BACKGROUND OF THE INVENTION

[0001] The present application relates to a method and apparatus for controlling more than one stepper motor using a single set of micro-controller outputs.

[0002] In modern mechanical applications where precision turning is required it is known to use a stepper motor. A stepper motor operates by turning a shaft of a motor a precise angle each time a positive pulse is received at the motor's input, and by turning the shaft an equal angle in the opposite direction, each time a negative pulse is received. Each of these partial turns is a referred to as a "step." Stepper motors can have a varied number of steps per full revolution depending on the precision desired.

[0003] A stepper motor is ideal for uses requiring a high degree of precision, while not requiring a high magnitude of torque. A typical use meeting these criteria would be gauges such as a fuel gauge or a coolant gauge in a vehicle. In these and similar cases it is desirable that the readings are accurate, and that instructions from a controller are interpreted precisely and identically each time they are sent in order to provide accurate feedback to an operator.

[0004] One disadvantage of using a stepper motor instead of a standard motor is that the control scheme of a stepper motor is more complex than that of a standard motor and requires more control signals from a controller. Additionally, due to the pulsed nature of a stepper motor control signal, a pulse width modulator is typically required to achieve accurate stepper motor controls. [0005] As a practical rule all systems have a physical limit on the number of stepper motors they can control with a single micro-controller. Typically this limit is defined by the number of output pins on the micro-controller design selected for the system. For example, if a micro-controller design has eight output pins it can typically control a maximum of two stepper motors using a closed loop control scheme. When multiple stepper motors are used in a given system it is often the case that the required number of stepper motor control inputs will exceed the possible micro-controller outputs. It is known in the art to introduce additional microcontrollers when a single micro-controller cannot provide enough output pins.

[0006] A typical stepper motor utilizes two micro-controller outputs if it is controlled with an open loop or four micro-controller outputs if it is controlled with a closed loop. In a closed loop control scheme, two of the four pins are utilized for pulse signals, and two of the four pins are used for the feedback control. Devices using enough stepper motors to require multiple micro-controllers are common in the art.

[0007] It is desirable to minimize the number of micro-controllers contained in a particular device, however current systems do not have a way to reduce the number of microcontrollers and, at the same time, adequately control the required stepper motors.

SUMMARY OF THE INVENTION

[0008] Disclosed is an apparatus and method for controlling a plurality of stepper motors using a single set of micro-controller output pins. The micro-controller outputs a multiplexed control signal which is then demultiplexed in a demultiplexer. The demultiplexer outputs a stepper motor control signal corresponding to each stepper motor, and transmits the stepper motor control signals to the stepper motors.

[0009] These and other features of the present invention can be best understood form the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is an example gauge assembly where multiple gauges are controlled by a single set of micro-controller outputs.

[0011] Figure 2 is an apparatus for controlling multiple stepper motors with a single set of micro-controller outputs.

[0012] Figure 3 is an apparatus for controlling multiple stepper motors with a single set of micro-controller outputs.

[0013] Figure 4 is a flowchart illustrating an example method for controlling multiple stepper motors with a single set of micro-controller outputs.

[0014] Figure 5 is a flowchart illustrating another example method for controlling multiple stepper motors with a single set of micro-controller outputs.

[0015] Figure 6 is a flow chart illustrating an example method using a pulse width modulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] Vehicle gauge assemblies often incorporate multiple gauges having independent readouts such as a fuel level gauge, an oil temperature gauge, a speedometer, a tachometer, etc. Typically each of these gauges will contain a stepper motor which is controlled by a set of micro-controller outputs. Figure 1 illustrates an example vehicle gauge assembly 20 according to the present application which uses a single set of micro-controller outputs 110 from a micro-controller 100 to control multiple gauges 12, 14, 16. The single set of micro-controller outputs 110 of Figure 2 are split into individual control signals in a demultiplexer 102 which then transmits the control signals 114, 116, and 117 to each of the gauges 12, 14, 16. Each of the gauges 12, 14, 16 of Figure 1 contains a stepper motor 104, 106, 108 (see Figure 2) which is used to turn a pointer. In the example embodiment of Figures 1, 2, and 3 the first stepper motor 104 is a component of the first gauge 12, the second stepper motor 106 is a component of the second gauge 14, and the third stepper motor 108 is a component of the third gauge 16.

[0017] It is recognized that alternate designs for gauge assemblies using stepper motor driven gauges could be constructed and still fall within the disclosure of this application. The method described herein is preferred for uses where the pointer is not moving very often (ie gauges which do not need frequent updating) such as fuel gauges, oil temperature gauges, or other similar gauges.

[0018] In order to control a typical stepper motor, a micro-controller must either output a pulse width modulated control signal or pass a control signal through a pulse width modulator prior to the control signal reaching its destination. Once the signal is pulse width modulated the signal can be used to accurately control a single stepper motor with no further conditioning. In order to independently control multiple stepper motors, additional control signals are typically required. Historically, the requirement for additional control signals has meant that more micro-controller outputs, and consequently more micro-controllers, are also required. In the example method illustrated in figure 2, multiple stepper motors are controlled using a single set of control signals output from the micro-controller.

[0019] Figure 2 illustrates a device for controlling multiple stepper motors with a single set of micro-controller outputs which includes a micro-controller 100 that initially outputs a multiplexed control signal 110 and a demultiplexer control signal 112. The multiplexed control signal of Figure 2 is pulse width modulated. A demultiplexer 102 accepts the multiplexed control signal 110 at its primary input, and the demultiplexer control signal 112 at a control input. The demultiplexer 102 utilizes information within the demultiplexer control signal 112 to demultiplex the control signal 110. Once the control signal 110 is demultiplexed the demultiplexer 102 outputs a control signal 114, 116, 117 to a designated stepper motor 104, 106, 108. Alternatively, the demultiplexer control signal 112 can be omitted and the demultiplexer 102 can use internal programming to perform the demutliplexing operation.

