Patent Application
20070200526
Glass inspection machines usually have a number of inspection stations at which a bottle carried through the machine will be inspected for defects. The machine may be an indexing, star wheel type machine. One or more of these inspection stations will include a stroke mechanism for displacing the inspection device from an up, retracted position, to a down, inspection, position. One such inspection device might be bottle specific gages mounted to a carriage. The carriage travels up and down on a linear guide system. The carriage is clamped to a timing belt that is supported by two pulleys. One of the two pulleys is attached to a gear head. The gear head is attached to a permanent magnet servo motor which is supplied by a suitable amplifier. The servo motor assembly contains a spring actuated, electromagnetically released, friction brake.
Machines will have an emergency stop button. If the E-Stop button is pressed or if the machine detects a dangerous condition, the machine stops the motion of all servo motors as fast as possible, pauses, drops the current that holds the motor brake in a released state, and releases the high voltage contractor (the motors are not moving when the brake is applied). In the E-Stopped state the star wheel is at a random position, and the stroke mechanisms are held at a random height. The star wheel may be moved by hand, the stroke mechanisms may not.
In the case of a power failure, the high voltage ceases to be available to the servo motors, the carriages continue in whatever direction they were headed. The current that holds the motor brake in a released state drops; the brake engages and stops the motor shaft from turning. This is the only condition that causes the brake to stop the rotation of the motor shaft. In the power failed state the star wheel is at a random position, and the stroke mechanisms are held at a random height. The star wheel may be moved by hand, the stroke mechanisms may not. The machine will remain in this state until power is restored and the start sequence is initiated.
The brake in the machine keeps the machine form damaging itself during a power failure and makes it easier to work on the machine during maintenance and set-up. If the stroke mechanisms did not have brakes, the mechanisms would move downward and hinder the technician's ability to move the star wheel during setup (E-Stop is recommended during set-up). The problem with the current design is that the brakes are not reliable. The brakes wear, create brake dust and fail. The failure causes the machine to shut down.
It is an object of the present invention to eliminate the requirement to use a motor with an internal brake.
Other objects and advantages of the present invention will become apparent from the following portion of this specification and from the accompanying drawings which illustrate, in accordance with the mandate of the patent statutes, a presently preferred embodiment incorporating the principles of the invention.
A 5 Volt D.C., 4 Amp Power Supply 20 is connectable to two of the three power leads of the servo motor when a pair of Low Current Solid State Relays (LC SSR) 22 are operated via signals from a PLC 24. The three power lines 16 are connectable to three high current circuits each having a regenerative resistor 26 when a pair of High Current Solid State Relays (HC SSR) 28 are operated via signals from the PLC.
Referring to
In the event the E-stop 33 is engaged, (E-Stop/Power Fails) 34, power will be removed from the servo amplifier and the control will Start Timer 36 and the PLC 24 sends High Current Solid State Relay Control Signals to the pair of High Current Solid State Relays 28 to actuate the relays which connect the three power leads to the regenerative resistors 20 shorting the three motor windings together (LC SSR “off”/HC SSR “on” 38). The back EMF created by the motor will slow the rotational output of the servo motor, stopping the motor. Once motor rotation has been stopped (Has 0.2 seconds Passed 40, for example), the High Current Solid State Relay Control Signals will be removed thereby disconnecting the three regenerative resistors from the three motor lead lines. At the same time the PLC sends Low Current Solid State Relay Signals to the pair of Low Current Solid State Relays which then operate to connect the DC Voltage (5 VDC/4 Amp Power Supply, for example) across two of the three servo motor windings to hold the motor where it has stopped (HC SSR UofF/LC SSR “on” 42).
This design has the following points in its favor:
No moving parts (if solid state relays are used) therefore, no problems with wear.
The high currents caused by braking are borne by passive components (resistors). Therefore, the DC Power supply need not be sized to endure 20+ amps of current.
Because the brakes have been removed from the system, the cost of the system has been reduced.
Because the brakes have been removed from the system, the reliability of the system has been increased.
