When using the LC-2/20, programming will be more lengthy because data must be transferred using repeated get/put (word) transfer instructions.

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2 Table of ontents

3 The Stepper Motor Positioning Assembly (cat. no. 77-QA) allows programmable control of stepper motors by Allen-Bradley programmable controllers. Data and commands set to the stepper positioning assembly are converted to a pulse output for a user-supplied stepper motor translator which in turn provides the proper voltage and current to the stepper motor to produce the desired motion. The stepper motor positioning assembly consists of: Stepper ontroller Module (cat. no. 77-M) Pulse Output Expander Module (cat. no. 77-OJ) Field Wiring Arm (cat. no. 77-WB) One stepper controller module can control up to three pulse output expander modules. The system can be expanded modularly from one to three axes per I/O chassis by placing from one to three output expander modules in the chassis (Figure.). The pulse output expander modules can be located in any slot except the left-most slot and in any order in the I/O chassis.

4 Stepper motor positioning assemblies can be used in applications requiring more than three axes by using additional I/O chassis. The stepper assemblies can be distributed throughout the plant using remote I/O or data highway configurations. Typically, each axis can control a linear slide although not limited to that type of mechanical load. The axes can be controlled independently or control of the axes can be synchronized. Programming is based on a data block format where blocks of data can be manipulated using block format instructions such as file-to-file move and block transfer read and write instructions. The stepper positioning assembly can be used with any Allen-Bradley programmable controller

5 that has block transfer capability and an expandable data table except for Mini-PL-2 (cat. no. 772-LN3) and PL-2/2 (cat. no. 772-LP) Processors. When using the L-2/2, programming will be more lengthy because data must be transferred using repeated get/put (word) transfer instructions. The number of axes that can be controlled and the complexity of motion will depend on the memory available for the positioning program after the data table of the P processor has been expanded to store the data blocks.

6 The stepper positioning assembly can be wired for -axis operation with a stepper translator and motor as shown in Figure 2.. One stepper controller module can control up to three pulse output expander modules installed in the same chassis. When the application calls for 2-or 3-axis control, each additional expander module should be wired as shown in Figure 2.. No more than one stepper controller module can operate in an I/O chassis. Pulse output expander modules can be controlled manually by the use of switch inputs for stop, jog forward and jog reverse. The stop switch will cause output pulses to the corresponding axis to cease instantaneously. Jog switches are operational only when the corresponding axis is at rest.

7 Input switch contacts should be compatible with the voltage and current levels of the input circuits. The pulse output expander module will accept from TTL up to 3V D inputs, and inputs from the Allen-Bradley Encoder/ounter Module (cat. no. 77-IJ, -IK). Refer to section titled Module Specifications for additional input specifications. Each module in the I/O chassis including the processor or adapter module draws power from the I/O (chassis) power supply. Some modules require an additional power source. Power is supplied through the I/O chassis backplane from the V D I/O power supply. The stepper controller draws all of its power (.7A, maximum) from the I/O power supply. Each pulse output expander module requires a current of.8a maximum. These amounts (4.A maximum for a 3-axis system) should be totalled with the current requirements of all other modules in the chassis so as not to exceed the maximum output current of the I/O chassis power supply. Pulse output expander modules require an additional power source for switch inputs to the module and for pulse outputs to the stepper translator and motor. The power source can be separate input and output power supplies for one, two or three axes, a combined power source for each axis, or a combined power source for up to three axes. Each input switch draws ma maximum when closed. The maximum output current for the pulse output expander module is ma. Refer to section titled Module Specifications for additional information concerning the auxiliary power supply requirements. The supply voltage can be any value chosen from V D to 3V D required by the user-selected stepper translator and/or the switch input circuits. The variation in the D voltage level due to ripple should not exceed the input specification for the stepper translator because the supply voltage ripple appears at the output terminals of the pulse output expander module. Power supplies with mv peak-to-peak ripple can be used. However, check the translator input specification to ensure that the power supply specifications meet translator input requirements. The supply may require input filtering to guard against electrical noise. The Allen-Bradley Power Supply (cat. no. 77-P) is recommended when the stepper translator requires 3mA or less current.

8 The stepper translator and power supply convert digital information from the pulse output expander module into the proper voltage and current for the precise control of a stepper motor. For compatibility with the pulse output expander module, the translator must accept low true logic. The programmed maximum pulse rate from the pulse output expander module to the translator can be any value up to 2, pulses per second. The stepper motor converts electrical pulses into mechanical movements. The motor shaft rotates through a specific angular rotation for each pulse. The movement is repeated precisely with each pulse and the shaft rotates in fixed, repeatable increments. When a threaded shaft is used to drive a linear slide, the velocity, distance and direction of the slide can be precisely controlled. The stepper motor, stepper translator and translator power supply should be grounded to guard against electrical noise interference in accordance with the manufacturer s specifications and guidelines. Improper grounding can result in unwanted extra pulses occurring at the stepper translator and/or stepper motor. Prior to installation, a pulse output expander module must be configured to correctly interface with the corresponding stepper translator. Adjustments are made using six switch assemblies. The functions of the switches are summarized in Table 2.A and described in subsequent paragraphs. The switch assemblies are located on the module printed circuit board. They are accessed by removing the module clean up as follows:. Remove the four screws from the upper and lower edges of the labeled cover. 2. Remove the printed circuit board from the covers and set it solder-side down.

