Multi-pulse driving circuit for power integration load

Abstract

A multi-pulse drive circuit and method for a load are described. In one example, a driver circuit includes a switch and a storage capacitor coupled on one side to the switch and on the other side to ground, the storage capacitor configured to power the switch. The switch is configured to alternately connect and disconnect the storage capacitor with the load. A control circuit is coupled to the switch, the control circuit configured to control operation of the switch to provide a drive cycle to the load, the drive cycle having a series of pulses.

Description

Technical Field

[0001] The invention relates to a multi-pulse drive circuit. Background Art

[0002] One class of small mechanical systems uses shape memory alloys (SMAs) as motors, replacing solenoids, stators, linear actuators, or other types of motors. Applying an electric current to the SMA causes it to heat up and expand or contract, depending on its properties. Removing the current returns the SMA to its original size. The SMA is connected to a drive mechanism, rocker, lever, actuator, or transducer to provide the desired effect.

[0003] Shape memory alloy actuators use one or more SMA transducers to convert electricity into motion. This motion is used to drive a lever, rod, gear, or another mechanical actuator to cause the desired motion. For small devices, SMAs can achieve simpler, smaller, and lighter actuators than solenoids, stepper motors, linear actuators, or other electrical actuators. Another type of small mechanical system uses resistive heaters. Other types of systems use loads that integrate power over time. These systems can be powered by batteries or other low-power energy sources. Summary of the Invention

[0004] In particular, multi-pulse drive circuits and methods for power-integrating loads are described. In one example, a drive circuit includes a switch and a storage capacitor coupled to the switch on one side, the storage capacitor configured to supply power to the switch. The switch is configured to alternately connect and disconnect the storage capacitor from the load. A control circuit is coupled to the switch, the control circuit configured to control operation of the switch to provide a drive cycle to the load, the drive cycle having a series of pulses.

[0005] In some embodiments, the control circuit further includes a stop port for receiving a stop signal from the load, and the control circuit is configured to cause the switch to disconnect the storage capacitor from the load in response to the stop signal.

[0006] In some embodiments, the load has an expected range of motion, and wherein the stop signal is received when the load reaches the expected range of motion.

[0007] In some embodiments, the control circuit includes a request port configured to receive a pulse request signal, wherein the control circuit initiates a drive cycle in response to receiving the pulse request signal.

[0008] In some embodiments, each pulse in the series of pulses has a voltage greater than a minimum effective voltage of the load.

[0009] Some embodiments include a voltage detector coupled to the control circuit, the voltage detector configured to detect a voltage of the storage capacitor, and wherein the control circuit is configured to stop a pulse in the series of pulses when the detected voltage is lower than the minimum effective voltage of the load.

[0010] In some embodiments, the control circuit is configured to initiate a pulse in the series of pulses in response to the detected voltage being above a high drive threshold.

[0011] In some embodiments, the control circuit includes logic circuitry that starts a pulse when a storage capacitor voltage exceeds a threshold, a pulse request is received, and a stop signal is not received.

[0012] In some embodiments, the control circuit includes a time reference and logic for determining the duration of a pulse, the frequency of the pulse within a drive cycle, and the number of pulses within a drive cycle.

[0013] In some embodiments, the power source includes a battery pack having one or more batteries.

[0014] Some embodiments include a pre-charge circuit coupled on one side to a power source and on another side to a capacitor, the pre-charge circuit configured to charge the capacitor with power from the power source.

[0015] In some embodiments, the voltage detector is coupled to the pre-charge circuit, wherein the pre-charge circuit includes a switch between the storage capacitor and the power supply, and wherein the pre-charge circuit is configured to charge the storage capacitor when the detected voltage is below a capacitor fill threshold.

[0016] In some embodiments, the pre-charge circuit is configured to disconnect the switch to stop charging the storage capacitor when the detected voltage is above the capacitor fill threshold.

[0017] In some embodiments, the pre-charge circuit includes a resistor coupled at one end to the storage capacitor and at an opposite end to a power source, the resistor configured to limit current from the power source to the storage capacitor.

[0018] In some embodiments, the pre-charge circuit includes a DC (direct current)-DC converter or a current-limited continuous-time voltage regulator configured to control current to the storage capacitor.

[0019] In some embodiments, the load comprises a shape memory alloy wire coupled to the workpiece.

[0020] In some embodiments, the load includes a plurality of loads, and the drive circuit further includes a multiplexing switch coupled to the control circuit to connect the storage capacitor to different ones of the loads in response to the control circuit.

[0021] In an embodiment, a method includes: receiving a drive cycle request at a control circuit; connecting a storage capacitor to a load via a switch between the storage capacitor and the load in response to the drive cycle request, the storage capacitor being coupled to the control circuit, the control circuit operating the switch in a drive cycle having a series of pulses to provide power to the load; and enabling a precharge circuit to provide current to the storage capacitor during the drive cycle.

[0022] Some embodiments include ending the drive cycle in response to receiving a stop signal at the control circuit.

[0023] Some embodiments include detecting a voltage at the storage capacitor, wherein enabling the pre-charge circuit includes enabling the pre-charge circuit to provide current to the storage capacitor in response to detecting a voltage below a capacitor fill threshold, and disabling the pre-charge circuit to stop providing current to the capacitor in response to detecting a voltage above the capacitor fill threshold, and wherein operating the switch includes disconnecting the storage capacitor from the load in response to detecting a voltage below a low drive threshold, and reconnecting the storage capacitor to the load in response to detecting a voltage above a high drive threshold.

