The Tack up Stand Control

The take up pack is driven by a Maxon DC motor; the operation of the motor is controlled by an EPOS Studio graphical user interface (GUI) (Maxon motor ag, 2010) on a control PC through a motor controller (Maxon EPOS2 24/5). Fig. 2.25 shows connections between the controls PC (GUI), the motor controller, and DC motor. The operator inputs desired angular speed of motor in rpm with acceleration and declaration gain in rpm/sec. Motor controller controls the motor’s rpm as desired by sending PWM signals to the motor based on the feedback encoder implemented within the motor. Measured rpm is also displayed on GUI as shown in Fig. 2.25.

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Fig. 2.25: A connection flowchart of the take up stand. 2.5.3 The Rotary Guider and the Supply Pack Control

AKI H8/3052f MCU control the operation of the tape supply pack driving motor and measures the travelling tape tension using the tension sensor. It then controls the rotary guider based on the measured tape tension. The driving motor for the supply pack is controlled by PWM of MCU and HB 25 motor controller. The motor controller amplifies the PWM signal generated from PWM port channel 1 of MCU to a stronger signal to drive the motor. Both measured analogue tension signal SG sets 1 and 2 are sent to the analogue-to-digital converter port channels 1 and 2 respectively and converted to digital signals. The resolution of the analogue signal is 10bit (1024). The converted digital signal is processed to calculate total tension within the MCU, and PWM port channel 2 sends a signal to the rotary guider to rotate the angle to regulate the tension. The operation of the system is commanded by the Windows Hyper Terminal based control GUI by establishing the serial communication line between the MCU and the control PC. MCU also replays responses to commands such as display the measured tape tension from both tension

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sensors; the current angle of rotary guider from control GUI. Fig. 2.26 illustrates the connections between MCU and other control components.

Fig. 2.26: A connection flowchart of the supply stand and rotary guider.

Fig. 2.27 shows the flowchart of the developed control GUI based on Windows Hyper Terminal. The control GUI initially opens up when the main menu is booted. To command the system, an operator chooses a mode from selections of automatic mode, manual mode, and rewinding mode. Automatic mode enables the tape tension regulation with dynamic tape path alternation. Manual mode enables the manual control of the rotary guider. Rewinding mode enables the reverse pass operation of tape transport. To enable each mode, input from a corresponding key is. For example, to enable Automatic Mode, pressing the 1 on the keyboard of the control PC.

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Fig. 2.27: A flowchart of developed Windows Hyper Terminal Based tape drives system control GUI.

2.6 Design Footsteps and Key Issues

Fig. 2.28 shows photographic images of early design and later design of the tape transport system; particularly the design of the rotary guider. In the early design of the rotary guider, the rotation centre of was not located at the flanged guide B when compared to its later design. The early design of the rotary guider had its workspace between 0° and 180° horizontally. However, the span between the flanged slider A and the flanged guide B differs corresponding to the rotation angle of rotary guider. That parameter increases the complexity of rotary guider dynamics; therefore, to reduce the parameter of rotary guider, the span between the flanged slider A and the flanged guide B are fixed by setting the rotation centre of the rotary guider as the flanged guide B as shown in the later design of the rotary guider in Fig. 2.28. Fig. 2.28: Screenshots of development steps of the tape transport system. A key issue of the developed tape transport system is the noise contained in the measured signal from the strain gauge based tension sensor. Fig. 2.29 shows the raw measured signal from the tension sensor SG set 1 with stationary tape. A huge amount of noise was observed. Therefore, conditioning of signal was essential to measure the tension accurately. An analogue low pass filter with its cut off frequency 1Hz is implemented as a simple signal condition after the bridge amplifier before the signal is converted to digital form at MCU. However, the effectiveness of low pass filter to noise is minor. Since the tape is axially moving the measured strain of the tension sensor is dynamic strain, appropriate signal conditioner is essentially required to clear the noises. In this tape system, the measured tension is recorded as a txt format file in digital form and offline analysis are performed using MATLAB environment with a digital low pass filter. However, for the real time processing of tension regulation at MCU, the noise of feedback signal degrades the accuracy of

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tension measurement drastically. It is recommended that developing a signal conditioner and implementing it in the bridge circuit in order to clear the noise of the tension sensor signal.

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Fig. 2.29: Raw output signal of tension sensor (SG set 1).