9 3. Locate the switch assemblies labeled S through S6 as shown in Figure 2.2.

10 4. Set the switches as described in the following sections. Some switches are labeled on/off. Others may be labeled open for the off position.. Reassemble the module. Start all four screws before tightening to facilitate alignment of the covers and printed circuit board. The output format that determines forward or reverse motion differs between translators. Therefore, the output terminals of the pulse expander module are user-selectable to match the required pulse input configuration of the translator. There are two basic translator input configurations. Some translators are designed to receive a pulse train at either one of two terminals, depending on the direction of rotation desired in the stepping motor. With this type of translator, a pulse train sent from the pulse output expander module to one of the translator terminals causes the stepping motor to rotate in the forward direction. An identical pulse train sent from the module to the other translator terminal causes the stepping

11 motor to rotate in the reverse direction. Output terminals on the pulse output expander module can be selected in accordance with Table 2.B. Other translators are designed to receive only one pulse train at a single pulse terminal. These translators usually have a separate terminal for direction information. If a high (or low) signal is sent to the direction terminal, the stepping motor rotates in the reverse direction. If a low (or high) signal is sent to this terminal, the stepping motor rotates in the forward direction. The rate of rotation (in either direction) is controlled by the pulse train at the pulse terminal. The status of the pulse output expander module s outputs when motion has stopped is also user-selectable. The settings of switch assembly S for the output format are summarized in Table 2.B. The choice of low true or high true logic for manual control of the pulse output expander module s hardware inputs is user-selectable. The S2 switch assembly settings are summarized in Table 2..

12 Each pulse output expander module must have its own (binary) address for communication with the stepper controller module. Allowable addresses are (), 2 () or 3 (). They can be set using switches and 2. Switch 3 is always off. No other combinations of the S3 switch assembly settings are valid. Refer to Table 2.D.

13 The choice of pulse output expander module output, either push-pull, current source (open emitter) or current sink (open collector), is user-selectable to best match the input characteristics of the stepper translator. PUSH-PULL-OPEN The push-pull output is compatible with many stepper translators. The expander module output is wired to the translator input as shown in Figure 2.. URRENT SOURE or URRENT SINK-OPEN When using the expander module as a current source or sink for the output pulses, it may be necessary to use a pull-down or pull-up resistor, respectively (Figure 2.3) Refer to the translator input specifications and installation instructions for correct use of this resistor if it is required.

14 The positive (+) and negative (-) terminals of the output power supply must be connected to the + D OUTPUT SUPPLY and OMMON terminals, respectively, of the module field wiring arm regardless of the choice of module output. AUTION: Avoid shorting any of the output terminals to ground, to the common terminal, or to the positive (+) terminal of a power supply. Damage to the module could occur. The settings of switch assemblies S4, S and S6 for the desired module output are summarized in Table 2.E. Set all switch positions in assemblies S4, S and S6 to the same output configuration. The stepper controller and pulse output expander modules have LED indicators. Their color and function are described in the following paragraphs. Three LED indicators are located on the upper front panel of the stepper controller module. They perform the following functions.

15 P OMMUNIATIONS FAULT (Red) This indicator is normally off. If a communications fault between the stepper controller module and the P processor is detected, or a stepper controller module hardware fault is detected, this indicator will illuminate. EXPANDER OMMUNIATIONS FAULT (Red) This indicator is normally off. If a communications fault between the stepper controller module and any one of the pulse output expander modules is detected, or a hardware fault in any one of the pulse output expander modules is detected, this indicator will illuminate. Important: If both red indicators illuminate simultaneously at power-up, the stepper controller module has a hardware fault. ATIVE (Green) This indicator illuminates unless a hardware fault on the stepper controller module is detected causing it to turn off. At power-up this LED will not illuminate until the P processor is in run mode. This indicator will flash on/off if, after power-up, an invalid expander address is detected, no expander module is present and/or another stepper controller module is detected in the same I/O rack. Five LED indicators are located on the upper front panel of the pulse output expander module (Figure 2.4). They perform the following functions: MODULE FAULT (Red) This LED is normally off. If an expander module hardware fault is detected, it will illuminate. OUTPUT PULSE RATE (Green) This LED is normally on or flashing at the output pulse rate whenever an output is present. STOP INPUT (Orange) This LED illuminates when a hardware stop input is asserted. JOG FORWARD (Orange) This LED illuminates when a hardware jog forward input is asserted. JOG REVERSE (Orange) This LED illuminates when a hardware jog reverse input is asserted.

