Abstract:
A servomotor controller provides nut runner and other functions in a set of stackable modules. Extended-function modules can be added into and removed from the stack as needed. Destacking of closely spaced, wall-mounted controllers can be performed without demounting. Module assemblies are dripproof. Multiple sizes of nutrunner driver electronics and multiple keyboard and display options can be selected. A reprogrammable central processor can identify newly installed or removed features within a controller and reconfigure itself F accordingly. Stackable modules include Ethernet(®, multiple-bit I/O, and proprietary interfaces for many industries. The other modules communicate with the processor module via a backplaneless bus architecture. The central processor supports master/satellite group operation, whereby one controller unit can command multiple others, and whereby a higher-level system can command multiple controllers or multiple master/satellite controller groups.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to electronic apparatus modularization. More particularly, the present invention relates to stackable electronic modules for customizable servomotor controller configuration.  
       BACKGROUND OF THE INVENTION  
       [0002]     Existing servomotor controller products are used for many purposes, including providing precisely controlled power to fastening tools known in the art as nutrunners. Servomotor controller products are presented in a variety of packaging configurations, as determined by such factors as operational requirements, marketing strategies, and cost considerations. For example, some servomotor controllers are offered by manufacturers as standalone entities with fixed envelope sizes and fixed lists of features. Other servomotor controller products are offered with multiple levels of capability; for these products, it is common to provide a fixed package size and a customizable list of features, with capabilities and options, including upgrades, typically factory installed.  
         [0003]     While the above configurations and others are known and accepted in the marketplace, they retain drawbacks. Among these is the drawback that a controller receiving an upgrade is likely to be unavailable for use during an installation period. Other drawbacks include the risk that an error in the upgrade process may cause protracted loss of use, and that a warranty or calibration certification may be voided by the work. Another drawback is the likelihood that an upgrade, once installed in one unit, is seldom removed and installed in a different unit, so that upgrades are often effectively permanent. This can lead to hesitation to acquire added capabilities for individual controllers, particularly if an added capability is needed in a particular controller for a short term.  
         [0004]     The expense of having the upgrade performed is in some cases increased by the cost of shipping and the risk of hidden damage taking place during shipping.  
         [0005]     Servicing of servomotor controllers is likewise affected by the unitized construction typical of controllers. Component swapping as a troubleshooting method is slowed by the often closely configured envelope size. Modularization by function within a controller is not assured, so that good components may be replaced along with faulty ones. This can lead to increases in the cost of replaced components as well as in time and labor expended.  
         [0006]     Accordingly, it is desirable to provide a method and apparatus that allow an electronic servomotor controller or related device to be reconfigured repeatedly without disassembly of an enclosed chassis and without the associated risks of loss of use or added incurred cost. It is further desirable to facilitate maintenance by enhancing modularization and by simplifying repair procedures.  
       SUMMARY OF THE INVENTION  
       [0007]     The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments stacks a number of functional units, using a stacking-connector-based system bus for communication between units. Typical functional units can include displays, controls, and other operator interface elements, communication links to standard external devices, premises power access and conditioning, and servomotor controller functions sufficient to establish a useful standalone product. Functional units in some embodiments are capable of performing inquiries by way of the system bus to determine if additional units are presently installed and of adjusting display information and control functionality to integrate add-on units.  
         [0008]     In accordance with one embodiment of the present invention, a modular expandable controller is presented. The modular expandable controller includes a drive module having connectors configured to provide connections to a tool, a first housing containing at least in part the drive module, a controller module in communication with the drive module and configured to send a control signal to the drive module, and a second housing containing at least in part the controller module.  
         [0009]     In accordance with another embodiment of the present invention, a modular expandable controller is presented. The modular expandable controller includes modular driving means having connectors configured to provide connections to a tool, first housing means containing at least in part the driving means, modular controlling means in communication with the driving means and configured to send a control signal to the driving means, and second housing means containing at least in part the controlling means.  
