DUAL ACCELEROMETER DETECTOR FOR CLAMSHELL DEVICES

A clamshell device with a dual accelerometer detector includes a first keyboard portion including a first accelerometer, a second display portion including a second accelerometer, and a hinge for coupling the first portion to the second portion. Circuitry coupled to the first and second accelerometers provides an output signal in response to the position of the first and second portions of the clamshell device. The output signal is provided to indicate a shutdown or standby mode, tablet operation mode, a partially shut or power savings mode, a normal operating mode, or an unsafe operating mode.

TECHNICAL FIELD

The present invention is related to clamshell devices and, more particularly, to a dual accelerometer detector for a clamshell device.

BACKGROUND

Today's mobile devices that have clamshell designs use a Hall sensor/magnet combination or switches to determine when the lid/display is closed. Examples of such mobile devices known in the art are cell phones, notebook computers, netbooks, and tablet personal computers, among many other such devices.

The “open/close” sensors contained in these devices are used to determine the state the device is in and impacts the operational mode of the device. For example, in notebook computers, when the device is closed, the LCD panel backlight is typically shut off. Closing the device can also cause a sleep or hibernation mode to be activated.

Magnetometers (electronic compass) are now being added into these mobile clamshell devices to assist in various new navigation applications. Removal of the existing Hall sensor/magnet is desirable because the magnet can cause an offset in the magnetometer reading, called a “hard iron” offset. Removal of simple switches is also desirable due to single point failure, wear, and reliability issues.

What is desired, therefore, is elimination of existing prior art closure detection mechanisms, while at the same time maintaining the ability to determine the relative positions of the keyboard and display portions in a mobile device in order to manage various operating modes thereof, including closure detection.

SUMMARY

In an embodiment, a clamshell device having a dual accelerometer detector includes a first portion including a first accelerometer, a second portion including a second accelerometer, a hinge for coupling the first portion to the second portion, and circuitry coupled to the first and second accelerometers for providing an output signal in response to the position of the first and second portions of the clamshell device. The first portion of the clamshell device typically includes a keyboard, wherein the first accelerometer is located in or coupled to a motherboard of the keyboard. The second portion of the clamshell device typically includes a display, wherein the second accelerometer is located in a camera module or a circuit board of the display. The physical orientation (X/Y/Z axes) of the first accelerometer in relation to the second accelerometer (X/Y/Z axes) is known. The output signal is provided to indicate a shutdown or standby mode, tablet operation mode, a partially shut or power savings mode, a normal operating mode, or an unsafe operating mode.

In an embodiment, a system comprises: a portable computing device having a clam shell configuration including a keyboard portion and a display portion, wherein the display portion is connected to the keyboard portion by a hinge; a first three-axis accelerometer circuit mounted to the keyboard portion; a second three-axis accelerometer circuit mounted to the display portion; the three-axes comprising an X-axis, a Y-axis and a Z-axis; and a processing circuit coupled to receive three-axis accelerometer data from the first and second three-axis accelerometer circuits and configured to process the three-axis accelerometer data to determine, for each of the keyboard portion and the display portion, a first tilt angle of the X-axis relative to horizontal, a second tilt angle of the Y-axis relative to horizontal and a third tilt angle of the Z-axis relative to horizontal, and further determine from the first, second and third tilt angles of each of the keyboard portion and the display portion a relative orientation of the keyboard portion to the display portion with respect to the hinge.

DETAILED DESCRIPTION

Referring now toFIG. 1, a clamshell device, in this case a personal computer, is shown having a first display portion102and a second keyboard portion104, joined by a swivel hinge106, as is known in the art. To accomplish the detection function, a first accelerometer108is located in a fixed, known orientation in the display portion102, such as embedded in the camera module. The second accelerometer110is placed in a fixed, known orientation on the second keyboard portion104located on, or operatively in communication with, the motherboard of the computer.

The first and second accelerometers should be three axis capable accelerometers with either an analog or digital output.

Referring now toFIG. 2, the personal computer200is shown in a position where neither the keyboard can be accessed nor can the display be properly viewed. In this example, the keyboard204is horizontal, and perpendicular with the Z-axis of accelerometer210. This implies that the keyboard204is at rest on a flat surface. Angle A of the display202is inclined approximately 45 degrees. The Z-axis of accelerometer208is perpendicular to the display202, and can provide the gravitational acceleration information associated with inclination tilt angle B. Knowing the fixed position and orientation of accelerometers208and210, and the relative tilt angle with respect to horizontal of each, the relative position of angle A can be calculated. The personal computer200is shown in schematic form in which the computer includes the display202having the first accelerometer208, and the keyboard204having the second accelerometer210, joined by hinge206. Using the method disclosed herein, when a relative angle of a predetermined number (for example, 10 degrees) is reached where neither the keyboard can be used nor the display seen, the backlight can be shut down, or a power savings mode can be entered.

