Self leveling Table

Hello Everybody,
We are worknig on a Self levelling table. Basically I am trying to build a table which will have a fixed leg in the middle connected with the ball joint to the table top so it will have 2 degree of freedom. This table is 12" X 18" and it will have 2 degree of freedom. The others legs will be connected in a right angle of each other. These two legs will be controlled by dc motor linear actuator and they will try to keep the surface of the table balanced when the platform of the table will be tilted by +/- 5cm.
This incline/tilt will be detected by inclinometer and I am hoping that some how I can interface inclinometer to LabView, and then the output should go to HB-25 (H-Bridge circuit) to drive the linear dc motor actuator.
I am hoping if you could help me finding the right hardware for this job. Currently our university has NI USB-6251, do you think this will be ok for our project if so then what kind of drivers or interface do we need so we can get the output from the inclinometer to computer and what do i need to interface with dc motor linear actuator so it can respond to that changes to make the table level. Thanks in advance.
Message Edited by Rajb on 09-29-2007 02:27 PM
Attachments:
self.jpg ‏17 KB

Hi Rajb,
You could use your USB-6251 to control the HB-25 with Pulse Width Modulation (PWM), as long as the current requirement is within the specification of the 6251. This however, would be software timed control, meaning it would be nondeterministic and you can't guarantee accurate control. I roughly estimate the latency between reading the inclinometer input and writing a PWM signal to the motors would be anywhere from 3-10 ms. That number comes from some rough tests I did on my computer, not from the user manual, so it is not a guaranteed statistic. However, it does serve to give you a basis for judgment on whether your 6251 will be sufficient as a controller. If that is insufficient, you will want to use a cRIO chassis, which is much faster, and deterministic. You would still control your motors with PWM through the H-Bridge and whatever software algorithm you write, but it would be on a Real Time target.
I hope this helps!
Maclean G.
Applications Engineering
National Instruments

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Please Mark This As Answer if it helps to solve the issue Visakh ---------------------------- http://visakhm.blogspot.com/ https://www.facebook.com/VmBlogs