         [0010]     In accordance with yet another embodiment of the present invention, a method of assembling a modular controller is presented. The method of assembling a modular controller includes configuring a first function performed by a controller, implemented using electronic devices, encased in a first housing to form a module, configuring a second function performed by a controller, implemented using electronic devices, encased in a second housing to form a module, and mechanically and electronically connecting the modules together.  
         [0011]     There have thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.  
         [0012]     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as in the abstract, are used for the purpose of description and should not be regarded as limiting.  
         [0013]     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be used as a basis for the design of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an exploded perspective view illustrating servomotor controller modules according to an embodiment of the invention.  
         [0015]      FIG. 2  is a block diagram of a modular servomotor controller including multiple modules, and further showing internal functional blocks, intermodule connectors, and external interface connectors for the controller.  
         [0016]      FIG. 3  is a perspective view showing modules partially separated.  
         [0017]      FIG. 4  is an enlarged view of a hinge mechanism in accordance with the invention.  
         [0018]      FIG. 5  is a section view of a joined latch between generic modules.  
         [0019]      FIG. 6  is a section view of a joined latch between a controller module and a Servo module. 
     
    
     DETAILED DESCRIPTION  
       [0020]     The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention provides a modular servomotor controller electronics stack that permits functionality embodied in electronic devices housed within one or more stackable modules to be augmented by connecting additional modules. In other words, the controller can be given additional capabilities and features by adding modules. Some embodiments of the invention use a stacking connector system rather than a separate backplane to interconnect the functional modules.  
         [0021]      FIG. 1  is an exploded perspective view of a servomotor controller  10 , assembled from representative set of modules, namely a User interface module  58 , a Control Module  36 , and a Servo module  12 , provided with a mounting base  32 .  
         [0022]     The modules in this embodiment perform a series of functions associated with the features visible in this view. For example, the bottommost module in  FIG. 1 , which is the Servo module  12 , is shown with a power input port  18 . Interfaces to the Servo module  12  may further include a power switch  20 , a protective device  22  such as a fuse, circuit breaker, or ground fault interruptor (GFI), and, in some embodiments, features such as premises voltage selection. There is further provision for a Servo Motor Controller (SMC) connecting cable socket  26 , where the SMC cable socket  26  allows connection to an SMC cable  28  terminated at a nutrunner  30 .  
         [0023]     The Servo module  12  also provides a stacking interface connector  34 . In the embodiment shown, the Servo module interface connector  34  is a 48-pin female Deutsche Industrie Norm (DIN) standard connector, which is one of several connector styles suitable for such applications; alternatives may be used in some embodiments.  
         [0024]     The Servo module  12  shown has a power driver circuit to actuate nutrunner devices  30  in a particular power range. When the controller  10  is to be applied to nutrunners  30  in other power ranges, the Servo module  12  can be removed and a substitute Servo module  12  better suited to the power range can be installed in its place.  
         [0025]     The Servo module  12  shown is in some embodiments further provided with provision for mounting. Where mounting is used, the servomotor controller  10  can be attached to a vertical surface, so that the connectors are oriented downward, reducing exposure to contamination by fluids and particulates.  
         [0026]     For clarity, the invention is presented in the drawings with the mounting bracket  32  down. Terms such as “top” and “bottom” used herein refer to this orientation. However, in many installations, the “bottom” surface as shown herein would preferably be mounted to a wall or other vertical surface, with the module edges into which external cables are plugged pointing downward. This orientation can permit multiple controllers to be mounted in close quarters, can allow displays to be viewed readily, and can ease sealing and strain relief requirements on cables and connectors.  
         [0027]     It is further understood that the term “stack” refers to connecting modules  58 ,  36 , and  12  together as described. Actual stacking of modules  58 ,  36 , and  12  one on top of another of course only occurs when the controller  10  is in an attitude such as that shown in  FIG. 1 . When the controller  10  is oriented to other positions, such as being rotated 90 degrees for wall mounting, the modules  58 ,  36 , and  12  can still be connected to each other, but are not necessarily mounted one on top of another.  