16 The stepper positioning system is susceptible to electrical noise unless the equipment is properly grounded, the cabling is properly shielded and the power supply(ies) is properly filtered. If not, an incorrect number of position pulses could result. The following should be connected to earth ground: Ground prong of all A line cords Negative (-) or common terminal of the I/O power supply(ies) One I/O chassis mounting stud Ground the drain wire of the cable connecting the pulse output expander module to the stepper translator. This cable should be grounded either at the translator or at the I/O chassis, but not both. See Shield onnection below. The stepper translator, power supply and motor should be grounded in accordance with the manufacturer s instructions. WARNING: Improper system grounding can result in additional unwanted pulses occurring at the stepper translator and/or stepper motor. Unpredictable machine motion could occur with possible damage to equipment and/or injury to personnel. The stepper translator should be wired to the field wiring arm using a twisted 3-conductor shielded cable such as Belden 877 or equivalent. The cable distance between the pulse output expander module and the stepper translator generally should not exceed 4 feet. Belden 877 or equivalent cable has a foil shield with a bare drain wire. The shield should be connected to each ground at one end of the cable only. This can be at the customer end of the cable or at an I/O chassis mounting bolt or stud. At the other end of the cable, the shield should be cut short, bent back and taped to insulate it from any electrical contact.

17 This practice helps to guard against unwanted radiated electrical noise and ground current loops. Plastic keying bands shipped with each I/O chassis provide an easy method for keying an I/O slot to accept only one type of module. Use of the keying bands is strongly recommended. The module is slotted in two places on its rear edge. The position of the keying bands on the backplane connector must correspond to the slots to allow insertion of the module so that only the desired module will fit in this slot. Refer to Figure 2.4 Snap the keying bands on the upper backplane connectors between these numbers printed on the backplane: Stepper ontroller 2 and 4 8 and Expander Module 8 and 22 and 24 Needle-noise pliers can be used to insert or remove keying bands.

18 An I/O chassis that contains a stepper controller module may not contain another master intelligent I/O module. The pulse output expander module specifications are listed in Table 2.F. The stepper controller module specifications are listed in Table 2.G.

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20 The desired motion of the stepper motor can be accelerated, decelerated or maintained at constant rate by controlling the pulse rate from the pulse output expander module. Motion can be rotational such as used to position an indexing table, or can be linear such as obtained when a linear slide is driven forward or backward by turning a threaded shaft. In either case, the position at any given moment is defined by the number of pulses sent to the stepper motor. It can result in some number of degrees of rotation or linear units of travel. The motion can be programmed by manipulating data table words (control blocks) arranged in a convenient format. Blocks of data are also used to indicate that commands were received and desired motion was implemented (status block). ontrol and status blocks are communicated bidirectionally between the P processor and stepper controller module by block transfer programming. The task of programming requires that control and status block be assigned in the data table and that control data be entered using the industrial terminal. ontrol blocks sent to the stepper controller module by write block transfers govern acceleration, deceleration, final rate and final position. ontrol blocks also contain control words. Bits in control words must be set according to the particular application and desired motion. The stepper controller module sends status blocks of data to the P processor using read block transfers. Status blocks contain current position information and diagnostic bits set by the stepper positioning assembly. The format of the data blocks and the function of status and control bits will be covered later in this chapter.

21 There are three stepper positioning concepts which should be understood before learning how the stepper positioning assembly is programmed. They are: Move Definition Moveset Positioning Modes A move in its simplest form consists of an acceleration of the stepper motor axis, a final rate, a deceleration to zero and a final position (Figure 3.). The value for an acceleration is the time required to achieve a final rate. Values can be chosen from seconds. The final rate determines the constant speed of machine motion. The final rate value can vary from to 2, pulses per second. The decel value, any value from seconds, is the time required to decelerate to zero pulses per second from a final rate. The final position of a move is the number of pulses between and 999,999 to be achieved by the move. The physical location will depend on the resolution (pulses per degree of rotation or pulses per inch of travel, etc.) of the stepper translator/motor configuration and the specific application (gearing threads per inch of the linear axis, etc.). Ramp (Accel) (-9.99 Sec) Decel (-9.99 Sec)

