STEP 600 XTPRO: Service & Maintenance Manual - rev. 1.1
Page 3.4
3.2. ALTERNATOR CONTROL
3.2.1. MECHANICS
The motion of the pedals imparts a rotation to the primary shaft via the chain connected to the 2
pedals. This chain actually consists of sections of chain coupled with springs. The primary shaft is
connected to the secondary shaft by means of a chain, which is in turn connected to the alternator by
means of a belt. In this way, the movement of the pedals is transferred to the alternator.
3.2.2. CONTROLS
The machine controls the difficulty level of the exercise by regulating the excitation of the
alternator, which generates a resistance to the movement proportional to the excitation level. To do
this, the CPU sends the alternator interface board a PWM (Pulse Width Modulation) signal which is
processed by the alternator interface board and then sent directly to the alternator itself. The
alternator filters the incoming PWM signal, extracting only its DC component: in other words, the
alternator sees the PWM signal as an analog voltage. The higher its value (corresponding to a PWM
duty cycle close to 100%), the higher the alternator excitation signal, and hence the greater the
resistance.
The alternator, rotating in the field produced by the excitation, generates electrical energy which is
dissipated on the power resistor.
During the movement, the alternator also outputs a square wave signal which indicates its speed: 6
pulses correspond to one rotation of the alternator. This signal reaches the alternator interface board,
where it is filtered and sent to the CPU board.
If the CPU board does not receive the speed signal, which means that the alternator is
not rotating, it does not transmit any PWM signal. Therefore the alternator does not
receive the excitation signal and there is no resistance at all.
The machine can only function with an independent stepping action. In this exercise mode, the user
moves at a constant speed (which increases with increasing difficulty level) to remain “afloat” on
the pedals. In this way, by using the alternator speed output as a feedback signal, the CPU board
regulates the PWM excitation signal to maintain a constant speed (closed loop control).
3.2.3. THE SIGNALS INVOLVED
The machine controls the difficulty level of the exercise by means of the CPU board, the alternator
interface board and the alternator as shown in the following figure:
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