         [0028]     Where a Servo module  12  is attached to a wall, the attachment may be direct, such as by provision of mounting ears on the Servo module  12  housing permitting application of bolts or the like, or may use an arrangement that can simplify installation and removal, such as a mounting base  32  as shown in  FIG. 1 . The mounting base  32  is configured to attach to a wall, as by bolting, and has hanging fingers  198  mateable with holes  192  in the Servo module  12 . The mounting base  32  further has a detent pin  194  over which a detent capture clip  196  on the Servo module  12  fits to provide positive retention. Other configurations are likewise possible in accordance with the invention. The configuration shown provides suspension of the servomotor controller  10 , both when properly clipped to the detent pin  194  and otherwise, preferably reducing risk of dropping and attendant damage.  
         [0029]     Into the Servo module  12  in the embodiment shown is plugged a Controller Module  36 . Electrical connection between the Servo module  12  and the controller module  36  is realized with mating 48-pin DIN connectors, of which the female  34  is visible in  FIG. 1 , and the male  38  is shown schematically in  FIG. 2 . The controller module  36  in the embodiment shown has bus connectors on its top surface that allow the controller module  36  to serve as the lowest module of an add-on-capable stack of control and support modules. The controller module top surface bus connectors in the embodiment shown are a first bus connector  40  and a second bus connector  42 , both of which, in the embodiment shown, are 96-pin DIN shells populated with female contacts (receptacles).  
         [0030]     The controller module  36  shown in  FIG. 1  includes additional connectors and features. These include a universal serial bus (USB)-compatible connector  44  that can drive at least a dedicated printer, and in some embodiments provides connectivity for configuring the servomotor controller  10  as a satellite unit. An RJ-11 (modular telephone style, configured as a serial port compliant with Electrical Industry Association (EIA) successor International Electrotechnical Commission (IEC) Recommended Standard (RS) IEC-232) connector  46  supports a variety of input/output functions such as printers, barcode scanners, transducers, and the like. An RJ-45 (Ethernet® 10/100baseT style) connector  48  is used in the controller module  36  for interface to a variety of proprietary communications protocols, such as Visual Supervisor®, the DiamlerChrysler Plant Floor Communication System (PFCS), and equivalent signals for General Motors (GM), Ford, and other manufacturers&#39; proprietary communication systems. A two-pin proprietary connector  50  provides backup power to the controller module  36 . The final connector shown in the controller module  36  embodiment is a 6-pin rectangular connector  52  of a proprietary style, which connector supports a proprietary bus, and may be used to connect the controller module  36  to selected external I/O devices with pin and protocol assignments supporting the proprietary bus.  
         [0031]     In addition to connectors, the embodiment shown includes switches, such as a multiple-position dual-inline-package (DIP) switch  54  that allows parameters to be selected by hand where automated detection may be ineffective or inconvenient, such as selection between PFCS and other proprietary communication protocols and the like, and a switch  56  enabling battery backup of clock and static memory functions.  
         [0032]      FIG. 1  further shows a Keypad/Display module  58  embodiment that sits atop a module stack. Most styles of Keypad/Display module  58  can provide at least minimal user interface, such as a torque readout display  60 , a keypad  62  for local input such as controlling the application of a nutrunner  30  to a load, and the like. Embodiments of a Keypad/Display module  58  that support added autonomy for a servomotor controller  10  can include numeric readouts or lamps showing additional information, keypads of varying complexity, such as to allow direct parameter entry, display panels for text and graphics in place of numeric readouts, and the like. Where no user interface is required at a controller  10 , a blank panel may be used.  
         [0033]     Any Keypad/Display module  58 , whether blank or not, may have additional connectors. Typical connectors for a Keypad/Display module  58  include an RJ-11 connector  64  (again configured as an IEC-232 serial port) to provide a detachable interface to a Visual Supervisor® master or another master control interface, and a Datakey® connector  66  (shown with a Datakey®  68  device inserted) for input of configuration or parameter information. Other or additional connector styles and functions may be used for some Keypad/Display module  58  embodiments.  