[0024] In an embodiment, an apparatus includes: means for receiving a drive cycle request at a control circuit; means for connecting a storage capacitor to a load via a switch between the storage capacitor and the load in response to the drive cycle request, the switch being coupled to the control circuit, the control circuit operating the switch in a drive cycle having a series of pulses to provide power to the load; and means for enabling a precharge circuit to provide current to the storage capacitor during the drive cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a block diagram of a driving circuit for a load according to embodiments herein.

[0026] Figure 2 is a single SMA wire used as a load according to the embodiments herein Figure 1 An example of a timing diagram of the operation of the driver circuit.

[0027] Figure 3 is an illustration of an example of an SMA multi-line driver coupled to a drive circuit according to embodiments herein.

[0028] Figure 4 is a diagram of an example SMA multi-line driver coupled to a drive circuit, wherein the drive circuit is coupled to a different one of a plurality of lines, according to embodiments herein.

[0029] Figure 5 is a signal timing diagram of example electrical signals involved in driving two time-division multiplexed loads according to embodiments herein.

[0030] Figure 6 is an example of a process flow diagram for operating a capacitor pre-charge circuit according to embodiments herein.

[0031] Figure 7 is an example of a process flow diagram of an example of operating a driver circuit according to embodiments herein.

[0032] Figure 8 is a block diagram of an example voltage detector-based control circuit according to embodiments herein.

[0033] Figure 9 is a block diagram of an example timing-based control circuit according to embodiments herein. DETAILED DESCRIPTION

[0034] Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0035] Figure 1 A drive circuit 100 for a load, such as a power integrating load, is shown. The power integrating load is shown as load 102. This load can be any combination of wires, SMA transducers, or any other power-controlled actuator or converter coupled to any mechanical device. In some examples, the load is a first SMA wire that pulls a lever in one direction and a second SMA wire that pulls the lever in the opposite direction at the end of the first wire's cycle. In other examples, the load can be any system that requires a certain amount of energy to operate. The load or mechanical device can also provide a signal to indicate when sufficient energy has been supplied to the load. The load can be a power integrating load because the load receives the supplied power and integrates the power in the voltage and current changes to perform the intended work.

[0036] Power supply 104 provides power to activate the load. The power supply is shown as a battery pack with two stacked cells, however, any other configuration may be used, or power may come from another device. The power supply is coupled to pre-charge circuit 106, which is coupled to capacitor voltage node 108. The capacitor voltage node is coupled to a first side of storage capacitor 110 and to ground 112 or other low-voltage node on the opposite side. Capacitor voltage node 108 is coupled to switch 118. Switch 118 is coupled to load 102. As shown, capacitor voltage node 108 is directly coupled to pre-charge circuit 106, storage capacitor 110, and switch 118. By distributing the power supplied to the load over time and assisting with capacitors rather than supplying power directly from the battery pack, some problematic characteristics of small or low-cost battery cells can be avoided. The current and voltage drops of the supplied power from the battery cells do not affect the load. The high series resistance of multiple battery cells connected in series also isolates the load.

[0037] The pre-charge circuit 106 can be as simple as a resistor to limit the pre-charge current (the resistor may include an enable switch in series), or as complex as a DC (direct current)-DC converter. A DC-DC boost converter allows the voltage to be increased for different battery types and numbers in the power supply, and allows the number of (cheap) batteries to be traded off to cover the additional cost of the converter. The pre-charge circuit can also be a step-down DC-DC buck converter. If the power supply 104 has a high internal resistance, for example, a stack of cheap batteries, the pre-charge circuit 106 may not require a resistor. The internal resistance of the battery pack acts as a resistor. The pre-charge circuit 106 can be eliminated. In some embodiments, the pre-charge circuit 106 also has an internal switch to connect and disconnect the power supply to the capacitor voltage node 108. In some examples, the pre-charge circuit can be implemented as a current source or current-limited continuous-time voltage regulator, or with a low-dropout (LDO) linear voltage regulator and a switch.

[0038] The switch 118 may be a simple switch, such as a low resistance field effect transistor, controlled by the control circuit 114 to couple the storage capacitor to the load in response to a signal received from an external control component at a pulse request port 116 of the control circuit 114. This switch 118 controls the connection between the capacitor voltage node 108 and the load 102. The control circuit 114 may also include a stop signal port 126 to receive a stop signal 122 from the load 102. The specific configuration of the inputs to the control circuit 114 may be modified to accommodate different implementations.

[0039] An optional voltage detector 124 is coupled to capacitor voltage node 108 to detect the voltage of storage capacitor 110. Such a voltage detector may be coupled to pre-charge circuit 106 and / or to control circuit 114. In some examples, voltage information is transmitted from voltage detector 124 to pre-charge circuit 106 and to control circuit 114. In some examples, voltage detector 124 compares the detected voltage to a threshold value. If the detected voltage is below the capacitor fill threshold, voltage detector 124 sends an enable signal to pre-charge circuit 106. Pre-charge circuit 106 charges storage capacitor 110 until the detected voltage is above the capacitor fill threshold. In some examples, a low fill threshold and a high fill threshold may be used to add some hysteresis around these thresholds to avoid continuous activation / deactivation of the pre-charge circuit due to, for example, noise or leakage current.