22 A moveset refers to the data used to control from to moves. Sequential moves can be blended to form a continuous move profile or can be implemented one move at a time where motion stops between moves. A moveset can be executed using a minimum of ladder diagram programming. Two or more movesets can be implemented sequentially as if they were a single large moveset. The stepper positioning assembly can store two movesets simultaneously for up to three axes. When one moveset is in operation (working moveset), the next moveset is in storage (storage moveset). In the continuous mode, the last move of the working moveset is blended with the first move of the storage moveset. In any mode, when the working moveset is finished, the storage moveset automatically becomes the next working moveset. Then another (storage) moveset can be block transferred to the stepper positioning assembly. In the continuous and independent modes of operation, the storage moveset must be received by the stepper controller module before the third from last move of the working moveset is complete (for example, move 8 of moves). In the single-step mode, the storage moveset must be received before the second from last move of the working moveset is completed. Skipped moves (section titled Move Block, Bit 2) and not counted. The use of multiple movesets allows long and complex positioning profiles or long sequences of single moves to be performed with little additional programming. The moveset is further defined in section titled Moveset Block. The stepper positioning assembly can be programmed for operation that is tailored to the application requirements. The positioning modes determine the type of positioning profile and the manner in which the axes of two or three stepper motors can be coordinated. The stepper positioning assembly can also be operated manually using hardware or software jog inputs. Single-Step Mode In the single-step mode, a moveset allows the individual moves to be controlled one at a time. A start command from the P processor starts the first move of the sequence. After the move is completed, the stepper motor axis stops and a done bit is set. In order for the next move to begin,

23 the P processor must transfer another start command to the stepper controller module (Figure 3.2). Jog A jog allows an axis to be manually controlled by an operator independent of other axes in the system. This can be done at any time except when a positioning profile is in progress. A jog can be initiated by a hardware or software input to the stepper positioning assembly. Jog data is one move block that controls one axis. The job move block typically is contained in a separate -move (-word) moveset. The jog move block can also be contained in a moveset with other moves. If so, the jog must be the first move of the moveset. The remaining moves will be ignored as a result of the stepper controller module processing the jog move block. After the jog has been executed as needed, the remaining moves can be initiated by again transferring the same moveset to the stepper controller module. This time a skip bit must

24 be set in the jog data and the jog load bit must be cleared. (These bits are described in section titled Move Block, Bit 2 and 3). The positioning profile will then start with move two and ignore the jog data. The jog can be initiated by jog forward or jog reverse user-supplied input switches or by ladder diagram logic. An axis must be at rest before a jog can be initiated. As long as the jog input is asserted, the jog will continue at the specified rate. Once released (off) the jog will decelerate to a zero rate over the time defined by the decel value programmed in the jog move. If desired, the final position value can serve as an upper (or lower) limit of jog travel. The jog will automatically decelerate to reach a zero rate at the programmed final position if the jog input is held on. If the final position value of the jog is programmed as zero, the limit of travel will be 999,999 pulses. If the decel value is programmed as zero, the jog rate will cease instantly when the jog input is turned off. AUTION: Avoid damage to the stepper motor and machine by selecting jog final rate and decel values which are compatible with the stepper motor/machine dynamics. ontinuous Mode The continuous mode allows moves of the moveset to be blended continuously into a move profile with fully programmed accelerations and decelerations. One start command is required for the entire positioning profile. A done bit is set at completion. Each move is defined as having a ramp, a final rate and a final position. The last move of the profile, in addition to the ramp, final rate and final position, contains a deceleration to zero (Figure 3.3). The decel value does not affect the positioning profile in any move except the last move.

25 Synchronization of Axes All axes (up to three) can be synchronized move-by-move in the single-step and independent modes. Each axis must complete a given move before any axis allowed to begin the next move. oordination is independent of P processor scan time. If two axes are synchronized, then the third axis, if used, must also be synchronized. Synchronized axes must operate in the same positioning mode. A start command can be programmed for only one of the synchronized axes. In the single-step positioning mode, this must be done for each move of the moveset. Start commands received during a move will be ignored. Done bits for all axes must be set before a start command is executed. In the continuous and independent modes, one start command is required at the beginning of the synchronized profiles. A done bit is set for each axis at completion of each positioning profile. If all axes (up to three) are not synchronized, then the control of any axis is completely independent of the other(s). Three different single-axis machines could be controlled by one stepper controller module and three pulse output expander modules in one I/O chassis. Independent Mode

26 The independent mode allows a chain of single-step moves to be sequentially executed. Each move is defined as having a ramp, final rate, decel (to Hz rate) and a final position. Typically there is a pause of -3msec from the end of one move to the beginning of the next (dwell at Hz rate). Refer to Figure 3.4. One start command is required for the entire positioning profile. A done bit is set at the completion of each move. Important: Done bits which are set between moves in the independent mode should not be used because they remain set for too short a time. Only the done bit of the last move should be examined. This can be achieved by examining the number that identifies the last move (status bit -3) and the done bit in the same rung. When using the independent mode and the axes are synchronized, all but the last axis to finish the move in process will stop motion when finished and wait for the last axis to complete its move. All axes will then begin the next move simultaneously as soon as the last axis has finished its positioning profile (Figure 3.).