         [0034]      FIG. 2  shows a block diagram  70  of a modular servomotor controller into which functional modules in addition to those described above have been integrated. Typical connectors of the types listed above are shown in this diagram, as well as internal elements of the modules.  
         [0035]     Viewing again from the lowest module, the Servo module  12  accepts input power  18 , converts it using an AC/DC power supply  72 , and furnishes the power  74  to the 48-pin DIN interface connector  34 . The Servo module  12  further includes a motor controller power supply  76  and appropriate control logic  78 , likewise interfaced  80  to the 48-pin DIN connector  34 , and allowing the Servo module  12  to operate an output driver  82  that provides  84  power to drive the external nutrunner  30 . A typical nutrunner  30  has “smart” feedback that not only operates in closed loop mode but can also provide some in-device storage and processing of information, including digitization. The telemetry from the nutrunner  30  is shown fed back  86  to the 48-pin DIN connector  34 . Additional functions of the Servo module  12  may include self-status monitoring such as temperature sensing on heat sinks in the power supply  76  and output driver  82 .  
         [0036]     The controller module  36  embodiment shown includes a microprocessor-based controller  88  that accepts multiple inputs and provides output command signals to the output driver  82  in the Servo module  12  via the mating 48-pin DIN connector  38 . It is to be understood that the microprocessor-based controller  88  referred to herein may include at least one off-the-shelf monolithic integrated circuit microprocessor device  90  functioning as a master. The controller may be realized using, instead of or in addition to monolithic processor technology, any of a variety of other technologies. Among available technologies is the embedment of an intellectual property (IP) processor core, other IP entities, storage registers, glue logic, analog functions, and the like, into programmable logic devices (PLDs) using such technologies as field-programmable gate arrays (FPGAs). Functionality within the controller module controller  88  may be partitioned in some embodiments, so that, for example, bus interface, communication, display, and the like are controlled by a monolithic processor  90 , while the nutrunner driver is controlled by an embedded processor core within an FPGA  92 .  
         [0037]     The controller module  36  can include interfaces to substantially all of the pins in the Servo module connector  38  and the first and second bus connectors  40  and  42 , respectively, by means of access portals such as FPGA  92  pins. Use of appropriately chosen FPGA  92  devices as interfaces can allow some signal lines in the bus connectors  40  and  42  to be unassigned at the time of manufacture of the controller module  36  but to accept reprogramming without need to perform any mechanical disassembly. Some FPGA devices allow reprogramming after installation, allowing interface pins to be activated as, for example input-only, output-only, or bidirectional ports, and can include high impedance options that support bus sharing. FPGA devices in many cases support extensive logic and memory functionality in addition to bus interface and physical-layer port connectivity. Standard functions, such as bus and port interfaces, parallel-to-serial converters, digital comparators, and the like can be compiled into images and downloaded into previously installed FPGA devices.  
         [0038]     The controller module  36  is further shown to include a power supply  94  that accepts 24 VDC power  74  from the Servo module  12  and provides regulated power required by other modules on the bus. An additional source of power is provided in some embodiments by connecting the 24 VDC power  74  from the Servo module  12  to bus connectors  40  and  42 , so that individual modules on the bus can use local regulators for power at voltages they require.  
         [0039]     At least one pin on the Servo module 48-pin DIN connector and on each of the bus connectors  40  and  42  is in some embodiments dedicated to a link  96  to the controller module  36 , verifying that all connections are intact before attempting operation. This may be a logic signal connected to, for example, the 24 VDC power supply  72  in the Servo module  12 .  
         [0040]     Bus assignments for the two  96  pin DIN connectors  40  and  42  in a preferred embodiment include a proprietary parallel expansion bus with address, data, and semaphore signals, an implementation of the Serial Peripheral Interface synchronous serial bus (SPI-bus®) with a specified multimaster protocol, and an implementation of the Controller Area Network serial bus(CANbus®). Alternative bus embodiments may be entirely custom, may be chosen to replicate such recognized standards as VMEbusφ, PCI bus®, PC/104®, and the like, or may combine bus and timing functions from multiple bus standards. Bus designs may require daisy chain connections, such as for handling prioritized interrupts by multiple peripherals.  