[0040] Voltage detector 124 may also be coupled to control circuit 114. If the detected voltage is above a high drive threshold, voltage detector 124 sends a drive-on signal to control circuit 114, and the control circuit may close switch 118 to connect storage capacitor 110 to load 102. This connection enables the energy stored in storage capacitor 110 to drive load 102. Additionally, pulse request signal 116 may, in some examples, be used by higher layers to request the initiation of a drive cycle. Control circuit 114 closes the switch only upon receiving pulse request signal 116. In some examples, a stop signal 122 or other mechanism may also be used to terminate a drive cycle, as explained in more detail below. The high drive threshold is the minimum voltage required by control circuit 114 in order to initiate a pulsed drive cycle to drive load 102. If the detected voltage is below a low drive threshold, control circuit 114 opens the switch to disconnect storage capacitor 110 from load 102. This disconnection prevents energy from being supplied to load 102. For many loads, there is a minimum effective voltage required for the supplied energy to have the desired effect on load 102. If the power supplied by the storage capacitor does not meet this minimum voltage, any energy from the storage capacitor will not have the desired effect.

[0041] The load 102 responds to a single long pulse with sufficient voltage and current to cause the load to produce the desired movement. This operation requires a capacitor with sufficient capacity to provide such a long pulse after being charged by the power supply. To reduce the size of the capacitor, according to some embodiments, the single long pulse is split into multiple smaller pulses. The storage capacitor is charged by the power supply during each pulse and between each pulse. This reduces the amount of current required by the battery cells, but allows the use of smaller and / or less expensive capacitors. In some embodiments, in one method, the drive circuit is operated to power the SMA wire actuator (e.g., a wire-based pump) using multiple small pulses per drive action. Small pulses allow for trade-offs in the number of battery cells, the energy of the battery cells, the size, or the chemistry of the storage capacitor. Utilizing small pulses can also reduce the required capacitance.

[0042] Figure 2 is for a single SMA wire as a load Figure 1 An example of a timing diagram of the operation of the driver circuit is shown in FIG. Figure 1 The pulse request 202 at the pulse request port 116 of the control circuit 114 initiates the sequence. In this example case, the power supply 104, which is a stack of two battery packs, is used to precharge the storage capacitor 110 to a sufficiently high voltage (V max )208 to deliver a certain amount of stored charge Q s and remains above the specified minimum value (V min )210. A sufficiently high voltage may correspond to a high drive threshold and also to a capacitor fill threshold. The specified minimum value may correspond to a low drive threshold that ends the pulse delivered to the load. The precharge current (I ch )212 may be predetermined or controlled by the pre-charge circuit 106 so that the current supplied from the battery pack does not exceed a specific value.

[0043] In principle, the size of the storage capacitor 110, V max With V min The difference between the load (I dr ) and the precharge current (I ch ) determines the frequency of the pulse. ch with I dr The ratio between the duty cycle of the pulses determines the duty cycle of the pulses. The number of pulses required (n) is determined by the total amount of energy required by the load (e.g., SMA wire) to complete its action or operation. These parameters can be configured into the control circuit 114 as predetermined parameter values, such as pulse width, timing, and number, or can be determined in whole or in part by the operation of the control circuit 114 and the voltage detector 124.

[0044] Initially, a pulse request 202 is received by the control circuit as a single pulse. The shape and configuration of the pulse can be adapted to suit different loads and different uses of the drive circuit and the load. In response to the pulse request 202, the control circuit turns on a first pulse 204 that connects the storage capacitor directly to the load, such as an SMA wire, a resistive wire, or other load, such as a power integrating load. With V above the high drive threshold, the storage capacitor is directly connected to the load. max The storage capacitor voltage, starting at 208 , begins discharging 222 to the load 102 with a first pulse 204 at time 220 .

[0045] After the switch 118 is connected, the storage capacitor voltage detected by the voltage detector 124 will begin to drop. Once the storage capacitor voltage drops below V max 208 or another capacitor fill threshold, the pre-charge circuit 106 is enabled and begins to refill the charge to the storage capacitor, such as through the positive current I ch 212. When the voltage of the storage capacitor drops to the low drive threshold V at 224 min When C sto The voltage of the storage capacitor at 226 reaches the maximum specified value (V max ), the control circuit 114 re-enables the switch 118 with a new pulse at 236. The pre-charge circuit can be disabled at 232 and then re-enabled almost instantaneously at 228 when the voltage of the storage capacitor drops. The capacitor fill threshold can alternatively be set just above the high drive threshold so that the pre-charge circuit remains on during each pulse until the end of the drive cycle at 242.

[0046] The square wave shape of the pulses 204, 236 at the control circuit does not indicate the form of the voltage delivered to the load, but rather the duty cycle of the switch connecting the storage capacitor to the load. The voltage delivered to the load is more like the downward portion 222 of the sawtooth wave of the storage capacitor voltage. This represents the voltage at the capacitor voltage node 108.

[0047] The operation of connecting and discharging the storage capacitor into the load while recharging the storage capacitor is repeated until a stop signal 240 is detected. The stop signal can be used to indicate that the wire or other load has reached its expected range of motion or expected temperature, but can also be constructed by a fixed or calculated time. The storage capacitor is recharged at 242 using current at 246 from the power supply to be ready for the next cycle. When the storage capacitor is fully charged, for example, when the storage capacitor voltage at the capacitor voltage node is greater than the capacitor fill threshold, the pre-charge circuit 106 disconnects the power supply from the storage capacitor at 248, and the system is placed in a parked state until the next pulse request is received. The pre-charge circuit 106 can remain active to keep the storage capacitor charged and ready for the next drive cycle.

