side brushes.
  The robots front bumper has two brass plates for connecting to the charger. The robot drives up to the flexible hoops, connects by confirming the presence of a voltage, then stops to charge. The hoops can be docked with from a wide variety of angles.
  Here is the front central bumper of the robot showing the two brass plates for charging.
  The robot homes in on the IR beacon on the charging base with this vane type two sensor detector, which contains two PN4602 IR prox sensors. Ive enclosed it in a plastic bubble to protect it.

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