27 Words that control the motion of the stepper motor axis, record position or monitor move diagnostics are stored in data table files. These words are grouped into the following three kinds of data blocks. Moveset Block Move Block Status Block

28 In addition to move data, the blocks contain special control or status words. The bits in these words affect how the motion is controlled or verify that the move commands and the move data were received and implemented. Moveset Block The moveset block is a data table file for storing data and controlling the motion of one stepper motor axis. It allows move data to be stored in consecutive data table words to control up to moves of a positioning profile. Each axis must have at least one moveset block. A moveset block must contain the following move data (Figure 3.6). Moveset ontrol Word Offset and Preset Words One or more Moves

29 Moveset ontrol Word A moveset block must contain a moveset control word as the first word in the block. Each of the bits of the moveset control word serves a function in the control of a stepper motor axis. Bit functions of the moveset control word are defined below and summarized in Figure 3.7. Bit Start ommand Bit. When this bit is set, the stepper controller module will start to execute the first move of a continuous or independent mode sequence or the next single step move. Bit, 2 Mode Select Bits. These two bits are used to determine the type of positioning profile. Bit =, Bit 2=: ontinuous Mode (Figure 3.3) Bit =, Bit 2=: Independent Mode (Figure 3.4) Bit =, Bit 2= or : Single-Step Mode (Figure 3.2) Refer to section titled Positioning Modes for mode descriptions.

30 Bit 3 Synchronized Axes Bit. If this bit is set for any axis, it must be set for the other axes so that all (two or three) axes controlled by the stepper positioning assembly are synchronized. Synchronized axes must be operating in the same positioning mode. (Bits, 2, and 3 must be set identically in the moveset control words of the synchronized axes.) Refer to Synchronization of Axes. Bit 4 Reset ommand Bit. A reset command can be limited to a single axis or can reset all axes (up to three) depending on the logic state of the global/axis bit (bit ). With the exception of the done bit and reset bit, all status and position information and all moveset data are cleared in the stepper controller module when the reset command bit is set. The reset bit and done bit are reset in the status word at the start of the first move in the next moveset. The user program should clear the reset bit after the reset has been executed as indicated by reset bit in the status word. Refer to section titled Status Block. Bit Global/Axis Bit (for stop or reset commands, only). When this bit is set, all axes controlled by the stepper positioning assembly are stopped or reset with one command. (The notation refers to a low logic state.) When this bit is zero, only the axis of the moveset defined by the axis address bits (bits and ) is stopped or reset. The function of this bit should be considered whenever the stop bit (bit 6) or the reset bit (bit 4) is programmed. Bit 6 Stop ommand Bit. When this bit is set, output pulses will cease either in a controlled decel or instantly, depending on how the decel/instantaneous bit (bit 7) is set. A stop command can be limited to a single axis or can apply to all axes (up to three) depending on how the global/axis (bit ) is set. All move profile data is cleared, but position and status information remains the same in the stepper controller module when this bit is set. The user program should clear the stop bit after the stop command has been executed as indicated by reset bit in the status word. Refer to section titled Status Block.

31 Bit 7 Decel/Instantaneous Bit. When this bit is set, the output pulse rate will decelerate to zero in accordance with the decel value in the move block that was being executed when a software stop command was received. When the decel/instantaneous bit is zero, output pulses will cease instantly when a software stop command is received. A hardware stop input in instantaneous, independent of the decal/instantaneous bit. This bit is generally set when a stop bit is set. Bits, Axis Address Bits. These bits define the axis to be controlled by the data and/or commands in the moveset block. The address in the moveset control word of the moveset block must be identical to the settings of the address switch assembly (S3) of the corresponding pulse output expander module. The address bits of the moveset block are generally set when the profile is initially programmed using the industrial terminal. The setting of bits and respectively are = axis, = axis 2, = axis 3. Bit 2 Must always be zero. Bit 3 Offset ommand Bit. When set, the value contained in the offset word (described below) will be added to or subtracted from the final position value(s) of all moves of the moveset blocks residing in the stepper controller module memory. In all modes, the final position of each move is shifted by the offset amount and direction. Bit 7 of the offset word determines the direction of the shift, for subtracted or for added. Important: The present move being executed and the move following may not be affected by the offset command in all but the single step mode. In the single step mode, only the present move will not be affected.

32 The user program should clear the offset bit and allow the stepper controller module to see the bit cleared before another offset for that axis is enabled. Bit 4 Software Jog Reverse ommand Bit. The axis will move in the direction indicated for as long as this bit is set or until the final position programmed in the jog move is reached. Hardware jog inputs are disabled during this time. The jog will follow the ramp, rate, decel and final position values programmed in the jog move block. In large systems or systems using remote I/O, the software jog timing will depend on block transfer timing. Refer to section titled Handshaking. The load jog command bit (bit 3 of the single move control word, defined in section titled Move Block ) must be set to identify jog move block data. The user program should clear the software jog reverse command bit and allow the stepper controller module time to see the bit cleared before another jog to that axis is enabled. Bit Software Jog Forward ommand Bit. Same as bit 4. See software jog reverse command bit. Bit 6 Moveset Bit. Successive movesets can be programmed for continuous execution using the moveset bit. This bit can be used to label each block transfer of move data as moveset or moveset. When movesets are alternately labeled for the first, for the second, for the third, etc., user program logic can sequence for movesets without interruption as if they were one large moveset. The number of successive movesets is limited only by processor memory. Once a positioning profile has begun, none of the moves of the working moveset can be updated. However, the storage moveset in the stepper controller module can be updated provided that the moveset bit in the transferred (updated) moveset has the same setting ( or ) as the storage moveset bit. Refer to section titled Movesets. In large systems or systems using remote I/O, moveset timing will depend upon block transfer timing.