[0048] As shown, a train of pulses 204, 236 is used to handle a single pulse request 202. This driver circuit delivers these pulses to the load without requiring a pulse request for each pulse. In practice, as the driver circuit performs its intended function over time, multiple pulse requests will likely occur within a much larger time window. The same driver circuit can be coupled to different loads, such as different SMA transducers, different resistive wires, different mechanical devices, and the like. In one example, a second SMA wire is coupled to the same driver circuit via a switch (not shown) that determines which wire is coupled to the storage capacitor. Both wires can be energized by the same storage capacitor because they are energized at different times. For an oscillating lever or rocker where one wire is pulled in one direction and the other in the opposite direction, power to the two wires can be interleaved.

[0049] In the context of a mechanical actuator, there is a relationship between the power available from the battery pack, the power that can be supplied by the storage capacitor, the duration and frequency of the pulses to the SMA transducer, and the physical properties of the shape memory alloy transducer. The duty cycle of the pulses 204, 236 is proportional to the pre-charge current 212, which is directly related to or the same as the current supplied by the battery pack. While a large number of smaller pulses can deliver the same power using a smaller capacitor, there may be a lower limit on these pulses because the SMA transducer may not be fully energized. The choice of components and the timing of the system's operations can be selected to suit the specific mechanical actuator and its power requirements to minimize cost, weight, or volume or to meet another design goal.

[0050] In some cases, Figure 2 The operation of the pre-charge circuit 106 and the control circuit 114 can be achieved by a common drive circuit clock (not shown) coupled to the pre-charge circuit 106 and the control circuit 114. A separate timing circuit can be provided to control the switch. The power supply 104, the storage capacitor 110 and the load 102 can be characterized in pre-production testing. Appropriate timing parameters can then be set for the pre-charge circuit 106 and the control circuit 114 to obtain Figure 2 A stop signal 122 may also be generated based on timing developed in the same pre-production testing.

[0051] In some examples, during operation of the driver circuit, the relative voltage is determined by voltage detector 124. Pre-charge circuit 106 and control circuit 114 operate based on the detected voltage. This allows the driver circuit to operate consistently despite battery pack degradation and without compensating for production variations in components.

[0052] As shown, pulse request 202 causes pulse 204 to be initiated at the control circuit. The control circuit can be configured to only generate a pulse when the detected capacitor voltage is above V max The control circuit continues the pulse until the storage capacitor voltage reaches V min 224, and disconnect the connection to the load. The control circuit may then continue to monitor the storage capacitor voltage and when the storage capacitor voltage again reaches V at 226 max When the voltage at the storage capacitor is reached, the control circuit closes the connection to the load. In this way, the length of each pulse 204, 236 is determined by the voltage at the storage capacitor. The capacitance of the storage capacitor and the characteristics of the load can vary, and the voltage detector will allow the system to compensate. Although this voltage is affected by many different characteristics of the drive circuit and the load, the control circuit automatically compensates for these and any changes in the characteristics of the drive circuit and the load over time by detecting and responding to the storage capacitor voltage.

[0053] Similarly, the precharge circuit 106 can also be configured to function in response to the voltage of the storage capacitor 110. As shown, when the storage capacitor is at V max 208, the precharge circuit does not provide current 212 to the storage capacitor. This is the initial state before the pulse request 202 and after the stop signal 240. When the storage capacitor drops below V max , then the precharge circuit begins charging the storage capacitor at 212. In this way, the operation of the precharge circuit 106 and the control circuit can be controlled by the voltage detector 124 at the capacitor voltage node 108.

[0054] As mentioned, the voltage supplied from the capacitor voltage node to the load can be part of a sawtooth waveform, with the downward slope 222, 228 of each sawtooth coupled to the load. In particular, in example embodiments where sufficient energy / heat conservation is in place, a power integrating load, such as an SMA wire, absorbs this energy almost completely, along with the longer constant voltage pulse, provided the applied voltage does not fall below a certain minimum voltage. Therefore, no smoothing circuit is required. The load is a power integrating load because it has sufficient capacitance and inductance to utilize the uneven power supplied and integrate the power internally through the load's inherent capacitance and inductance or other physical properties. In some examples, the power integrating load includes internal smoothing circuitry. For other applications, a smoothing circuit (not shown), such as an inductor, resistor, etc., can be added between the control circuit 114 and the load 102.

[0055] Figure 3 FIG2 is a diagram of an example SMA multi-wire actuator coupled to a drive circuit. The SMA actuator has a first workpiece 312 coupled to a first SMA wire 308 and a second workpiece 314 coupled to a second SMA wire 310. The first workpiece 312 is coupled by being directly or indirectly attached to the first SMA wire 308. The first SMA wire 308 contracts to move the first workpiece. In this example, when the first SMA wire 308, attached to the left side of the first workpiece 312, contracts, the first workpiece 312 translates laterally to the left as shown in the figure. The second workpiece 314 is coupled by being directly or indirectly attached to the second SMA wire 310, which contracts to translate the second workpiece 314 laterally to the left as shown.

