Essential components

3rd of November 2021
Essential components

The right choice of electronic components in a cleaning machine is just as important as the ergonomics and mechanical design. Marco Bruni at SED Special Electronic Design explains why in this exclusive piece for ECJ.

The right choice of the electronic components of a cleaning machine is as important as the good ergonomics and mechanical design to determine the success of a machine. Each manufacturer and brand uses electronics not only for “powering” a machine but also for achieving important functionality and the user experience.

Several functions previously managed using levers or mechanisms are today more and more delegated to an electronic system. Typically, the electronics in a modern cleaning machine, like a wet scrubber or sweeper, consists of:

• a central unit (namely motors controller) that drives the main motors such as the traction, the sweeping brushes, the valves and electric actuators
• a user-machine-interface (namely HMI) that allows the user to easily command the functions and receive messages from the vehicle.

Let’s start our journey into electronics for cleaning machines by looking at the motor controller technology, and then we will better see how an HMI works.

The basic function of a motor controller is simple: by varying the voltage applied to an electrical motor, the controller can adjust the motor speed enabling the machine to execute functions, enhance process control, reduce energy needs and optimise vehicle operations.

Different motor technologies of course need of course different driving technologies. The most common used in professional cleaning machines is called PMDC (referred also as brushed motors) and it uses a permanent magnet to create the magnetic field required for the operation of a DC motor. This motor normally requires an electronic architecture that foresees a microprocessor, some drivers, and an H bridge.

The architecture, the number of drivers and the H-bridge design depend on several factors. The most crucial is whether the motor has to spin on a mono-direction (eg, vacuum motor) or on a bi-direction (eg, traction motor).

The so-called ‘single quadrant’ (often called 1Q) controller  can only apply torque in the same vector polarity as the velocity ie, accelerating forwards (motoring). The ‘two quadrants’ (2Q) controller can apply a negative torque, but only when the velocity is negative ie, accelerating in reverse (motoring).

The last category of motor controller is called ‘four quadrants’ (4Q) which means it can mix the two components despite their polarity.  4Q technology is also called H-bridge due to its H-shaped structure. This type of driver can apply a negative torque to a positive velocity to decelerate something that is already in motion and vice versa (generating). To do so the 4Q drive must overcome the back EMF (counter-electromotive force) generated by the motor.

The four quadrants controller has the added benefit of regeneration. The kinetic energy in the decelerating can be transferred to electrical energy and then to the battery to increase the operation time of the machine. In multi-motors controllers, the 1Q-2Q-4Q categories can be mixed as required by the machine design, eg, a 4Q stage for traction can be packed with two 2Q stage to power the brushes.

How to combine the different technologies in one or more controller is usually a strategy of the machine manufacturer. The table on this page summarises some key aspects used to choose the electronics architecture of a machine.

Let’s see now how each component of the controller architecture works. The microprocessor is the brain of the controller. It is responsible for monitoring the input status and the power supply level (for safety reasons). When it detects a change in the input status, it sends a signal to the drivers. The drivers are special components that can produce a PWM (Pulse Width Modulation) when activated in order to apply a voltage at the Mosfets (Metal–Oxide–Semiconductor Field-
Effect Transistor).

PWM speed control works by driving the motor with a series of on/off pulses and by varying the duty cycle of the pulses while keeping the frequency constant. The PWM given by the driver is afterwards transformed into ‘power applied to the motor’ by the mosfets.

The mosfets are types of transistor. The voltage applied between gate and source pins determines the electrical conductivity of the device, therefore the electrical current across the component, up to the motor. Therefore, the driver and the mosfets control motor output by varying the width of these applied pulses and the average DC voltage applied to the motors terminals.

By changing or modulating the timing of these pulses, the motor speed can be controlled, ie, the longer the pulse is ‘on’, the faster the motor rotates and likewise, the shorter the pulse is ‘on’ the slower the motor rotates.

Motor controllers in modern cleaning machines are very sophisticated. They should also be capable of reading the motor status and react to current or speed variation, or even to motor positions (this is the case of autonomous cleaning machines) to precisely drive a machine and ensure a smooth end-user experience. Technicians talk about closed control loops. There are three levels of complexity in closed loop controls: control of current, control of speed, control of position.

In addition, a modern motor controller microprocessor combines several logical functions between motors and other inputs-outputs (eg, pumps flowrate), manages the current absorbed by each motor (eg, adaptive pressure) and controls ramp-up and ramp-down of a motor during start or stop respectively while it transmits real time data to the other equipment present on the machine or sends the data to a telematic system.

Hence, a typical multi-motor controller that manages several machine functions like brushes, traction, vacuum, actuators for squeegee, pumps etc has a great responsibility.

For example, in a small walk-behind machine a typical controller manages brush and vacuum motor, plus the electro valve for liquids, but in a ride-on machine things are much more complex because there could be several brushes to be managed, the traction, the dosing pumps, the vacuum system, the floats and the actuators used on a motorised squeegee.

If the motor controller remains hidden for most part of the time, the HMI is at the forefront. Users will interact with it daily, reading the machine status, using it for adjusting the machine settings, speed and recall functions. There are several types of HMI. There are simple HMI using switches and a simple charge battery status display, HMI with LEDs and touch-buttons and finally the most advanced ones that use graphic displays and multi-level menus.

Now that the two main characters are established, there is one last thing to be set: the communication between the two. The controller must continuously exchange data with the HMI and vice-versa in order to accomplish their respective functions.

There are several available communication technologies, usually digital. The most popular standards are serial communication or CANbus communication. While the first is usually more traditional and customised, the CANbus is a modern and universal standard.


Our Partners

  • ISSA Interclean
  • EFCI
  • EU-nited