Using 8051 family - Microcontroller

Hi,

I've written a solution for the below problem, I would like you to tell me is my solution correct and provide me with feedback on any issue.

Your consultancy has been called in to make proposals for a control system to be used to control a hydraulic bearing press. When a bearing is to be inserted in position, the work is mounted in a jig and the press is required to operate at a closely-controlled pressure in order to successfully insert the bearing into its boss without damage to the boss. The operating pressure is defined by the machine’s operator through the use of a numeric keypad, in response to prompts displayed on a simple tow line-line LCD.  In order to ensure that the operator keys in a plausible pressure, each jig is fitted with one of six coding pegs. Each peg, which interacts with one of six microswitches mounted on the press, relates to a particular pressure range and, effectively, sets the minimum pressure for correct bearing seating and maximum pressure to which parts in a given jig may be subjected. The process of pressing the bearing into its boss relies upon the application of the programmed pressure for a pre-programmed time.

The operator is able to “program” the press whilst a two-position switch is in the “Enter” position and the machine runs only when the switch is turned to the second “Run” position. Before bearing seating pressure is applied, the jig is clamped in position by a hydraulic clamp, operated by a solenoid under software control. Hydraulic pressures for the clamp and for the main press are derived from separate pumps, each under software control. Both pumps are required to run throughout the press cycle, but should be switched off when the press is in “Enter” mode. Simple pressure switches on the two pumps indicate when the respective systems at operating pressure. The operator is protected from injury by a simple guard, whose correct positioning is detected by a microswitch. The press cycle is started by the operator pressing the “Start” button and may be stopped before the expiry of the selected time by means of the “Stop” button. Note that neither the “Start” nor “Stop” button is on the keypad, but rather on the control panel. Whilst the press is in operation, the controlling software lights a “Run” lamp and provides feedback on operator’s display of target pressure, actual pressure and time to run.

During the press cycle, the controlling software is expected to cycle on and off a solenoid valve controlling the main hydraulic ram’s feed in order to maintain the desired pressure. At the end of the cycle, the pressure must be relieved by a further solenoid valve that unloads the press head.

Your prospective client hopes to sell this machine into a number of industries. As a result, various parameters concerned with operating pressure and the tuning of the machine’s performance are not known at this stage. As a result such parameters will need to be transferred into the press controller down a serial line and stored in some non-volatile memory.

The client has cooperated with your consultancy on projects in the past and is quite comfortable with the use of the 8051 family of microcontrollers. Provide a detailed specification of your system, showing a block-diagram of the hardware that you would propose. Give an account of the operation of the controlling software.

Solution:

The system will use a three-position main switch. Switch position one will disconnect all power via a hard-wired relay in the power supply of the entire station. This is a safety matter and will allow the safe repair of the system. Position two will power the control electronics only, this is for programming of parameters into the flash memory of the Atmel AT89C51AC3. The AT89C5AC3 will allow for head room in the program and A/D structure should expansion to a different clamping structure be desired at a later date.
Switch position three will run the machine at its automated settings.

      The System consists of three main sections the pumps for pressuring the hydraulics, the clamps for holding the part in place, and the main cylinder for pressing the bearing into place. We well be adding pressure sensors to each pump hose to monitor output pressure and change the setting on the pressure control valves on each hose should an over or under pressure event occur. A pair of load cells on the clamping structure will detect the pressure used to clamp the item under work in place, and also to detect the pressure applied during insertion of the bearing.

Hydraulic source: each hose will have inserted at the pump a valve that is electronically controlled by an 8051. This 8051 will receive information from three sources, valve position digitally from the valve, and pressure in the line digitally from an inline pressure sensor and operator set point from the AT89C51AC3.

Clamping Structure: the jaws of this device will close on the part under operation. The clamping pressure will be detected using a small load cell placed in each jaw; these analog signals will be transmitted to the AT89C51AC3. The AT89C51AC3 will use it’s internal A/D block to shift this into a digital signal and will compare it to the operator set point for it’s pressure settings. When the pressure is at the correct level it will lock the pressure at a steady state. When the bearing insertion is complete the AT89C51AC3 will reverse the operation of clamp using the 8051 and pressure control valves.

Main Cylinder: this hydraulic cylinder will be used to press the bearing into place it’s pressure will be detected by the same load cells as the clamping pressure. The signal from the load cells will be analyzed by the AT89C51AC3 . When the pressure is at the correct level it will reverse the operation of the main cylinder by using the 8051 and pressure control valves.

AT89C51AC3:
Analog inputs:
       2 inputs from load cells, using internal A/D and multiplexing –2 pins.
Analog outputs: None.      
Digital inputs:
       Control signals from the 8051s – 8 pins.
       Parallel data in for Keyboard reading – 4 pins.
Digital outputs:
Control signals to 8051s – 8pins.
      Serial out to LCD unit 2pins.

8051:
Digital inputs
      1 valve position, parallel 4 pins
      1 pressure senor, parallel 4 pins
Digital outputs:
      1 control signal for valve, parallel 4 pins

Software: On start up the AT89C51AC will pole both 8051s and send a zero to each for initial valve settings, the 8051s will then run the pumps and valves to a line pressure of  zero. Once the initial setting are done the operator will be queried via the LCD display for each of the pressure setting for the clamp and main cylinder. The main processor will then send appropriate signals to the 8051s to activate the clamp and main cylinder. Each pump will be controlled by it’s 8051 until the set pressure is arrived at. Each 8051 will send control signals to the valves to open them and then check pressure on the hoses every millisecond. In case of an over pressure the valves will be closed. The load cells on the clamp will be poled every millisecond by the main processor when clamping pressure is reached this value will be used as base for the insertion of the bearing using the main cylinder. When the main processor shows correct insertion pressure it will send a end signal to the 8051s and they will return the hydraulics to rest and zero the pressures.
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