[0056] While a simple lateral motion is shown as an example, the first SMA wire 308 and the second SMA wire 310 can be coupled to other structures to enable a different motion or multiple different motions to occur. There may be more or fewer wires and workpieces. The first workpiece 312 can be attached to the second workpiece 314 directly or through a mechanism for performing work on the workpiece (not shown). In addition to or in lieu of one of the wires, the system may include springs and other mechanical components. The SMA wires 308, 310 are coupled to the drive circuit 304 via the switch 306. The drive circuit is powered by the power supply 302 and is coupled to the controller 316. In an embodiment, the controller generates the pulse request and may have other communications with the controller.

[0057] In this example, the load includes a first shape memory alloy wire 308 for driving a workpiece 312 and a second shape memory alloy wire 310 for driving a workpiece 314. A switch 306 coupled to the drive circuit 304 is used, and the switch, in response to a control circuit, connects a storage capacitor to different ones of the loads. Pulses can be interleaved by the switch, which multiplexes the drive cycles of the pulses. The SMA wire pulls the workpiece when energized. As shown, the switch 306 is coupled to the second SMA wire 310 and contracts to move the second workpiece 314 to a position sensor 332 that generates a stop signal 334. In this example, the contact 320 and the stop sensor 322 can be considered circuit nodes that short when touched. The short between the two networks can be used as a closure of the switch to engage the stop signal 324. The switch 306 is disconnected from the first SMA wire 308, and therefore the first workpiece 312 is not pulled to the position sensor 322. The first workpiece can be pulled to the right in the figure by another SMA wire, a spring, or any other suitable force source.

[0058] In this specification, the SMA wire is referred to as a power-integrating load from the perspective of the electrical components of the driver circuit 304. However, a different load, including a resistive wire, can be used to act as the heater element, or a combination of different power-integrating loads can be used. The first workpiece 312 and the second workpiece 314 represent workpieces from the perspective of the SMA wire. These workpieces can be any suitable workpiece having any suitable mechanical structure. For resistive heaters, the workpiece can be a substance to be heated or any other suitable workpiece.

[0059] Figure 4 3 is a diagram of an example SMA multi-wire driver coupled to a drive circuit, wherein the drive circuit is coupled to different wires in the plurality of wires. Thus, the workpiece is moved by the SMA wires. A first workpiece 312 has a contact 320 attached directly or indirectly to the first workpiece 312. When the contact reaches a position sensor 322, a stop signal 324 is generated. Figure 3 In , the first workpiece contact member 320 is displaced from the position sensor 322 and no stop signal 324 is generated. Similarly, in Figure 3 In FIG, the second workpiece 314 has a contact member 330 that contacts a position sensor 332 to generate a stop signal 334. Figure 4 , the second workpiece has been moved away from the position sensor by the force of a spring, SMA wire, or another component, and no stop signal 334 is generated. The contacts and position sensor illustrate the electrical connections used when the workpiece has reached the end of its intended range of motion; however, any other type of sensor may be used. Another sensor may be used to determine movement in the opposite direction.

[0060] The SMA actuator, timer, motion sensor, or any other suitable component or sensor may also be used to generate a stop signal 324, 334, for example, when the first workpiece 312 has reached its intended range of motion. When the first workpiece 312 has completed the drive cycle of the SMA actuator, the stop signal 324 is coupled to the drive circuit 304 to end the drive cycle of the first SMA wire 308. The drive circuit 304 ends the drive cycle by no longer energizing the first drive wire 310. In some embodiments, the drive circuit then energizes another SMA drive wire to drive the first workpiece 312 back to the desired range of motion. Figure 3 of the parking position or effect another movement.

[0061] As shown, the switch 306 is coupled to the first SMA wire 308, which contracts to move the first workpiece 312 to the position sensor 322, which generates a stop signal 324. The switch 306 is disconnected from the second SMA wire 310, and thus the second workpiece 314 is not pulled to the position sensor 332.

[0062] Figure 5 is driving two time-division multiplexed loads (e.g. Figure 3 or Figure 1 1 . A signal timing diagram of example electrical signals involved when operating an SMA drive circuit (e.g., an SMA drive circuit). Other types of loads can be driven in the same manner. Top line 502 is a pulse request signal from controller 316 to the drive circuit. Second line 512 is a lower SMA wire driver signal 516, 518 generated by the drive circuit 304 and used to energize the lower SMA wire 310. Drive signal pulses 516 are generated by the drive circuit in response to receiving lower pulse requests 504, 506. As the SMA drive wire pulls the workload, the workload reaches the end of its drive cycle and triggers a stop. Third line 522 is a stop signal 524, 526. Stop signals 524, 526 at the drive circuit cause the drive circuit to end the SMA wire drive cycle of pulse signals 516, 518. The stop signal may persist for a longer or shorter time as the lower SMA wire relaxes to its starting condition.

[0063] Upper pulse requests 508, 510 are generated by the controller and sent to the drive circuit to drive the upper SMA wire 308. In response, the drive circuit generates the correct SMA wire drive signals 534, 536 shown on the fourth line to energize the correct SMA wire in response to the pulse request. The upper workpiece is driven by the upper SMA wire until it comes to a stop and a stop signal 544, 546 is generated. The stop signal 544, 546 causes the drive circuit to stop energizing the upper SMA wire 308. When the upper SMA wire relaxes, another lower pulse request begins a new drive cycle.