         [0041]     The functions performed by the Servo module  12 , the controller module  36 , and the Keypad/Display module  58  in the embodiment shown provide functionality for a servomotor controller product. These functions include power, torque feedback, communication to standard interfaces, and the like. The partition of this embodiment into a processor module, a power driver module, and a display module provides a configuration that is useful, but is not limited to these functions only. It is to be understood that other partitioning concepts can be realized and may be used in some applications.  
         [0042]     Additional functions, used in some environments, are provided by separate modules that can be stackably joined to those discussed above. Typical modules for providing additional functions include those shown in  FIG. 2 , such as a Synchronous Data Link Control (SDLC®) module  98 , a Fieldbus® module  100 , and a multiple pin input/output (I/O) module  102 . Still other module types can be developed, provided a compatible and operational module set can be brought together. At least the module types described below are directly applicable to current usage in industry.  
         [0043]     The SDLC module  98  supports a form of Wide Area Network (WAN) that allows, among other capabilities, external control of a servomotor controller  10 . In a representative embodiment, multiple controllers  70  connected by SDLC can be controlled by one of their number serving as a master, while the rest are satellites coordinated with that master. This may apply, for example, to a manufacturing fixture in which several nutrunners are set up to operate together in driving a set of fasteners, such as in mounting a cylinder head to an engine block. Each satellite senses the applied torque on its own fastener, but all drive simultaneously using the timing and operational parameters from the master.  
         [0044]     The SDLC module  98  may communicate using, for example, IEC Recommended Standard IEC-485 on an input connector  104  and an output connector/termination port  106 . The SDLC module  98  may instead use Ethernet®, if preferred. SDLC module addresses can be unique and embedded on an SDLC circuit board  108 , dynamically assigned, or set by switches located on the same accessible face of the module  98  as the connectors  104  and  106 . The default interface for SDLC under IEC-485 is three shielded twisted pairs supporting a full-duplex, synchronous, multimastering, differential serial bus.  
         [0045]     The Fieldbus module  100  is intended for tailoring to a specific application. Many large-scale manufacturers have adopted proprietary communications standards, which in many instances support serial communication with specific physical, data link, and network layer characteristics such as baud rates, media access control (MAC) addresses, handshaking and error detection procedures, and the like. Information passed using a Fieldbus module  100  can include a variety of performance information for statistical analysis and process control, as well as command signals directed to individual servomotor controllers  10 . A Fieldbus module  100  may have a single circuit board  110  which, depending on requirements, is manufactured for a specific user, is a generic board with installed firmware, or is a generic board with dedicated FPGA functionality unique to that user. A Fieldbus module  100  may also have additional components besides a single board  110 , may have a bus mastering processor  112 , or may be a fixed-function satellite. Interface to a Fieldbus module  100  may include features such as indicators  114 , switches  116  for configuration selection, and connectors  118  for end-user preferred interfaces. The default interface for Fieldbus is a single shielded twisted pair supporting a multidrop serial bus with a scheduler-arbitrated multimastering protocol.  
         [0046]     An I/O module  102  is a multiple port data capture and data output device to manage data elements in an installation, wherein the data elements are not integrated into conventional operational control signals. A controller can in some embodiments benefit from provision of data input  120  and output  122  ports that can accommodate a variety of formats, amplitudes, timing characteristics, and the like. For example, a user may wish to provide, as part of a safety interlock circuit, a nutrunner actuating switch separate from the nutrunner tool  30  itself. An input from such a switch can be sent to an I/O module input  120  and processed by the controller module  36 . It is to be understood that more than one I/O module  102  may be needed in an application, so that the module can be provided with an automatic addressing scheme.  