33 Bit 7 Override ommand Bit. The override bit is set in the moveset containing the override data. When the override command is enabled, the override bit causes the current moveset to be interrupted and the override moveset to be blended immediately. The first move of the override moveset is blended with the interrupted move in progress. Refer to section titled Override Ramp Time onsiderations to ensure that the first move of the override moveset will be compatible with any worst case move in progress. Generally, bits of the moveset control word are set by user program logic. A command to the stepper controller module should be cleared and the stepper controller module allowed sufficient time to see the bit cleared before the next command is transferred. See sectio titled Handshaking. Avoid sending multiple commands to the stepper controller module at the same time. A programming error could result or the data/command could be ignored. All bits must be set carefully to tailor the move profile(s) to the application requirements and to avoid illegal bit combinations. If only one command is transferred at a time with proper handshaking, no difficulty should be encountered. An illegal bit combination will cause a programming error when data is received by the stepper controller module or when move data is processed for execution. Once the definitions of the bit functions have been learned, the table of illegal bit combinations found in section titled Illegal Bit ombinations, can be consulted as an aid in avoiding programming errors when programming the required move profile(s). Offset Word The position offset allows an entire positioning profile (all moves of the profile) to be shifted to compensate for machine wear without reprogramming the profile (Figure 3.8). The offset value between and 7,999 pulses, can be added to or subtracted from the final position of each move in the moveset(s).

34 The offset value is entered in BD in bits -6 of the offset word. Bit 7 is the control bit that determines whether the offset will be added to or subtracted from the final position (Figure 3.9). The value entered in the figure is the maximum allowable value of offset. Refer to offset command bit 3 of the moveset control word described earlier in this section

35 The moves affected by the offset will be those stored in the working and storage moveset when the command is received. If additional movesets have been programmed, the offset command must be re-enabled when additional movesets are transferred to the stepper controller module. Preset Word The preset word can store values that serve two functions. One function, initialization preset, is used by the stepper controller module to define the starting point value of the positioning profile. The other function, move preset, can be used to extend one or more moves of the profile beyond the 999,999 pulse (position) limit of the stepper controller module. In either case, the preset word can be loaded with the necessary value, the function enabled and another value loaded as needed. When used, the preset value becomes the new position reference of the profile. The preset can be any value between and 999,999. Preset data is contained in two words, one for the most significant (MS) 3 digits, the other for the least significant (LS) 3 digits (Figure 3.9). Preset values are entered in BD in bits -3. Bits 4-7 in the LS preset word and bits 4-6 in the MS preset word are undefined and must be loaded with zeros. Bit 7 of the MS preset word is the assert bit for the initialization preset. Initialization Preset Typically it may be necessary to jog the machine to a starting position before the positioning profile(s) is (are) started. The position register of the stepper controller module will read some number of position pulses representing the machine starting position. The initialization preset can be used to reset the value of the position register to zero, or to any value that would be used as the profile starting value. If the preset value were not set equal to zero (or not equal to the profile starting value), when started, the first move(s) of the profile would be shortened or lengthened. The amount would be the difference between the initialization preset and the starting point value: shortened if the preset exceeded the starting point value or lengthened if the value were less than the starting point value (Figure 3.).

36 AUTION: All moves must achieve a final rate for a minimum duration of 2msec or a programming error and a system fault will result. The minimum duration of a move is covered in section titled Application onsiderations. Bit 7 of the MS preset word is the assert bit for the initialization preset. When this bit is set, the preset value will be written over whatever value is in the position register of the stepper controller module. Once the positioning profile has been started, bit 7 must not be set or a programming error will occur. Move Preset The move preset can be used to adjust the starting point value of any move in a moveset whenever necessary. For example, the move preset can extend one or more moves of the profile beyond the 999,999 pulse limit of the stepper controller module. The move preset is enabled by bit in the single move control word (see sectio titled Move Block ). When this bit is set, the position register of the stepper controller module and the starting point value of the move block will become the value stored in the preset words. The final position value of the move block and all subsequent move blocks will be referenced to this new starting point value.

37 If a move profile extends beyond 999,999 pulses and the application calls for a return to the home position, it may be necessary to change the preset value and again set the move preset bit (Figure 3.). When necessary, this must be done before the move to home position is started. Reverse travel to the home position can require two moves if the total travel exceeds 999,999 pulses.