Referring now toFIG. 3, first and second block diagrams300and302are shown for the electronic processing circuitry used to process the information from the first and second accelerometers. The solution shown inFIG. 3is a system level solution. In the case of a notebook computer, the processing implementation can be accomplished by connection of the display accelerometer302and the keyboard accelerometer304through an I2C or SPI bus to a Platform Controller Hub (PCH) or I/O Controller Hub (IOCH)308that is resident in the notebook directly. The Hub308is in communication with the resident computer processor core306. Alternatively, an analog or digital display accelerometer302and an analog or digital keyboard accelerometer304can be coupled to an embedded controller310(typically the keyboard controller) through an I2C, SPI, or analog bus. The embedded controller then communicates with the PCH/IOCH308, which is in communication with the resident computer processor core306. Software drivers running on the resident computer processor core306are used to calculate the absolute angles of the display and keyboard and determine the relative angle to each other. Based on the relative calculated angles of the keyboard and display with respect to horizontal, the Operating System software running on the resident computer processor core306can adjust the system functional state accordingly. The implementation for other clamshell style devices such as a cell phone would be similar to that shown inFIG. 3.

Referring now toFIG. 4, the output of a single axis of a typical three axis analog accelerometer is shown. In this case, let us assume the X axis output. There are two accelerometers shown inFIG. 4. Accelerometer410is associated with a resting keyboard of a personal computer, for example. The analog voltage output of accelerometer410is about 2.5 volts for a typical five volt supply voltage when the X axis is perfectly horizontal. This is known as the zero g level. As shown inFIG. 4, accelerometer410is in the “zero g” position, since the force of gravity is orthogonal to the sensitive axis of the accelerometer. There is no force of gravity in the sensitive axis of accelerometer410. The output of sensor408, however, is calculated as given by the equation below:

For a typical accelerometer, the sensitivity is about one volt per “g” unit of gravity. Thus, the output voltage can be seen in the table given inFIG. 4, wherein an angle of zero degrees results in the same “zero g” sensor position and results in an output voltage of about 2.5 volts. An angle of 30 degrees with a sensitivity of 1V/g results in an output voltage of about 3.0 volts. An angle of 60 degrees with the same sensitivity results in an output voltage of about 3.37 volts. The entire 360 degree output response is given in the table ofFIG. 4in 30 degree increments. The output voltage is used to calculate the absolute positions of both the keyboard and the display, and then the relative position therebetween. This relative position calculation is used to control various operating modes of the clamshell device, which are listed in detail below.

Referring now toFIG. 5, the output of a single axis of a typical three axis digital accelerometer is shown. In this case also, let us assume the X axis output. There are two accelerometers shown inFIG. 5. Accelerometer510is associated with a resting keyboard of a personal computer, for example. The digital output stored in an internal register of accelerometer510is 2048 counts when the X axis is perfectly horizontal. This is known as the zero g level. As shown inFIG. 5, accelerometer510is in the “zero g” position, since the force of gravity is orthogonal to the sensitive axis of the accelerometer. There is no force of gravity in the sensitive axis of accelerometer510. The output value stored in the internal register of sensor508, however, is calculated as given by the same equation below:

For a typical accelerometer, the sensitivity is about 1024 counts per “g” unit of gravity. Thus, the digital output can be seen in the table given inFIG. 5, wherein an angle of zero degrees results in the same “zero g” sensor position and results in an output value of 2048 counts. An angle of 30 degrees with a sensitivity of 1024 bits/g results in an output value of 2560 counts. An angle of 60 degrees with the same sensitivity results in an output value of 2935 counts. The entire 360 degree output response is given in the table ofFIG. 5in 30 degree increments. The digital output value is used to calculate the absolute positions of both the keyboard and the display, and then the relative position therebetween. This relative position calculation is used to control various operating modes of the clamshell device, which are listed in detail below.

It can be seen in tables ofFIG. 4andFIG. 5that the output value is the same for 60 degrees as it is for 120 degrees due to the nature of the sine function. As such, it is impossible to determine the relative angle of the display and keyboard using a single axis. Using a three axis device, we can calculate the relative tilt angles for the X, Y and Z axis. With this data, the position of the accelerometer with respect to horizontal can be determined.