[0064] The drive signal pulses are shown as examples. There may be only upper drive cycle pulses or only lower drive cycle pulses. The pulses may be spaced or numbered as appropriate for the properties of the SMA actuator. The SMA actuator shown may be modified or interchanged for any other suitable SMA actuator and any other suitable workpiece or combination of workpieces. The SMA transducer may be a wire of any suitable length and shape or of various material configurations.

[0065] Figure 6 is an example of a process flow chart for operating the capacitor pre-charge circuit described above. At 602, the voltage at the storage capacitor is detected. This can be performed during the entire operation of the driver circuit. The detected storage capacitor voltage V STO With a low capacitor fill threshold V LO FILL The storage capacitor voltage is compared to determine whether to charge the storage capacitor. If the storage capacitor voltage is not below the low capacitor fill threshold, the process returns to the beginning. The storage capacitor may lose charge due to current leakage or through connection to the drive circuit. Specifically, when the storage capacitor discharges into the SMA actuator, the storage capacitor voltage provides information that can be used to operate the pre-charge circuit. At 604, if the storage capacitor voltage is below the low capacitor fill threshold, the pre-charge circuit is coupled to the storage capacitor. In response to detecting the voltage below the low capacitor fill threshold, the pre-charge circuit provides current to the storage capacitor to charge the storage capacitor.

[0066] At 606, the detected storage capacitor voltage V STO With a high capacitor fill threshold V HI FILL . If the detected storage capacitor voltage is below the high capacitor fill threshold, the process loops back and the comparison is performed again while the storage capacitor continues to be charged by the power supply. If the storage capacitor voltage exceeds the high capacitor fill threshold, then at 608 the pre-charge circuit is disabled or disconnected from the storage capacitor at 608, and the process loops back to the beginning until the detected voltage again falls below the low capacitor fill threshold. In summary, the pre-charge circuit can autonomously receive the detected storage capacitor voltage and be disabled at 608 to stop providing current to the storage capacitor in response to detecting a voltage above the high capacitor fill threshold. The pre-charge circuit can also provide current to the storage capacitor at 604 in response to detecting a voltage below the low capacitor fill threshold.

[0067] Figure 7is an example of a process flow chart for operating the driver circuit described above. The process begins at 702, where a drive cycle request is received at a control circuit of a driver circuit, such as a line driver. The process returns until a drive cycle request is received. At 704, if a drive cycle request has been received, the detected storage capacitor voltage V STO With high drive voltage threshold V HIDRIVE This test is to determine if the storage capacitor has sufficient stored charge to drive the load. If the detected storage capacitor voltage exceeds the high drive voltage threshold, the control circuit responds to the pulse request by connecting the storage capacitor of the driver circuit to the load (e.g., an SMA wire for an SMA actuator) at 706. The storage capacitor discharges to the SMA actuator. In an embodiment, the storage capacitor is directly coupled to the SMA material without any need for filtering, smoothing, or other circuitry.

[0068] At 712, the storage capacitor voltage detected during the discharge of the storage capacitor to the SMA actuator drops below the low voltage drive threshold V LO DRIVE As long as the storage capacitor is coupled to the load, the charge on the storage capacitor is reduced. After a certain time, in response to the comparison at 712, the storage capacitor is disconnected from the SMA driver at 714 in response to the detected storage capacitor voltage being below the low voltage drive threshold. The storage capacitor may be connected to the load through the pre-charge circuit and Figure 6 The process receives current to charge the storage capacitor before and after disconnecting the load. The process returns to the test at 704 to determine the detected storage capacitor voltage V STO Is it higher than the high voltage drive threshold V HIDRIVE If yes, then a new pulse is started by connecting the storage capacitor to the load at 706. If no, then the process waits until the detected storage capacitor voltage increases further.

[0069] In this example, the current from the pre-charge circuit is less than the current to the load. Therefore, even while being charged by the pre-charge circuit, the storage capacitor is also being discharged by the load. After the load is disconnected at 714, the pre-charge circuit can increase the charge on the storage capacitor until the storage capacitor voltage is greater than the high voltage drive threshold at 704. At 706, the storage capacitor is coupled to the load and a new drive pulse begins, thereby discharging the storage capacitor again. The process from 704 to 714 can be repeated to provide power to the SMA actuator by connecting the storage capacitor, disconnecting and recharging the storage capacitor, and reconnecting the storage capacitor until the SMA actuator has performed the requested work.

[0070] For some SMA actuator configurations, the drive circuit may also be coupled to a stop signal. The process may include receiving the stop signal at the control circuit at 708 and ending the drive cycle by disconnecting the storage capacitor from the load in response to the stop signal at 710. The process then returns to the start at 702 to wait for another drive cycle request.

[0071] Figure 6 process and Figure 7 The process is only achieved by storing the capacitor voltage V STO Connection. Two processes may operate independently of each other, or there may be an explicit association through a shared controller, timer, event manager, etc.

[0072] Figure 1 The control circuit 114 operates the switch 118 that connects the storage capacitor 110 to the load 102. Figure 3 As shown in FIG, there may be multiple switches for multiple loads. The control circuit receives the storage capacitor voltage V from the voltage detector 124. STO , receives the pulse request signal 116 and receives the stop signal 122 as inputs. The control circuit operates the switch 118 based on these inputs. The control circuit can take any of a number of suitable forms, and one such form is Figure 8 Shown in.