         [0047]     An I/O module  102  may, in some embodiments, have a circuit board  124 , on which there are conventional port interface components  126  or their FPGA equivalents, to acquire and/or transmit data elements using a specific number of ports. A typical I/O module  102  may be equipped with eight digital inputs and eight digital outputs and provided with connectors  120  and  122  with sufficient pins to support each of the inputs and outputs as a dry contact, moderate current, or other configuration of signal, as suited to each embodiment.  
         [0048]     The input and output signal lines in an I/O module  102  may be individually configurable by the controller module  36  through one of the bus interfaces in the stacking 96 pin DIN connectors  40  and  42 , or may be configurable in groups of varying sizes, hard-wired with fixed parameters, or otherwise integrated into the servomotor controller  10  system.  
         [0049]      FIG. 3  shows a perspective view  124  of two generic module housings  126  and  128 , respectively, hinged open for examination of their mating surfaces  130  and  132 , respectively. Each of these housings uses two common-design clamshell-style housing halves  134 . Each housing provides enclosure for at least one printed wiring board (PWB) and includes a separate end plate  164  (see  FIG. 1 ) for mounting connectors, lights, switches, and the like. The housing further includes alignment pins  138  and receptacles  140  integral with its structure, which alignment pins  138  and receptacles  140  permit stacking to be accomplished with low position error. The alignment pins  138  in some embodiments protrude beyond the connectors, protecting both the connectors and any electronics contained within the housing.  
         [0050]     A housing in the embodiment shown uses a single design of shell half that serves for both top and bottom, because the alignment pin locations are chosen so that the exteriors of two correctly aligned shell halves  134  mate. Top  130  and bottom  132  surfaces include penetrations  142 ,  144 ,  146 , and  148 , respectively, for connector halves  150  and  152  on the top surface  130 , which mate with connector halves  154  and  156  on the bottom surface  132 . The bottom surface of an controller module  36  requires a variation of the housing penetration arrangement shown in order to provide for the single, smaller connector  34  joining the controller module  36  to the Servo module  12 . Similarly, the top housing half of a Keypad/Display module  58  does not need hinges and latches, and requires an arrangement of penetrations suitable to accommodating a selected keypad and display. The top housing half of a typical Keypad/Display module  58  can be sealed with, for example, an adhesive-backed film that allows viewing a display through a transparent window and operating the keypad by deflecting the surface of the film.  
         [0051]     Assembly of two housing halves  134  in the embodiment shown uses multiple screws  158  that keep the halves together. Alternative embodiments may be held together by integral detents, rivets, gluing or crimping of the shell halves, or other methods. The embodiment shown captures a PWB between the shell halves. Resilient sealing elements  160  provided between the shell halves seal the modules, while additional sealing elements  162  between modules seal the connector regions, as shown in  FIG. 1 . The sealing elements  160  provide a so-called drip-proof seal, which resists penetration by water, oils, solvents, and particulates. Downward orientation of the end plate  164  in some embodiments can reduce the requirement for leak resistant connectors.  
         [0052]     The embodiment shown further provides continuous mating lips  166  along the sidewalls  168 . The lips  166  may include interlocking elements, which elements can, in some embodiments, be of opposite sex on the two sides of each housing half  134  to allow the same design to be used for both halves of a module  126  and  128 . The interlocking elements may include pin and socket features, for example, to provide positioning to the resilient sealing elements  160 .  
         [0053]      FIGS. 4-6  show elements of the locking connection between adjacent modules  126  and  128 , respectively, as provided through a combination of hinging clips and latches.  FIG. 4  shows a male hinging clip  170  and a female hinging clip  172 , both of which are integral with each housing half  134 .  FIG. 1  shows one of a mated pair of alternate hinging clips  174  suitable for attachment to an extruded housing such as that of the Servo module  12 .  
