Patent Application
20110221380
In most motor drive applications, the parameters to determine operations are the speed and torque of the motor. These relate to how fast the motor has to rotate to generate the desired movement of the system that the motor is driving. This system could be the movement of the hook of a crane, the velocity of a wheel, the speed of a fan, or any type of process or control that requires the use of a motor. The second parameter has to do with how much torque is required by the motor to provide this movement. With these parameters in mind, the motors are selected or designed, and the controls are selected or designed to meet these needs. The general operation of a switched reluctance (SR) motor is well known to those experienced in the state of the art.
The SR motor has some distinctive features that allow the precise positioning of and the holding of the motor rotor at a fixed point. The unique construction of stator poles with windings, and the rotor poles without windings, permits a set of poles to line up and hold at a fixed preset position. To rotate the rotor still requires the production of torque and speed, but in this application the control utilizes a decision-making process to move the rotor from pole to pole.
The instant application allows the motor to be utilized in a manner where a precise number of rotations and a precise point of the final rotation is identified and found. In addition, this point can be held until the mechanical brakes or holding device is engaged and the system is shut down. It can then be restarted and held at this point, without movement, even if external forces are applied at the output. In most existing drive controls, there is movement at the load end when the system is first energized if external forces are applied to the motor and drive (e.g. a load suspended on a crane hook will move when the brakes are released until the system generates adequate holding torque).
An apparatus is provided for utilizing a switched reluctance (SR) motor to position and hold a load in a desired position. In operation, one or more (SR) motors are capable of operating in a stepping control mode in a first device. Additionally, a second device is capable of providing precise position control for the first device, while the one or more SR motors are operating in the stepping control mode.
The overall SR Motor Control Functional Block Diagram for both a parametric (speed torque) and a stepping SR motor is shown in
With respect to
The SR motor has some innate distinctive features that allow the precise positioning and holding of the motor rotor at a fixed point. The unique construction of rotor poles without windings or slip rings or commutating bars or brushes, permits a set of poles to line up and hold at a fixed position without heating the rotor and without any limits due to the windings, commutator, or brushes. Incorporating magnetic attraction for torque development means that each phase activation results in a rotor position that is monostable against counter-torque in either direction. These features of SR drives are fully leveraged in this new method of control by stepping.
This embodiment of precise SR motor position control uses SR stepping control, where one step equals one Pole Position (PP) (which, for example, may be 15 degrees in the background example). SR stepping control may include at least five new SR control functions as described below.
Function 1, the Actual Rotor Position Accounting is shown in
This process may detect where the rotor currently is within a single revolution; that is, each and every pole position by unique PP number 302. It may determine if an illegal position is detected 304 and may report that to the Motor Position Control schemes 312. It also may account for where the rotor is within multiple revolutions in normal mode PP form across the entire range of machine operation 306. This process may include displaying the actual rotor position in operating units 308. It may determine how quickly the rotor gets from one pole position to the next 314 (by means of a clock 316) and may display this as angular velocity in operating units if required 310. This process may perform the above for all machine axes controlled by SR stepping.
Function 2, the Target Rotor Position Accounting is shown in
This process may detect the manual or automatic operation of target position input devices 402 (slider, knob, dial, retained position Joystick, touch screen, etc.). It may decode said inputs using, for example, a decoder 408. It also may detect the manual or automatic operation of activation input devices 404 (pushbutton, touch screen, etc.), and may decode said inputs using a decoder 408. This process may detect the manual or automatic operation of special variation input devices 406 (gain, vernier, etc.), and may decode said inputs using a decoder 408. It may account for the aggregate of all inputs using a computer or computational device 410, and it may convert the target position inputs into the normal mode multi-rev PP form. This process further may determine if an illegal target position or other errors 414 are detected and then may report those errors to the path calculation scheme. It may display the resulting target on the target display 412 in operating units and displays status indications 416 (i.e. Run/Stop) as required. This process may perform the above for all machine axes controlled by SR stepping.
Function 3, the Rotor Position Limit Maintenance is shown in
This process may input static 504, dynamic 506 or operator-set 508 limitations of rotor motion as a range of inclusion or exclusion (e.g. by means of a hardware or software device). This process may decode the limiting inputs 502 for PP conversion. It may convert the decoded limits 510 into the multi-rev normal mode PP form used as inputs to the path calculation 512. This process may perform the above for all machine axes controlled by SR stepping.
Function 4, the Rotor Position Path Calculation is shown in
This process may calculate and optimize a machine path 604 for every movement, dictated by the actual 610 and target 612 rotor positions, and, for example, limited by the rotor position limits 608 as described in
Function 5, the Motor Position Control is shown in
On/Off 702 may be the process that receives the external commands (via an operator or some automatic or remote means) to start or stop the system. When Start occurs, the system may go through an Initialization 706 process, readying the system of operation. The result may be an Error condition which may result in returning to a Park 704 state. Alternatively, if the Initialization 706 confirms the system is ready, the motor may go into a Hold condition 708.
Holding the motor at the current pole position may require executing the Hold process 708 just once. It may be the default state of the Motor Position Control. It may cause the motor to be energized at one pole position with sufficient torque to hold the maximum load. If entering Hold 708 from Initialization 706, the next process may immediately be Decide 710. Errors that occur during the initial Hold process may be reported to the Decide process for proper responses. If no errors are present, the Decide process 710 may always result in either Hold 708 or Turn Motor 712. Decide may include a number of operations and inputs. Commands may go to the Decide process 710 from path calculation logic (
A command to the Decide process can begin the Stop sequence with an Off command if at anytime the operator or some automatic control wants to stop the motor. When a command function inputs the Decide process 710 with an “off” command, an orderly shutdown may then initiated by the Decide process 710 function, which in turn may park the motor and shuts down the system.
Actual rotor positions from the encoder may be monitored by the Decide process 710 to verify un-commanded movement. Physical limits may be monitored by the Decide process 710 to ensure the control system is prohibited from working beyond those limits regardless of commands. The system may go to the Hold process when the target is reached and stops in the target position. Errors discovered by or during the Decide process 710 may cause the system to go into Park 704.
The Hold process 708 may be used to maintain a fixed rotor position in the face of varying machine dynamics. Hold may include a variety of operations. After the initial entry to the Hold step, every subsequent entry to the Hold process 708 may come from the Decide process 710. The loop from Decide 710 to Hold 708 and back to Decide 710 is called the Stay Loop. To maintain the currently held position, the Hold condition may be adjusted in torque or direction by the Decide process 710. Errors that occur during the Hold process may be reported to the Decide process for proper responses. The Decide process may return as often as needed to the Hold step.
The Turn Motor process 712 may be used to increment the rotor position one pole position in either direction at commanded torque and speed. The loop from Decide 710 to Turn Motor 712 and back to Decide 710 is called the Turn loop. The Turn loop may be executed repeatedly until the Decide process 710 sees the target position is reached. Errors that occur during the Turn Motor process may be reported to the Decide process for proper responses.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
| Number | Date | Country | |
|---|---|---|---|
| 61312613 | Mar 2010 | US |