Referring now toFIG. 6, the tilt angle calculation using three axes is shown. The formulas for α, β and γ are given inFIG. 6, wherein Alpha is equal to the tilt angle of the X-axis with respect to horizontal. Beta is equal to the tilt angle of the Y-axis, and Gamma is the tilt angle of the Z-axis with respect to horizontal. Ax, Ay, and Az are the accelerations measured along the X, Y, and Z axes, respectively, wherein:

Referring now toFIG. 7, further analysis of the position between the keyboard and the display of a clamshell device is given. A clamshell device in, for example, a closed mode of operation is shown in the upper part ofFIG. 7, wherein a first portion702with a first accelerometer708, and a second portion704with a second accelerometer710, are coupled together with a hinge706. A zero tilt angle for the X-axis is measured for both accelerometers for the device in this position. A −90 degree Z-axis tilt angle is measured by first accelerometer708, and a +90 degree Z-axis tilt angle is measured by the second accelerometer710. Knowing the fixed locations and orientations of these accelerometers in the system, it can be determined that the clamshell device is closed. A clamshell device in, for example, a partially open mode of operation is shown in the lower part ofFIG. 7, wherein a first portion702with a first accelerometer708, and a second portion704with a second accelerometer710, are coupled together with a hinge706. A −15 degree X-axis tilt angle is calculated for both accelerometers for the device in this position, along with a −75 degree Z-axis tilt angle for accelerometer708, and a +75 degree Z-axis tilt angle for accelerometer710. Using this information it can be determined that the relative position of the display to the keyboard is 30 degrees. How the tilt angle is translated into controlling various operating modes is explained below with respect toFIGS. 8-12.

Referring now toFIG. 8, a shutdown or standby mode is shown for a clamshell device having a first portion802with an accelerometer808and a second portion804with an accelerometer810. The algorithm for the shutdown or standby mode is as follows:

IFThe X-Axis of 808 is equal to the X-Axis of 810ANDThe Z-Axis of 808 is equal and opposite sign of Z-Axis of 810ANDThe X-Axis of 808 is +/−10 degreesTHENThe system is ‘flat’ and can be placed into a sleep or standby mode.ELSE

The device is tilted greater than 10 degrees and should be put into a ‘safe’ power down mode for carrying.

Referring now toFIG. 9, a partial shutdown or power saving mode is shown for a clamshell device having a first portion902with an accelerometer908and a second portion904with an accelerometer910. The algorithm for the partial shutdown mode is as follows:

The display is tilted toward the keyboard and can not be accurately viewed. The system can be placed in a standby/sleep state OR the LCD backlight can be turned off to conserve power while keeping the rest of the system in a full-on state.

Referring now toFIG. 10, a normal operating mode is shown for a clamshell device having a first portion1002with an accelerometer1008and a second portion1004with an accelerometer1010. The algorithm for the normal operating mode is as follows:

IFThe X-Axis of 1010 is +/−10 degreesANDThe Z-Axis of 1010 is +90 degrees +/−10 degreesTHENThe keyboard is ‘flat’ and can be used.IFThe X-Axis of 1008 is −60 degrees to −90 degrees (for example)ANDThe Z-Axis of 1008 is either positive or negativeTHEN

The Display is rotated open from 60 degrees up to 120 degrees and the system can be used in a full and normal manner as shown inFIG. 10.

Referring now toFIG. 11, a tablet operating mode is shown for a clamshell device having a first portion1102with an accelerometer1108and a second portion1104with an accelerometer1110. The algorithm for the tablet operating mode is as follows:

IFThe X-Axis of 1108 is equal to the X-Axis of 1110ANDThe Z-Axis of 1108 is equal to the Z-Axis of 1110THEN

The system is in ‘tablet’ mode with the display rotated ‘up’, and the device can be used in Tablet mode.

Portrait and Landscape detection can be used for the tablet by reading the X, Y and Z-axis values of1108. The largest negative value will determine the ‘down’ side of the device, and the display image can be rotated accordingly.

Referring now toFIG. 12, an unsafe carrying mode is shown for a clamshell device having a first portion1202with an accelerometer1208and a second portion1204with an accelerometer1210. The algorithm for the unsafe carrying mode is as follows:

The system keyboard is not flat, and the device can be put into a ‘safe’ carrying mode—with Hard Disk Drive retracted and powered down.

The present invention is not limited to any particular clamshell device, or to the display/keyboard embodiment shown herein. Other types of clamshell device would also take advantage of the principles of the present invention.

Although an embodiment of the present invention has been described for purposes of illustration, it should be understood that various changes, modification and substitutions may be incorporated in the embodiment without departing from the spirit of the invention that is defined in the claims, which follow.