[0073] Figure 8 FIG2 is a block diagram of an example voltage detector-based control circuit 800 suitable for use with various embodiments described herein. The control circuit 800 generates a drive on / off signal 826 to set the state of a switch or gate 802. The switch or gate 802 alternately connects and disconnects a storage capacitor 806 from a load 804. The voltage detector-based control circuit 800 is coupled to a voltage detector 810 that detects the voltage of the storage capacitor 806 in any suitable manner. The voltage detector sends a voltage signal 812 to a high voltage drive threshold comparator 814 and to a low voltage drive threshold comparator 816. Although the signal switch or gate 802 is shown for a single load 804, multiple switches and multiple loads may be present to accommodate different configurations.

[0074] Alternatively, the comparator can be incorporated into the voltage detector. If the voltage signal 812 exceeds the high voltage drive threshold, the high voltage drive threshold comparator 814 generates a high drive signal 818 that is sent to the latch 822 and sets the latch 822 to high. If the voltage signal 812 is lower than the low voltage drive threshold, the low voltage drive threshold comparator 832 sends a clear signal 820 to the latch 822 to reset the latch 822 to low. From the beginning of the pulse when the latch is set to high to the end of the pulse when the latch is reset to low, the latch 822 controls the transmission of each pulse. The duration of the pulse is controlled by the voltage of the storage capacitor 806 measured by the voltage detector 810, and is therefore determined by the characteristics of the capacitor, the characteristics of the load, the path between the capacitor and the load, the voltage drive threshold (high and low) and the magnitude and operation of the precharge current.

[0075] The control circuit 800 also receives a pulse request signal 830 at a second latch 832. The pulse request signal 830 sets the latch 832 high, which generates a request signal 834 to the AND gate 824. The AND gate receives the request signal 834 and the latch 822 signal output. If both the request signal 834 and the latch 822 signal output are high, the AND gate sends a drive signal 826 to the switch OR gate 802 to connect the storage capacitor to the load. If either input is not high, meaning that the storage capacitor has insufficient voltage or a drive cycle is not requested (or the drive cycle has ended), or both, the drive signal 826 is low, and the switch OR gate 802 disconnects the storage capacitor 806 from the load 804.

[0076] The control circuit 800 also receives a stop signal 836 from the load, a timer, or another component. The stop signal 836 indicates the end of the drive cycle, for example, because the load or attached workpiece has reached its expected range of motion or temperature. The stop signal 836 is applied to the second latch 832 to clear the second latch 832 and reset the output request signal 834 to low. This ends the drive signal 826 at the AND gate 824. The example logic-based control circuit can be modified to have more or fewer inputs and outputs, and any signal indicated as high can be converted to low by appropriate adjustments to the components herein. The described logic can be implemented using different logic circuits or different types of logic circuits, and can alternatively be implemented as firmware or software in a suitable integrated circuit, or even implemented using alternative but equivalent analog building blocks.

[0077] Figure 99 is a block diagram of an example timing-based control circuit 900 suitable for use with various embodiments described herein. The control circuit 900 uses a time base 922 as a timing reference applied to counter logic 920 to determine the state of a drive signal 908. The drive signal 908 determines the state of a switch 902 that connects a storage capacitor 906 to a load 904. Although a single switch 902 is shown, multiple switches and loads may be present to accommodate different configurations.

[0078] The control circuit 900 also receives a pulse request 930 at the first port. The pulse request 930 indicates a drive cycle of pulses. The pulse request is received at the counter logic, which then generates a pulse train. The pulses are based on a time base 922 and stored parameters. The parameters may include the frequency of the pulses 924 (e.g., the duration between the start and stop of each pulse), the pulse width 926 (e.g., the duration between the start and stop of each pulse), and the number of pulses 928 (i.e., how many pulses are provided in response to a single pulse request). These parameters can be set by first characterizing the system of the storage capacitor 906, the load 904, and the power supplied to recharge the capacitor.

[0079] Counter logic 920 uses drive signal 908 to operate switch 902 to generate pulses with stored parameters of pulse frequency, pulse width and number of pulses to realize single drive cycle. Counter logic can adopt any suitable form with counter, gate and other components to operate drive signal 908. In some examples, instead of or supplementing the number of pulse parameters, a stop signal can be coupled to control circuit 900 at stop signal port 932 and applied to counter logic or applied to a separate gate to end the drive cycle. The output of the control circuit based on the voltage detector is similar to the output of the control circuit based on timing, and will cause a similar drive current to the load. The control circuit based on the voltage detector allows system operation to adapt to the changes and variations in the system components. The control circuit based on timing eliminates the cost of detectors and comparators and provides consistent and reliable drive signals. The control circuit based on timing can be more suitable for embodiments in which components can accurately characterize and remain stable within their expected service life.

[0080] The boundaries between the above operations are provided as examples. Multiple operations may be combined into a single operation, a single operation may be dispersed among additional operations, and the execution of operations may at least partially overlap in time. Furthermore, alternative embodiments may include multiple instances of a particular operation, and in various other embodiments, the order of the operations may be altered.

[0081] Although the operations of the methods herein are shown and described in a particular order, the order of operations of each method may be changed so that certain operations may be performed in reverse order, or so that certain operations may be performed at least partially simultaneously with other operations. In another embodiment, instructions or sub-operations of different operations may be implemented in an intermittent and / or alternating manner.