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JoeNH2k wrote:
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insert into modifier (mod_id, parent_mod_id) values ('aaa', 'aa');
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insert into modifier (mod_id, parent_mod_id) values ('aba', 'ab');
insert into modifier (mod_id, parent_mod_id) values ('abb', 'ab');
insert into modifier (mod_id, parent_mod_id) values ('abc', 'ab');
insert into modifier (mod_id, parent_mod_id) values ('aca', 'ac');
insert into modifier (mod_id, parent_mod_id) values ('acb', 'ac');
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insert into modifier (mod_id, parent_mod_id) values ('ba', 'b');
insert into modifier (mod_id, parent_mod_id) values ('bb', 'b');
insert into modifier (mod_id, parent_mod_id) values ('bc', 'b');
insert into modifier (mod_id, parent_mod_id) values ('baa', 'ba');
insert into modifier (mod_id, parent_mod_id) values ('bab', 'ba');
insert into modifier (mod_id, parent_mod_id) values ('bac', 'ba');
insert into modifier (mod_id, parent_mod_id) values ('bba', 'bb');
insert into modifier (mod_id, parent_mod_id) values ('bbb', 'bb');
insert into modifier (mod_id, parent_mod_id) values ('bbc', 'bb');
insert into modifier (mod_id, parent_mod_id) values ('bca', 'bc');
insert into modifier (mod_id, parent_mod_id) values ('bcb', 'bc');
insert into modifier (mod_id, parent_mod_id) values ('bcc', 'bc');
commit;
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2    from modifier
3   start with parent_mod_id is null
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ITEM
a
aa
    aaa
    aab
    aac
ab
    aba
    abb
    abc
ac
    aca
    acb
    acc
b
ba
    baa
    bab
    bac
bb
    bba
    bbb
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bc
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i_mod_id in varchar2
,i_parent_mod_id in varchar2
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v_dummy varchar2(10);
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exception
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SQL> insert into modifier (mod_id, parent_mod_id) values ('bcc', 'b');
insert into modifier (mod_id, parent_mod_id) values ('bcc', 'b')
ERROR at line 1:
ORA-20000: Cannot insert or update because of recursive relationship.
ORA-06512: at "RC.BIU_MODIFIER", line 3
ORA-04088: error during execution of trigger 'RC.BIU_MODIFIER'
Here is a statement that should succeed:
SQL> insert into modifier (mod_id, parent_mod_id) values ('aaaa','aaa');
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DELETE WHERE a.id IS NULL
WHEN NOT MATCHED THEN
INSERT (
ID,
parent_id
VALUES (
A.ID,
A.PARENT_ID);
SQL Error: ORA-02291: integrity constraint (SCOTT.FK_FKV_PAID) violated - parent key not found
ROLLBACK;
rollback complete.
Ok, even it is not a good solution, I try deferrable constraint:
ALTER TABLE fkv DROP CONSTRAINT fk_fkv_paid;
ALTER TABLE fkv ADD CONSTRAINT fk_fkv_paid FOREIGN KEY (parent_id) REFERENCES fkv(id) DEFERRABLE INITIALLY DEFERRED;
table FKV altered.
table FKV altered.
MERGE INTO fkv USING (
SELECT
2 AS id,
2 AS PARENT_ID
FROM
DUAL
) a
ON (
fkv.id = a.id
WHEN MATCHED THEN
UPDATE SET
fkv.parent_id = a.parent_id
WHERE
A.ID IS NOT NULL
DELETE WHERE a.id IS NULL
WHEN NOT MATCHED THEN
INSERT (
ID,
parent_id
VALUES (
A.ID,
A.PARENT_ID);
1 rows merged.
COMMIT;
SQL Error: ORA-02091: transaction rolled back
ORA-02291: integrity constraint (SCOTT.FK_FKV_PAID) violated - parent key not found
... deffered constraint did not help :-(
Let's try another way - errorlog table; for the first with the not deferrable constraint again:
ALTER TABLE fkv DROP CONSTRAINT fk_fkv_paid;
ALTER TABLE fkv ADD CONSTRAINT fk_fkv_paid FOREIGN KEY (parent_id) REFERENCES fkv(ID) NOT DEFERRABLE;
table FKV altered.
table FKV altered.
BEGIN
sys.dbms_errlog.create_error_log (
dml_table_name => 'FKV',
err_log_table_name => 'ERR$_FKV'
END;
anonymous block completed
Toys are prepared, let's start with error logging:
MERGE INTO fkv USING (
SELECT
2 AS id,
2 AS PARENT_ID
FROM
DUAL
) a
ON (
fkv.id = a.id
WHEN MATCHED THEN
UPDATE SET
fkv.parent_id = a.parent_id
WHERE
A.ID IS NOT NULL
DELETE WHERE a.id IS NULL
WHEN NOT MATCHED THEN
INSERT (
ID,
parent_id
VALUES (
A.ID,
A.PARENT_ID)
LOG ERRORS INTO err$_fkv;
1 rows merged.
Cannot belive, running SELECT for confirmation:
SELECT * FROM err$_fkv;
SELECT * FROM fkv;
no rows selected
ID PARENT_ID
1 1
2 2
Ok, COMMIT:
COMMIT;
commited.
SELECT for confirmation again:
SELECT * FROM err$_fkv;
SELECT * FROM fkv;
no rows selected
ID PARENT_ID
1 1
2 2
Using deffered constraint and error logging is working well too.
Metalink and Google did not help me. I am using databases 10.2.0.5 and 11.2.0.3.
Has somebody encountered this problem too or have I missed something?
Thank you
D.

drop table fkv;
CREATE TABLE fkv (
id NUMBER(1) CONSTRAINT nn_fkv_id NOT NULL,
parent_id NUMBER(1) CONSTRAINT nn_fkv_paid NOT NULL
CREATE INDEX PK_FKV_ID ON FKV(ID);
ALTER TABLE fkv ADD CONSTRAINT pk_fkv_id PRIMARY KEY (id);
ALTER TABLE FKV ADD CONSTRAINT FK_FKV_PAID FOREIGN KEY (PARENT_ID) REFERENCES FKV(ID);Now run your MERGE statement and it works with non deferrable constraints.
Personally, I would contact support about this before depending on it in production.
P.S. I was not able to reproduce your findings that dropping and re-adding the constraints changes things. I suspect that when you dropped the constraint the index was NOT dropped, so you kept a non-unique index.
Try again using ALTER TABLE FKV DROP CONSTRAINT PK_FKV_ID drop index;

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