[0020] Figure 3 illustrates another example device for controlling multiple stepper motors with a single set of micro-controller outputs. The example of Figure 3 includes the micro-controller 100 which initially outputs a multiplexed control signal 110, as well as a demultiplexer control signal 112. The multiplexed control signal 110 is sent to a pulse width modulator 122 where it is converted into a pulse width modulated signal 120. The pulse width modulated signal is utilized to control the stepper motors 104, 106, 108. The pulse width modulated signal 120 is then accepted by the demultiplexer 102. The demultiplexer 102 also accepts the demultiplexer control signal 112. Once both signals 120, 112 have been accepted by the demultiplexer 102 the device operates in an identical fashion as the device of Figure 5. [0021] The illustrated examples include three stepper motors 104, 106, 108 being controlled using a single set of micro-controller outputs; however any number of stepper motors could be controlled in the same manner. The multiple controlled stepper motors 104, 106, 108 can be used to control any number of devices according to known methods. One application of systems such as the ones illustrated in Figures 2 and 3 is to control a needle on multiple gauges (such a fuel gauge) in a vehicle, while at the same time minimizing cost by utilizing a single micro-controller.

[0022] The control of multiple stepper motors 104, 106, 108 with a single set of micro-controller signals 110 can be achieved through a method known in the art as multiplexing. Multiplexing refers to combining multiple signals into a single data stream. This is typically coupled with a demultiplexing operation on a receiver end where the single data stream is split into multiple signals. A group of signals may either be output individually and then combined in a multiplexer component, or output by a controller as a single multiplexed signal. A method for performing multiplexing is illustrated in Figure 4, and a second method for performing multiplexing is illustrated in Figure 5.

[0023] The method of Figure 5 begins by initially outputing a set of multiplexed control signals 110 containing control information for a plurality of stepper motors 104, 106, 108 from a single set of output pins to a demultiplexer 102 (Step 150). The demultiplexer 102 then demultiplexes the signal 110 by splitting the information contained on the control signal 110 into multiple individual control signals (step 160). Once the control signal 110 has been demultiplexed, the demultiplexer 102 generates a unique control signal 114, 116, 117 for each stepper motor (step 170) and transmits the unique control signals 114, 116, 117 to the corresponding stepper motor 104, 106, 108 (step 180).

[0024] The demultiplexer 102 then determines which stepper motor control signal 114, 116, 117 a time period applies to and sends all control signals 110 received from the microcontroller 100 within that time period to the designated stepper motor 114, 116, 117. The example method of Figure 2 operates using a sequence of three time periods, where the microcontroller 100 outputs a multiplexed control signal 110 containing a control signal for the first stepper motor 104 during a first time period, outputs a multiplexed control signal 110 containing a control signal for the second stepper motor 106 during a second time period, and outputs a multiplexed control signal 110 containing a control signal for the third stepper motor 108 during a third time period. The time period used may be any time period that suits the desired application. The sequence then repeats, thereby allowing the three stepper motors 104, 106, 108 to be continuously controlled with a single set of micro-controller output pins.

[0025] Once the corresponding stepper motor 104, 106, 108 for a time period has been determined, the demultiplexer 102 outputs the individual control signal 114, 116, 117 only at an output connected to the corresponding stepper motor 104, 106, 108. In this way the example method of Figure 4 controls each stepper motor 104, 106, 108 with updates during the stepper motor's designated time period each time the sequence repeats.

[0026] Another example method uses a demultiplexer control signal 112 instead of the predefined time period of the above described embodiment and is illustrated in Figure 5. In the method of Figure 5, a micro-controller 100 outputs a demultiplexer control signal 112 (step

210) simultaneously with a stepper motor control signal 110 (step 220). The demultiplexer control signal 112 contains instructions for a demultiplexer 102 which provides for the demultiplexer 102 to determine what stepper motor 104, 106, 108 a portion of the stepper motor control signal 110 received from the micro-controller 100 corresponds too. The demultiplexer 102 then demultiplexes the control signal 110 (step 230) and generates an individual control signal 114, 116, 117 for each stepper motor 104, 106, 108 (step 240). Once the control signals 114, 116, 117 have been generated, the demultiplexer 100 sends the corresponding control signal 114, 116, 117 to each of the stepper motors 104, 106, 108 (step 250).

[0027] The example method of Figure 5 provides for instructing the demultiplexer 102 to send a portion of the multiplexed signal 110 to multiple stepper motors 104, 106, 108 simultaneously instead of sending the same control instruction on the multiplexed signal multiple times (as in the example method of Figure 4). For example if the micro-controller 100 needs to turn stepper motors 104 and 102 one step it can send the instruction once and have the demultiplexer control single 112 indicate that the instruction should be sent to both stepper motors 102, 104. This provides the advantage of a faster response time and more efficient controls. The example methods of Figures 4 and 5 utilize a micro-controller 100 which outputs a pulse width modulated signal 110.

[0028] While two methods of demultiplexing a signal are described above, other known methods of demultiplexing a signal are within the contemplation of this invention.

[0029] For a system where the micro-controller 100 does not output a pulse width modulated stepper motor control signal 110, and the stepper motors require a pulse width modulated control signal, an additional pulse width modulation step is performed between the micro-controller output and the demultiplexer input. Referring to Figure 6, another example method provides a pulse width modulated step (step 310) where the micro-controller output 110 is converted into a pulse width modulated stepper motor control signal 120 using any known technique. The pulse width modulated stepper motor control signal 120 can then be properly interpreted by the stepper motors 104, 106, 108.

[0030] Although multiple embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.