38 A move block contains ramp, final rate, final position and deceleration data that characterize a move. A moveset block must contain from to move blocks. A move block contains the following words (Figure 3.2): Single Move ontrol Word Move Data Single Move ontrol Word The single move control word is the first word in each move block. The word contains two identification bits (bits 6, 7) and four bits which affect the operation of the move (bits -3). The function of each bit is defined below and summarized in Figure 3.2. Bit Move Preset Bit. This bit, when set, causes the value contained in the preset words of the moveset block to become the starting point value for that move. The position register becomes this value. The preset value can be changed and re-enabled as needed to further extend the position limit or to allow the profile to return to the home position. Refer to Move Preset.

39 Bit Rate Multiplier Bit. When the rate multiplier bit is set, final rates can be selected in pulses per second increments between and 2, pulses per second. When this bit is zero, any final rate from to 9,999 pulses per second can be selected in pulse per second increments. This bit would typically be set when ramp, rate and decel values are initially set in the data table using the data monitor mode of the industrial terminal. Bit 2 Skip Bit. The skip bit allows one or more moves of a moveset to be ignored without reprogramming. When this bit is set, the corresponding move block is skipped over. When operating in the continuous mode, the move preceding the skipped move and the move following the skipped move are blended automatically. Refer to section titled Application onsiderations to ensure that the blend is achievable without a programming error. When operating in the independent mode, the move following the skipped move begins as soon as the one preceding the skipped move is done. Skip bits can be set initially in the data table when move data is entered or they can be set by user program logic. Skip bits must be set before the moveset is transferred to the stepper controller module. Once the moveset is transferred, additional skip bits cannot be set in that moveset. Bit 3 Load Jog Bit. This bit is set to identify the accompanying move block as jog data. Bit 4 software jog reverse command or bit software jog forward of the moveset control word can be programmed to initiate the jog. Jog data (with the load jog bit set) can be transferred to the stepper controller module with the software jog forward or reverse command (bit or 4), or jog data can be transferred to the stepper controller module in advance. See software jog forward and reverse command bits and 4 of the moveset control word described earlier in this section. Refer to the section titled Jog. An axis reset command will clear any previously transferred jog data for that axis. Bit 4- Must always be zero.

40 Bit 6, 7 Identification Bits. Both bits must be set to identify each single move control word. Otherwise, a programming error will occur. Generally, bits of the single move control word are set by user program logic. A command to the stepper controller module should be cleared and the stepper controller module allowed sufficient time to see the bit cleared before the next command is transferred. See Handshaking. Avoid sending multiple commands to the stepper controller module at the same time. A programming error could result or the data/command could be ignored. Move Data Move data is contained in the remaining five words of the move block (Figure 3.3). Values are entered in BD. Those shown in Figure 3.3 are the maximum allowable values. Undefined bits (bits 4-7) in the words specifying the ramp, decel and position must be filled with zeros. Ramp Time

41 The ramp value is the number of seconds the positioning assembly will take to reach a (new) final rate. In the continuous mode, the final rate can be greater than or less than the starting rate. Ramp time can be any value between and 9.99 seconds. Refer to section titled Application onsiderations. Final Rate The final rate value determines the constant speed of the move. The rate can be any value between and 9,999 pulses per second or in increments of pulses per second between and 2, pulses per second. Refer to section titled Application onsiderations. Important: When the rate multiplier bit (bit ) of the single move control word is set, the resulting rate will be equal to the programmed rate value times ten. Decel The deceleration value is the number of seconds the positioning assembly will take to decelerate to zero pulses per second. It should not be confused with a ramp to a lower final rate other than zero. The decel is an active part of the move profile in the single step and independent modes. In the continuous mode, the decel value is not used in the move profile except for the last move. However, the decel value has a special purpose in the continuous mode: it allows a controlled decel to Hz rate under two conditions:. If a system fault is detected, the move in progress will decel to a Hz rate (come to a stop) in the time defined by the decel value. 2. If a software stop command is received by the stepper controller module, a controlled decel to a Hz rate will occur during the move in progress. This will happen only if the decel/instantaneous bit of the moveset control word is set. Otherwise the stop will be instantaneous.

42 AUTION: Select a decel value for a controlled stop that is compatible with the stepper motor and system dynamics in order to avoid damage to the equipment. Refer to section titled Application onsiderations. Position The position value defines the final position of any particular move. It is the number of position pulses from a reference value such as the beginning of the move profile. When the number of pulses defined in the position words of a move block equals the number of pulses sent from the pulse output expander module to the stepper translator, that particular move is done. The most significant digits of the position value are contained in the MS position word, the least significant digits in the LS position word. Use leading zeros when necessary. The status block is a data table file used to store position and diagnostic information received from the stepper controller module. The status block contains the following word storage for each pulse output expander module (axis). Status Word Position Word The first word in the status block is reserved for future use (Figure 3.4). Each expander module then uses three words, the first of which is the status word. The remaining two are position words. The number of status and position words returned to the P processor depends on the highest numbered axis in the stepper positioning assembly, not on the number of axes used. The status block must contain four words if only axis is in the system, seven words if axis 2 is the highest numbered axis, and ten words if axis 3 is in the system.