[0082] It should also be noted that at least some operations of the methods described herein can be implemented using software instructions stored on a computer-usable storage medium for computer execution. For example, an embodiment of a computer program product includes a computer-usable storage medium for storing a computer-readable program.

[0083] Alternatively, embodiments of the present invention may be fully implemented in hardware or in an implementation scheme containing hardware elements and software elements. In an embodiment using software, the software may include but is not limited to firmware, resident software, microcode, etc.

[0084] The connections discussed herein may be any type of connection suitable for transmitting signals or power from or to a corresponding node, unit, or device, including via an intermediate device. The connection may be shown or described as a single connection, multiple connections, a unidirectional connection, or a bidirectional connection. However, different embodiments may change the implementation of the connection. For example, a separate unidirectional connection may be used instead of a bidirectional connection, and vice versa. In addition, multiple connections may be replaced by a single connection that transmits multiple signals in serial or in a time-division multiplexed manner. Similarly, a single connection carrying multiple signals may be divided into various different connections that carry subsets of these signals. The term "coupling" or similar language may include direct physical connections or connections through other intermediate components, even if these intermediate components change the form of coupling from source to destination.

[0085] The described examples may be implemented on a single integrated circuit, for example, in software in a digital signal processor (DSP) that is part of a radio frequency integrated circuit (RFIC). The described examples may also be implemented in hardware in a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), or in other electronic devices. The described examples may be implemented in analog circuitry, digital circuitry, or a combination of analog and digital circuitry. Alternatively, the circuit and / or component examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. Alternatively, the examples may be implemented as software or code representations of physical circuitry or as logical representations convertible into physical circuitry, for example, in a hardware description language or any other suitable form.

[0086] It should be readily understood that the components of the embodiments generally described herein and illustrated in the accompanying drawings may be arranged and designed in a wide variety of different configurations. Therefore, the more detailed description of the various embodiments represented in the figures is not intended to limit the scope of the present disclosure, but is merely illustrative of the various embodiments. Although various aspects of the embodiments are presented in the figures, the figures are not necessarily drawn to scale unless otherwise indicated.

[0087] The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects as illustrative only and not restrictive. The scope of the present invention is, therefore, indicated by the appended claims rather than by the foregoing description. All variations that come within the meaning and range of equivalency of the claims are intended to be embraced within the scope of these claims.

[0088] References to features, advantages, or similar language throughout this specification do not imply that all features and advantages that may be realized with the present invention should be or are present in any single embodiment of the present invention. Rather, language referring to features and advantages should be understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of features and advantages and similar language throughout this specification may, but do not necessarily, refer to the same embodiment.

[0089] Furthermore, the described features, advantages, and characteristics of the present invention may be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize, in view of the description herein, that the present invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other cases, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present invention.

[0090] Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated.The scope of the invention should be defined by the claims appended hereto and their equivalents.

Claims

1. A drive circuit for a load, characterized in that: The circuit comprises: switch; a storage capacitor coupled on one side to the switch and configured to supply power to the switch, the switch being configured to alternately connect and disconnect the storage capacitor from the load; and A control circuit is coupled to the switch, the control circuit being configured to control operation of the switch to provide a drive cycle to the load, the drive cycle having a series of pulses.

2. The driving circuit according to claim 1, wherein: The control circuit additionally includes a stop port configured to receive a stop signal from the load, the control circuit causing the switch to disconnect the storage capacitor from the load in response to the stop signal.

3. The driving circuit according to claim 2, wherein: The load has an expected range of motion, and wherein the stop signal is received when the load reaches the expected range of motion.

4. The driving circuit according to claim 1, wherein: The control circuit includes a request port configured to receive a pulse request signal, wherein the control circuit initiates a drive cycle in response to receiving the pulse request signal.

5. The driving circuit according to claim 1, wherein: Each pulse in the series of pulses has a voltage greater than a minimum effective voltage of the load.

6. The driving circuit according to claim 5, wherein: Also includes: a voltage detector coupled to the control circuit, the voltage detector being configured to detect a voltage of the storage capacitor, and The control circuit is configured to stop a pulse in the series of pulses when the detected voltage is lower than the minimum valid voltage of the load.

7. The driving circuit according to claim 1, wherein: The control circuit includes logic circuitry that starts a pulse when a storage capacitor voltage exceeds a threshold, a pulse request is received, and a stop signal is not received.

8. The driving circuit according to claim 1, wherein: Additionally included is a pre-charge circuit coupled on one side to a power source and on another side to the capacitor, the pre-charge circuit configured to charge the capacitor with power from the power source.

9. A method, characterized in that include: receiving a drive cycle request at a control circuit; connecting the storage capacitor to the load via a switch between the storage capacitor and the load in response to the drive cycle request, the storage capacitor being coupled to the control circuit, the control circuit operating the switch in a drive cycle having a series of pulses to provide power to the load; as well as A precharge circuit is enabled during the drive cycle to provide current to the storage capacitor.

10. A device, characterized in that include: means for receiving a drive cycle request at the control circuit; means for connecting the storage capacitor to the load via a switch between the storage capacitor and the load in response to the drive cycle request, the switch being coupled to the control circuit, the control circuit operating the switch in a drive cycle having a series of pulses to provide power to the load; as well as Means for enabling a pre-charge circuit to provide current to the storage capacitor during the drive cycle.

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