         [0054]      FIG. 5  is a section view showing a latched pair of latch halves  176  and  178 , respectively, one of which is integral with each housing half in the modules  126  and  128 , respectively. One of the latch halves  178  in each assembled housing module  126  and  128 , respectively, includes a detent finger  180  backed by a spring  182  retained by a clip  184 . Assembly of adjacent modules  126  and  128  involves fitting the hinging clip halves  170  and  172  together on each side of the modules while keeping the modules spread apart, as shown in  FIG. 3 , then closing the modules together so that the guide pins  138  and receptacles  140  and the connectors mate. As the modules are being mated, the latch halves  176  and  178  align so that the detent  180  is first retracted by a bevel  186  of the opposite latch half  176 , then allowed to spring outward and engage the opposite latch half  176  in a strike  188 . Release of the latched elements can be realized in some embodiments by inserting an oblong object of suitable size and rigidity into the latch half  176  far enough to press the detent  180  free of the strike  188 .  
         [0055]      FIG. 6  is a section view of a latch between a Servo module  12  and an controller module  36 , wherein the latch  190  for the Servo module  12  is a separate, attached part rather than an integral component of a module housing.  
         [0056]     Typical latching provisions allow stacking of any number of modules, and allow removal and replacement of any module in a stack by releasing a single latch to withdraw the part of the stack including, for example, a module to be removed. Release of that module from the removed portion of the stack then allows reassembly without that module, replacement with another module, or addition of one or more modules.  
         [0057]     Some embodiments of the latching provisions according to the invention may require a release tool, such as the oblong object referred to above. Other embodiments may allow toolless disassembly by providing a built-in releasing device.  
         [0058]     It may be observed that the latching provision described permits a tool to be inserted above a mounted servomotor controller  10  to release modules, so that a controller  10  can be disassembled and reassembled without removing it from its mount.  
         [0059]     The description of the housing herein refers to forming the housing from an unspecified plastic. However, a variety of materials may be suitable for specific embodiments, including particular engineering plastics such as polyethers, polyesters, polystyrenes, copolymers, and the like, which may in some embodiments include fillers such as mica, fibers, or other materials, and which may be mixed or finished with materials supporting static dissipation, electrical conduction, magnetic shielding, or other properties. Forming options include injection molding, comolding of resilient elements, rotary molding, vacuum forming, and the like. The housing may also be cast, drawn, or otherwise formed from metals such as aluminum, zinc, steel, or suitable alloys. Alternative forming options for some metals and plastics include extrusion and impact extrusion.  
         [0060]     It is understood that the assembly technique indicated herein, in which each two modules are hooked together at one end using integral fittings, then pivoted sufficiently to align and mate one or more connectors of opposite sexes, the connecting elements of which are largely perpendicular to the largest face of each module, and finally latching the modules together, is one of many equivalent configurations for connecting modules. Others include configuring modules to mate with their large faces essentially parallel during the mating, then attaching the modules together using clips or equivalent holding devices. Another method for mating can use connectors whose mating direction is substantially parallel to the largest face of each module, with the modules first positioned offset, then slid together to mate, and with a suitable clip or latch holding the modules in the assembled configuration. Still another method can use noninserting signal transfer points between modules, such as ball grid array contacts, retracting pins against flat surfaces, fiber optic or transformer coupling, and the like, in which the joining of adjacent modules can use still another process. It is thus anticipated that any attachment method that can provide signal integrity and sufficient electrical power transfer to allow modules to function falls within the scope of the invention.  
         [0061]     Although an example of a stackable electronics package is shown configured as a servomotor controller supporting both local controls and multiple remote interfaces, it will be appreciated that other electronically controlled apparatus, such as welders, hoists, robotic positioners, mixers, pumps, materials handlers, materials processors, and numerous other devices, can be realized with such a configuration. Also, although the servomotor controllers described herein are useful to operate handheld and fixture-mounted nut spinners and related assembly tools in the automotive and electronics industries, they can also be used to operate other devices, electric powered or electrically controlled, both closed loop and open loop, and-can be applied in other manufacturing, production, and distribution industries as well as maintenance and service industries.  
         [0062]     The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.