43

44 Status Word The bits in the status word allow the P program to verify that move commands have been received and implemented. The bits can be monitored visually or used to display which portion of the positioning profile is currently in operation, the status of the current move and the nature of any fault or error detected by the stepper controller module. The functions of the status word bits are defined below and summarized in Figure 3.. Status Bits Except as noted below, the status bits verify that a particular command has been received by the stepper controller module. Bit ommand Verify Bit. This bit is set to verify that a command bit (start, stop, offset, jog reverse, jog forward, override, initialization preset or load jog) has been received. Bit Data Received Bit. This bit toggles alternately to to every time a new write block transfer is received.

45 Bit 2 Direction Bit. This bit indicates the direction of rotation, for forward or for reverse. Bit 3 System Fault Bit. This bit is set if a system failure such as a communication error is detected in the stepper positioning assembly, or invalid data is detected. The output decelerates to Hz at the programmed decel value when a system failure is detected. Bit 4 Programming Error Bit. This bit will be set for a number of error conditions including the following. Illegal bit combinations exist in the data transferred to the stepper controller module. Refer to Table., Illegal Bit ombinations, in hapter. The identification bits (bits 6 and 7) of the SMW are not set. Any undefined bit is set (other than zero) in the following words: MS Preset (bits 4-6) LS Preset (bits 4-7) Ramp (bits 4-7) Decel (bits 4-7) MS Position (bits 4-7) LS Position (bits 4-7) Rate values exceed 2, pulses per second. Ramp or decel values exceed 9.99 seconds. Preset or position values exceed 999,999 pulses. Important: The stepper controller module checks these conditions when data is first received. At a later time when a move is being processed for execution, other invalid data can be detected. Invalid data (such as that which would cause the final rate of a move to be held for less than 2msec) will cause both a programming error (bit 4) and a system fault (bit 3). The positioning profile would then cease.

46 Bit Reset Bit. This bit is set when a reset command is received and at power-up. Anytime a reset command is received, the done bit and reset bit will be on. Both bits are reset when the first move of the next moveset begins. Bit 6 Software Stop Bit. This bit is set when a software stop command is received. Bit 7 Hardware Stop Bit. This bit is set when a hardware stop (E-STOP) command is received. Bits -3 Move in Progress Bits. The bit pattern in Hex shows which move (-) of the moveset is currently being executed. (decimal =Hex A). Bit 4 Jog Reverse Bit. This bit is set when a software jog reverse command has been received or when a hardware jog reverse input is asserted. Bit Jog Forward Bit. This bit is set when a software jog forward command has been received or when a hardware jog forward input is asserted. Important: If the jog final position value is reached (upper or lower limit) during a software jog, the status bit 4 or will be reset even if the software jog command remains asserted. However if a hardware jog is being executed, the status bit 4 or will remain set until the hardware jog input is removed. Bit 6 Moveset Bit. This bit indicates the number ( or ) of the current moveset being executed. The moveset bit will alternately toggle to or when multiple movesets are executed. Bit 7 Done Bit. This bit will be set after every move in the single-step mode or independent mode; or after a move profile is completed in the continuous mode. It is reset when the first move of the next moveset begins. Refer to independent mode in section Positioning Modes concerning the use of this bit in the independent mode.

47 Position Words Position words report the number of pulses that have been sent to the stepper translator (provided that the position register in the stepper controller module has not been changed by a preset). The P processor can then continually monitor the number of output pulses which in turn indicates the present position of the machine. Two position words are required to store the number of position pulses, one to store the three most significant digits and the other to store the three least significant digits. The position pulses which can range from to 999,999 are stored in BD in the lower 2 bits of each word (Figure 3.4). The values shown in the figure are the maximum allowable values for position pulses. Bits 4,, 6 of the MS position word and the upper four bits of the LS position word are undefined. They will be read block transferred to the P processor as zeros. Bit 7 of the MS position word is used to indicate a negative position. For example, a reverse jog to below zero will set bit 7. Bit 7 is zero for a position between and 999,999 pulses. All communications between the stepper controller module and the P processor data table are controlled by program logic using block transfer programming. The Mini-PL-2/ and PL-2/3 programmable controllers use block transfer instructions. The PL-2/2 uses multiple get instructions for programming block transfer. Refer to the July 982 or later edition of the Programming and Operations Manual for the Mini-PL-2/ or PL-2/3 or the PL-3 Programming Manual for a detailed description of block transfer. These are publications , and 77-8, respectively. The remainder of this section describes block transfer concepts applicable to the stepper controller assembly using block instructions with the Mini-PL-2/ or PL-2/3 programmable controller. The stepper controller is a bidirectional block transfer module. Bidirectional Block Transfer